Fortnightly modulation of San Andreas tremor and low-frequency earthquakes

Proceedings of the National Academy of Sciences
By: , and 

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Abstract

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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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Fortnightly modulation of San Andreas tremor and low-frequency earthquakes
Series title Proceedings of the National Academy of Sciences
DOI 10.1073/pnas.1524316113
Volume 113
Issue 31
Year Published 2016
Language English
Publisher National Academy of Sciences
Contributing office(s) Earthquake Science Center
Description 5 p.
First page 8601
Last page 8605
Country United States
State California
Other Geospatial San Andreas Fault