Kiribati: Review of Data available for Tsunami Inundation Modelling

SOPAC/GA Tsunami Hazard & Risk Assessment Project 

Report 03 

Inventory of Geospatial Data and Options for 

Tsunami Inundation & Risk Modelling 

Tarawa and Abaiang Islands Bathymetry 

KIRIBATI 

Helen Pearce 

(helen@sopac.org) 

SOPAC Miscellaneous Report 653 

December 2007 

Banaba Bathymetry

[2] 

Complied by 

Helen Pearce 

Ocean & Islands Programme 

SOPAC Secretariat 

This report may also be referred to as SOPAC Miscellaneous Report 653 

Copies of this report may be obtained from: 

SOPAC Secretariat 

Private Mail Bag 

GPO, Suva 

Fiji Islands 

Phone: (679) 3381377 

Fax: (679) 3370040 

http://www.sopac.org 

E-mail: director@sopac.org 

[SOPAC Miscellaneous Report 653 – Pearce]

[3] 

TABLE OF CONTENTS 

ACKNOWLEDGEMENTS ................................................................................................4 

ACRONYMS.....................................................................................................................4 

1 INTRODUCTION........................................................................................................5 

2 SOURCES OF TSUNAMI HAZARD ..........................................................................6 

3 VULNERABILITY/EXPOSURE..................................................................................8 

4 OVERVIEW OF TSUNAMI HAZARD AFFECTING SW PACIFIC .............................9 

(i) Summary Extracts: .........................................................................................................9 

(ii) Summary and Interpretation for Kiribati.........................................................................13 

(a) Composite of Tsunami generated by 8.5 Mw Sources around Pacific.....................................13 

(b) Composite of Tsunami generated by 9.0 Mw Sources around Pacific.....................................14 

5 DATA AVAILABLE AT SOPAC FOR INUNDATION MODELLING........................15 

(i) Global bathymetry datasets...........................................................................................15 

(ii) SOPAC/EU and other deep-water survey bathymetry ..................................................15 

(iii) Additional Bathymetry for Abaiang and Tarawa Lagoons .............................................18 

(iv) Admiralty Chart Details..................................................................................................20 

(v) Inter-tidal Information.....................................................................................................22 

(vi) Satellite Imagery............................................................................................................27 

(vii) Topography and Coastline Information .........................................................................28 

(viii) Infrastructure .................................................................................................................28 

(ix) Modelling options...........................................................................................................28 

(x) Data Summary...............................................................................................................30 

6 SUMMARY...............................................................................................................31 

7 REFERENCES.........................................................................................................33 

APPENDIX 1: Datum and Defintitions ........................................................................35 

1 Seaframe Gauge Datum for Betio, Tarawa.......................................................................35 

2 Definitions and Acronyms for Tsunami, Tide and Wave Levels........................................36 

APPENDIX 2: Historical Events Affecting Kiribati .....................................................42 

1 Previous Tsunami that have impacted on Kiribati .............................................................42 

2 Comparison of Chile 1960 Tsunami Run-ups and Deep-water Modelling ........................42 

3 PTWC Warnings for Kiribati during Solomons 2 April Tsunami ........................................43 

4 Tsunami Warning Related Background ............................................................................52 

(i) Tsunami travel times.....................................................................................................................52 

(ii) Summary of JMA/PTWC causal earthquake criteria ....................................................................53 

(iii) Real-time sea level data available for tsunami monitoring ...........................................................54 

APPENDIX 3: Additional Modelling .............................................................................58 

1 Modelling of major tsunami for sources around the Pacific...............................................58 

2 MOST model scenario for sources affecting Kiribati .........................................................64 


[4] 

ACKNOWLEDGEMENTS 

The assistance of Mary Power, Arthur Webb and Jens Kruger of SOPAC, Phil Cummins, Chris 

Thomas and Jane Sexton of Geoscience Australia, Ruth Broco of NGDC Tsunami Database and 

project funding from AusAid is gratefully acknowledged. 

ACRONYMS 

(Also see Appendix 1-3) 

ABoM Australian Bureau of Meteorology 

ATAS Australian Tsunami Alert Service (superseded by JATWC) 

CD Chart Datum 

DART Deep-ocean Assessment and Reporting of Tsunami. 

DEM Digital Elevation Model 

DSM Digital Surface Model 

EEZ Economic Exclusion Zone 

GA Geoscience Australia 

GNS Geological and Nuclear Sciences, New Zealand 

GTS Global Telecommunications System 

HAT Highest Astronomical Tide 

IOC Intergovernmental Oceanographic Commission 

ITIC International Tsunami Information Centre 

JMA Japan Meteorological Agency 

JATWC Joint Australian Tsunami Warning Centre 

LIDAR Light Detection and Ranging 

LAT Lowest Astronomical Tide 

MOST Method of Splitting Tsunami ( type of numerical model) 

MSL Mean Sea Level 

NGDC National Geophysical Data Centre (NOAA) 

PIC Pacific Islands Countries 

PDC Pacific Disaster Centre 

PTWC Pacific Tsunami Warning Centre 

SOPAC Pacific Islands Applied Geoscience Commission 

SPSLMP South Pacific Sea Level and Climate Monitoring Project 

UNESCO United Nations Environmental, Scientific and Cultural Organisation 

UTC Universal Time Coordinate (also referred to by Z or GMT) 

UTM Universal Transverse Mercator 

WGS World Geodetic System 

WMO World Meteorological Organization 


[5] 

1 INTRODUCTION 

SOPAC and Geoscience Australia, funded by AusAid have established the first component of a 

multi-stage project to look at tsunami hazard and risk assessment in the Southwest Pacific. As 

part of that project Geoscience have produced a tsunami hazard assessment for the Southwest 

Pacific based on a deterministic deep-water tsunami propagation model (A Preliminary Study 

into the Tsunami Hazard faced by Southwest Pacific, Thomas et al. 2007). That report is 

available at via the Pacific Disaster Net (http://www.pacificdisaster.net/drm/). In parallel with that 

component of the project, a review of data available for inundation modelling in Southwest 

Pacific is being conducted by SOPAC. Inundation modelling requires significantly higher 

resolution bathymetry, inter-tidal and coastal topography than the deep-water propagation 

models. 

Deep-water models alone are not sufficient to develop detailed understanding of tsunami 

inundation on coastlines and ultimately it is proposed that, where possible, the deep-water model 

output will be used to define the boundary conditions to allow more detailed, site specific tsunami 

inundation modelling of key and priority PIC coastal areas. The combination of the deep-water 

propagation and inundation model output will then be used to provide information and tools for 

emergency management and infrastructure planning in the Pacific Island Countries (PICs). 

However, detailed tsunami inundation modelling can only be undertaken if bathymetric (seafloor 

maps) and topographic (land elevation or height) data of adequate quality and coverage exist. 

SOPAC, through EU funded projects, has been addressing the some of the needs in the Pacific 

Region for high-resolution bathymetry data. This data is underpinning a number of critical 

technical projects in the areas of Marine boundaries, Fisheries, Coastal processes, and in 

hydrodynamic modelling for projects in support of reducing impacts of aggregate mining etc. 

However there is very little in the way of high resolution coastal and inter-tidal topography data 

available in the Region, suitable for inundation and sea-level change modelling and monitoring. 

This report for Kiribati is the third of a series of reports covering SOPAC member country and 

reviews the availability of high resolution inshore bathymetry and also inter-tidal and coastal 

topography of low lying coastal areas and options for inundation modelling. Kiribati is spread 

from 170 E to 150 W along the equator (Figure 1) with the population centred predominantly in 

the Gilbert Islands group, in particular in the capital Tarawa (Table 1). 

Table 1: Kiribati Geographic Information. 

Kiribati consists of 3 distinct archipelagos, the Gilbert Islans, the 

Phoenix Isalands and the Line Islands. They are spread over 

Location 

more than 45º of longitude in the central Pacific, straddling the 

Equator and the International Date Line. 

Capital Tarawa in the Gilbert Island Group. 

Population 88 600 (1999 est.) 

The total land area is about 811 km 

Land area 

2 made up of 33 islands with 

Kritimati Island accounting for half the land area. The only raised 

atoll is Banaba with a maximum elevation of 87 m. Only 20 of 

the islands are populated,17 of these in the Gilbert Islands. The 

Phoenix group is very sparsely populated and as are the Line 

Island group where most of the population is around Kritimati, 

Teraina and Tabaeran islands. 

Exclusive economic zone, EEZ Approximately 3.6 million km 2 in the central Pacific 


[6] 

Figure 1: The Republic of Kiribati consists of three distinct archipelagos, the Gilbert Islands, the Phoenix 

Islands and the Line Islands. There are 33 small islands, of which only 20 are inhabited, and 17 of these 

are in the Gilbert Islands. 

2 SOURCES OF TSUNAMI HAZARD 

Major trenches are the predominant source of earthquakes large enough to generate regional or 

ocean-wide tsunami. They are the main focus of the preliminary hazard analysis report (Thomas 

et al. 2007) which models magnitude 8.5 and 9 earthquake source tsunami generation discussed 

in section 4. The location and names of these trenches are shown below in Figure 3. 

A table of the causal earthquake criteria for local, regional and ocean-wide and the possible 

range of expected destructive impact (i.e. 100 km, 1000 km, >1000 km), similar to that used for 

warning purposes by Japan Meteorological Agency (JMA), Pacific Tsunami Warning Centre 

(PTWC) and Australian Tsunami Alert Service (ATAS) is described at Appendix 2 Section 2. 

Tsunami can also be generated from other processes such as meteors, volcanic eruption, 

volcanic collapse and submarine landslide. The latter are often triggered by earthquakes and are 

commonly attributed to the earthquake. Kiribati has no active volcanoes, however recent 

bathymetric surveys and analysis by SOPAC of Banaba Island indicate a large submarine land 

slide occurred on the southern side, some time in the distant geological past. The landslide scar 

suggests it was large enough to possibly have generated a significant local tsunami. 

There are 3 sea level recording sites in Kiribati that can be used for monitoring tsunami. They 

are on Tarawa in the Gilbert Islands, Kanton in Phoenix Islands and Kritimati in Line Islands. The 

gauges at Kanton and Kritimati are operated by the University of Hawai’i and the gauge at 

Tarawa by the Australian Bureau of Meteorology (ABoM). Recorded historical tsunami affecting 

Kiribati are discussed at Appendix 2, along with some of the tsunami warning issues for the 

Solomons 2 April 2007 Tsunami and the recorded tsunami at the Tarawa tide gauge. 


[7] 

Figure 2: Map of Major plate boundaries in Pacific Ocean with subduction zones labelled as follows: AlT- 

Aleutian Trench, ChT- Chile Trench, CsT- Cascadia Trough, HT- Hikurangi Trough, IBT- Izu_Bonin 

Trench, JpT- Japan Trench, KmT- Kermadec Trench, KrT- Kuril Trench, MT- Mariana Trench, MAT- Middle 

America Trench, NT- Nankai Trench, NGT– New Guinea Trench, NHT- New Hebrides Trench, PhT- 

Philippines Trench, PrT– Peru Trench, PyT- Puysegur Trench, RT- Ryukyu Trench, SST- South Solomons- 

Trench, TnT- Tonga Trench. Subduction Plate margins are shown in blue and are the source of the largest 

earthquakes in history (Thomas et al. 2007). Kiribati tide gauge locations are marked in purple. 


3 VULNERABILITY/EXPOSURE 

[8] 

The Line Islands, in the east of Kiribati, have recorded the highest tsunami. Kritimati Island 

recorded 0.3 m for the Chile Tsunami in 1960 which was generated by a 9.5 Mw earthquake and 

the 1957 Andreanof Is tsunami (Aleutian Trench) generated by a 9.1 Mw earthquake. For the 

Chile event the comparative recorded impacts in the region highlight the local variation caused 

by bathymetry and shoaling e.g. Hawai’i 2-11 m and Kritimati 0.3 m. The affects of shoaling in 

this event was considerably less for atolls such as Kritimati and Kanton Islands than on Samoa, 

Hawai’i or Japan etc. 

Since all the islands of Kiribati (except Banaba) are low lying atolls, the lack of any high ground 

may appear to make these islands especially vulnerable to tsunami. On the other hand, because 

such atolls often have steep drop-offs in which ocean depths increase very rapidly with distance 

from the fringing reef, there may not be a pronounced shoaling effect (Thomas et al. 2007). 

However, even relatively small tsunami, when timed with high tides may have a significant 

impact on communities on low lying atolls. 

Water supply and possibilities of inundation of fresh water lens are also critical issues for atolls. 

As such, the influence of the characteristic bathymetry/topography of such islands on the 

potential damage a tsunami can cause requires further investigation. Therefore it is important to 

use the deep-water modelling as input into island specific, finer resolution tsunami inundation 

modelling to understand the potential risk and possible impacts and for communicating the 

comparative risk and consequences within the all hazard framework and action plans 

Figure 3: Tsunami generation not influenced by climate change, however indirectly influences impact 

(Glassey 2005). 

Tsunami generating mechanisms are themselves not known to be impacted on by climate 

change directly. However, climate change may impact indirectly (Figure 3) by reducing the innate 

resilience of coastal systems; e.g. increased sea-level, erosion, etc. and there by, leaves coastal 

communities in a position of greater vulnerability. A further example is the timing of impact with 

sea state and high tides; e.g. if a tsunami strikes at spring low tide (Appendix 1, Section 2) the 

impacts would be less than if it arrived during spring high tide. 


[9] 

4 OVERVIEW OF TSUNAMI HAZARD AFFECTING SW PACIFIC 

A deterministic broad scale tsunami hazard assessment for the SW Pacific based on the deepwater 

tsunami propagation model was conducted (Thomas et al. 2007) by Geoscience Australia 

focusing at the major trench sources (Figure 2) around the Pacific. Section (i) below contains 

summary extracts from that report and section (ii) extracts specific to Kiribati and some added 

interpretation. Kiribati was ranked Category 2 and 3 in the preliminary tsunami hazard study. 

(i) Summary Extracts: 

“To aid in interpretation of the results, offshore tsunami amplitudes have been categorized into 5 ranges (Table 

1). Categories corresponding to a higher range of offshore tsunami amplitudes can presumably be associated 

with a higher level of hazard on coastlines of similar type. This categorization has been adopted throughout 

this report. It is important to note, however, that these ranges do not reflect the inundation that normally causes 

damage and/or fatalities and which can often vary widely depending on local bathymetry and topography. The 

categories indicated in Table 1 are therefore best viewed as indicating a relative level of hazard over areas of 

broad geographic extent. For example, a Category 5 tsunami along the coast of Papua New Guinea represents 

a higher level of hazard than a Category 2 tsunami along the coast of New Caledonia. 

It is premature, however, to interpret Table 1 in terms of impacts. This is especially true for low lying atolls such 

as Kiribati and Tuvalu. On the one hand, the lack of any high ground may appear to make these islands 

especially vulnerable to tsunami, so that even a Category 2 tsunami may be a cause for serious concern. On 

the other hand, because such atolls often have steep drop-offs in which ocean depths increase very rapidly 

with distance from the fringing reef, there may not be a pronounced shoaling effect, so that these islands may 

never experience a large tsunami. Such considerations require much more modelling to address and are 

beyond the scope of the present study, although it is intended that they be considered in a later phase of this 

project. In particular, the information presented in this report should not be used as a guide for responding to 

tsunami warnings. The information presented here is preliminary and is only intended as a rough guide for 

prioritizing work in subsequent phases of this project. 

Table 1: Categorisation of offshore tsunami amplitudes, normalised to equivalent depth of 50 metres. The “Colour“ 

column refers to the colour used for amplitudes of this category which have been used throughout this report 

Tsunami generated by two suites of simulated earthquakes were studied: Suite 1 consisted of 187 moment 

magnitude (Mw) 8.5 earthquakes and Suite 2 comprised 39 Mw 9.0 earthquakes (Figures 5 and 7, pages 11 

and 13). The results are summarised in Table 2 for both suites of earthquakes the nations most affected were 

in the south and west of the study area, including Vanuatu, Papua New Guinea, Guam, Solomon Islands and 

Tonga, each of which recorded Category 5 amplitude tsunami from the Suite 1 (Mw 8.5 Earthquakes). This is 

due to the proximity of these countries to the subduction zones and the orientation of the fault lines which acts 

to direct the tsunami towards these nations”… 

… Nations in the north and east of the study area, such as Kiribati, Marshall Islands, 

Nauru, Cook Islands, French Polynesia and Tuvalu were much less affected by the Suite 1 Tsunami and only 

experienced Category 1 or 2 sized waves. As is to be expected, Suite 2 events produced greater effects than 

those of Suite 1 on all nations. Notable in this respect is Fiji which experienced Category 5 amplitudes from 

Suite 2 events. However it should be noted that without further investigation it is not possible to say that even 

Category 2 amplitudes will not produce significant run-up at some locations. 


[10] 

The figures in Appendix A show that Suite 1 events (Mw = 8.5) from the subduction Zones in the eastern and 

far northern rims of the Pacific did not produce effects larger than Category 2 on any of the nations studied. 

However some Suite 2 events (Mw = 9.0) in the Peru-Chile, Aleutians and Kuril subduction zones did produce 

Category 3 or above effects for some nations. 

Table 2: Summary of results. Categories represent the highest amplitude recorded for that nation, and should be 

interpreted according to Table 1. 

….Events from Suite 1 in the subduction zones of the east, north and northwest rim of the Pacific have less 

effect on the region, either because of their distance, because the orientation of the fault lines acts to direct 

tsunami energy away from the region, or because of intervening bathymetric features. They rarely produced 

normalised amplitudes greater than Category 1, and never greater than Category 2. 

[SOPAC Miscellaneous Report 653 – Pearce] 

.

[11] 

Table 3: Most significant source regions for each nation, based on model output points that 

recorded a maximum amplitude exceeding 75 centimetres for Suite 1 (Mw 8.5). 

….This modelling pays no regard to the probability of events of various magnitudes occurring on any of these 

subduction zones. While there is no doubt that the Chile sub-duction zone can host an earthquake exceeding 

Mw 9.0 (the 1960 event was magnitude 9.5) there is as yet no consensus on a reliable method of determining 

the absolute maximum magnitude on any given subduction zone. We believe that most seismologists would 

agree that a magnitude 8.5 event is plausible on any of the subduction zones considered here, and that a 9.0 

event is impossible to rule out. Hence we consider both magnitudes. A probabilistic tsunami hazard study 

would consider a range of earthquake magnitudes and weight them according to estimates of their likelihood, 

in a similar way to the method described in Burbidge et al, (2007). 

….Like Suite 1, the nations most affected by the Suite 2 events were those in the south and 

West of the study area, as a result of the subduction zones in that region. However the plots in Appendix A 

show that Suite 2 events in the Chile-Peru, Cascadia, Aleutians and Kuril subduction zones produced 

significant (Category 3 or above) normalised amplitudes for some nations. For example the simulations 

indicate that the Chile-Peru zone is a significant source of hazard from Mw 9.0 events for Fiji and French 

Polynesia, as are the Aleutian and Kuril subduction zones for Guam, Federated States of Micronesia, Papua 

New Guinea, the Solomon Islands and Vanuatu. Significant normalised amplitudes were produced in Papua 

New Guinea and the Solomon Islands from modelled events in the Cascadia Subduction Zone. 


[12] 

Table 4: Most significant source regions for each nation, based on model output points that recorded maximum amplitude 

exceeding 75 centimetres for Suite 2 (Mw 9). 


(ii) Summary and Interpretation for Kiribati 

[13] 

The analysis for Kiribati is complicated by the island group’s spaning a large part of the Pacific 

and critical sources varying across the 3 main island groups. 

(a) Composite of Tsunami generated by 8.5 Mw Sources around Pacific 

Based of Figures 4 and 5 below, for an 8.5 Mw generated tsunami event, Peru, Tonga and 

Middle America Trench could potentially produce a Category 2 off-shore (deep-water) event for 

the Line Islands. Mariana and Solomons Trench sources could produce similar Category 2 for 

Gilbert Islands. None of the sources produced Category 2 for the Phoenix Islands. 

Figure 4: Composite of normalised Source 8.5 Mw Tsunami for Pacific. Maximum wave heights for the 

187 tsunami of Suite normalised to a standard depth of 50 m using Green's Law (Thomas et al. 2007). The 

approximate locations of the 3 Kiribati Island groups are marked with purple crosses. 

Figure 5: Magnitude 8.5 earthquakes ranked by the category of off-shore tsunami they could cause at 

parts of Kiribati. Each bar is displayed at the position of a magnitude 8.5 earthquake for which a tsunami 

was modelled, and the height and colour of the bar indicates the category (Section 4, Table 1) of the 

offshore tsunami modelled at Kiribati (Thomas et al. 2007). 


[14] 

(b) Composite of Tsunami generated by 9.0 Mw Sources around Pacific (normalised to 

50m depth). 

Based on Figures 6 and 7 below, for a 9Mw generated event the Peru Trench could possibly 

produces Category 3 off-shore (deep-water) for the Line Islands. Also most sources around the 

Pacific could potentially produce Category 2 for some part of Kiribati. Chile, Middle America, 

Cascadia, Aleutians, Kuril, Japan, Izu-Bonin, Tonga could produced Category 2 for Line Islands. 

Mariana, Solomon, New Hebrides, Tonga, Kuril, Japan Aleutians and Peru could produce 

Category 2 for Gilbert Islands. Chile, Japan, Kuril, Aleutians, Tonga, Peru, Cascadia, New 

Hebrides sources could produce Category 2 for Phoenix Island Groups. 

Figure 6: Composite of normalised source 9 Mw Tsunami for Pacific. Maximum wave heights for the 39 

tsunami normalised to a standard depth of 50 metres using Green's Law. (Thomas et al. 2007). 

Figure 7: Magnitude 9 earthquakes ranked by the category of off-shore tsunami they could cause at parts 

of Kiribati. Each bar is displayed at the position of a magnitude 9 earthquake for which a tsunami was 

modelled, and the height and colour of the bar indicates the category (Section 4, Table 1) of the offshore 

tsunami modelled at Kiribati (Thomas et al. 2007). 


5 DATA AVAILABLE AT SOPAC FOR INUNDATION MODELLING 

[15] 

Global bathymetry and topography data sets were sufficient for the deep-water tsunami 

modelling used in the preliminary hazard assessment (Thomas et al. 2007). However inundation 

modelling requires significantly higher resolution bathymetry as well as inter-tidal and coastal 

topography than the deep-water propagation models. The composites at Figures 17 to 19 show 

the difference in detail for the higher resolution SOPAC multi-beam bathymetry over the S2004 

global equivalent. 

A review of the data available at SOPAC to support tsunami inundation modelling has been 

conducted. 

(i) Global bathymetry datasets 

S2004 (Global 1 minute, ~2km) 

S2004 global data is available for Kiribati. It is available via ftp from 

ftp://falcon.grdl.noaa.gov/pub/walter/Gebco_SandS_blend.bi2. S2004 merges the satellite 

altimeter data derived Smith and Sandwell (1997) grid with GEBCO over shallow depths (Marks 

and Smith 2006). 

(ii) SOPAC/EU and other deep-water survey bathymetry 

The SOPAC/EU Multi-beam bathymetry of outer reef drop offs are only available for 5 islands, all 

in the Gilbert Islands group: Abaiang, Tarawa, Abemama, Banaba, and Onotoa (Table 2, Figures 

4 & 5). However coverage is not continuous around all these islands. The formats of the 

SOPAC/EU data are at Table 3. 

The SOPAC/EU bathymetry surveys of 5 Islands in the Gilbert group were conducted from 15 

September – 19 October 2005 (Kruger et al. 2005). The data sets are outside the fringing reefs 

with a minimum depth of between 50 and 10 m, depending on how close the survey vessel could 

approach the reef. 

Table 2: SOPA/EU Multi-beam Bathymetry for Kiribati. 

Location Coverage of Area covered 

by MBES 

Depth 

Maximum 


Date of MV Summer 

Spirit Survey 

15/9 –19/10 2005 

Abaiang 2 km offshore all around 1 500 m 17-22/9 2005 

Abemama 500 m offshore all around 300 m 15-17/10/2005 

Banaba 2 km offshore all around 1 700 m 29/9 02/10 2005 

Onotoa 1 km off the eastern barrier 

reef ( partial coverage) 

400 m 18-19/10/2005 

Tarawa 3 km offshore all around 1300 m 27/9-13/10 2005

4° 

2° 

0° 

-2° 

Banaba 

Abaiang 

Butaritari 

Tarawa 

Tabiteuea 

Abemama 

Nonouti 

Onotoa 

[16] 

-4° 

168°E 170°E 172°E 174°E 176°E 178°E 180°E 

0 m 


500 m 

1000 m 

1500 m 

2000 m 

2500 m 

3000 m 

3500 m 

4000 m 

4500 m 

5000 m 

5500 m 

6000 m 

6500 m 

Figure 8: The SOPAC/EU multi-beam bathymetry of outer reef drop offs are only available for 5 islands in 

the Gilbert island group: Abaiang, Tarawa, Abemama, Banaba, and Onotoa, although coverage is 

significantly less for Onotoa and Abemama. Abaiang and Tarawa Lagoons also have Satellite and single 

beam bathymetry available. Due to the shallow nature of lagoons, satellite derived bathymetry has been 

used in conjunction with the to single beam coverage to filling in the gaps in other bathymetry data 

sources for previous modelling projects. 

Table 3: Formats for SOPAC Bathymetry Survey Data.

Abaiang coverage 

Tarawa Coverage 

Banaba coverage 

[17] 


Abemama coverage 

Onotoa coverage 

Figure 9: SOPAC/EU Bathymetry for 5 Kiribati Islands. Onotoa deep water coverage is only partial. 

Abemama and Onotoa maximum depths are significantly less than others.

Other Surveys 

[18] 

Data from RV Melville Multibeam Survey 1999 is also available to the west of Abaiang and 

Tarawa from http://www.ngdc.noaa.gov. The coverage is shown in Figure 10. 

(iii) Additional Bathymetry for Abaiang and Tarawa Lagoons 

Bathymetry data sources and coverage for 

Abaiang. 

Bathymetry data sources and coverage for 

Tarawa. 

Figure 10: Additional Bathymetry available for Tarawa and Abaiang (Kruger 2007). 

SOPAC Single-beam Bathymetry for Lagoons 

Abaiang and Tarawa Lagoons also have single beam bathymetry available (Figures 11 and 12). 

Tarawa Lagoon 

Single-beam bathymetry was collected by SOPAC Survey (Smith, R., et al. 1994, 1995), 

Datum: LAT, Projection: UTM, Zone 59 N, WGS 84 (Figure 11). 


[19] 

Figure 11: Single-Beam Bathymetry for Tarawa Lagoon over Landsat imagery. 

Abaiang Lagoon 

Single-beam bathymetry data was collected for the Abaiang lagoon (Figure 12) for hydrodynamic 

modelling in support of Aquaculture in the Lagoon (Lelaurin, 2000) Datum: LAT, Projection UTM, 

Zone 59 N (WGS 72). 

Figure 12: SOPAC single-beam bathymetry for Abaiang lagoon. 

SPC Landsat Satellite Bathymetry 

As part of the Hydrodynamic Model for Tarawa Lagoon (Damlamian, 2006), Satellite derived 

bathymetry was generated for the Tarawa lagoon (Morgan 2004). Several imagery products 

were used e.g. Landsat, 2002, 2003, and IKONOS for part of Lagoon. The lagoon is mostly less 

than 20 m deep with a lot of single-beam soundings available for calibration. Only satellite 

bathymetry for points less than or equal to 15 m depth were useful as the accuracy decreases 

with depth, Datum: MSL, Projection: UTM, Zone 59 N, WGS 84. 


[20] 

(iv) Admiralty Chart Details 

A review of the available charts for Kiribati indicates limited coverage of lagoons in terms, of 

bathymetry at reasonable scales. Typically dates on publications are 30 years old, small scale 

with detail data restricted to passage, wharf or anchorage area. The Table 4 is a list of the charts 

as extracted from the Admiralty Catalogue. Charts for Abaiang and Tarawa are at Figures 13 

and 14. 

Table 4: Marine charts for Kiribati (Smith et al. 1994, 1995). 

Island Atoll Publication 

date 

Latest 

Edition 


Scale Comments 

Abemana 12/04/1963 12/04/1963 50000 Reasonable detail showing whole 

lagoon 

Gilbert group 22/04/1994 22/04/1994 800000 Small scale showing whole group 

from Butaritari to Arorae 

Maina to 

Marakei 

17/07/1964 17/07/1964 175000 4 atolls in chart Maina, Abaiang, 

Tarawa and Marakei 

Abaiang 17/07/1964 17/07/1964 50000 Part lagoon only –bathymetric map 

produced by SOPAC 

Tabiteaua 06/01/1966 06/01/1966 50000 Part lagoon south portion 

Nonouti 27/10/1967 27/10/1967 50000 

Arorae 27/10/1967 27/10/1967 100000 

Tabiteuea 27/10/1967 27/10/1967 75000 

Onotoa 23/07/1948 13/11/1964 150000 

Kuria 150000 

Butaritari 151200 

Butaritari 

Anchorage 

35000 

Nikunau 49910 

Betio 

Anchorage, 

Tarawa 

30070 

Beru 75000 

Tamana 

15000 

Atolls on one sheet -small scale. 

Detail only of Peacock anchorage in 

Tabiteuea 

Plans on one sheet limited 

bathymetry and scale.

Figure 13: Abaiang marine chart. 

Figure 14: Tarawa marine chart with location of Betio tide gauge circled in yellow. 

[21] 


(v) Inter-tidal Information 

[22] 

The inter-tidal zone is extensive and complex. Level surveys of 3 eastern Tarawa inter-tidal 

channels was done as part of an EU EDF project. This data was collected to estimate tidal flows 

through these and remaining channels during the development of MIKE21 Hydrodynamic model 

(Damlamian et al. 2006). There are 12 intertidal channels on eastern Tarawa (Figures 16) and a 

number on Abaiang. The extent of the inter-tidal zone can be defined from satellite imagery; 

however the channels in the bathymetry/topography data sets may need supplementation for 

inundation modelling. 

Figure 15: Areal view looking south-east along the central North Tarawa area (Kairiki) showing the 

complex and extensive nature of the intertidal channels in North Tarawa (Courtesy T. Falkland, 2005). 

This photo also highlights the typical low-lying nature of the atoll islands and gives an indication of rapid 

drop off on the ocean side – note the deep water outside the wave break zone. 


[23] 

Figure 16: IKONOS Imagery of 12 eastern Tarawa channels. 


Figure 17: Composite of available bathymetry data for Tarawa (Kruger 2007). 

[24] 


Figure 18: Composite of available bathymetry data for Abaiang (Kruger 2007). 

[25] 


Figure 19: Composite of available bathymetry data for Banaba (Kruger 2007). 

[26] 


(vi) Satellite Imagery 

Landsat imagery: covering Abaiang and Tarawa, 30m resolution (Figure 11). 

Quickbird Imagery: covering Tarawa. (0.6m pan sharpened). 

IKONOS Imagery 2005: covering part of Tarawa Lagoon 4m resolution (Figure 20). 

Figure 20: IKONOS 2004 Image of Tarawa. 

[27] 


(vii) Topography and Coastline Information 

Space Shuttle Topography Mission: 90 m grid is available for all of Kiribati. However the 

resolution is insufficient for tsunami inundation modelling. 

Data Directory: http://seamless.usgs.gov. 

Survey maps: 

Tarawa: 1:50,000 and 1:25,000, 1981, Transverse Mercator, datum: Secor Astro 1966. 

Coastline and only elevation at trig points. All trig points less that 5 m. 

[28] 

Abaiang: 1:50,000, Transverse Mercator, datum: HMS Cook Astro 1962 

Coastline and only elevation at trig points. All less that 5 m. 

Banaba: 1:10,000, 1990, Datum WGS 72 UTM Zone 59. Coastline and 

contours at 5 m intervals, maximum height 87 m. 

Tarawa also has additional spot values vertical resolution 0.1m, datum Tide Gauge Zero (Betio), 

provided for Kiribati by Australian Air Force (Figure 21). 

(viii) Infrastructure 

Some infrastructure information is available but little attribute information attached to it. Tarawa 

was not part of the Pacific Cities Project which collated this data for 5 capital cities in the Pacific. 

However this should be relatively easy to derive from high resolution satellite imagery when 

required. 

Water supply and possibilities of fresh water lens inundation are critical issues for atolls and 

would need to be considered in risk modelling. 

(ix) Modelling options 

Sufficient high resolution bathymetry to support tsunami inundation modelling is only available for 

three Islands in the Gilbert Group, Banaba, Abaiang and Tarawa. Abaiang and Tarawa could be 

modelled together as the islands are close together and linked by an undersea ridge. The 

orientation of the ridge, north-south, and the relative openness of the lagoons to the west 

suggests potential vulnerability to the Mariana Trench in particular. These orientation 

characteristics are representative of the remaining lagoon islands in the Gilbert’s Group, however 

there are 5 additional islands which do not fit this pattern having either enclosed lagoons or being 

reef islands with no lagoon. 

Banaba Island is a geographically isolated and would need to be modelled separately. It is a 

raised atoll with a maximum elevation of 87 m. The availability of higher ground provides 

evacuation options that are not available to a low lying atoll. 


Figure 21: Small area of Tarawa with spot elevation points (datum: tide gauge zero at Betio) over Quickbird satellite imagery. 

[29] 


(x) Data Summary 

Table 5: Summary of Available Data. 

[30] 

Type 

Bathymetry 

Resolution Metadata 

available 

Datum/Projection Format 

S2004 Global 1 minute, ~2km Yes WGS 84/MSL ASCII grid, xyz 

Deep-water Multibeam Various 

Yes UTM Zone 59N, WGS 84, Points xyz 

Survey data 

LAT 

Grid created from 

Survey data 

Abaiang 

Banaba 

Inter-tidal flats and 

channels 

10m 

Mapinfo Backdrop 

Satellite 30m horizontal 

UTM Zone 59N, WGS 84/ 

1-1.5, 1.5-5, 5-10, 0- 

15,15-20 m vertical 

MSL 

Single-beam Various 

Yes 

UTM Zone 59N, WGS 84/ 

LAT 

Grid 30m (with Sat) Yes 

Marine charts 

Coastlines 

Various UTM Zone 59N, WGS 72, 

LAT 

Tarawa 

From 4m IKONOS No UTM Zone 59N, WGS 84, 

imagery Possibly redo 

from QB 

MSL 

Topography 

Topographic maps 

Tarawa 

Abaiang 

Additional spot point 

data and derived 1 m 

contours 

Imagery 

Tarawa and Abaiang 

Landsat 

Tarawa only I 

IKONOS 

Quickbird 

Banaba 

Landsat 

Infrastructure 

Roads 

Airport 

Landsat 30m 

Landsat 30m 

Extent digitised from 

satellite imagery 

3 channel cross 

sections 

1;25,000 

1:50,000 

Yes UTM Zone 59 N, WGS 84, 

MSL 

Trig pts only 

Trig pts only 


TM Secor Astro1966 

TM, HMS Cook Astro 1962 

xyz (Surfer .grd) 

Mapinfo 

xyz 

MapInfo 

xyz 

Mapinfo 

Grid 

Paper 

MapInfo 

Lines 

MapInfo 

Paper Chart 

Banaba 

1;10,000 

5 m contours UTM Zone 59 N WGS72 Contours Digitised 

from Chart as 

Digitised Contours 

MapInfo Lines for 

Banaba 

Banaba only 

Satellite DEM 90m Yes WGS 84/MSL xyz 

Tarawa 

Provided by 

Australian Air UTM Zone 59 N, WSG 84 xyz 

0.1 m 

Force. 1998. Vertical datum: Tide Gauge 

Zero at Betio 

Mapinfo lines 

30m 

4m 

0.6m 

30m 

Yes 

Digitised from 

Topography 

maps/satellite 

imagery 

UTM Zone 59 N, WGS 84 

UTM Zone 59 N, WGS 84 

Geo-referenced 

TIF (Mapinfo) 

MapInfo 

Lines/polygons

[31] 

6 SUMMARY 

There are three main issues that will influence the priorities for and ability to do tsunami 

inundation modelling: 

1) Hazard Category from deep-water modelling; 

2) Vulnerability/Exposure; 

3) Requirement for high resolution bathymetry, inter-tidal and coastal topography data. 

Kiribati was ranked Category 2 and 3 in the preliminary tsunami hazard study based on deepwater 

modelling (Thomas et al. 2007). For low-lying atolls such as Kiribati, the lack of any high 

ground may appear to make these islands especially vulnerable to tsunami, so that even a 

Category 2 tsunami may be a cause for serious concern. On the other hand, because such atolls 

often have steep drop-offs in which ocean depths increase very rapidly with distance from the 

fringing reef, there may not be a pronounced shoaling effect. 

However, even small tsunami when timed with high tides may have a significant impact on an 

atoll community. Therefore it is important to use the deep-water modelling as input into island 

specific, finer resolution inundation modelling to understand the possible impacts and for 

communicating the comparative risk and consequences within an all hazard framework. 

Tsunami generating mechanisms are themselves not impacted on by climate change. However, 

climate change does impact indirectly on the vulnerability of communities to tsunami through 

increased stress on coastal systems. As well as issues with the timing of tsunami arrival with 

sea state or high tides, there are longer term issues through sea level and temperature changes 

which impact on the health of carbonate reefs which protect islands from affects of wave energy 

and contribute to beach building process. 

Tarawa & Abaiang Banaba 

Figure 22: Bathymetry of Tarawa, Abaiang and Banaba (Kruger 2007). 

According to the NGDC tsunami database (Appendix 2, Section 1), of the 3 Kiribati Island 

groups, the Line Islands have recorded the highest tsunami (0.3 m at Kritimati Is) for the Chile 

Tsunami in 1960 and the 1957 Andreanof Is (Aleutian Trench) earthquakes. The modelling of the 

1960 Chile tsunami (Appendix 2, Section 2) and the recorded impacts highlight the variation in 

local impact caused by shoaling that can occur with similar results from the deep water modelling 

eg Hawaii 2-11 m and Kritimati 0.3 m. The affects of shoaling are considerably less for atolls 

such as Kritimati and Kanton Islands than on Pitcairn Island, Samoa, Hawai’i or Japan etc. The 

most significant sources for the Line Islands (eastern Kiribati) are the South American trench 

sources around Peru and Chile and also the Aleutian sources. However Mariana, New Hebrides, 

and Kuril Trench sources are more significant for Gilbert Islands (western Kiribati). 

The sufficiently high resolution bathymetry to support inundation modelling is only available for 

three Islands, all in the Gilbert Group, Banaba, Abaiang and Tarawa (Figure 22). Abaiang and 


[32] 

Tarawa could be modelled together as the islands are close together and linked by an undersea 

ridge. The orientation of the ridge, north-south, and the relative openness of the lagoons to the 

west suggests potential vulnerability to the Mariana Trench (Figure A3-1[23]) in particular. 

Tarawa and Abaiang both have elevations less than 5 metres. Only Tarawa has additional spot 

valued at a finer resolution. 

Most infrastructure data could be derived from satellite imagery. Water supply and possibilities of 

fresh water lens inundation are critical issues for atolls and would need to be considered in risk 

modelling. 

Banaba Island is a geographically isolated and would need to be modelled separately. Its 

topographic data sets have been derived from 5 m contours and are therefore relatively course 

for inundation modelling. It is a raised atoll with a maximum elevation of 87 m. The availability of 

higher ground provides more options for evacuation of the coastal areas than are available to a 

low-lying atoll. 


[33] 

7 REFERENCES 

ABoM, 2007. Australian Bureau of Meteorology Web Site 

http://www.bom.gov.au 

Burbidge, D., Cummins, P. and Mleczko, R. 2007. A Probablistic Tsunami Hazard 

Assessment for Western Australia: Report to the Fire and Emergency Services Authority of 

Western Australia, Geoscience Australia. 

Cummins, P., April, 2007. The Solomon Islands Earthquake and Tsunami. Risk Research 

Group, Geoscience Australia. 

Damlamian, H., and Webb, A., 2005. Inter-tidal Channel Flow in North Tarawa (Draft), 

EU EDF SOPAC Report. 

Glassey, P., Heron, D., Ramsey, D., & Salinger, J. 2005 Identifying Natural Hazards and the 

risk they pose to Tonga. Geosource Tonga, Study Report 4. 

Kruger, J., & Sharma, S. 2007. Bathymetry of Kiribati (in prep.) EU- 

SOPAC Report. 

Lelaurin, J. 2000. Hydrodynamic Simulation with MIKE 21 of Abaiang Atoll, Kiribati SOPAC 

Training Report 87. 

Marks, K.M., & Smith W H F. 2006. An evaluation of publicly available global bathymetry 

grids. Marine Geophysical Researches. 

Morgan, F. 2004 Shallow water bathymetry mapping from Satellite Images, IRD. 

NGDC, 2007. National Geophysical Data Centre:-Historical Tsunami Run-up Database 

http://www.ngdc.noaa.gov/seg/hazard/tsu_db.shtml 

Pearce, H. 2006. ATAS/AusTWC Decision Processes, NMOC, 2006. ABoM. 

Pearce, H., 2007. (a) Inventory of Available Geospatial Data and Options for Tsunami 

Inundation & Risk Modelling, Tonga. SOPAC Miscellaneous Report MR651. 

Pearce, H., 2007. (b) Inventory of Geospatial Data and Options for Tsunami Inundation & 

Risk Modelling, Niue. SOPAC Miscellaneous Report MR652. 

Pearce, H., 2008.(a) Inventory of Geospatial Data and Options for Tsunami Inundation & 

Risk Modelling, Solomon Islands. SOPAC Miscellaneous Report MR654. 

Pearce, H., 2008. (b) Inventory of Geospatial Data and Options for Tsunami Inundation & 

Risk Modelling, Fiji. SOPAC Miscellaneous Report MR655. 

Pugh, D. 2004. Changing Sea Levels, Effects of Tides, Weather and Climate. 

Shlencker Mapping Pty Ltd., 1998. Report on GPS Ground Control Survey, Tarawa, Republic 

of Kiribati. 

Smith, R., Young, S., Biribo, N. 1994. Bathymetric, seismic and alternative sand and gravel 

resource surveys, Tarawa Atoll, Kiribati. SOPAC Preliminary Report 72. 

Smith, R., Biribo, N. 1995. Marine aggregate resources, Tarawa Lagoon, Kiribati – including 

current meter studies at three localities. SOPAC Technical Report 217 


SPSLCMP Pacific Country Report, June 2005. Sea Level & Climate: Their Present State 

Kiribati. 

Thomas, C., Burbidge, D., & Cummins, P., 2007. A Preliminary Study into the Tsunami 

Hazard faced by Southwest Pacific Nations, Risk and Impact Analysis Group, Geoscience 

Australia 

[34] 

Tomita, T., Arikawa, T., Tatasumi, D., Honda, K., Higashino, H, Watanabe, K, and Takahashi, S., 

2007. (in prep.) Preliminary Report on Field Survey of Solomon Islands Earthquake in 

April 2007. 

PTWC, 2007. Tsunami Warning Operations: Sea Level monitoring tide tool, display and 

decode of sea level data transmitted over the WMO Global Telecommunications System. 

USGS 2007. United Stated Geological Survey web site, http://earthquake.usgs.gov/ 

Warne, J. 2007. Australian Tsunami Warning System Sea Level Observation System, 

ASLOS Network Design, Australian Bureau of Meteorology (ABoM). 

Wikipedia, 2007.Tides, http://en.wikipedia.org/wiki/Tide 


[35] 

APPENDIX 1 

Datum and Definitions 

1 Seaframe Gauge Datum for Betio, Tarawa 

Figure A1-1: Seaframe Gauge Location at Betio on Tarawa and Datum (SLCMP Country Report 2005) 

Mean Sea Level (MSL) in Figure A1-1 is the average recorded level at the gauge over the three 

and a half year period 1974/1977. The 1974/1977 MSL at Tarawa was 1.189 metres above the 

UH Tide Staff Zero (and the SEAFRAME zero level). 

Regular surveys are undertaken by Geoscience Australia of the Sea Level and Climate 

Monitoring Program (SLCMP) for the Seaframe gauge at Betio, Tarawa. 


[36] 

2 Definitions and Acronyms for Tsunami, Tide and Wave Levels 

Figure A1-2: Datum. 

HAT (highest astronomical tide) LAT (lowest astronomical tide) 

These are the highest and lowest levels which can be predicted to occur under average 

MHHW (mean higher high water) The height of MHHW is the mean of the higher of the 

two daily high waters over a long period of time. When only one high water occurs on a 

day, this is taken as the higher high water. 

Meteorological effects on tides 

Meteorological conditions which differ from the average will cause corresponding 

differences between the predicted and the actual tide. Variations in tidal heights are 

mainly caused by strong or prolonged winds and by unusually high or low barometric 

pressure. 

Tidal predictions are computed for average barometric pressure. Low pressure systems 

tend to raise sea-levels and high pressure systems tend to lower them. The water does 

not, however, adjust itself immediately to a change of pressure. It responds, rather, to the 

average change in pressure over a considerable area. 

The effect of wind on sea-level and therefore on tidal heights and times is variable and 

depends on the topography of the area in question. In general, it can be said that wind will 

raise the sea-level in the direction towards which it is blowing. A strong wind blowing 

straight onshore will "pile up" the water and cause high waters to be higher than 

predicted, while winds blowing off the land will have the reverse effect. 

MSL (mean sea level) 

The average level of the sea over a long period or the average level which would exist in 

the absence of tides. 


[37] 

Storm surge (http://en.wikipedia.org/wiki/Storm_surge) 

A storm surge is an offshore rise of water associated with a low pressure weather system, 

typically a tropical cyclone. Storm surge is caused primarily by high winds pushing on the 

ocean's surface. The wind causes the water to pile up higher than the ordinary sea level. 

Low pressure at the center of a weather system also has a small secondary effect, as can 

the bathymetry of the body of water. It is this combined effect of low pressure and 

persistent wind over a shallow water body which is the most common cause of storm surge 

flooding problems. The term "storm surge" in casual (non-scientific) use is storm tide; that 

is, it refers to the rise of water associated with the storm, plus tide, wave run-up, and 

freshwater flooding. When referencing storm surge height, it is important to clarify the 

usage, as well as the reference point. NHC tropical storm reports reference storm surge as 

water height above normal astronomical tide level, and storm tide as water height above 

mean sea level. 

In areas where there is a significant difference between low tide and high tide, storm 

surges are particularly damaging when they occur at the time of a high tide. In these cases, 

this increases the difficulty of predicting the magnitude of a storm surge since it requires 

weather forecasts to be accurate to within a few hours. The most extreme storm surge 

events occur as a result of extreme weather systems, such as tropical cyclones. Factors 

that determine the surge heights for landfalling tropical cyclones include the speed, 

intensity, size of the radius of maximum winds (RMW), radius of the wind fields, angle of 

the track relative to the coastline, the physical characteristics of the coastline and the 

bathymetry of the water offshore. 

Figure A1-4: Storm surge (http://en.wikipedia.org/wiki/Storm_surge) 

Sieches (Pugh 2004) 

Tide gauge records, particularly those from islands and places linked to oceans by narrow 

continental shelfs, often show high-frequency oscillations superimposed on the normal tidal 

changes of sea-level. These oscillations, called seiches, are due to local resonant 

oscillations of the harbours and coastal areas. The period depends on the horizontal 

dimensions and depth of water in the harbour. There are a number of triggers for seiching 

such as gravity waves, winds, atmospheric pressure disturbances and seismic activity. 

When the energy for sieching comes from external wave sources e.g. a tsunami, the size 

of the entrance to an oscillating basin is critical. 

Shoaling 

As a tsunami leaves the deep water of the open-ocean and travels into the shallower water 

near the coast, it transforms. A tsunami travels at a speed that is related to the water depth 

- hence, as the water depth decreases, the tsunami slows. The tsunami's energy flux, 

which is dependent on both its wave speed and wave height, remains nearly constant. 

Consequently, as the tsunami's speed diminishes, its height grows. This is called 

shoaling. Because of this shoaling effect, a tsunami that is unnoticeable at sea, may grow 

to be several metres or more in height near the coast. 

The increase of the tsunami's waveheight as it enters shallow water is given by: 


[38] 

where hs and hd are wave-heights in shallow and deep water and Hs and Hd are the depths 

of the shallow and deep water. So a tsunami with a height of 1 m in the open ocean where 

the water depth is 4000m would have a wave-height of 4 to 5 m in water of depth 10 m. 

Just like other water waves, tsunami begin to lose energy as they rush onshore - part of 

the wave energy is reflected offshore [and in the case of an atoll, around the island], while 

the shoreward-propagating wave energy is dissipated through bottom friction and 

turbulence. Despite these losses, tsunami can still reach the coast with tremendous 

amounts of energy. Depending on whether the first part of the tsunami to reach the shore 

is a crest or a trough, it may appear as a rapidly rising or falling tide. Local bathymetry may 

also cause the tsunami to appear as a series of breaking waves. 

Tsunami 

A tsunami is a series of ocean waves with very long wavelengths (typically hundreds of 

kilometres) caused by large-scale disturbances of the ocean, such as: 

• earthquakes 

• landslide 

• volcanic eruptions 

• explosions 

• meteorites 

These disturbances can either be from below (e.g. underwater earthquakes with large 

vertical displacements, submarine landslides) or from above (e.g. meteorite impacts). 

Tsunami is a Japanese word with the English translation: "harbour wave". In the past, 

tsunami have been referred to as "tidal waves" or "seismic sea waves". The term "tidal 

wave" is misleading; even though a tsunami's impact upon a coastline is dependent upon 

the tidal level at the time a tsunami strikes, tsunami are unrelated to the tides. (Tides result 

from the gravitational influences of the moon, sun, and planets.) The term "seismic sea 

wave" is also misleading. "Seismic" implies an earthquake-related generation mechanism, 

but a tsunami can also be caused by a non-seismic event, such as a landslide or meteorite 

impact. 

Tsunami are also often confused with storm surges, even though they are quite different 

phenomena. A storm surge is a rapid rise in coastal sea-level caused by a significant 

meteorological event - these are often associated with tropical cyclones. 

Tsunami Travel Times 

Tsunami can have wavelengths ranging from 10 to 500 km and wave periods of up to an 

hour. As a result of their long wavelengths, tsunami act as shallow-water waves. A wave 

becomes a shallow-water wave when the wavelength is very large compared to the water 

depth. Shallow-water waves move at a speed, c, that is dependent upon the water depth 

and is given by the formula: 

where g is the acceleration due to gravity (= 9.8 m/s 2 ) and H is the depth of water (m). 


[39] 

As the travel times are dependant on depth of the water [H] rather than magnitude of the 

earthquake, scenario based travel times to any location can be pre-computed for any 

earthquake tsunami source. 

In the deep ocean, the typical water depth is around 4000 m, so a tsunami will therefore 

travel at around 200 m/s, or more than 700 km/hr. 

For tsunami that are generated by underwater earthquakes, the amplitude (i.e.wave 

height) of the tsunami is determined by the amount by which the sea-floor is displaced. 

Similarly, the wavelength and period of the tsunami are determined by the size and shape 

of the underwater disturbance. 

As well as traveling at high speeds, tsunami can also travel large distances with limited 

energy losses. As the tsunami propagates across the ocean, the wave crests can undergo 

refraction (bending), which is caused by segments of the wave moving at different speeds 

as the water depth along the wave crest varies. 

Types of waves (http://amath.colorado.edu/courses/4380/All/ii43.pdf) 

There are a number of types of wave with a range of causes, physical mechanisms, 

periods, velocity and regions of influence affecting the oceans affecting the oceans and 

therefore the tide gauge. These are shown in Table A1-1. 

A1-1: A number of wave types that can be found in lakes and oceans. 

Tidal heights 

The height of the tide, in metres, is reckoned from the port datum (lowest astronomical tide 

(LAT) datum). 

Tidal range variation: springs and neaps (http://en.wikipedia.org/wiki/Tide) 

The semidiurnal tidal range (the difference in height between high and low tides over about 

a half day) varies in a two-week or fortnightly cycle. Around new and full moon when the 

Sun, Moon and Earth form a line the tidal forces due to the Sun reinforce those of the 

Moon. The tide's range is then maximum: this is called the spring tide, or just springs and 

is derived not from the season of spring but rather from the verb meaning "to jump" or "to 

leap up". When the Moon is at first quarter or third quarter, the Sun and Moon are 

separated by 90° when viewed from the earth, and the forces due to the Sun partially 

cancel those of the Moon. At these points in the lunar cycle, the tide's range is minimum: 

this is called the neap tide, or neaps. Spring tides result in high waters that are higher than 

average, low waters that are lower than average, slack water time that is shorter than 


[40] 

average and stronger tidal currents than average. Neaps result in less extreme tidal 

conditions. There is about a seven day interval between springs and neaps. 

The changing distance of the Moon from the Earth also affects tide heights. When the 

Moon is at perigee the range is increased and when it is at apogee the range is reduced. 

Every 7½ lunations, perigee coincides with either a new or full moon causing perigean 

tides with the largest tidal range. If a storm [or tsunami] happens to be moving onshore at 

this time, the consequences (in the form of property damage, etc.) can be especially 

severe. 

Tsunami run-up (http://walrus.wr.usgs.gov/tsunami/basics.html). 

As the tsunami wave travels from the deep-water, continental slope region to the nearshore 

region, tsunami run-up occurs. Run-up is a measurement of the height of the water 

onshore observed above a reference sea level. Contrary to many artistic images of 

tsunami, most tsunami do not result in giant breaking waves (like normal surf waves at the 

beach that curl over as they approach shore). Rather, they come in much like very strong 

and very fast tides (i.e., a rapid, local rise in sea level). Much of the damage inflicted by 

tsunami is caused by strong currents and floating debris. The small number of tsunami that 

do break often form vertical walls of turbulent water called bores. Tsunami will often travel 

much farther inland than normal waves. 

At a gauge reference sea level is the predicted tide height. Without a gauge it is often the 

MHW mark or MSL. 

Figure A1-3: Definitions of inundation and run-up height (Tomita et al. 2007). 

Wavelength 

The mean horizontal distance between successive crests (or troughs) of a wave pattern. 

Wave period 

The average time interval between passages of successive crests (or troughs) of waves. 

Wave height 

Generally taken as the height difference between the wave crest and the preceding 

trough. 

Wave amplitude 

Generally taken as the height above mean of wave, approximately half wave height. 


Further information on tsunami 

[41] 

More information can be found at the following web sites: 

• General information 

International Tsunami Information Center 

Welcome to tsunami! 

Tsunami database (U.S. National Geophysical Data Center [NGDC]) 

• Tsunami warning centres and hazard mitigation 

International Coordination Group for the Tsunami Warning System in the Pacific 

Pacific Tsunami Warning Center 

West Coast and Alaska Tsunami Warning Center 

U.S. National Tsunami Hazard Mitigation Program 

• Earthquake information 

Geoscience Australia 

U.S. National Earthquake Information Centre 

European-Mediterranean Seismological Centre 

• The Indian Ocean tsunami of Dec. 26th 2004 

Scientific Background (from Columbia University) 

• Tsunami research 

Tsunami Research Center (University of Southern California) 

Tsunami Research Program (Pacific Marine Environmental Laboratory) 


[42] 

APPENDIX 2 

Historical Events Affecting Kiribati 

1 Previous Tsunami that have impacted on Kiribati 

Table A2-1(a) & (b): Extract from NGDC Tsunami data base. 

The extract from the National Geographic Data Centre (NGDC) Tsunami data base in Table A2- 

1 (a) and (b), shows the tsunami for range of sources that have been recorded or reported in 

Kiribati. The list is not necessarily complete as without a tide gauge it is difficult to identify small 

tsunami effects from normal background wave activity. Even with the gauge in the lagoon at 

Betio, readings for small tsunami will be difficult to distinguish. 

2 Comparison of Chile 1960 Tsunami Run-ups and Deep-water Modelling 


[43] 

The modelling of the 1960 Chile tsunami (Figure A2-1) and the recorded impacts highlight the 

variation in local impact caused by shoaling that can occur with similar results from the deepwater 

modelling eg Hawaii 2-11 m and Kritimati 0.3 m. The affects of shoaling are considerably 

less for atolls such as Kritimati and Kanton Islands than on Pitcairn Island, Samoa, Hawaii or 

Japan etc. 

Recorded run ups 

Pitcairn 12.2 m 

Kritimati, Kiribiti 0.3 m 

Kanton, Kiribati 0.1 m 

Hawai’i 2-11 m 

Apia, Samoa 4.9 m 

Suva, Fiji 0.5 m 

Truk, FSM 0.3 m 

Japan 1-6 m 

(NGCC Tsunami Database 

2007) 

From deep-water modelling: 

Line Island Group: Category 3 & 4 

Phoenix Island Group: Category 3 

Gilbert Island Group: Category 2 & 3 


(Thomas et al. 2007) 

Figure A2-1: Normalised Deep-water modelling of 1960 Chile tsunami and the recorded impacts. Location 

if Kiribati tide gauges are marked with purple cross. 

3 PTWC Warnings for Kiribati during Solomons 2 April Tsunami

Figure A2-2: Travel times map and model scenario for Solomons tsunami 2 April 2007 

[44] 

The enormous area covered by Kiribati from 173 E to 151 W causes some unique issues and 

problems. The range of longitudes for the 3 island groups means that different tsunami sources 

are more significant for each island group. Warnings were recently issued by PTWC for Kiribati 

for the Solomons event of 2 April 2007. Scenario modelling and forecast Travel times for this 

event are shown in Figure A2-2. The warning points used by PTWC for Kiribati are shown in 

Table A2-2, and examples of 2 PTWC warnings affecting Kiribati for this event are also shown 

below. 

Table A2-2: Kiribati warning locations used by PTWC. During the PTWC expanding 

warning/watch phase, once any of the locations below is within 3 hour travel time for the 

predicted expanding tsunami, all Kiribati will be included in the warning/watch process. Travel 

times are then provided for all Kiribati locations whether in warning or watch range. 

Tarawa Is. Gilbert Is. Group 1.5N 173.0E 

Kanton Is. Phoenix Is. Group 2.8S 171.7W 

Christmas Is. (Kritimati Is) Line Is. Group 2.0N 157.5W 

Malden Is. Line Is. Group 3.9S 154.9W 

Flint Is. Line Is. Group 11.4S 151.8W 

Once the western group, the Gilbert Islands, were included in the warning, by default the rest of 

Kiribati was also included with forecast arrival times. However, when Wallis-Futuna / Howland- 

Baker Is / Tokelau / Samoa / Wake Is / American Samoa / Tonga / Niue / Jarvis Is. / Palmyra Is. / 

Johnston Is were removed from Watch status and Marshall’s from PTWC Warning or Watch 

status, the current PTWC process did not provide a mechanism to remove the Phoenix and Line 

Islands groups from the warning/watch status as well. A similar problem would occur for another 

large Chile event, where a warning for the Line Island group in the east would automatically 

initiate a potentially unnecessary warning for the Gilbert Island group in the west. Kiribati does 

not have yet have, or have Regional support for, additional interpretation of PTWC warnings at a 

National level. This issue needs to be raised with the PTWC as it may be more appropriate to 

split the warning areas for Kiribati into three groups. 


[45] 

Figure A2-3: Relative location of Kiribati warning points (purple cross) and other countries referred to in 

PTWC warnings. 

Example 1 TSUNAMI BULLETIN NUMBER 002 

PACIFIC TSUNAMI WARNING CENTER/NOAA/NWS 

ISSUED AT 2132Z 01 APR 2007 

THIS BULLETIN IS FOR ALL AREAS OF THE PACIFIC BASIN EXCEPT 

ALASKA - BRITISH COLUMBIA - WASHINGTON - OREGON - CALIFORNIA. 

... A TSUNAMI WARNING AND WATCH ARE IN EFFECT ... 

A TSUNAMI WARNING IS IN EFFECT FOR 

SOLOMON IS. / PAPUA NEW GUINEA / VANUATU / NAURU / CHUUK / 

NEW CALEDONIA / POHNPEI / KOSRAE / AUSTRALIA / INDONESIA / 

TUVALU / KIRIBATI / MARSHALL IS. 

A TSUNAMI WATCH IS IN EFFECT FOR 

GUAM / FIJI / N. MARIANAS / YAP / HOWLAND-BAKER / 

WALLIS-FUTUNA / BELAU / TOKELAU / KERMADEC IS / SAMOA / 

NEW ZEALAND / MARCUS IS. / WAKE IS. / AMERICAN SAMOA / TONGA / 

NIUE / COOK ISLANDS / PHILIPPINES / JARVIS IS. / PALMYRA IS. / 

JOHNSTON IS. / JAPAN 

FOR ALL OTHER PACIFIC AREAS, THIS MESSAGE IS AN ADVISORY ONLY. 

AN EARTHQUAKE HAS OCCURRED WITH THESE PRELIMINARY PARAMETERS 


ORIGIN TIME - 2040Z 01 APR 2007 

COORDINATES - 8.6 SOUTH 157.2 EAST 

LOCATION - SOLOMON ISLANDS 

MAGNITUDE - 8.1 

EVALUATION 

[46] 

IT IS NOT KNOWN THAT A TSUNAMI WAS GENERATED. THIS WARNING IS 

BASED ONLY ON THE EARTHQUAKE EVALUATION. AN EARTHQUAKE OF THIS 

SIZE HAS THE POTENTIAL TO GENERATE A DESTRUCTIVE TSUNAMI THAT CAN 

STRIKE COASTLINES NEAR THE EPICENTER WITHIN MINUTES AND MORE 

DISTANT COASTLINES WITHIN HOURS. AUTHORITIES SHOULD TAKE 

APPROPRIATE ACTION IN RESPONSE TO THIS POSSIBILITY. THIS CENTER 

WILL MONITOR SEA LEVEL DATA FROM GAUGES NEAR THE EARTHQUAKE TO 

DETERMINE IF A TSUNAMI WAS GENERATED AND ESTIMATE THE SEVERITY OF 

THE THREAT. 

ESTIMATED INITIAL TSUNAMI WAVE ARRIVAL TIMES. ACTUAL ARRIVAL TIMES 

MAY DIFFER AND THE INITIAL WAVE MAY NOT BE THE LARGEST. THE TIME 

BETWEEN SUCCESSIVE TSUNAMI WAVES CAN BE FIVE MINUTES TO ONE HOUR. 

LOCATION COORDINATES ARRIVAL TIME 

-------------------------------- ------------ ------------ 

SOLOMON IS. MUNDA 8.4S 157.2E 2039Z 01 APR 

FALAMAE 7.4S 155.6E 2103Z 01 APR 

PANGGOE 6.9S 157.2E 2120Z 01 APR 

HONIARA 9.3S 160.0E 2121Z 01 APR 

GHATERE 7.8S 159.2E 2122Z 01 APR 

AUKI 8.8S 160.6E 2134Z 01 APR 

KIRAKIRA 10.4S 161.9E 2140Z 01 APR 

PAPUA NEW GUINE AMUN 6.0S 154.7E 2124Z 01 APR 

KIETA 6.1S 155.6E 2133Z 01 APR 

RABAUL 4.2S 152.3E 2145Z 01 APR 

LAE 6.8S 147.0E 2218Z 01 APR 

KAVIENG 2.5S 150.7E 2223Z 01 APR 

MADANG 5.2S 146.0E 2241Z 01 APR 

PORT MORESBY 9.5S 147.0E 2254Z 01 APR 

MANUS IS. 2.0S 147.5E 2259Z 01 APR 

WEWAK 3.5S 143.6E 2325Z 01 APR 

VANIMO 2.6S 141.3E 2350Z 01 APR 

VANUATU ESPERITU SANTO 15.1S 167.3E 2236Z 01 APR 

ANATOM IS. 20.2S 169.9E 2322Z 01 APR 

NAURU NAURU 0.5S 166.9E 2311Z 01 APR 

CHUUK CHUUK IS. 7.4N 151.8E 2329Z 01 APR 

NEW CALEDONIA NOUMEA 22.3S 166.5E 2338Z 01 APR 

POHNPEI POHNPEI IS. 7.0N 158.2E 2345Z 01 APR 

KOSRAE KOSRAE IS. 5.5N 163.0E 2345Z 01 APR 

AUSTRALIA CAIRNS 16.7S 145.8E 2349Z 01 APR 

BRISBANE 27.2S 153.3E 0033Z 02 APR 

SYDNEY 33.9S 151.4E 0114Z 02 APR 

GLADSTONE 23.8S 151.4E 0139Z 02 APR 

MACKAY 21.1S 149.3E 0144Z 02 APR 

HOBART 43.3S 147.6E 0245Z 02 APR 

INDONESIA JAYAPURA 2.4S 140.8E 2354Z 01 APR 

WARSA 0.6S 135.8E 0037Z 02 APR 

MANOKWARI 0.8S 134.2E 0056Z 02 APR 

PATANI 0.4N 128.8E 0158Z 02 APR 

GEME 4.8N 126.8E 0202Z 02 APR 

MANADO 1.5N 124.8E 0242Z 02 APR 

TARAKAN 3.3N 117.6E 0400Z 02 APR 

SINGKAWANG 1.0N 108.8E 1240Z 02 APR 

PANGKALPINANG 2.0S 106.2E 1547Z 02 APR 

TUVALU FUNAFUTI IS. 7.9S 178.5E 2359Z 01 APR 

KIRIBATI TARAWA IS. 1.5N 173.0E 0007Z 02 APR 

KANTON IS. 2.8S 171.7W 0121Z 02 APR 

CHRISTMAS IS. 2.0N 157.5W 0325Z 02 APR 

MALDEN IS. 3.9S 154.9W 0336Z 02 APR 

FLINT IS. 11.4S 151.8W 0408Z 02 APR 

MARSHALL IS. KWAJALEIN 8.7N 167.7E 0022Z 02 APR 

MAJURO 7.1N 171.4E 0028Z 02 APR 

ENIWETOK 11.4N 162.3E 0037Z 02 APR 

GUAM GUAM 13.4N 144.7E 0035Z 02 APR 

FIJI SUVA 18.1S 178.4E 0038Z 02 APR 

N. MARIANAS SAIPAN 15.3N 145.8E 0041Z 02 APR 

YAP YAP IS. 9.5N 138.1E 0048Z 02 APR 

HOWLAND-BAKER HOWLAND IS. 0.6N 176.6W 0057Z 02 APR 

WALLIS-FUTUNA WALLIS IS. 13.2S 176.2W 0100Z 02 APR 

BELAU MALAKAL 7.3N 134.5E 0103Z 02 APR 

TOKELAU NUKUNONU IS. 9.2S 171.8W 0119Z 02 APR 


[47] 

KERMADEC IS RAOUL IS. 29.2S 177.9W 0131Z 02 APR 

SAMOA APIA 13.8S 171.8W 0135Z 02 APR 

NEW ZEALAND NORTH CAPE 34.4S 173.3E 0138Z 02 APR 

EAST CAPE 37.5S 178.5E 0214Z 02 APR 

AUCKLAND(W) 37.1S 174.2E 0238Z 02 APR 

GISBORNE 38.7S 178.0E 0247Z 02 APR 

MILFORD SOUND 44.5S 167.8E 0249Z 02 APR 

NEW PLYMOUTH 39.1S 174.1E 0310Z 02 APR 

NAPIER 39.5S 176.9E 0316Z 02 APR 

WESTPORT 41.8S 171.2E 0332Z 02 APR 

AUCKLAND(E) 36.7S 175.0E 0332Z 02 APR 

WELLINGTON 41.5S 174.8E 0333Z 02 APR 

BLUFF 46.6S 168.3E 0351Z 02 APR 

NELSON 41.3S 173.3E 0426Z 02 APR 

LYTTELTON 43.6S 172.7E 0439Z 02 APR 

DUNEDIN 45.9S 170.5E 0506Z 02 APR 

MARCUS IS. MARCUS IS. 24.3N 154.0E 0138Z 02 APR 

WAKE IS. WAKE IS. 19.3N 166.6E 0141Z 02 APR 

AMERICAN SAMOA PAGO PAGO 14.3S 170.7W 0144Z 02 APR 

TONGA NUKUALOFA 21.0S 175.2W 0152Z 02 APR 

NIUE NIUE IS. 19.0S 170.0W 0209Z 02 APR 

COOK ISLANDS PUKAPUKA IS. 10.8S 165.9W 0212Z 02 APR 

PENRYN IS. 8.9S 157.8W 0316Z 02 APR 

RAROTONGA 21.2S 159.8W 0324Z 02 APR 

PHILIPPINES DAVAO 6.8N 125.7E 0215Z 02 APR 

LEGASPI 13.2N 124.0E 0248Z 02 APR 

ZAMBOANGA 7.0N 122.2E 0256Z 02 APR 

PALANAN 17.1N 122.6E 0307Z 02 APR 

LAOAG 18.2N 120.6E 0352Z 02 APR 

PUERTO PRINCESA 9.8N 119.0E 0404Z 02 APR 

SAN FERNANDO 16.6N 120.3E 0421Z 02 APR 

ILOILO 10.8N 122.8E 0438Z 02 APR 

MANILA 14.5N 120.8E 0517Z 02 APR 

JARVIS IS. JARVIS IS. 0.4S 160.1W 0256Z 02 APR 

PALMYRA IS. PALMYRA IS. 6.3N 162.4W 0300Z 02 APR 

JOHNSTON IS. JOHNSTON IS. 16.7N 169.5W 0308Z 02 APR 

JAPAN KATSUURA 35.1N 140.3E 0312Z 02 APR 

OKINAWA 26.2N 128.0E 0318Z 02 APR 

SHIMIZU 32.8N 132.8E 0359Z 02 APR 

KUSHIRO 42.8N 144.2E 0410Z 02 APR 

HACHINOHE 40.5N 141.8E 0415Z 02 APR 

BULLETINS WILL BE ISSUED HOURLY OR SOONER IF CONDITIONS WARRANT. 

THE TSUNAMI WARNING AND WATCH WILL REMAIN IN EFFECT UNTIL 

FURTHER NOTICE. 

Note: The warning was issued at 2132Z. Only Tarawa (and by association Gilbert Islands, western 

Kiribati) are in 3 hour warning status. Kanton, Christmas (Kritimati), Malden and Flint Islands are in 

watch stage. 

Country Location Lat/Long Expected arrival time 






Example 2 TSUNAMI BULLETIN NUMBER 006 

PACIFIC TSUNAMI WARNING CENTER/NOAA/NWS 

ISSUED AT 0158Z 02 APR 2007 

THIS BULLETIN IS FOR ALL AREAS OF THE PACIFIC BASIN EXCEPT 

ALASKA - BRITISH COLUMBIA - WASHINGTON - OREGON - CALIFORNIA. 

NOTE: AREAS TO THE NORTH OF THE SOLOMON ISLANDS SHOULD NOT 

BE SIGNIFICANTLY AFFECTED 

... A TSUNAMI WARNING AND WATCH ARE IN EFFECT ... 

A TSUNAMI WARNING IS IN EFFECT FOR 

SOLOMON IS. / PAPUA NEW GUINEA / VANUATU / NEW CALEDONIA / 


NORTHEASTERN AUSTRALIA / TUVALU / KIRIBATI / FIJI / 

KERMADEC IS / NEW ZEALAND 

[48] 

FOR ALL OTHER PACIFIC AREAS, THIS MESSAGE IS AN ADVISORY ONLY. 

AN EARTHQUAKE HAS OCCURRED WITH THESE PRELIMINARY PARAMETERS 

ORIGIN TIME - 2040Z 01 APR 2007 

COORDINATES - 8.6 SOUTH 157.2 EAST 

LOCATION - SOLOMON ISLANDS 

MAGNITUDE - 8.1 

MEASUREMENTS OR REPORTS OF TSUNAMI WAVE ACTIVITY 

GAUGE LOCATION LAT LON TIME AMPL PER 

------------------- ----- ------ ----- --------------- ----- 

MANUS PG 2.0S 147.4E 0040Z 0.09M = 0.3FT 40MIN 

VANUATU VU 17.8S 168.3E 0114Z 0.14M = 0.5FT 28MIN 

HONIARA SB 9.4S 160.0E 2308Z 0.20M = 0.6FT 62MIN 

LAT - LATITUDE (N=NORTH, S=SOUTH) 

LON - LONGITUDE (E=EAST, W=WEST) 

TIME - TIME OF THE MEASUREMENT (Z = UTC = GREENWICH TIME) 

AMPL - TSUNAMI AMPLITUDE MEASURED RELATIVE TO NORMAL SEA LEVEL. 

IT IS ...NOT... CREST-TO-TROUGH WAVE HEIGHT. 

IT IS ...NOT... CREST-TO-TROUGH WAVE HEIGHT. 

VALUES ARE GIVEN IN BOTH METERS (M) AND FEET (FT). 

PER - PERIOD OF TIME IN MINUTES(MIN) FROM ONE WAVE TO THE NEXT. 

NOTE: PTWC HAS RECEIVED REPORTS OF TSUNAMI RELATED FATALITIES IN 

SOUTHEAST PAPUA NEW GUINEA AND THE SOLOMON ISLANDS. 

EVALUATION 

SEA LEVEL READINGS INDICATE A TSUNAMI WAS GENERATED. IT MAY HAVE 

BEEN DESTRUCTIVE ALONG COASTS NEAR THE EARTHQUAKE EPICENTER AND 

COULD ALSO BE A THREAT TO MORE DISTANT COASTS. AUTHORITIES SHOULD 

TAKE APPROPRIATE ACTION IN RESPONSE TO THIS POSSIBILITY. THIS 

CENTER WILL CONTINUE TO MONITOR SEA LEVEL DATA TO DETERMINE THE 

EXTENT AND SEVERITY OF THE THREAT. 

FOR ALL AREAS - WHEN NO MAJOR WAVES ARE OBSERVED FOR TWO HOURS 

AFTER THE ESTIMATED TIME OF ARRIVAL OR DAMAGING WAVES HAVE NOT 

OCCURRED FOR AT LEAST TWO HOURS THEN LOCAL AUTHORITIES CAN ASSUME 

THE THREAT IS PASSED. DANGER TO BOATS AND COASTAL STRUCTURES CAN 

CONTINUE FOR SEVERAL HOURS DUE TO RAPID CURRENTS. AS LOCAL 

CONDITIONS CAN CAUSE A WIDE VARIATION IN TSUNAMI WAVE ACTION THE 

ALL CLEAR DETERMINATION MUST BE MADE BY LOCAL AUTHORITIES. 

ESTIMATED INITIAL TSUNAMI WAVE ARRIVAL TIMES. ACTUAL ARRIVAL TIMES 

MAY DIFFER AND THE INITIAL WAVE MAY NOT BE THE LARGEST. THE TIME 

BETWEEN SUCCESSIVE TSUNAMI WAVES CAN BE FIVE MINUTES TO ONE HOUR. 

LOCATION COORDINATES ARRIVAL TIME 

-------------------------------- ------------ ------------ 

SOLOMON IS. MUNDA 8.4S 157.2E 2039Z 01 APR 

FALAMAE 7.4S 155.6E 2103Z 01 APR 

PANGGOE 6.9S 157.2E 2120Z 01 APR 

HONIARA 9.3S 160.0E 2121Z 01 APR 

GHATERE 7.8S 159.2E 2122Z 01 APR 

AUKI 8.8S 160.6E 2134Z 01 APR 

KIRAKIRA 10.4S 161.9E 2140Z 01 APR 

PAPUA NEW GUINE AMUN 6.0S 154.7E 2124Z 01 APR 

KIETA 6.1S 155.6E 2133Z 01 APR 

RABAUL 4.2S 152.3E 2145Z 01 APR 

LAE 6.8S 147.0E 2218Z 01 APR 

KAVIENG 2.5S 150.7E 2223Z 01 APR 

MADANG 5.2S 146.0E 2241Z 01 APR 

PORT MORESBY 9.5S 147.0E 2254Z 01 APR 

MANUS IS. 2.0S 147.5E 2259Z 01 APR 

WEWAK 3.5S 143.6E 2325Z 01 APR 

VANIMO 2.6S 141.3E 2350Z 01 APR 

VANUATU ESPERITU SANTO 15.1S 167.3E 2236Z 01 APR 

ANATOM IS. 20.2S 169.9E 2322Z 01 APR 

NEW CALEDONIA NOUMEA 22.3S 166.5E 2338Z 01 APR 

AUSTRALIA CAIRNS 16.7S 145.8E 2349Z 01 APR 

BRISBANE 27.2S 153.3E 0033Z 02 APR 

SYDNEY 33.9S 151.4E 0114Z 02 APR 

GLADSTONE 23.8S 151.4E 0139Z 02 APR 


[49] 

MACKAY 21.1S 149.3E 0144Z 02 APR 

HOBART 43.3S 147.6E 0245Z 02 APR 

TUVALU FUNAFUTI IS. 7.9S 178.5E 2359Z 01 APR 






FIJI SUVA 18.1S 178.4E 0038Z 02 APR 

KERMADEC IS RAOUL IS. 29.2S 177.9W 0131Z 02 APR 

NEW ZEALAND NORTH CAPE 34.4S 173.3E 0138Z 02 APR 

EAST CAPE 37.5S 178.5E 0214Z 02 APR 

AUCKLAND(W) 37.1S 174.2E 0238Z 02 APR 

GISBORNE 38.7S 178.0E 0247Z 02 APR 

MILFORD SOUND 44.5S 167.8E 0249Z 02 APR 

NEW PLYMOUTH 39.1S 174.1E 0310Z 02 APR 

NAPIER 39.5S 176.9E 0316Z 02 APR 

WESTPORT 41.8S 171.2E 0332Z 02 APR 

AUCKLAND(E) 36.7S 175.0E 0332Z 02 APR 

WELLINGTON 41.5S 174.8E 0333Z 02 APR 

BLUFF 46.6S 168.3E 0351Z 02 APR 

NELSON 41.3S 173.3E 0426Z 02 APR 

LYTTELTON 43.6S 172.7E 0439Z 02 APR 

DUNEDIN 45.9S 170.5E 0506Z 02 APR 

BULLETINS WILL BE ISSUED HOURLY OR SOONER IF CONDITIONS WARRANT. 

THE TSUNAMI WARNING AND WATCH WILL REMAIN IN EFFECT UNTIL 

FURTHER NOTICE. 

Note: The warning was issued at 0158Z. All of representative locations are now within the 3 hour 

warning range. However initial tsunami wave should have passed though Tarawa and Kanton 

Islands and registered on Tarawa Tide Gauge. 

Country Location Lat/Long Expected arrival time 






Even though Wallis-Futuna / Howland-Baker / Belau / Tokelau / Kermadec Is / Samoa / Wake 

Is. / American Samoa / Tonga / Niue / Cook Is / Jarvis Is. / Palmyra Is. / Johnstone Is were 

removed from Watch status and Marshall’s from Warning or Watch status at this stage. The 

warning read as still current for eastern Kiribati, Phoenix and Line Island groups. 


[50] 

Tide Gauge Information for Solomons Event 2 April 2007 

The tide gauge at Betio, located in the Tarawa lagoon, is available in real-time for tsunami 

warning and monitoring. The Solomons tsunami was barely distinguishable at the Tarawa 

gauge. 

(a) 

(b) 

Figure A2-4: Seaframe Tide gauge recording at Betio for period of Solomons tsunami. Predicted arrival 

time: 2 April 0007 UTC. (a) Predicted and actual tide data, (b) Residuals with predicted tide removed. The 

gauge is protected in the lagoon and any recorded signal is less than 5 cm and to difficult to pick from 

other seiching. 


[51] 

Figure A2-5: Tide gauge recordings for Solomon Islands tsunami 2 April, 2007 

Figure A2-6: Tide gauge recording for Solomon Islands tsunami over the deep-water model scenario 

closest to the event. 


4 Tsunami Warning Related Background 

(i) Tsunami travel times 

[52] 

As tsunami travel times are dependant on the depth of the water (Appendix1 Section 2), 

approximate travel times from any source location can be precomputed. Figures A2-7 a-c 

provide reverse travel times to Tarawa, Kanton and Kritimati Islands from any source location. 

(a) 

(b) 

Tarawa 

Kanton 


(c) 

[53] 

Figure A2-7a-c: Tsunami travel times (hours) from any Pacific location to (a) Tarawa, Gilbert Islands, (b) 

Kanton, Phoenix Islands, (c) Kritimati, Line Islands. 

(ii) Summary of JMA/PTWC causal earthquake criteria 

Table A2-3: JMA and PTWC use simple criteria based on magnitude of the earthquake as a first 

guess assessment of an earthquakes potential to generate local, regional and ocean-wide 

Tsunami (Pearce 2006). 

Magnitude* (Mw) 

if less than 100km deep 

6.5 to 7.5 

7.6 to 7.8 

7.9 and above 

Kritimati 

PTWC & JMA Bulletin/Warning 

* Mw and depth may change in first hour 

** Amplitude for destructive tsunami > 0.5 m 

Potential for a locally destructive** tsunami 

within 1 hr (100km) 

Potential for a regionally destructive** 

tsunami within 3 hr (1000km ) 

Potential for an ocean wide destructive ** 

tsunami 

Table A2-3 provides a summary of the simple criteria, based on magnitude, from PTWC/JMA 

and ATAS, used as a first approximation of an earthquake’s potential to produce a local, regional 


[54] 

or ocean-wide tsunami. Maximum tsunami wave height is more directly proportional to the 

vertical displacement of the rupture; however as magnitude can generally be determined within 

10-15 minutes, it is used in the waarning process to provide a quick approximation.The vertical 

displacement takes considerably longer and is more difficult to estistimate. 

If an earthquake is deeper than 100km in the Earth’s crust, no tsunami will be generated. An 

event in the range 6.5 to 7.5 Mw could produce a locally destructive tsunami affecting an area 

within 100 km or 1 hour’s travel time. An event between 7.6 to 7.9 Mw could produce a regionally 

destructive tsunami affecting an area within 1000 km or 3 hrs travel time. Anything 7.9 Mw and 

above has the potential to produce an ocean-wide destructive tsunami. The PTWC & JMA also 

use the criteria, equal to or greater than 0.5 m amplitude as the definition of a destructive 

tsunami. 

The PTWC Bulletins are issued as advice to government agencies. Only national and local 

government agencies have the authority to make decisions regarding the official state of alert in 

their area and any actions to be taken in response. All PTWC warnings and travel-times are in 

UTC (equivalent Z and GMT). 

It is a National responsibility to provide public information; e.g. expected time of arrival in local & 

UTC time, recorded heights, the need to wait approx 2-3 hours from expected or actual time of 

arrival for all clear. 

(iii) Real-time sea level data available for tsunami monitoring 

Real-time sea level data for monitoring tsunami in the Pacific is available to all National 

Meteorological Agencies through the World Meteorological Organisations (WMO) global 

telecommunications system (GTS) network. Software is available from the IOC to decode and 

display this data. SOPAC are looking at a range of options for making this data and the analysis 

tools available to PICs. 

Currently most Pacific island countries access even their own data through web services such as 

University of Hawai’i (Figure A2-8) and Australian Bureau of Meteorology (ABoM) (Figure A2-9 

and Table A2-4). 

There are 3 sea-level gauges in Kiribati with real-time data access that can be used for tsunami 

monitoring. They are the ABoM Seaframe gauge at Betio, Tarawa and the University of Hawai’i 

gauges at Kritimati and Kanton islands. There are also a number of real-time data gauges in the 

region that can be used to monitor tsunami before they reach parts of Kiribati. These are shown 

in Figure A2-9. The only site were Kiribati can access all 3 of the Kiribati gauges and those of the 

countries nearby is from is the University of Hawai’i web site 

http://uhslc.soest.hawaii.edu/uhslc/data.html. Unfortunately this site is not supported out of 

normal working hours (not 24*7). 

Most of these gauges are in lagoons or harbours and readings will include a range of additional 

affects such as shoaling and seiching as well as other background noise which can make it hard 

to distinguish a small tsunami signal. Tidal information to compliment that can complement 

Tsunami warning arrival times is available at: 

http://www.bom.gov.au/oceanography/tides/MAPS/pac.shtml. 

NOAA DART Buoy network data (Figure A2-10) is available in semi real-time through 

http://www.ndbc.noaa.gov/dart.shtml these gauges are in deep water (about 3000 m) and are 

not affected by shoaling or seiching. A tsunami generated by the US and Aleutians and the 

Mariana trench sources could be confirmed by the DART buoy network. 


[55] 

NOAA’s proposed DART Buoys just below the equator at 170 E will assist monitoring for events 

from New Hebrides and Tonga Trenches. The proposed buoys for off the Kuril Trench and of 

Chile will also assist with monitoring events that will affect Kiribati. 

Figure A2-9: Location of Australia’s Seaframe tide gauge sites for SW Pacific. This network is also used 

for tsunami monitoring (Warne 2007). 


Figure A2-8: Location of University of Hawaii real-time sea level gauge sites (http://uhslc.soest.hawaii.edu/uhslc/data.html). 

[56] 


[57] 

Table A2-4: List of ABoM Seaframe gauges in Pacific and update frequency available for monitoring 

tsunami. The update frequency of the Pacific array is in the process of being upgraded to 10min updates. 

Figure A2-10: Deep ocean tsunami monitoring buoy network. 


[58] 

APPENDIX 3 

Additional Modelling 

1 Modelling of major tsunami for sources around the Pacific 

The deep-water modelling for the 39 magnitude 9 tsunami sources around the Pacific, used in 

the composite in section 4, are shown in Figure A3-1. Note that the main energy is beamed 

perpendicular to the trench and then channelled by bathymetry. 

1 

3 

5 6 

2 

4 


7 8 

9 

11 12 

13 

10 

14 

[59] 


15 

17 18 

19 

21 22 

16 

20 

[60] 


23 24 

25 26 

27 

29 30 

28 

[61] 


31 

33 34 

35 36 

37 38 

32 

[62] 


39 

[63] 

Figure A3-1: Sources for 9 Mw generated tsunami around the Pacific (prior to being normalised) (Thomas, 

written comm. 2007). The locations of the 3 Kiribati tide gauges are marked with purple crosses. 


[64] 

2 MOST model scenario for sources affecting Kiribati) 

Additional MOST (Method of Splitting Tsunami) deep-water model scenarios are available from 

ABoM web site for 7.5, 8.0, 8.5 and 9.0 Mw events for sources around the Southwest Pacific. 

The scenarios affecting the Gilbert Island group are at Figure A3-2. 

(i) Mariana Trench 

Figure A3-2: Mariana Trench a critical source for Gilbert Islands (ABoM 2007). 


(ii) Solomons/Northern New Hebrides Trench 

Figure A3-3: New Hebrides trench a critical source for Gilbert Islands (ABoM 2007). 

[65] 


(iii) Solomons Trench 

[66] 

Figure A3-4: Pink represents area ruptured during 2 April 2007 event. Grey the area that would need to 

rupture to produce a Magnitude 9 generated tsunami event (Cummins 2007). 

Figure A3-5: At magnitudes > 8.5 Solomons trench can be significant to north towards Kiribati (ABoM 

2007).

Kiribati: Review of Data available for Tsunami Inundation Modelling

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