Stress Drop Mapping in the Northern Chilean Subduction Zone

The Northern Chilean subduction zone has been monitored by the IPOC network for more than ten years. During this time period two very large earthquakes occurred, the 2007 M_W7.7  Tocopilla earthquake and the 2014 M_W8.1 Iquique earthquake. Over the entire subduction zone a vast amount of seismic activity has been recorded and a huge catalog was compiled including over 100000 events (Sippl et al. 2018). With this exceptional data base we attempt a systematic analysis of the stress drops of as many events from the catalog as possible. We apply different estimation techniques, namely the spectral ratio type, the spectral stacking approach, and the lower bound method. A goal of our research is a comparison and possibly a combination of the techniques to obtain reliable and well constrained results.

The data set covers events at the interface, within the subducting plate, crustal events, and intermediate depth events. It therefore bears a great potential to better understand the stress drop distribution within a subduction zone. Also, the long observation interval allows to analyze temporal variations according to pre-, inter-, and post-seismic phases of megathrust earthquakes.   

We present preliminary results where a subset of 730 events with a magnitude range of M_L2.7 - M_L4.8  was used for analysis with the spectral ratio technique. For these events we show maps of spatial stress drop variation, and we analyze the time dependent stress drop variance.