[S02-1] World overview of anthropogenic seismicity I

[S02-1-05] Rupture Process of the 2014 Orkney Earthquake, South Africa

^○Makoto Okubo¹, Artur Cichowicz², Hiroshi Ogasawara^2,3, Osamu Murakami^2,4, Shigeki Horiuchi⁵ (1.Kochi University, Kochi, Japan, 2.JST-JICA SATREPS, Tokyo, Japan, 3.Ritsumeikan University, Kusatsu, Japan, 4.Tono Research Institute of Earthquake Science, Association for the Development of Earthquake Prediction, Mizunami, Japan, 5.Home Seismometer Corporation, Shirakawa, Japan)

An earthquake occurred at 10:22:33 UT on 5 August 2014 in the Klerksdorp district, the North West province of South Africa. This epicenter locates beneath Orkney town, which has 10 more than gold mines. The Council for Geoscience (CGS) in South Africa reported that the magnitude and depth was ML5.5 and 4.7 km, respectively. CGS have operated 17 seismic accleration observations on surface, and continuous acceleration seismograms were obtained at the time of the 2014 Orkney earthquake and following aftershocks. In this study, we analyzed the main shock rupture processof this earthquake, by using these accelation seismograms. First, we analyzed seismograms of mainshocks, found the initial rupture before main shock. That initial rupture has occured 0.3 sec before mainshock with a magnitude less than 4. By operating detailed aftershock distribution analysis, we found most of aftershocks occured surrounding mainshock and a seismic gap between aftershocks and goldmine blastings. Finally, to understand rupture process of the main shock, we surveyed for strong motion generating area (SMGA) by appling Isochrone backprojection method (IBM) to the mainshock's waveforms. SMGA distribution will fill the vacant space of the aftershocks distribution and main shock (initial rupture) hypocenter.