Reduced Compressional Wavespeeds and Poisson's Ratios Along the Nicoya Peninsula Seismogenic Zone, Costa Rica
Abstract
We present high-resolution compressional (Vp), shear (Vs), and Vp/Vs images of the Nicaragua/Costa Rica subduction seismogenic zone derived using double-difference local earthquake tomography methods. This study integrates data from onshore/offshore seismic networks along the Osa and Nicoya Peninsulas, Costa Rica, collected as part of CRSEIZE (PIs. S. Schwartz/L. Dorman) and along central Costa Rica and Nicaragua collected as part of the SFB 574 program (PIs. E. Flueh/W. Rabbel). Our data does not include the M7.6 2012 Nicoya Peninsula mainshock or aftershock sequence but does image the region that slipped during the earthquake. We find that microseismicity along the plate interface is confined to a low Vp and low Vp/Vs region extending from 30-50 km distance from the trench to approximately the slab-continental Moho intersection, though there is along-strike variability. Along the Nicoya Peninsula, the velocity feature extends updip of the interseismic microseismicity and includes the 2012 mainshock asperity and the region of high interplate coupling reported by Feng et al. (2012). The low Vp and Vp/Vs feature is bounded updip by increased Vp and Vp/Vs. We hypothesize that the variable velocity anomalies reflect changes in overpressure along the plate interface, following a model put forward by Saffer and Tobin (2011). The low Vp and Vp/Vs anomalies indicate moderate overpressures along the plate interface and define the seismogenic zone. The high Vp and Vp/Vs anomalies may reflect transitions updip and downdip to more extreme overpressures and conditions along the fault that would favor slow slip and tremor processes. Because this hypothesis relies on having well-resolved Vp/Vs, a notoriously difficult parameter to constrain using local earthquake tomography, we will use cross-correlation based P and S differential times to determine local Vp/Vs in regions with high seismicity rates.
- Publication:
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AGU Spring Meeting Abstracts
- Pub Date:
- May 2013
- Bibcode:
- 2013AGUSM.S44A..04D
- Keywords:
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- 7240 SEISMOLOGY / Subduction zones;
- 7270 SEISMOLOGY / Tomography;
- 8170 TECTONOPHYSICS / Subduction zone processes;
- 7230 SEISMOLOGY / Seismicity and tectonics