With the aim of delineating the subducting Indian Plate beneath the Burma Plate, we have relocated earthquakes by employing teleseismic P-wave arrival times. We were able to obtain the detailed geometry of the subducting Indian Plate by constructing iso-depth contours for the subduction earthquakes at depths of 30-140 km. The strikes of the contours are oriented approximately N-S, and show an "S" shape in map view. The strike of the slab is N20 • E at 25 • N, but moving southward, the strike rotates counterclockwise to N20 • W at 20 • N, followed by a clockwise rotation to a strike of N10 • E at 17.5 • N, where slab earthquakes no longer occur. The plate boundary north of 20 • N might exist near, or west, of the coast line of Myanmar. The mechanisms of subduction earthquakes are down-dip extension, and T axes are oriented parallel to the local dip of the slab. Subcrustal seismicity occurs at depths of 20-50 km in the Burma Plate. This activity starts near the 60-km-depth contour of the subduction earthquakes and becomes shallower toward the Sagaing Fault, indicating that this fault is located where the cutoff depth of the seismicity becomes shallower.

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Myanmar is situated within a region of active tectonic blocks with boundaries defined by a variety of tectonic settings (Figure 1a). The Burma sliver plate is characterized by the highly oblique convergence of the Indian plate (∼18 mm/yr) at its western boundary while the ∼N-S striking right-lateral Sagaing Fault (∼20 mm/ yr) defines its eastern boundary bordering the Shan Plateau on the Sunda plate (Mallick et al., 2019;Socquet

Earthquake monitoring in Myanmar has improved in recent years because of an increased number of seismic stations. This provides a good quality dataset to derive a minimum 1D velocity model and local magnitude (ML) scale for the Myanmar region, which will improve the earthquake location and magnitude estimates in this region. We combined and reprocessed earthquake catalogs from the Department of Meteorology and Hydrology of Myanmar and the International Seismological Centre. Additional waveform data from various sources were processed as well. A total of 419 earthquakes were selected based on azimuthal gap, minimum number of stations, and root mean square travel‐time residuals. A set of initial seismic velocity models was derived from various seismic velocity models. These models were randomly perturbed and used as initial models in a coupled hypocenter and 1D seismic velocity inversion procedure. We compared the average mean travel‐time residuals from the initial and inverted models. The best final model showed an improvement of location standard errors compared to the old model. Furthermore, the local magnitude scale inversion for the Myanmar region was performed using 194 earthquakes having a minimum of two amplitude observations. The following ML scale was obtained ML=logA(nm)+1.485×logR(km)+0.00118×R(km)−2.77+S. This scale is valid for hypocentral distance up to 1000 km and magnitudes up to ML 6.2.

The source process of an intra-slab intermediate depth earthquake (h=90 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 directivity. Based on this analysis, we prefer the sub-horizontal fault plane where the rupture propagated downdip. The T-axis showed down-dip extension while the P-axis showed slab normal compression.We obtained an effective fault length of 20 km and effective fault width of 18 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 the Mexican subduction zone, by conducting ground motion modeling at five regional strong motion stations. The 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.