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Seismic Attenuation Monitoring of a Critically Stressed San Andreas Fault
Author(s) -
Malagnini Luca,
Parsons Tom
Publication year - 2020
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2020gl089201
Subject(s) - san andreas fault , geology , seismology , attenuation , fault (geology) , physics , optics
We show that seismic attenuation ( Q S − 1 ) along the San Andreas fault (SAF) at Parkfield correlates with the occurrence of moderate‐to‐large earthquakes at local and regional distances. Earthquake‐related Q S − 1anomalies are likely caused by changes in permeability from dilatant static stress changes, damage by strong shaking from local sources, and pore unclogging/clogging from mobilization of colloids by dynamic strains. We find that, prior to the 2004 M 6 Parkfield earthquake, prefailure conditions for some local events of moderate magnitude correspond to positive anomalies of Q S − 1on the Pacific side, with local and regional earthquakes producing sharp attenuation reversals. After the 2004 Parkfield earthquake, we see higher Q S − 1anomalies along the SAF, but low sensitivity to local and regional earthquakes, probably because the mainshock significantly altered the permeability state of the rocks adjacent to the SAF, and its sensitivity to earthquake‐induced stress perturbations.