Physics and structure of subduction-induced geodynamic transients in terms of reflection seismic and micro-seismological signatures
Zusammenfassung der Projektergebnisse
Using a combination of active and passive seismic imaging techniques we obtained an improved, high-resolution image of the Central Andean forearc system in North Chile. We reprocessed the ANCORP’96 dataset by a 3D coherency-based prestack depth migration method of all 130 gathers. The new image resolves structures both in the upper and the lower crust not revealed by previous prestack- and poststack migration studies. Concurrently, a micro seismic reflection imaging workflow was developed and applied successfully to a subset of the local micro earthquakes recorded by our West Fissure seismic network. A 15° westward dipping reflector at depths of 5-25km could be imaged which coincides with a distinct boundary of the seismicity distribution. The micro seismic imaging work is based on precisely determined event hypocenters, which were previously obtained also during this project. One major result of our work is the identification and imaging of a megathrust splay fault beneath the Longitudinal Valley. The joint interpretation of the active and passive seismic images and the hypocenters of the observed seismicity suggests a connection of the reflectivity on top of the subduction plate interface and the Precordilleran Fault system known at the surface. We further used the recorded micro seismicity to resolve the stress field of the Precordilleran Fault system by inverting 214 focal mechanisms. Cluster analysis of the seismicity was also performed both to improve the relative location quality and to study spatio-temporal patterns of seismicity. We detected several crustal earthquake clusters which may indicate the influence of fluids in triggering the seismic activity. A systematic search for potential non-volcanic tremors showed no evidence for tremor-like signals in the North Chile subduction zone during the recording period. Finally, we performed a feasibility study to determine the local 3-D Vp/Vs distribution in the Northern Chile subduction zone, indicating systematic variations of the Vp/Vs ratio within the down going Nazca slab.
Projektbezogene Publikationen (Auswahl)
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(2014), High-resolution image of the North Chilean subduction zone: seismicity, reflectivity and fluids, Geophysical Journal International 2014
Bloch,W., Kummerow, J., Salazar, P., Wigger, P., Shapiro, S. A.
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Microseismic reflection imaging of the Central Andean crust. GJI Geophysical Journal International, Volume 204, Issue 2, 1 February 2016, Pages 1396–1404
Schmelzbach, C., J. Kummerow, P. Wigger, A. Reshetnikov, P. Salazar, and S. A. Shapiro
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Seismic imaging of a megathrust splay fault in the North-Chilean subduction zone (Central Andes). Tectonophysics
Volume 689, 15 October 2016, Pages 157-166
Storch, I., Buske, S., Schmelzbach, C., Wigger, P.
