Fault Structure, Earthquake Interaction, and Source Properties of Two Small (Mw < 4) Sequences in the Walker Lane
Abstract
We analyze two well-recorded earthquake sequences within the Walker Lane tectonic region revealing fault structures, fault and source properties, and migration rates implying both fluids and aseismic slip. We use absolute and relative relocation and source parameter analysis, including stress drop and directivity, to investigate the 2017 Truckee and the 2014 Virginia City sequences.
In the 2017 Truckee sequence, two events (Mw 3.65 foreshock and Mw 3.85 mainshock), occurred ∼20 km north of Truckee, California, on 27 June 2017. We relocate 50 out of 52 earthquakes within the sequence, which define a single structure between 5 and 6 km depth, trending ∼N45°E and dipping ∼70°-80° to the northwest. The distribution of relocations matches the northeast-striking plane from two moment tensor solutions and computed first-motion focal mechanisms, indicating sinistral strike-slip motion on a previously unmapped fault. We observe stress drops ranging from 0.8-12.3 MPa, averaging ∼5 MPa using P and S waves and spatial variation related to the rupture areas of the foreshock and mainshock. We are able to detect components of directivity toward the northeast for the foreshock, and directivity toward the southwest for the mainshock, both aligning with the fault plane. The Virginia City, Nevada earthquake sequence (ML ≤ 3.2) began in early 2014, with the main part of the sequence occurring over a 10 day period in late January. We are able to relocate 366 of the 429 catalog events, which reveal three well-defined planar structures spanning 1 km, ranging from 8-10 km in depth. Observations show a clear migration of seismicity, from east to west, with each structure activating in turn. We attain stress drops for 12 of the events in the sequence, averaging 3.5 MPa for both P and S waves. Key observations of event migration and stress drop suggest that fluids and aseismic movement play a role within this sequence. This analysis illustrates the ability to extract details in fault characteristics, source properties, and rupture propagation for small sequences and can potentially provide data for more informed seismic hazard assessment.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.S41C0551H
- Keywords:
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- 7215 Earthquake source observations;
- SEISMOLOGYDE: 7223 Earthquake interaction;
- forecasting;
- and prediction;
- SEISMOLOGYDE: 7230 Seismicity and tectonics;
- SEISMOLOGYDE: 8118 Dynamics and mechanics of faulting;
- TECTONOPHYSICS