Hasbi Ash Shiddiqi

Source study of the 24 August 2016 Chauk earthquake, Myanmar

The source process of an intra-slab intermediate depth earthquake (h=92 km) that occurred near Chauk, Central Myanmar on 24 August 2016 was investigated using teleseismic body-wave inversion. The focal mechanism solution showed a thrust mechanism with nearly vertical or sub-horizontal fault planes. The slip inversion results for both fault planes gives similar variances and show a simple slip distribution. The fault-plane ambiguity was resolved by analyzing apparent source time functions for teleseismic stations affected by the directivity effect. Based on this analysis, we prefer the sub-horizontal fault plane where the rupture propagated down-dip. The T-axis showed down-dip extension while the P-axis showed slab normal compression. We obtained an effective fault length = 21.9 km and effective fault width = 18.1 km. A Stress drop of 20 bars was estimated by using the relation of effective fault dimension and seismic moment obtained from the slip inversion. Furthermore, we tested the stress drop, and the assumption of quality factor, which is adopted from another subduction zone, by conducting the earthquake ground motion modeling at five regional strong motion stations. A stress drop of 20 bars can produce reasonable ground motion for these stations. One of the most prevailing hypothesis of the generating mechanism of sub-horizontal faulting in intermediate-depth is related to the dehydration embrittlement which either reactivated an existing fault before it was subducted or newly created fault after, e.g., due to slab unbending processes.