Identification of seismogenic structures with influence on the subduction interface in Northern Chile and their signature in seismological data
Final Report Abstract
Identification of seismogenic structures with influence on the subduction interface in Northern Chile and their signature in seismological data: The crustal setting of the overriding South American Plate in the North Chile subduction zone is characterized by large batholothic structures, remnants of the Late Jurassic – Early Cretaceous volcanic arc along the convergent plate boundary. The major aim of the project was to study the role of these batholiths in terms of influencing the nucleation, propagation and location of large earthquakes on the subduction interface between the down-going oceanic Nazca plate and the overriding South American plate. To investigate the interaction of the subduction zone seismicity with these dense batholithic structures in the crust, we carried out gravity field measurements and installed a local network of 14 broad band and 7 short period seismological stations around the city of Iquique. The M 8.2 megathrust earthquake of April 1st 2014, showed that the network site and layout were well chosen as it covered exactly the N-S extension of the earthquake rupture. Throughout the networks operation, the recordings revealed enormous daily seismic activities in all magnitude ranges from micro seismicity (M<0) to small scale and intermediate seismicity up to larger events. Earthquake locations and clustering analysis exhibited that migration of activities obviously played a role in the preparation phase of the megathrust event. The alignment of co-seismic slip areas point to the possibility that the batholiths can play a role in the stopping phase of the earthquake rupture as well as in the pattern of largest energy release on the co-seismic rupture plane. Both would be important in hazard and risk assessment for all human structures on the Earths’ surface. While the Iquique Local Network (ILN) contributed to a detailed knowledge about all seismic activity in the area by compacting the general network of the Integrated Plate Boundary Observatory in North Chile, the processing of the gravity data was leading to a new and detailed density model for North Chile and delivered an insight into correlations between gravity anomalies and coupling coefficients of between upper and lower plate as derived by GPS measurements. These results complemented the seismological data and led to a study of the amount of vertical stress the batholiths are posing on the subduction interface. The amount of data outcome from the project is vast and therefore further studies are still ongoing. One seismological station of the ILN is collocated with a creep-meter instrument to measure directly the actual deformation on the active Chomache fault on the southern part of the study area. First results show that faults can get activated under certain circumstances also by earthquakes which occur far away from the fault itself. Therefore, for further open use in research, the ILN data can be accessed through the GEOFON website at www.gfz-potsdam.de.
Publications
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(2013), High-resolution relocation and mechanism of aftershocks of the 2007 Tocopilla (Chile) earthquake, Geophys. J. Int.
Fuenzalida, A., B. Schurr, M. Lancieri, M. Sobiesiak, and R. Madariaga
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(2014), Structure and State of Stress of the Chilean Subduction Zone from Terrestrial and Satellite-Derived Gravity and Gravity Gradient Data. Surv Geophys 35, 1417–1440
Gutknecht, B. D., H.-J. Götze, T. Jahr, G. Jentzsch, R. Mahatsente, St. Zeumann
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Segmentation of the Andean Margin by Isostatic Models and Gradients. Journal of South American Earth Sciences, Volume 59, April 2015, Pages 69-85
Schaller, T., J. Andersen, H.-J. Götze, N. Koproch, S. Schmidt, M. Sobiesiak, S. Splettstößer
