Abstract

Seismic tomography is a powerful tool to study forearc structure and its variability along a subduction margin. In this study we perform a 3D seismic tomography in the area of the 2014 Mw 8.1 Iquique earthquake in northern Chile, using both data from an amphibious active source experiment and local seismicity. This area, considered by many authors as a seismic gap, is of great interest to the seismic community, even more after the 2014 earthquake and its intense foreshock and aftershock sequences. One of the research projects aimed at studying the area was PICTURES in 2016, which consisted of an offshore controlled source seismic experiment. We used the marine airgun shots from PICTURES recorded at a temporary inland seismic network as an input for the seismic tomography, as well as the local seismicity recorded over the period of the network operation. To complement this dataset, we also used local seismicity recorded in three networks installed at different time periods, before and after the main event. First arrival times of the shots were estimated using CORREL, a novel technique for automated picking of active seismicity developed by the authors, while onsets of local seismicity were estimated with the Regressive ESTimator package (REST). Using the available onsets, we performed seismic tomography to derive the velocity field in the marine forearc and explore the relevance of incorporating or not the arrival times of the shots in the final inversion result. For this purpose, we also performed a seismic tomography using only the local seismicity data and both were compared with an existing regional 3D velocity model.