Archaeoseismology and Palaeoseismology in the Alpine ... - Tierra

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Sliding The sliding processes along the escarpment are closely linked to the genesis of hanging valleys. Buoyant water forces, weathering and possible seismic activity seem to be important trigger mechanisms for the examined sliding events but the principal reason for reducing slope stability lies within the intersection of tension cracks. Close to the triangular facets and hanging valleys north‐ and southwards dipping discontinuities often build a line of intersection that is inclined out of the slope (Fig. 7). Thereby it forms a sliding axis and causes wedge failures, a special type of movement for which Norrish and Wyllie (1996) declare the following necessary condition: slope > line of intersection > friction Fig. 7: Wedge failure on two intersecting discontinuities with a line of intersection which “daylights” the slope Even if statistical evaluations indicate that most of the intersection linears dip gently, the friction angle can be exceeded because of water in cracks, that clearly reduces shear strength. A wedge failure also might be triggered by seismic energy. Recent tectonic is related to the ground failures and architectural disturbances, which are recorded at the nearby ancient Roman city of Baelo Claudia (Silva et al., 2009). All mentioned internal and external influences cause the formation of hanging valleys which work as channels, guiding the debris and boulders down the slope. RUNOUT DISTANCES AND ROCK DEPOSITS According to the steep slope below the range front falling blocks reach distances of up to 600 m. In the course of this study these long runout rockfalls as well as boulders and debris up to a size of 2 m³ close to the range front have been analysed with the software ROCKFALL 6.1. Considering to selected slope and rock properties, 1 st INQUA‐IGCP‐567 International Workshop on Earthquake Archaeology and Palaeoseismology 164 Fig. 8: Simulated rockfall along a section shape showing the steepest path from the source zone rockfalls have been simulated along several section shapes showing the steepest pathes from the source zone on. Exemplary, one of the calculated runout distances is shown in Fig. 8 that also illustrates the energy and the amplitude of a block versus distance to the source. Most of the results concur with observed deposits being mapped along the slope during the field work. It shows that Rockfall 6.1 can offer a realistic simulation, however only approximated values are used for parameter input. This is helpful for classifying rockfalls and creating hazard maps. References Dikau, R., Schrott, L. & Dehn, M. (1996). Topple. In: R. Dikau, D. Brunsden, L. Schrott & M.‐L. Ibsen [Hrsg.], Landslide Recognition, Identification, Movement and Courses, Wiley, Chinchester, 29‐41. Durand‐Delga, M. (2006). Geological adventures and misadventures of the Gibraltar Arc. Z. dt. Ges. Geowiss., 157, 687‐716. Norrish, N.I. & Wyllie, D.C. (1996). Rock slope stability analysis. In: A.K. Turner & R.L. Schuster [Hrsg.], Spezial Report 247: Landslides, Investigation and Mitigation, TRB, National Research Council, National Academy Press, Washington, D.C., 391‐425. Silva P.G., Reicherter K., Grützner C., Bardají T., Lario J., Goy J.L., Zazo C., & Becker‐Heidmann P., (2009). Surface and subsurface palaeoseismic records at the ancient Roman city of Baelo Claudia and the Bolonia Bay area, Cádiz (South Spain). Geological Society, London, Special Publications 2009; v. 316: Palaeoseismology: Historical and prehistorical records of earthquake ground effects for seismic hazard assessment. Weijermars, R. (1991). Geology and tectonics of the Betic Zone, SE Spain. Earth‐Sci. Rev., 31, 153‐236.
1 st INQUA‐IGCP‐567 International Workshop on Earthquake Archaeology and Palaeoseismology PALAEOTSUNAMI SIGNATURES IN HOLOCENE COASTAL GEO‐ARCHIVES OF THE EASTERN IONIAN SEA REGION, GREECE A. Vött, G. Bareth (1), H. Brückner (2), I. Fountoulis (3), F. Lang (4), D. Kelletat (5), D. Sakellariou (6), A. Scheffers (7) and S. Scheffers (7) (1) Institute for Geography, Universität zu Köln, Albertus‐Magnus‐Platz, 50923 Köln (Cologne), GERMANY. andreas.voett@uni‐koeln.de (2) Faculty of Geography, Philipps‐Universität Marburg, 35032 Marburg, GERMANY. (3) Department of Dynamic, Tectonic, Applied Geology, National and Kapodistrian University of Athens, 15784 Athens, GREECE. (4) Department of Classical Archaeology, Technische Universität Darmstadt, El‐Lissitzky‐Str. 1, 64287 Darmstadt, GERMANY. (5) Institute for Geography, Universität zu Köln, Albertus‐Magnus‐Platz, 50923 Köln (Cologne), GERMANY. (6) Hellenic Centre for Marine Research, 19013 Anavissos, GREECE. (7) School of Environmental Science and Management, Southern Cross University, PO Box 157, Lismore NSW 2480. AUSTRALIA. Abstract: This paper gives an overview of four different groups of tsunami signatures encountered in near‐coast geological archives along the shores of the eastern Ionian Sea, Greece. As the study sites are exposed towards the seismically highly active Hellenic Arc, the palaeotsunami events are suggested to have been triggered by seismic events or related landslides over or underwater. The group of sedimentary tsunami signatures comprises (i) dislocated blocks and boulders, (ii) allochthonous marine sediments deposited in littoral or near‐shore environments and often mixed with terrigenous material and cultural debris, (iii) allochthonous fine‐grained marine deposits intersecting in‐situ sediments of near‐shore swamps, quiescent freshwater lakes or lagoonal environments, and (iv) beachrock‐type calcarenitic tsunamites. Results from case studies are presented for each group of tsunami signatures. Key words: Palaeotsunami, dislocated boulders, sandwich layers, beachrock INTRODUCTION Tsunami hazard in the eastern Mediterranean belongs to the highest worldwide. This is mostly due to the high seismic activity along the Hellenic Arc where the African Plate is being subducted under the Eurasian Plate inducing numerous strong tsunamigenic earthquakes. Also, the Arabian Plate, moving northward by high rates, is a serious source of seismically related hazards. Further potential tsunami triggers in the Mediterranean are submarine slides, meteorite impacts, and explosional volcanic activity, for instance around Sicily or in the Aegean Sea. The eastern Mediterranean is characterized by comparatively short shore‐to‐shore distances, a highly variable underwater topography and thousands of kilometers of coastline with numerous indentations. In terms of tsunami hazard, this constellation implicates short time intervals for advance warning of local populations, strong refraction effects difficult to predict and a variety of secondary, mostly earthquake‐related hazards such as rockfall, liquefaction and subaerial and underwater landslides. Palaeotsunami research in the eastern Mediterranean has been strongly intensified during the past decades, in order to improve our understanding of the dimension and the dynamic of tsunami landfalls and to gain reliable background information for future risk assessment. Besides archival studies based on ancient accounts and historical data related to extreme wave events in the Mediterranean, an increasing number of geo‐scientific field studies have been carried out to detect palaeotsunami deposits. These tsunami deposits can be classified into four main groups. 165 DISLOCATED BOULDERS – THE CAPE SKALA CASE STUDY The first group comprises dislocated boulders, originating from bedrock units within the littoral zone, that were torn out, uplifted, turned over and/or transported dozens of meters inland by tsunamigenic wave action. Such deposits are reported from southern Italy (Puglia), Greece (Ionian Islands, Peloponnese, Crete), southern Turkey, Cyprus and from the Levant. In the western Mediterranean, tsunamigenically dislocated boulders were recently described from the Algerian and Tunisian coasts. Fig. 1: Dislocated boulders near Cape Skala, southern Peloponnese with imbrications structure. Person as scale measures approx. 1.65 m. Within the framework of our studies, tsunamigenically dislocated boulders were encountered west of Cape Skala at the Lakonian Gulf, southern Peloponnese. Large boulders were found more than 150 m inland and up to
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Abstracts Volume Archaeoseismology
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Edita e imprime: Sección de Public
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1 st INQUA‐IGCP‐567 Internation
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the importance of performing absolu
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indicative of strike‐slip faultin
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DISCUSSION Based on detailed field
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Table 1: Source parameters used in
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elations. However, the attenuation
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mostly concentrated on the DST in I
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continuous support. N. Shalev, G. G
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The tumulus initial morphology show
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our understanding and prediction of
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spans, with a threefold increase fr
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Nevertheless the lack of research,
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earthquake. In uncertain cases, as
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The site reconnaissance successfull
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Table 1: Surface faulting extent re
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The graben has a markedly asymmetri
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are a valuable addition to the rout
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to 400 m) the calculated values for
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RISK ANALYSIS The created hazard ma
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290 m water depth the basin accumul
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CONCLUSIONS From the palaeostress a
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Fig. 2: Geological map of the study
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however, the massive 1995 earthquak
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mapped on the slopes above Qiryat
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interpreted as either an expression
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The Shepran Cave is located on the
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properties. The mean value of speci
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excavated a deep trench, thus provi
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Fig. 8: Seismic ground shaking may
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elevant qualitative criteria are po
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CONCLUDING REMARKS The exposed exam
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produced by significantly different
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It is possible that a portion of th
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In addition, the Database of histor
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were published by IGME (1983) and E
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Page 115 and 116: The city collapsed and it was aband
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Page 119 and 120: Fig. 4: Slipped lintel in a window
Page 121 and 122: to overcome shear resistance and in
Page 123 and 124: Newmark, N.M. (1965). Effects of ea
Page 125 and 126: associated with various tsunamis (<
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Page 133 and 134: etween pieces. Fragments have not f
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Page 139 and 140: THE ARCHAEOLOGICAL ZONE COLOGNE Aft
Page 143 and 144: affecting the Alcázar was about 50
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Page 149 and 150: In the area later occupied by Vilni
Page 155 and 156: Fig. 2: Assemblage of landforms ass
Page 157 and 158: Fig. 8: Data and regression for mag
Page 159 and 160: Fig. 3: Relationships among magnitu
Page 161 and 162: CONCLUSIONS 1. Spatial distribution
Page 163 and 164: The stratigraphic sequence (Fig. 4)
Page 165: especially in the zones of hanging
Page 169 and 170: interpretations are based on relati
Page 173 and 174: Fig. 5: Gray‐scale value laser im
Page 177 and 178: (~40 cm), F‐ rotated building str
Page 179 and 180: Index 1 st INQUA‐IGCP‐567 Inter
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Archaeoseismology and Palaeoseismology in the Alpine ... - Tierra

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