IPOC Gravity survey

Gravity survey in the IPOC-Array, Iquique, Northern Chile (IPOC-Grav)

DFG-Proposal: GO 380/29-1

Proponents: H.-J. Götze und M. Sobiesiak

Processing: H.-J. Götze, A. Boockmeyer, and the CAU Gravity Group MIGRA-2011

Field Crew: Anke Boockmeyer, Hans-Jürgen Götze, Oscar Lücke and Rezene Mahatsente Motivation Over the last years specific correlations between residual gravity anomalies and seismological data gained insight into the behaviour of dynamic processes at convergent plate margins (e.g. Oncken et al., 2006; Alasonati Tašárová, 2007; Tassara, 2010).

It was shown that the combination/assimilation of spatially distributed gravity anomalies with areas of seismological moment release bears information on material and structural behaviour of the causing seismological structures. They can affect also the propagation of earthquake rupture zones which is strongly related to the flexural rigidity of the lithosphere. If it is possible to tie these structures with geological and tectonical observations we can hope to make conclusions toward a temporal consistency of these structures, even over several seismic cycles. The detection of such structures and the explanation of their physical relevance for the rupture process provide additional information to investigate the seismic risk - particularly in locally limited areas. Over the last years several authors described spatial relationships between trench-parallel gravity anomalies (TPGA) and the distribution of maximum co-seismic displacement and/or the maximal reduction of seismic moment (asperities) at the earthquake rupture zone (Wells et al., 2003, Song and Simons, 2003, Fuller et al., 2006, Raeesi and Atakan, 2009). Here, mostly Bouguer-anomalies were analyzed, which image basin structures in the forearc area. Furthermore, they correlate with domains of maximum co-seismic moments. Wells et al. (2003) assume, that these basin structures are proxies for long-term reduction of the seismic moment. Song und Simons (2003) correlate positive trench-parallel topographic anomalies with distributions of maximum co-seismic displacements. These positive correlations are typical for many subduction zones around the Pacific. However, such areas own certain geometrical properties of the plate boundary where the building of sedimentary basins at deep sea terraces is possible. New results show that density anomalies in the upper plate can control the seismological behaviour in subduction zones (e.g. Tassara, 2010).