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STP-02 Deducing nature and magnitude of paleoearthquakes: Finding paleoevents and quantifying them
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Sedimentary, paleoseismic and archaeological record of earthquakes in moderate seismic zones. An example in the SE of Spain
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Miguel Angel Rodríguez-Pascua, IGME (Spain)
Raúl Pérez-López, Universidad San Pablo (Spain)
Jorge Luis Giner-Robles, Universidad San Pablo (Spain)
James Bischoff, USGS (United States)
Victor Hugo Garduño-Monroy, Universidad Michoacana SNH (Mexico)
Isabel Israde-Alcántara, Universidad Michoacana SNH (Mexico)
Pablo Gabriel Silva, Universidad de Salamanca (Spain)
José Pedro Calvo-Sorando, IGME (Spain)
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The identification of Holocene earthquakes in the geological record requires the combination of different techniques. Large active faults control the genesis of sedimentary basins. The sedimentary record of such basins is the goal of paleoseismological research of active faults using across-fault trenches. Prehistoric earthquakes can be identified by discontinuties, and correlated with archaeological data. The active Pozohondo Fault is located within the Prebetic Zone (SE Spain) showing dextral strike-slip movement. An active segment of this fault generated several Holocene endorheic basins (the Cordovilla closed-lake Basin). The sedimentary infill began during the Middle Pleistocene and continues to the present time. The lacustrine and palustrine sequences suggest three phases of movement from the Middle Pleistocene. By using radiometric dating (U-Th ages) combining with structural and stratigraphical studies of the basin, the slip-rate in this active segment is estimated to be 0.08 mm/yr. In this present study we present preliminary paleoseismological observations on the Tobarra-Cordovilla active segment (Pozohondo Fault), a complex graben basin (NW-SE) with back-tilting. We performed a 3D trenching survey at the distal NW part of the antithetic fault in the graben. From preliminary analysis, we have interpreted three recent seismic events (< 125 ka). Hence, the recurrence interval calculated is 1 - 10 ka for moderate-strong earthquakes (6 < Mw < 7). The archaeological site of Tolmo de Minateda, located long the faults trace 15 km SW from the Cordovilla Basin, contans a continuous record from 3.500 yr BP to present. Within the archaeological sequence, two gaps were identified sudden and unclear abandonment of the city (centuries VII and IX-X). We have carried out an archaeological study to consider seismic events that could explain these sudden abandonments: oriented fallen columns, collapsed walls, abandonment of irrigation systems for cultivation, etc.
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