The April 1, 2014 Pisagua Earthquake as a Natural Laboratory for Studying the Effect of Geologic Heterogeneity on Earthquake Slip

Wednesday, 17 December 2014
Anne M Trehu1, C David Chadwell2, Eduardo Contreras Reyes3, Francisco Ortega3, Javier A Ruiz3, Emilio E. Vera3, Andrei Maksymowicz3, Alexander de Moor1, Jose Antonio Mieres3, Edmundo O Norabuena4, Mark Simons5, Dietrich Lange6 and Heidrun Kopp6, (1)Oregon State University, Corvallis, OR, United States, (2)Scripps Institution of Oceanography, La Jolla, CA, United States, (3)University of Chile, Santiago, Chile, (4)Instituto GeofĂ­sico del PerĂș, Lima, Peru, (5)California Institute of Technology, Pasadena, CA, United States, (6)GEOMAR, Kiel, Germany
The April 1, 2014 Pisagua earthquake in Chile is interesting because the preparatory period before the April 1 main shock was very distinct and longer than usual. As a result, study of this sequence should provide clues to the processes leading up to large slip events on subduction plate boundaries. Moreover, the relationship between pre-event geodetic strain accumulation and the 2014 earthquake sequence is especially well documented because the event occurred in a known seismic gap that has attracted intensive monitoring efforts by the Chilean/French/German IPOC (Integrated Plate Boundary Observatory Chile) program and the Peru/United States CALTECH Tectonics Observatory for the past decade. Understanding of this sequence, however, is hindered by a lack of basic information from the offshore region, which is where most of the slip occurred. Even core information like swath bathymetry are lacking in most of the region. In this poster, we summarize current knowledge of continental margin structure in this region as inferred from low-resolution, bathymetrically-corrected satellite-derived gravity gravity and bathymetric data and a single seismic refraction profile located ~200 km south of the main shock epicenter. A strong qualitative correlation is observed between the temporal and spatial distribution of seismic activity leading up to, during and after the main shock, suggesting that the pre-event locking pattern and temporal pattern of earthquake activity are controlled by heterogeneity in the structure of the upper and/or lower plates. We also discuss the impact of the absence of offshore geodetic data on the resolution of the locking and slip distributions derived from onshore geodetic data and conclude that the value of this earthquake sequence as a natural laboratory for understanding the processes of strain accumulation and release through seismogenic slip and aseismic creep on plate boundaries would be greatly enhanced by acquisition of new offshore bathymetric, potential field, seismic and geodetic data.