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Title: Fortnightly modulation of San Andreas tremor and low-frequency earthquakes

Earth tides modulate tremor and low-frequency earthquakes (LFEs) on faults in the vicinity of the brittle-ductile (seismic-aseismic) transition. Our response to the tidal stress carries otherwise inaccessible information about fault strength and rheology. 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. Furthermore, 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.
Authors:
 [1] ;  [2] ;  [3] ;  [2]
  1. United States Geological Survey, Pasadena, CA (United States). Earthquake Science Center
  2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Geophysics Group
  3. United States Geological Survey, Pasadena, CA (United States). Volcanic Science Center
Publication Date:
Report Number(s):
LA-UR-15-27728
Journal ID: ISSN 0027-8424
Grant/Contract Number:
AC52-06NA25396
Type:
Accepted Manuscript
Journal Name:
Proceedings of the National Academy of Sciences of the United States of America
Additional Journal Information:
Journal Volume: 113; Journal Issue: 31; Journal ID: ISSN 0027-8424
Publisher:
National Academy of Sciences, Washington, DC (United States)
Research Org:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; faults; low-frequency earthquakes; tidal triggering; fortnightly tides
OSTI Identifier:
1340914