Characterization of Holocene Sediments Using Geophysical Methods and Borehole Information - Ebro Delta (Spain)
B. Benjumea, A. Gabàs, A. Macau, F. Bellmunt, S. Figueras and M. Vilà
Event name: 23rd European Meeting of Environmental and Engineering Geophysics
Session: Integrated Approaches in Near-surface Geophysics II
Publication date: 03 September 2017
Info: Extended abstract, PDF ( 1.53Mb )
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Identification of zones vulnerable to subsidence is a critical task for planning protection actions in deltas. This identification mainly relies on Holocene sediments characterization. Geophysical studies have been carried out in the Ebro Delta (Spain) with this objective. In this paper we focus in two borehole sites where several surface geophysical techniques have been applied to find geophysical patterns that help to characterize the Holocene sequence. The applied methods are: active and passive seismic (H/V and array), electrical resistivity tomography (ERT) and audiomagnetotellurics methods (AMT). Shear wave velocity from active seismic can help to discriminate between surficial sediment facies. Combining this method with array measurements allows obtaining a complete Vs profile for the Holocene sediments. Another targets included in delta sediments characterization are depth and thickness of the Prodelta marine clays due to their particular geotechnical characteristics. These sediments are the origin of dominant higher modes of surface waves which help to their identification. Finally, ERT and AMT results show a resistivity change that can be related to the transition between Holocene sediments to Pleistocene gravels. This contact also produces a second peak in H/V spectral ratio that can be used to estimate the depth of Holocene delta base.