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Title: Repeating Earthquakes With Remarkably Repeatable Ruptures on the San Andreas Fault at Parkfield
Abstract

We calculate rupture directivity and velocity for earthquakes in three well‐recorded repeating sequences (2001–2016) on the San Andreas Fault at Parkfield usingPwaves from borehole recordings and the empirical Green's function method. The individual events in each sequence all show the same directivity; the largest magnitude sequence (M ~ 2.7, 8 events) ruptures unilaterally NW (at ~0.8Vs), the second sequence (M ~ 2.3, 9 events) ruptures unilaterally SE, and the smallest magnitude sequence (M ~ 2, 11 events) is less well resolved. The highly repetitive rupture suggests that geometry or material properties might control nucleation of small locked patches. The source spectra of theM ~ 2.7 sequence exhibit no detectable temporal variation. The smallerMsequences both exhibit a decrease in high‐frequency energy following theM6 earthquake that recovers with time. This could indicate a decrease in stress drop, an increase in attenuation, or a combination of the two, followed by gradual healing.

 
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NSF-PAR ID:
10451675
Author(s) / Creator(s):
 ;  ;  
Publisher / Repository:
DOI PREFIX: 10.1029
Date Published:
Journal Name:
Geophysical Research Letters
Volume:
47
Issue:
23
ISSN:
0094-8276
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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