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

Abstract

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:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1340914
Report Number(s):
LA-UR-15-27728
Journal ID: ISSN 0027-8424
Grant/Contract Number:
AC52-06NA25396
Resource Type:
Journal Article: 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)
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; faults; low-frequency earthquakes; tidal triggering; fortnightly tides

Citation Formats

van der Elst, Nicholas J., Delorey, Andrew A., Shelly, David R., and Johnson, Paul A.. Fortnightly modulation of San Andreas tremor and low-frequency earthquakes. United States: N. p., 2016. Web. doi:10.1073/pnas.1524316113.
van der Elst, Nicholas J., Delorey, Andrew A., Shelly, David R., & Johnson, Paul A.. Fortnightly modulation of San Andreas tremor and low-frequency earthquakes. United States. doi:10.1073/pnas.1524316113.
van der Elst, Nicholas J., Delorey, Andrew A., Shelly, David R., and Johnson, Paul A.. Mon . "Fortnightly modulation of San Andreas tremor and low-frequency earthquakes". United States. doi:10.1073/pnas.1524316113. https://www.osti.gov/servlets/purl/1340914.
@article{osti_1340914,
title = {Fortnightly modulation of San Andreas tremor and low-frequency earthquakes},
author = {van der Elst, Nicholas J. and Delorey, Andrew A. and Shelly, David R. and Johnson, Paul A.},
abstractNote = {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.},
doi = {10.1073/pnas.1524316113},
journal = {Proceedings of the National Academy of Sciences of the United States of America},
number = 31,
volume = 113,
place = {United States},
year = {Mon Jul 18 00:00:00 EDT 2016},
month = {Mon Jul 18 00:00:00 EDT 2016}
}

Journal Article:
Free Publicly Available Full Text
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Cited by: 3works
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  • The San Andreas, San Jacinto, and Imperial faults in California are divided into 19 segments; conditional probabilities are calculated that a particular segment will be the site of a large plate rupturing earthquake, i.e., an event that breaks the entire down-dip extent of the seismogenic zone, during the next 20 years. The sizes of such events, which account for most of the slip that occurs seismically, appear to vary greatly for different segments of these faults. Repeat time of large shocks, coseismic displacement, moment release, rupture length, and seismic magnitude appear to correlated with one another and to be amore » function of the tectonic style of different parts of those fault zones. Tectonic inhomogeneities on a scale of about 1 to 100 km are much larger than displacement in any single seismic event and may be regarded as being invariant in their effects upon earthquake generation over many cycles of large shocks. It is this invariance that appears to lead to a given segment of a fault rupturing repeatedly in events of nearly the same size. Since repeat time varies, however, for a given segment of a fault, a simple probabilistic approach is used to forecast the likelihood of large future earthquakes for each segment, using as input the time of the last large shock, the average recurrence time, and the standard deviation of time intervals between events. Dates of the last large shocks are available for most of the segments investigated. Repeat times are estimated from times of historic and prehistoric events, tectonic similarity, and times calculated from coseismic displacement in the last large shock divided by a rate of fault motion or strain buildup.« less
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