A Test Case for the Source Inversion Validation: The 2014 ML 5.5 Orkney, South Africa Earthquake

William L. Ellsworth, Margaret S. Boettcher, & Hiroshi Ogasawara

Submitted August 8, 2017, SCEC Contribution #7444, 2017 SCEC Annual Meeting Poster #199

The ML5.5 earthquake of August 5, 2014 occurred on a near-vertical strike slip fault below abandoned and active gold mines near Orkney, South Africa. A dense network of surface and in-mine seismometers recorded the earthquake and its aftershock sequence. In-situ stress measurements and rock samples through the damage zone and rupture surface are anticipated to be available from the “Drilling into Seismogenic Zones of M2.0-M5.5 Earthquakes in South African gold mines” project (DSeis) that is currently progressing toward the rupture zone (Science, doi: 10.1126/science.aan6905). As of 24 July, 95% of drilled core has been recovered from a 427m-section of the 1st hole from 2.9 km depth with minimal core discing and borehole breakouts. A 2nd hole is planned to intersect the fault at greater depth. Absolute differential stress will be measured along the holes and frictional characteristics of the recovered core will be determined in the lab. Surface seismic reflection data and exploration drilling from the surface down to the mining horizon at 3km depth is also available to calibrate the velocity structure above the mining horizon and image reflective geological boundaries and major faults below the mining horizon. The remarkable quality and range of geophysical data available for the Orkney earthquake makes this event an ideal test case for the Source Inversion Validation community using actual seismic data to determine the spatial and temporal evolution of earthquake rupture.

We invite anyone with an interest in kinematic modeling to develop a rupture model for the Orkney earthquake. Seismic recordings of the earthquake and information on the faulting geometry can be found in Moyer et al. (2017, doi: 10.1785/0220160218). A workshop supported by the Southern California Earthquake Center will be held in the spring of 2018 to compare kinematic models. Those interested in participating in the modeling exercise and the workshop should contact the authors for additional information.

Key Words
SIV, rupture kinematics, source inversion validation, workshop

Citation
Ellsworth, W. L., Boettcher, M. S., & Ogasawara, H. (2017, 08). A Test Case for the Source Inversion Validation: The 2014 ML 5.5 Orkney, South Africa Earthquake. Poster Presentation at 2017 SCEC Annual Meeting.


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