Source Parameter Study for Confined Lab Earthquakes on a 3 m Biaxial Apparatus
Abstract
We study the source parameters (seismic moment, stress drop, slip rate, etc) of contained ruptures on a 3 m biaxial friction apparatus at Cornell University. In a typical experiment, two rectangular granite blocks are squeezed together under 1 to 12 MPa of normal pressure (1 to 12 million N on a 1 square meter simulated fault surface), and then shear stress is increased until the fault slips 10 - 400 microns in a sequence of dynamic rupture event similar to M -2 to M -3 earthquakes. In addition to conventional stick-slip events that rupture the entire fault surface, we also observe contained ruptures that arrest before reaching the sample ends. We compute source parameters for both stick-slip events and contained rupture events for comparisons with natural earthquakes. Seismic moment is computed statically using local slip measured along the fault at 16 locations. We also compute seismic moment from recorded ground motions, and we us this to determine seismic coupling coefficient , defined as the ratio of seismically-to-statically computed seismic moment (0 for aseismic slip and 1 for fully coupled dynamic events). We found = 1 for most contained rupture events whereas ≈ 0.1 for stick-slip events that rupture the entire sample. This suggests a fundamental difference in their rupture mechanisms, perhaps caused by differences in the stiffness felt by the rupture events. We computed stress drop both statically and dynamically using rupture dimensions (max slip and rupture length) and corner frequency, respectively. Considering the contained rupture events, we observe a spectrum of behavior ranging from slow events (peak slip rate < 10 mm/s) with somewhat low stress drops (0.07) and lower to fully dynamic events consistent with standard earthquakes (0.7 MPa stress drops), lower = 1. We find that is correlated with peak slip velocity, analogous to previous models [Scholz and Campos 1995] proposed to explain the variation of among subduction zones.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.T11E0192W
- Keywords:
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- 3902 Creep and deformation;
- MINERAL PHYSICSDE: 7215 Earthquake source observations;
- SEISMOLOGYDE: 8118 Dynamics and mechanics of faulting;
- TECTONOPHYSICSDE: 8163 Rheology and friction of fault zones;
- TECTONOPHYSICS