Comparison of Source Inversions and Stress Drops with In-Situ Observations of Faulting

Pamela A. Moyer, Margaret S. Boettcher, & William L. Ellsworth

Submitted August 24, 2016, SCEC Contribution #6979, 2016 SCEC Annual Meeting Poster #053

A Mw 5.4 earthquake, which occurred on 5 August, 2014 beneath the Moab Khotsong gold mine, in Ornkey, South Africa provides a unique opportunity to directly compare seismological inferences with in-situ observations of faulting. The Mw 5.4 earthquake sequence was recorded by a dense surface seismic network, in-mine seismometers, and a strainmeter. In addition, the Mw 5.4 earthquake is the primary target of the proposed DSeis International Continental scientific Drilling Program project. With abundant, high quality waveforms, in-situ stress measurements, and fault core, this earthquake can be an important test case for the Source Inversion Validation (SIV) community.

Using the surface seismic network data, we have developed an initial source model of the space and time evolution of rupture of the Mw 5.4 Orkney earthquake. The inversion for a one-dimensional velocity model for the rupture area will be obtained using VELEST. The finite fault inversion will be formulized using minimal assumptions and we will require the grid model to be consistent with the frequency content of the data in both space and time. The displacement seismograms will be modeled to capture near field phases with a causality condition applied, but no other constraints will be placed on the rupture evolution. We will use our kinematic model to infer the frictional evolution during rupture and an empirical green's function spectral ratio technique to obtain corner frequency for stress drop of foreshocks and aftershocks of the Orkney earthquake. Our results will be compared with direct evidence of the fault zone material from fault cores through the rupture surface and stress measurements performed in and surrounding the fault zone.

Key Words
source inversion validation, earthquake stress drop, mining induced seismicity

Moyer, P. A., Boettcher, M. S., & Ellsworth, W. L. (2016, 08). Comparison of Source Inversions and Stress Drops with In-Situ Observations of Faulting. Poster Presentation at 2016 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)