Rupture process for micro-earthquakes inferred from borehole seismic recordings

We investigate the spatial extent of rupture and variability in fault slip for micro-earthquakes by inverting seismic moment rate functions derived from empirical Green’s function deconvolution. By using waveforms from an array of borehole seismometers, we determine the spatial distributions of faul...

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Bibliographic Details
Published in:International journal of earth sciences : Geologische Rundschau 2015-09, Vol.104 (6), p.1499-1510
Main Authors: Taira, Taka’aki, Dreger, Douglas S., Nadeau, Robert M.
Format: Article
Language:English
Subjects:
Boreholes
Earth and Environmental Science
Earth Sciences
Earthquakes
Fault lines
Geochemistry
Geology
Geophysics/Geodesy
Mineral Resources
Original Paper
Plate tectonics
Sedimentology
Seismic activity
Seismology
Spatial distribution
Structural Geology
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Summary:We investigate the spatial extent of rupture and variability in fault slip for micro-earthquakes by inverting seismic moment rate functions derived from empirical Green’s function deconvolution. By using waveforms from an array of borehole seismometers, we determine the spatial distributions of fault slip for M 3+ earthquakes that occurred along the Hayward fault in central California and identify a variety of slip behaviors including subevents, directivity, and high stress drop. The 2013 M w 3.2 Orinda earthquake exhibits a complex rupture process involving two subevents with northwest and up-dip directivity. The two subevents release 43 and 18 % of the total seismic moment (6.7 × 10 13  N m), and their inferred peak stress drops are 18 and 8 MPa. The 2011 M w 4.0 Berkeley and 2012 M w 4.0 El Cerrito earthquakes are marked by high stress drop. The inferred peak and mean stress drops are about 100–130 and 40 MPa, respectively, which suggests that there are locally high levels of fault strength on the Hayward fault. Our finite-source modeling suggests that the radiation efficiency determined for these two earthquakes is very low (
ISSN:1437-3254
1437-3262
DOI:10.1007/s00531-015-1217-8