Rupture imaging of the 2021 Ms 6.4 Yangbi, China, earthquake: Implications for the diffuse deformation in the northern region of the Red River fault

Abstract

In May 2021, a Ms 6.4 earthquake occurred in the Yangbi Country, Yunnan, China, located in the northern region of the Red River fault, resulting in three deaths. It is a typical foreshock-mainshock-aftershock sequence. However, the kinematic rupture process and the interplay between foreshocks, the mainshock, and aftershocks associated with the Yangbi event remain controversial. Here, we decipher the detailed rupture process associated with this moderate event by jointly inverting the teleseismic body waves, three-component regional waveform, near-field Global Positioning System offsets, and Interferometric Synthetic Aperture Radar data. Results show that the rupture expands as a narrow slip-pulse that propagates southeastward. This event is dominated by the dextral movements with minor normal components, cohere with the tectonic shear and dilation strain partitioning. The high slip is concentrated within the depth range of 5–13 km, spanning ∼12 km along strike. A significant shallow slip deficit is identified, perhaps related to the fault being immature. The foreshocks, coseismic slips, and aftershocks reveal a complementary pattern, together releasing the accumulated stresses on the fault. Their distribution areas and Coulomb stress changes suggest that the Yangbi seismic sequence follows the rupture cascade. The absence of large earthquakes, dispersed seismicity, and diffuse strain rate patterns indicate that strain accumulates over a wide area around the northern region of the Red River fault, leading to small-scale ruptures distributed over the area and a low possibility of M ≥ 6.5 events in the near future.