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Title: Constraints on Friction, Dilatancy, Diffusivity, and Effective Stress From Low-Frequency Earthquake Rates on the Deep San Andreas Fault

Families of recurring low-frequency earthquakes (LFEs) within nonvolcanic tremor on the San Andreas Fault in central California are sensitive to tidal stresses. LFEs occur at all levels of the tides, are strongly correlated and in phase with the ~200 Pa shear stresses, and weakly and not systematically correlated with the ~2 kPa tidal normal stresses. Here, we assume that LFEs are small sources that repeatedly fail during shear within a much larger scale, aseismically slipping fault zone and consider two different models of the fault slip: (1) modulation of the fault slip rate by the tidal stresses or (2) episodic slip, triggered by the tides. LFEs are strongly clustered with duration much shorter than the semidiurnal tide; they cannot be significantly modulated on that time scale. The recurrence times of clusters, however, are many times longer than the semidiurnal, leading to an appearance of tidal triggering. In this context we examine the predictions of laboratory-observed triggered frictional (dilatant) fault slip. The undrained end-member model produces no sensitivity to the tidal normal stress, and slip onsets are in phase with the tidal shear stress. The tidal correlation constrains the diffusivity to be less than ~1 × 10 -6/s and the productmore » of the friction and dilatancy coefficients to be at most 5 × 10 -7, orders of magnitude smaller than observed at room temperature. In the absence of dilatancy the effective normal stress at failure would be about ~55 kPa. Finally, for this model the observations require intrinsic weakness, low dilatancy, and lithostatic pore fluid.« less
Authors:
ORCiD logo [1] ; ORCiD logo [2] ; ORCiD logo [3] ; ORCiD logo [4]
  1. USGS Cascades Volcano Observatory, Vancouver, WA (United States)
  2. Univ. of Oregon, Eugene, OR (United States). Dept. of Earth Sciences
  3. Univ. of California, Berkeley, CA (United States). Earth and Planetary Science
  4. U.S. Geological Survey, Menlo Park, CA (United States). Volcano Science Center
Publication Date:
Grant/Contract Number:
AC02-05CH11231
Type:
Accepted Manuscript
Journal Name:
Journal of Geophysical Research. Solid Earth
Additional Journal Information:
Journal Volume: 123; Journal Issue: 1; Journal ID: ISSN 2169-9313
Publisher:
American Geophysical Union
Research Org:
Univ. of California, Berkeley, CA (United States); USGS Cascades Volcano Observatory, Vancouver, WA (United States); U.S. Geological Survey, Menlo Park, CA (United States)
Sponsoring Org:
USDOE; United States Geological Survey (USGS)
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; friction; effective stress; low-frequency earthquake
OSTI Identifier:
1479375

Beeler, N. M., Thomas, Amanda, Bürgmann, Roland, and Shelly, David. Constraints on Friction, Dilatancy, Diffusivity, and Effective Stress From Low-Frequency Earthquake Rates on the Deep San Andreas Fault. United States: N. p., Web. doi:10.1002/2017JB015052.
Beeler, N. M., Thomas, Amanda, Bürgmann, Roland, & Shelly, David. Constraints on Friction, Dilatancy, Diffusivity, and Effective Stress From Low-Frequency Earthquake Rates on the Deep San Andreas Fault. United States. doi:10.1002/2017JB015052.
Beeler, N. M., Thomas, Amanda, Bürgmann, Roland, and Shelly, David. 2017. "Constraints on Friction, Dilatancy, Diffusivity, and Effective Stress From Low-Frequency Earthquake Rates on the Deep San Andreas Fault". United States. doi:10.1002/2017JB015052. https://www.osti.gov/servlets/purl/1479375.
@article{osti_1479375,
title = {Constraints on Friction, Dilatancy, Diffusivity, and Effective Stress From Low-Frequency Earthquake Rates on the Deep San Andreas Fault},
author = {Beeler, N. M. and Thomas, Amanda and Bürgmann, Roland and Shelly, David},
abstractNote = {Families of recurring low-frequency earthquakes (LFEs) within nonvolcanic tremor on the San Andreas Fault in central California are sensitive to tidal stresses. LFEs occur at all levels of the tides, are strongly correlated and in phase with the ~200 Pa shear stresses, and weakly and not systematically correlated with the ~2 kPa tidal normal stresses. Here, we assume that LFEs are small sources that repeatedly fail during shear within a much larger scale, aseismically slipping fault zone and consider two different models of the fault slip: (1) modulation of the fault slip rate by the tidal stresses or (2) episodic slip, triggered by the tides. LFEs are strongly clustered with duration much shorter than the semidiurnal tide; they cannot be significantly modulated on that time scale. The recurrence times of clusters, however, are many times longer than the semidiurnal, leading to an appearance of tidal triggering. In this context we examine the predictions of laboratory-observed triggered frictional (dilatant) fault slip. The undrained end-member model produces no sensitivity to the tidal normal stress, and slip onsets are in phase with the tidal shear stress. The tidal correlation constrains the diffusivity to be less than ~1 × 10-6/s and the product of the friction and dilatancy coefficients to be at most 5 × 10-7, orders of magnitude smaller than observed at room temperature. In the absence of dilatancy the effective normal stress at failure would be about ~55 kPa. Finally, for this model the observations require intrinsic weakness, low dilatancy, and lithostatic pore fluid.},
doi = {10.1002/2017JB015052},
journal = {Journal of Geophysical Research. Solid Earth},
number = 1,
volume = 123,
place = {United States},
year = {2017},
month = {12}
}