A Crustal Focal Mechanism Catalog for Northern Chile: Initial Results
Chile experiences considerable seismic hazard from interplate, intraplate and crustal earthquakes. Due to their large magnitudes and frequent occurrence in the Nazca subduction zone, interplate and intraplate earthquakes have been widely studied with broadband and strong motion networks. However, the smaller-magnitude crustal seismicity has been studied much less, and the lack of sufficiently dense seismic networks over most of the country makes comprehensive studies of crustal events very challenging.
In Northern Chile, the interseismic gap since the last giant thrust earthquake in 1877 has motivated the deployment of several temporary and permanent seismic networks since the early 2000s, thus providing new opportunities to carry out seismological studies in the area, especially between latitudes 18°S and 24°S.
We select more than 800 ML ≥ 3.0 crustal earthquakes that occurred between 2005 and 2018, reported in two recently-published earthquake catalogs for the area, and calculate their focal mechanisms using P-wave polarities and S/P amplitude ratios from broadband and short-period waveform data recorded by local stations.
Our initial results show a variety of faulting geometries, with some trends becoming evident. Several offshore crustal events show north-south strike with thrust mechanisms, indicating strong influence of the main plate subduction. However, several onshore events near 21°S show a clear east-west strike, with north-south horizonal pressure axes, which may indicate the existence of additional local tectonic features in compressive regime. Further inland, persistent seismicity occurs in the Andes mountains in a small area near latitude 19.7°S, which could be related to the 2001 Mw 6.3 Aroma crustal earthquake.
Our compilation of crustal-earthquake results for Northern Chile can provide clues to local and regional faulting patterns, and serve as a basis for crustal stress mapping studies in the region.
Presenting Author: Carlos Herrera
Additional Authors
Carlos Herrera carlosfherrera@uvic.ca University of Victoria, Victoria, British Columbia, Canada Presenting Author
Corresponding Author
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John F Cassidy john.cassidy@canada.ca Geological Survey of Canada, Sidney, British Columbia, Canada |
Stan E Dosso sdosso@uvic.ca University of Victoria, Victoria, British Columbia, Canada |
Wasja Bloch wasja@gfz-potsdam.de GFZ Research Center for Geosciences, Potsdam, , Germany |
Christian Sippl sippl@ig.cas.cz Czech Academy of Sciences, Prague, , Czech Republic |
A Crustal Focal Mechanism Catalog for Northern Chile: Initial Results
Category
Earthquake Source Parameters: Theory, Observations and Interpretations