[S01-P] Poster

[S01-P-04] The Mechanism of Rare Earthquakes in Pidie Jaya, Aceh Derived from Source Parameter and Shear Wave Splitting Tomography

^○Rexha Verdhora Ry^{1, 2}, Andri Dian Nugraha^{1, 2}, Sri Widiyantoro^1,2, Riskiray Ryannugroho¹, Kadek Hendrawan Palgunadi¹, Muksin Umar³, Zulfakriza Zulfakriza⁴, Kemal Erbas⁵ (1.Institut Teknologi Bandung, Bandung, Indonesia, 2.Global Geophysical Research Group, Bandung, Indonesia, 3.Syah Kuala University, Aceh, Indonesia, 4.Department of Mining and Energy Resources, Aceh, Indonesia, 5.GFZ Postdam, Germany)

On December 7, 2016, a rare and unexpected earthquake with a moment magnitude (Mw) of 6.5 struck Pidie Jaya, Aceh. According to Indonesian Meteorological, Climatological, Geophysical Agency (BMKG), the earthquake was located in 5.19o N, 96.36o E, with a depth of 10 km. Approximately 11,000 houses and 104 dead casualties were reported. It was assumed that the earthquake relates to Samalanga Sipopok fault which is located in the northern part of Aceh and has a mechanism of strike-slip. In regard to this event, we deployed 9 seismometers for a month in this area to identify aftershocks. The objective was to confirm the geometry of fault plane and the earthquake mechanism. We recorded 330 aftershocks between December 14, 2016 and January 15, 2017. We manually picked P- and S- wave arrival times and applied probabilistic non-linear method to locate hypocenters. Furthermore, we calculated the moment magnitudes using Brune's model and processed several samples of focal mechanisms using full waveform inversion. It can be observed that the aftershocks are distributed in Southwest – Northeast direction from the mainshock. The magnitudes decreased along with time and the focal mechanism shows a strike-slip faulting. Moreover, we also analyzed anisotropy parameter using 3-D shear wave splitting (SWS) tomography to delineate the fault plane. The high degree of anisotropy and crack density were observed around the interpreted fault structure. The distribution of earthquakes and anisotropy may reveal an unprecedentedly unknown fault in the study region.