Archaeoseismology and Palaeoseismology in the Alpine ... - Tierra

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1 st INQUA‐IGCP‐567 International Workshop on Earthquake Archaeology and Palaeoseismology Fig. 1: Geomorphological map of the Río Grío Graben. 44
The graben has a markedly asymmetric geometry. The southwestern margin is controlled by two linear and well‐ defined normal faults; the 15.5 km long Vicort Fault and the 5.9 km long Modorra Fault. North of La Aldehuela the trace of NE‐dipping Vicort Fault coincides with that of the SW‐dipping Jarque or Inogés Thrust mapped by Aragonés et al. (1980). Both the Vicort and Modorra faults have a conspicuous geomorphic expression, showing linear mountain fronts with triangular facets up to 230 m. The trace of the fault coincides with the sharp rectilinear apical boundary in the alluvial fans deposited on the hanging wall. Unfortunately, no exposures showing the expectable normal fault contact between the alluvial fan sediments and the Paleozoic rocks of the uplifted blocks have been found along these range fronts. Some of the morphometric parameters of the mapped faults are presented in table 1. The Vicort and Modorra fault are separated in Codos area by a gap with a traverse tectonic depression controlled by NNE‐SSW‐ and NE‐SE‐trending cross‐faults and drained by the Güemil River. Table 1. Strike (St) and length (L) of the main mapped faults, dominant lithology (Lith) in the range front, height (H) and slope (S) of the largest triangular facet and expected moment magnitudes based on the fault length and the regressions proposed by Wells and Coppersmith (1994) for normal faults (Mw W‐C) and by Stirling et al. (2002) for preinstrumental earthquakes (Mw S). Lithology: Q: Quartzite; L: Limestone; C: Conglomerate; A: Argillite. Fault St L Lith H S Mw Mw W‐C S Vicort 135 15.5 Q 230 27 6.2 6.8 Modorra 136 5.9 Q 140 23 5.9 6.5 F1 148 1.7 L F2 147 2.8 L 5.4 6.2 F3 147 6.5 C, L 60 21 5.9 6.5 F4 146 5.8 Q 60 19 5.9 6.5 F5 148 5 Q 50 26 5.8 6.4 F6 155 4.5 A, Q 60 13 5.7 6.4 F7 137 4.1 Q 90 30 5.7 6.4 The northeastern margin of the depression is controlled by a series of shorter faults with a less obvious geomorphic expression. The trace of some of these faults coincides with the scarped northeastern margin of the Grío River fluvial valley (faults F7, F6 and southern portion of F3). Consequently, the triangular facets mapped along the northeastern margin of the Río Grío valley, generally steeper, may have a mixed tectonic and fluvial origin. The fault situated SE of Codos (F7) runs next and parallel to the Datos Thrust, suggesting that it may correspond to the postorogenic negative reactivation of the latter. In its NW portion this fault (F7) has offset alluvial fan deposits (Fig. 2) creating a downhill‐facing scarp around 37 m high. The anomalous oblique orientation of some tributary drainages in the NE margin of the depression seems to be controlled by uplifted (Horcajo Stream) or backtilted fault blocks (Valmiñano Stream) in combination with stepovers. The northern sector of the graben shows a more complex structure composed of a sequence of horsten and grabens around 1 km wide controlled by NW‐SE‐trending normal faults with an en échelon right‐stepping arrangement. Here, the Grío River constitutes an oblique drainage with respect to the graben faults rather than a longitudinal 1 st INQUA‐IGCP‐567 International Workshop on Earthquake Archaeology and Palaeoseismology 45 one. These faults are defined by linear scarps with triangular facets and an abrupt termination of the alluvial fan units. The graben bounded by fault F5 and the Vicort Fault corresponds to the southernmost sector of the so‐ called Morés Graben, in which Triassic formations are downfaulted between fault blocks of Paleozoic rocks. The termination of these faults in our map is based on the disappearance of triangular facets and alluvial fan sediments in the downdropped block. A normal fault contact between the alluvial fan sediments and the footwall bedrock has been inferred from an outcrop of fault F1 southwest of Mularroya. To the NE of Fault F2 and at the left margin of the Grío Valley, a small drainage has exposed alluvial fan deposits affected by several vertical failure planes. A N145E strike has been measured in one of these fault planes. Between faults F1 and F2, in cuttings of the A‐2302 and the old N‐II roads, the alluvial fan deposits are affected by failure planes attributable to paleocollapse structures caused by the karstification of the underlying Triassic evaporites. In a cutting of the abandoned N‐II road, tilted alluvial fan sediments are downdropped within highly brecciated early Jurassic carbonate rocks. We attribute this structure that does not appear in the opposite cut to evaporite interstratal dissolution and collapse. Fig. 2: Normal fault F7 juxtaposing alluvial fan deposits against strongly deformed Paleozoic rocks. The Río Grío graben depression is largely occupied by dissected alluvial fans. The majority of these fans are situated to the west of the Grío River. In the northern sector the NE inclination of the fan surfaces is controlled by the NW‐SE trending horst and graben structure, rather than being directed towards the Grío River. The alluvial fan deposits overlie a very irregular paleorelief and show a highly variable thickness, typically higher than 30 m. Locally the alluvial fill is interrupted by rounded inliers of Paleozoic or Mesozoic rocks that protrude over the top of the fan surfaces. In Tobed area, where the base of the basin fill is probably below the current base level, we have measured a minimum thickness of 90 m of alluvium. The alluvial sequence is dominated by tabular bodies of massive angular gravels and boulders with a sandy matrix and of massive sands with scattered clasts (sheetflood deposits). Some gravel beds with a matrix‐supported texture correspond to debris flow facies. Several terrace levels have been mapped north of Codos inset with respect to the alluvial fan units. This morpho‐stratigraphic sequence records two main evolutionary phases: (1) A first period of alluvial filling controlled by tectonic subsidence. (2) A second period in which tectonic subsidence was not high enough to counterbalance the
Page 1: Abstracts Volume Archaeoseismology
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Page 9 and 10: the importance of performing absolu
Page 11 and 12: indicative of strike‐slip faultin
Page 13 and 14: DISCUSSION Based on detailed field
Page 15 and 16: Table 1: Source parameters used in
Page 17 and 18: elations. However, the attenuation
Page 19 and 20: mostly concentrated on the DST in I
Page 21 and 22: continuous support. N. Shalev, G. G
Page 23 and 24: The tumulus initial morphology show
Page 27 and 28: our understanding and prediction of
Page 29 and 30: spans, with a threefold increase fr
Page 31 and 32: Nevertheless the lack of research,
Page 33 and 34: earthquake. In uncertain cases, as
Page 35 and 36: The site reconnaissance successfull
Page 43 and 44: Table 1: Surface faulting extent re
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Page 53 and 54: are a valuable addition to the rout
Page 55 and 56: to 400 m) the calculated values for
Page 57 and 58: RISK ANALYSIS The created hazard ma
Page 59 and 60: 290 m water depth the basin accumul
Page 61 and 62: CONCLUSIONS From the palaeostress a
Page 63 and 64: Fig. 2: Geological map of the study
Page 71 and 72: however, the massive 1995 earthquak
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Page 77 and 78: interpreted as either an expression
Page 79 and 80: The Shepran Cave is located on the
Page 87 and 88: properties. The mean value of speci
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1 st INQUA‐IGCP‐567 Internation
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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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The city collapsed and it was aband
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Fig. 4: Slipped lintel in a window
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to overcome shear resistance and in
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Newmark, N.M. (1965). Effects of ea
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associated with various tsunamis (<
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this method, the magnitude of the e
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etween pieces. Fragments have not f
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on the exact date of the earthquake
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THE ARCHAEOLOGICAL ZONE COLOGNE Aft
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affecting the Alcázar was about 50
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archaeoseismology could instead bec
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In the area later occupied by Vilni
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Fig. 2: Assemblage of landforms ass
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Fig. 8: Data and regression for mag
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Fig. 3: Relationships among magnitu
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CONCLUSIONS 1. Spatial distribution
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The stratigraphic sequence (Fig. 4)
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especially in the zones of hanging
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interpretations are based on relati
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Fig. 5: Gray‐scale value laser im
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(~40 cm), F‐ rotated building str
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Index 1 st INQUA‐IGCP‐567 Inter
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