We image the rupture process of the 2021 Mw 7.4 Maduo, Tibet earthquake using slowness‐enhanced back‐projection (BP) and joint finite fault inversion, which combines teleseismic broadband body waves, long‐period (166–333 s) seismic waves, and 3D ground displacements from radar satellites. The results reveal a left‐lateral strike‐slip rupture, propagating bilaterally on a 160 km long north‐dipping sub‐vertical fault system that bifurcates near its east end. About 80% of the total seismic moment occurs on the asperities shallower than 10 km, with a peak slip of 5.7 m. To simultaneously match the observed long‐period seismic waves and static displacements, potential deep slip is required, despite a tradeoff with the rigidity of the shallow crust. The deep slip existence, local crustal rigidity, and synthetic long‐period Earth response for Tibet earthquakes thus deserve further investigation. The WNW branch ruptures ∼75 km at ∼2.7 km/s, while the ESE branch ruptures ∼85 km at ∼3 km/s, though super‐shear rupture propagation possibly occurs during the ESE propagation from 12 to 20 s. Synthetic BP tests confirm overall sub‐shear rupture speeds and reveal a previously undocumented limitation caused by the signal interference between two bilateral branches. The stress analysis on the forks of the fault demonstrates that the pre‐compression inclination, rupture speed, and branching angle could explain the branching behavior on the eastern fork.
A good understanding of earthquake rupture segmentation is important to characterize fault geometries at depth for follow-up tectonic, stress-field or other analyses. We propose a data-driven strategy and develop pre-optimization methods to support finite fault inversions with independent prior estimates on earthquake source parameters. The first method we develop is a time-domain, multi-array and novel multiphase backprojection (BP) of teleseismic data. This method infers the spatio-temporal evolution of the rupture process, including a potential occurrence of rupture segmentation. Secondly, we apply image analysis methods on InSAR surface displacement maps to infer rupture characteristics (e.g. strike and length) and the number of potential segments. Both methods can provide model-independent constraints on fault location, dimension, orientation and rupture timing, applicable to form priors of model parameters before detailed modelling. We demonstrate and test our methods based on synthetic tests and an application to the 25.11.2016 Muji Mw 6.6 earthquake. Our results indicate segmentation and bilateral rupturing for the 2016 Muji earthquake. The results of the BP of the Muji Mw 6.6 earthquake using high-frequency filtered teleseismic waveforms in particular shows the capability to illuminate the rupture history with the potential to resolve the start and stop phases of individual fault segments.
more » « less- NSF-PAR ID:
- 10379444
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Geophysical Journal International
- Volume:
- 232
- Issue:
- 3
- ISSN:
- 0956-540X
- Page Range / eLocation ID:
- p. 1482-1502
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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