A unified earthquake focal mechanism catalog for the Myanmar region and new insights to the seismotectonics.

We derive a five year (2016-2021) focal mechanism catalog composed of ~160 M>4 earthquakes in the Myanmar region. Using a combination of broadband seismic data from multiple regional seismic networks, we refine the earthquake hypocenter by travel-time relocation and then invert for the focal mechanism solution using the Cut-And-Paste (CAP) waveform inversion method. Various 1D velocity models are tested to select the best model for the region. Uncertainties of earthquake source parameters in focal mechanism solutions are determined in a bootstrapping manner. The new earthquake catalog is combined with focal mechanism solutions from GCMT and other studies since 1963 to produce a unified catalog. Our catalog shows that most crustal events are shallower than 15 km, occurring along the Sagaing Fault as strike-slip events and within the Central Myanmar Basin (CMB) as a combination of strike-slip and thrust-faulting events, with the P-axes oriented NE-SW. CMB events indicate that the upper crust of the Burma plate is partially accommodating the deformation due to hyper-oblique subduction to the west. Meanwhile, deeper events (> 45 km) beneath the Indo-Burma Range (IBR) occurring within the subducting Indian plate mostly present strike-slip solutions (NE-SW P-axes) north of 22N while normal faulting is more prevalent to the south. West of the Wuntho-Popa volcanic arc beneath the CMB, the earthquakes show a combination of strike-slip and thrust faulting solutions with P-axes oriented mostly N-S. These events are interpreted to be intraslab events in the Indian plate and accommodate the N-S oriented stresses induced by the dominating northward mantle flow. Interestingly, we do not observe thrust-faulting events on the plate interface in this 58-year catalog. However, we observe a cluster of thrust-faulting events with P-axes oriented E-W at a depth of 30-45 km beneath the eastern edge of the IBR. These events may occur within the lowermost crust or the uppermost mantle of the Burma plate and may indicate compression of the lower crust/mantle wedge. Overall, more intraslab events occur north of 20N while more crustal events occur south of 20N. The refined seismicity catalog reveals the lack of events on the plate interface, the complexity in deformation of the subducting slab and the active seismicity occurring within the CMB.