Sub-Shear Rupture on Bifurcating Faults: Kinematics and Dynamics of the 2021 M_w7.4 Maduo Earthquake in Qinghai

Creators: Xu, Liuwei; Meng, Lingsen; Ji, Chen; Yunjun, Zhang; Fielding, Eric J.; Zinke, Robert; Bao, Han

Abstract

We utilize the slowness-enhanced back projection (SEBP) and joint finite fault inversion (FFI), which combines body waves, surface waves, and 3D ground displacements to image the rupture process and slip distribution of the M_w7.4 Maduo earthquake. The results indicate a 160-km-long bilateral rupture occurring on a north-dipping fault. The WNW branch ruptures a length of ~75 km at 2.7 km/s, while the ESE branch ruptures a length of ~85 km at 3 km/s. Most slip concentrates above 10 km depth, with several major slip patches up to 5.7 m located on the east segment of the main fault and on the bifurcated branching fault. The comparison between SEBP and FFI shows the consistency between large slip pulses and high-frequency sources. We observe up to 3 m slip with large uncertainty in depth beyond 20 km, which is abnormal since it requires rupture penetrating into the ductile layers. We propose that the apparent deep slip could be an artificial compensation to match the observed moment, which indicates that the crust in the source region is more rigid than the current understanding. Or the deep creeping fault is turned into seismic ones by the strain localization and dynamic weakening. The stress analysis on the forks of the fault demonstrates that the branching behavior on the eastern fork could be well explained by the pre-stress inclination, rupture speed, and branching angle.

Additional Information

This work is supported by the NSF CAREE grant EAR-184846 and the Leon and Joanne V. C. Knopoff Fund. Part of this research is performed at the Jet Propulsion Laboratory, California Institute of Technology under contract with the National Aeronautics and Space Administration (80NM0018D0004) and supported by the Earth Surface and Interior focus area. We thank L. Shi for sharing the velocity model of northeast Tibet, W. Wang for sharing the aftershock catalog, and Z. Jin, S. Hong, C. Xu, J. Geng, and Q. Li for sharing their slip models. We thank Z. Jin for fruitful discussions. The broadband seismograms are provided by the Incorporated Research Institutions for Seismology (IRIS, www.iris.edu) and Observatories & Research Facilities for European Seismology (ORFEUS, www.orfeus-eu.org). The Python software package Obspy (www.obspy.org) is used for data requesting, waveform filtering, and cross-correlation processing. This work contains modified Copernicus data from the Sentinel-1A and -11B satellites provided by the European Space Agency (SA). Figures are produced using Generic Mapping Tools (GMT) (Wessel et al., 2013), Matlab, Matplotlib and Cartopy. The static displacement data is downsampled by InSamp (https://github.com/williamBarnhart/InSamp). Dt Availability Statement. The Copernicus Sentinel-1A data are made available by the ESA and mirrored by the Alaska Satellite Facility (ASF; https://www.asf.alaska.edu/sentinel/). The InSar Scientific Computing Environment(ISCE) software used for processing the Sentinel-1 SAR data is available at https://github.com/isce-framework/isce2. The moment tensor solutions come from the U.S Geological Survey(USGS; https://earthquake.usgs.gov) and the Global Centroid Moment Tensor project (CMT; http://www.globalcmt.org). The teleseismic data and surface wave data used in this study come from the IRIS Data Management Center (https://ds.iris.edu/wilber3/find_event) and Observatories & Research Facilities for European Seismology (ORFEUS, www.orfeus-eu.org). The relocated aftershock data is from Wang et al. (2021), which can be accessed through https://doi.org/10.1007/s11430-021-9803-3. The USTClitho2.0 model is from Han et al. (2021), which can be accessed through https://doi.org/10.1785/0220210122. The velocity model of northeast Tibet is from Xia et al. (2021), which is obtained through the request of the corresponding author.

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