Stanford University
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Greg McLaskey, Cornell University, Simulation of Dynamic Earthquake Rupture in a 3 m Rock Experiment

When:
Thursday, Nov 21, 2019 12:00 PM
Where:
Mitchell 350/372
Audience:
Faculty/Staff, Students, Alumni/Friends
Sponsor:
Geophysics Department

Earthquake Nucleation, Seismic Wave Radiation, and Termination of Dynamic Rupture in a 3 m Rock Experiment

Date: Thursday, November 21st 2019

Location:  Mitchell 350/372

Time:  12:00 pm - 1:15 pm

Host:  Paul Segall

I describe sequences of laboratory earthquakes generated on a 3-meter laboratory rock experiment that provide insights into how earthquakes initiate, radiate seismic waves, and terminate. Most of these laboratory earthquakes exhibit a meter-sized zone of slow slip (nucleation zone) that expands and accelerates until reaching seismic slip speeds (>0.1 m/s) suggesting that critical nucleation length scale h* ~ 1 m. However, we find that loading rate and strength heterogeneity cause large variation in observed h*, which has implications for how natural earthquakes initiate, and the interpretation of foreshocks. Many laboratory-generated events not rupture the sample ends because they propagate into unfavorable stress conditions. We study the stress drop and radiated energy of these contained events since they are less influenced by the machine stiffness and are more representative of natural earthquakes than standard complete-rupture stick-slip events. We observe a spectrum of slow to fast events depending on how far the earthquake can rupture before encountering unfavorable stress conditions. Slow events, with 0.5 mm/s slip rates and 50 kPa stress drops radiate tremor-like signals and have w-1 spectral falloff, consistent with slow events observed in nature. Fast events have 100 mm/s slip speeds, 0.4 MPa stress drop, and source spectra consistent with a Brune mode.

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