Coseismic Underground Rupture, Geometry, Historical Surface Deformations and Seismic Potentials of the March 28, 2019 Mw 5.04 Mangya earthquake fault

Abstract : The March 28, 2019 Mw 5.04 Mangya earthquake damaged eight ongoing drilling boreholes in the oil‐production Yingxiong Ling (YXL) area, southwestern Qaidam of northern Tibet. The borehole damages provide an opportunity to measure directly the coseismic slips, the rupture area, and the seismic moment. The damages reveal the underground rupture area of 45.30 ± 10.24 km2, the maximum slip of 400 ± 13 mm, and the seismogenic fault dip of ~38.6°. These parameters generate a seismic moment of (1.81 ± 0.47) ×1017 Nm and a moment magnitude of 5.47 ± 0.16. Seismic exploration reveals that the geometry of the SZG ramp, the uppermost part of the multi‐bend Yingxiong Ling thrust system, agrees primarily with the rupture plane derived from the borehole damages and one plane of the focal mechanism solution. This suggests that this earthquake resulted from slipping on the ramp. The hanging wall of the YXL thrust system forms the complex fault‐bend fold YXL anticlinorium. Active thrusting and folding along both edges of YXL attest to the southwestern vergence of this thrust system. Growth strata demonstrate average slip rates of the thrust system ranging from ~0.2 mm/yr to ~0.3 mm/yr. The thrusted and folded recent alluviums along the southwestern edge indicate two thrusting events with coseismic slips of 1.7 ± 0.15 m and 3.5 ± 0.15 m at 6.16 ± 0.52 ka and ~35.91 ka, respectively. The entire rupturing of the thrust system can produce Mw 7.65 ± 0.03 earthquakes.