The ascending and descending interferometric synthetic aperture radar data are used to investigate the fault rupture and slip model of the 2018 Mw 7.5 Sulawesi, Indonesia, earthquake. The best fitting slip model indicates that this earthquake ruptured not only a segment extending the Palu fault to the north but also a northwestern segment offshore. The slip on the onshore fault is predominant left‐lateral strike slip. The slip on the offshore fault is dominated by normal faulting with a maximum slip of ~6.3 m. The newly discovered offshore normal faulting is likely to be the cause of the tsunami after the shock. Combined with previous geomorphic, tectonic, geodetic, and modeling studies, we suggest that the kinematics of the Palu fault maintained the same style of faulting from north to south, which resulted from an oblique extension occurred on an east dipping fault at depths. The deformation pattern of NW Sulawesi is dominated by this slip mechanism.
The 2013 Mw6.8 Lushan, China earthquake occurred in the southwestern end of the Longmenshan fault zone. We jointly invert local strong motion data and geodetic measurements of coseismic surface deformation, including GPS and InSAR, to obtain a robust model of the rupture process of the 2013 Lushan earthquake. Our joint inversion best model involves the rupture of two opposing faults during the Lushan earthquake, a main fault and a secondary fault. It is only when the secondary fault is included that both the GPS and InSAR measurements are fit along with the near-field strong motion. Over 75% of the computed moment was released in slip on the main fault segment, a northwest dipping, listric thrust fault, with buried thrust and dextral strike-slip at hypocenter depths, and with only minor slip closer to the surface. The secondary fault mainly involved oblique thrust slip or pure dextral strike-slip at shallower depths, and accounts for just under 24% of the moment released in the Lushan earthquake. Coulomb stress changes of about 0.5 MPa on the secondary fault segment at the time coseismic slip initiated on that fault indicate that slip was likely triggered by the coseismic slip on the main blind thrust fault. Our coseismic slip model is consistent with a sub-horizontal and east-west to southeast-northwest trending most compressive stress. Our inferred coseismic slip model is also consistent with previous GPS derived models of strain accumulation on the Longmenshan fault system.
An Mw 5.9 thrust earthquake occurred on 21 January 2016 in the northeastern Tibetan plateau, where another similar earthquake had ruptured in 1986. Because of the complexity and close proximity of multiple faults in this area, the exact causative fault sources for these two events have not previously been determined. We determined the seismogenic fault structural geometry of the 2016 event by analyzing the coseismic deformation from Sentinel-1A images, aftershock relocations, and geological data. Furthermore, field investigations and the relocated aftershocks for the 1986 event were used to investigate its seismogenic fault and relation with the 2016 Menyuan earthquake. The results indicate that the reverse slip of both events was distributed on the southwest-dipping Minyue-Damaying fault, where the 2016 event ruptured the deep segment and the 1986 event ruptured the shallow segment. We envision that the depth segmentation played an important role in the occurrence of two moderate earthquakes rupturing the same active fault but separated by almost 30 yr, which is thought much shorter than the average earthquake recurrence cycle. Our study indicates that seismic risks could be underestimated if depth segmentation is not considered.
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