Guam Hazard Mitigation Plan - Western States Seismic Policy Council

SECTIONFIVERisk AssessmentEarthquake: Fault Proximity (Surface Fault Rupture)Similar to results from earlier versions of the Guam HMP, a moderate percentage of Guam’spopulation (about 16 percent) was found to be directly exposed to surface faulting while a similarproportion of the GBS was exposed at about 16 percent, or 6,385 buildings. In addition, 71Essential Facilities (worth $168.9 million), 83 Major Utilities (worth $177.2 million), and 43Transportation Systems (worth $13.0 million) are located in this hazard area.The assessment of the vulnerability to surface faulting represents an overemphasis of the hazardbecause a larger area has been determined to be exposed than actually will be exposed andbecause the analysis assumes all characterized faults to rupture across the island at the same time.Two different data sources of surface fault locations often characterize different faults anddifferent fault locations. Research has not been conducted to verify which dataset of faults iscorrect. In addition, the location of these surface faults has not been specifically characterized.Therefore, to remain conservative in assessing Guam’s vulnerability, both datasets are used and a984-foot buffer around each fault is used to describe the exposed area.As shown in Tables F-3 and F-4 (Appendix F [Vulnerability and Potential Loss Results byVillage]), in terms of village-level population exposed to surface faulting, Yigo leads with 5,757people (25.3 percent of village population), followed by Tamuning (4,502 people, 21.3 percent ofvillage population) and Dededo (4,251 people, 8.5 percent of village population).Exposure of the Essential Facilities is spread throughout all affected villages. The village with themost exposure of Essential Facilities is Hagatna, with 25 facilities that are worth $17.8 million. Inaddition, the most concentrated number of exposed Major Utilities are located in Yigo (16facilities valued at $28.6 million), Tamuning (10 facilities valued at $34.5 million), and Dededo(10 facilities worth $13.0 million). Hagatna and Tamuning also have the most concentratednumber of Transportation Systems, with 7 facilities valued at $5.9 million and 7 facilities valuedat $2.0 million, respectively.In terms of village-level GBS exposure, Yigo has the highest number of exposed GBS with 1,065(21.7 percent of village structures) worth $97.7 million. In this hazard area, Tamuning has 942GBS (26.6 percent) worth $388.7 million and Santa Rita has 786 GBS (29.5 percent) worth $61.9million.Earthquake: LiquefactionSimilar to the earlier versions of the Guam HMP, a relatively small population of 1,182 people(0.7 percent) on Guam currently resides in areas with very high or high levels of exposure toliquefaction, as shown in Tables 5-20 and 5-21. The percentage of EFMUTS located in areaswith very high or high levels of exposure is also relatively low with 26 Essential Facilities (worth$75.2 million), 13 Major Utilities (worth $204.6 million), and 19 Transportation Systems (worth$67.6 million). The exposed GBS is also relatively low with 584 structures (1.5 percent), valuedat $110.4 million.The high value of the Transportation Systems located in the hazard area is due to the location ofport facilities in Apra Harbor. In addition to the potential costs of replacement of the facilities atthe port, irreparable damage to these facilities could severely affect all movement of goods on andoff Guam. A value for the normal and daily functions of these facilities has not been assessed forthis analysis, but would be a secondary potential effect of this hazard event.5-63