Open AccessFortnightly modulation of San Andreas tremor and low-frequency earthquakes
Author(s) -
N. van der Elst,
A. A. Delorey,
D. R. Shelly,
Paul A. Johnson
Publication year - 2016
Publication title -
proceedings of the national academy of sciences
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.1524316113
Subject(s) - brittleness , seismology , san andreas fault , geology , slip (aerodynamics) , stress (linguistics) , fault (geology) , amplitude , modulation (music) , geotechnical engineering , materials science , engineering , physics , composite material , acoustics , optics , linguistics , aerospace engineering , philosophy
Earth tides modulate tremor and low-frequency earthquakes (LFEs) on faults in the vicinity of the brittle-ductile (seismic-aseismic) transition. The response to the tidal stress carries otherwise inaccessible information about fault strength and rheology. Here, we analyze the LFE response to the fortnightly tide, which modulates the amplitude of the daily tidal stress over a 14-d cycle. LFE rate is highest during the waxing fortnightly tide, with LFEs most strongly promoted when the daily stress exceeds the previous peak stress by the widest margin. This pattern implies a threshold failure process, with slip initiated when stress exceeds the local fault strength. Variations in sensitivity to the fortnightly modulation may reflect the degree of stress concentration on LFE-producing brittle asperities embedded within an otherwise aseismic fault.
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