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In-situ observation of pre-, co- and post-seismic shear slip at 1.5 km depth
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  • Martin Schoenball,
  • Yves Guglielmi,
  • Jonathan Blair Ajo-Franklin,
  • Paul J Cook,
  • Patrick Dobson,
  • Chet Hopp,
  • Timothy J Kneafsey,
  • Florian Soom,
  • Craig Ulrich
Martin Schoenball
Lawrence Berkeley National Laboratory

Corresponding Author:[email protected]

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Yves Guglielmi
Lawrence Berkeley National Laboratory
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Jonathan Blair Ajo-Franklin
Rice University
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Paul J Cook
LBNL
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Patrick Dobson
Lawrence Berkeley National Laboratory (DOE)
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Chet Hopp
Lawrence Berkeley National Laboratory
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Timothy J Kneafsey
Lawrence Berkeley Laboratory
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Florian Soom
Lawrence Berkeley National Laboratory
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Craig Ulrich
Lawerence Berkeley National Laboratory
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Abstract

Understanding the initiation and arrest of earthquakes is one of the long-standing challenges of seismology. Here we report on direct observations of borehole displacement by a meter-sized shear rupture induced by pressurization of metamorphic rock at 1.5 km depth. We observed the acceleration of sliding, followed by fast co-seismic slip and transient afterslip. Total displacements were about 7, 5.5 and 9.5 micrometers, respectively for the observed pre-slip, co-seismic slip and afterslip. The observed pre-slip lasted about 0.4 seconds. Co-seismic slip was recorded by the 1 kHz displacement recording and a 12-component array of 3-C accelerometers sampled at 100 kHz. The observed afterslip is consistent with analytical models of arrest in a velocity-strengthening region and subsequent stress relaxation. The observed slip vector agrees with the activation of a bedding plane within the phyllite, which is corroborated by relocated seismic events that were observed during the later stages of the injection experiment.