The 2007 Ning’er Mw 6.1 Earthquake: A Shallow Rupture in Southwest China Revealed by Insar Measurements

Date: 4/25/2019

Time: 06:00 PM

Room: Fifth Avenue

The Ning’er Mw 6.1 earthquake on June 3, 2007, occurred in the south-central section of the South-North seismic belt in China. The epicenter is in the southwestern to the Sichuan-Yunnan rhombic block with complicated seismic structures. The focal depth determined by the U.S. Geological Survey (USGS) is only 5 km, but the field earthquake investigation did not find obvious surface ruptures in the epicenter area. In addition, the magnitude obtained by inverting the broadband waveforms is Mw6.4 that is much larger than the Mw6.1 determined by USGS and Global Centroid Moment Tensor (GCMT), indicating the complexity of the earthquake. The Interferometric Synthetic Aperture Radar (InSAR) is used to study the fault geometry, coseismic slip model, and Coulomb stress changes around the seismic region firstly. It shows that this event is mainly dominated by a right-lateral strike-slip fault with a slight thrust component. The coseismic slip is 28 km along the strike and 14 km along the dip and the most slips are concentrated within the upper 7 km of the crust. The maximum slip is up to 1.02 m at a depth of 3.6 km and the released moment is 2.57 × 1018 Nm, corresponding to a magnitude of Mw 6.25, which is between Mw 6.4 from the broadband waveform inversion and Mw 6.1 from GCMT and USGS. The shallow source of this event is related to the local tectonics and inelastic off-fault deformations along the fault. The lack of obvious surface rupture indicates that the strain is not completely released and remains underground. The coseismic Coulomb stress changes suggest that this earthquake has enhanced the stress on the Puwen fault and the Mohei fault. The seismic risks for these two faults and its adjacent regions cannot be ignored in the future since aftershocks are fewer and the accumulation of residual strain from the Ning’er event.

Presenting Author: Wei Chen

Authors