Joint InSAR and Field Constraints on Faulting During the Mw 6.4, July 23, 2020, Nima/Rongma Earthquake in Central Tibet

The accumulation and partitioning of crustal strain in central Tibet remain debated. July 23, 2020, Mw 6.4 earthquake in the Nima region (approximate to 86.864 degrees E/33.144 degrees N) thus provides an opportunity to gain insight into local, ongoing deformation. Here, we use Sentinel-1 SAR data to assess co-seismic deformation during that earthquake, and nonlinear/linear inversions to determine the location and geometry of the source and the finite fault slip distribution. The results show that the maximum surface subsidence was approximate to 25 cm, the causative fault had a approximate to N28 degrees E strike and approximate to 48 degrees dip eastwards, and that the largest normal slip, with a peak of approximate to 1.5 m, occurred between 5 and 10 km depths. Details of the earthquake surface rupture were derived from a UAV-based field survey. At three distinct sites, the high-resolution UAV images revealed discontinuous, approximate to N35 degrees E-trending arrays of fresh en-echelon cracks and <= 20 cm-high, free-faced normal scarps, along a approximate to 10 km-long, approximate to 20 m-wide zone following the approximate to vertically projected western limit of maximum interferometric synthetic aperture radar slip at depth. These results, consistent with an earthquake intensity distribution based on building damage inspection, show that 2020 earthquake only broke a short segment of the west Yibu Chaka normal fault, along the middle stretch of the 300 km-long Riganpei Co-Yibu Chaka-Jiangai Zangbo fault zone. Regional Coulomb stress changes suggest that larger, Mw 7+ earthquakes should be expected on the geomorphologically more prominent, approximate to 50 km-long normal faults bounding the east side of the Yibu Chaka lake pull-apart, and on the 120 km-long, sinistral Riganpei-Co fault to the southwest. Plain Language Summary 2020, Mw 6.4, Nima/Rongma earthquake provides new insights on crustal deformation across central Tibet. By combining Sentinel-1 SAR data inversions with a detailed, UAV-based survey of surface deformation in the field, we determine the geometry of the fault source, the finite fault slip distribution, and the length of the co-seismic surface rupture. These results, which are consistent with the earthquake intensity distribution based on building damage, indicate that this earthquake ruptured a deep, similar to 15 km-long patch of the northeast-striking West-Yibu Chaka normal fault. Primary normal slip (up to 1.5 m), mostly between 10 and 5 km depth, triggered extensional craking and smaller (<= 20 cm) dip-slip along a small, sub-parallel fault splay and a similar to 60 m-high ridge at the surface. The combined, regional Coulomb stress changes due both to the 2020 event and 2008 (Mw 6.4 and 5.9) earthquakes farther south imply that the broad, central Tibetan region north of Nima remains at risk of larger (Mw approximate to 7) events along the geomorphologically more prominent East Yibu Chaka and Riganpei Co faults to the northeast and southwest, respectively.