On 11 January 2018 (18:26 UTC), a Mw 6.0 earthquake occurred approximately 30 km west of the Sagaing Fault in the Bago-Yoma Range (BYR). Using a local broadband seismic network and regional seismic stations, we refine the source parameters of the earthquake sequence. We relocate ~100 earthquake epicenters and determine the focal mechanism and centroid depth of the mainshock and 20 aftershocks with Mw>4. The relocated epicenters are distributed in an elongated zone oriented in a NW-SE direction that is consistent with the strike of the mainshock fault plane solution and the slip distribution derived from ALOS-2 InSAR observations. Most of the aftershocks have a pure thrust focal mechanism similar to the mainshock, except for four strike-slip aftershocks. The refined source parameters of the thrust events clearly delineate a fault dipping ~40˚ to the southwest at a depth range of 3-7 km, indicating that the earthquake sequence ruptured a previously unmapped, active fault. We interpret the earthquake sequence to be associated with pre-existing faults within the BYR anticlinorium. This earthquake sequence and historical seismicity indicate that the upper crust of the BYR is highly stressed, resulting in ongoing distributed deformation between the oblique Rakhine megathrust and the dextral Sagaing Fault. The seismic hazard posed by these active faults has been increasing with the development of infrastructure such as dams within the BYR. Our study highlights the need for high-resolution earthquake source parameter and strong ground motion attenuation studies for seismic hazard preparation and further understanding of the neotectonics of Myanmar.

The rupture process of earthquakes at intermediate depth (~70-300 km) have been rarely illuminated by a joint analysis of geodetic and seismic observations, hindering our understanding on their dynamic rupture mechanisms. Here we present detailed rupture process of the 2019 Mw8.0 Peru earthquake at the depth of 122 km with a holistic approach reconciling InSAR and broadband seismological waveform data. The joint inversion of InSAR observations and teleseismic body waves results in a finite rupture model that extends ~200 km along strike, with unilateral rupture towards north that lasted for ~60 s. There are four major asperities in the finite fault model which are well corresponding to position and timing of the sources in back-projection (BP) and multiple points source (MPS) results. The largest asperity, which occurred ~40 s after the rupture initiation, was featured with longer and smoother risetime, and radiated much weaker high-frequency seismic waves compared to other smaller asperities. This distinct frequency-dependent rupture requires a strong dynamic weakening mechanism, likely thermal pressurization of pore free water rather than thermal runaway. Our frequency content analysis could be generalized to study other earthquakes including those deeper than 300 km.