Preliminary focal mechanism pattern along the central part of the Great Sumatran Fault, Indonesia

According to the world stress map, the regional in-situ stress along the Great Sumatran Fault (GSF) is assumed to be strike-slip, and the maximum principal stress (SHmax) is oriented toward N15°E. However, this was estimated from limited global focal mechanisms available along the GSF. A larger dataset of focal mechanisms along the GSF is required to revise the solution and infer the local stress perturbation. To create a new focal mechanism catalogue of local events, we worked on waveform data from a joint seismic network of 35 stations deployed by the Indonesian Agency for Meteorology, Climatology, and Geophysics (BMKG) and the GeoForschungZentrum (GFZ) Germany. The seismic network has a full coverage of the Sumatran fault. From October 2008 to February 2017, there were 476 events with magnitude (Mw) greater than 3 and focal depth shallower than 100 km that occurred in the central part of GSF. Arrival time picking of P and S waves and polarity identification were performed manually using Seisgram. The polarity of P waves was then used to obtain the focal mechanism of the events in the 4 segments of GSF branches (Northwest, Southwest, Northeast, and Southeast). The new local focal mechanism catalogue can be used, together with the global one, to invert the detailed stress heterogeneity in the study area.