This study is conducted by a team led by Dr. Xiong XIONG (School of Geophysics and Geomatics, China University of Geosciences, Wuhan, China). In a paper published in 2015 in the Geophysical Journal International, the team noticed that the Maqin-Maqu segment of the Eastern Kunlun fault with an estimated recurrence time of 600 years might be very close to rupture, since it has been silent for over 500 years, and the stress accumulation due to major earthquakes nearby is equivalent to tectonic accumulation of about 160 years. Therefore, after the Ms7.4 Maduo Earthquake struck near the Maqin-Maqu segment on May 21st, 2021, the team conducted a stress perturbation analysis based on the Coulomb failure criterion. A finite-fault rupture model was derived from teleseismic body wave data by Dr. Chengli LIU (see Figure 1 below). In particular, the fault geometries manifested by the relocated aftershock catalogue is taken into consideration, and the team spotted a small-angle bend on the eastern end, which is directed towards the Maqin segment of the Eastern Kunlun fault (see Figure 2 below). "What if there exists an unmapped fault along the trend between the Maduo Earthquake rupture and the Maqin segment? Will it be positively stressed by the Maduo Earthquake and promote earthquakes on the Maqin-Maqu gap?" Xiong asked.
Dr. Yashan FENG and Dr. Bin SHAN conducted calculations and analysis of Coulomb stress changes brought about by the Maduo Earthquake to its surrounding faults, and found that If there exists an unmapped fault along the trend of the eastern end of the Maduo Earthquake rupture, it is likely to be substantially stressed (0.67 MPa at maximum) (see Figure 2 below). Even if it doesn't meet the Eastern Kunlun fault, its possible rupture will significantly stress the Eastern Kunlun fault, and superimposed with the stress increase due to the Maduo Earthquake encourages seismic activities on the seismic gap.
The team also made a quantitative forecast of the seismic rate map in the next decade in the surroundings of the Maduo Earthquake, based on the rate-state frictional law, with rate-state parameters constrained by observed fault slip rates. Under this forecast, active seismicity will probably be observed on the northwestern portion of the Maduo-Gande fault, the Eastern Kunlun fault segment near Maqin, the western end of the Kunlun Mountain Pass-Jiangcuo fault and the western portion of the Qingshuihe fault. "We hope that this forecast can provide reference for seismic hazard assessment in this region, and it may also serve as a case of proactive forecast for future tests." Feng says.
Studies in intra-plate earthquakes are not as thorough as inter-plate earthquakes, since earthquake samples are much less and related plate deformations are much smaller. As a result, it is much more challenging to study intra-plate earthquakes. In the present, few high-resolution investigation of the internal structure of the China continent is available, and few is known about the detailed partitioning of slip and deformation among major and secondary faults. This deficiency adds to the challenge in intra-plate earthquake studies. "In our study, both the estimates of fault stressing rate and calculation of rate-state parameters for the forecast of future seismicity rate are based on fault geometries and slip rates, yet the present monitoring of the internal structure and minor deformation within the plate is far from enough for high-resolution studies." Feng says. Therefore, studies of intra-plate earthquakes may benefit from detailed investigations of the structure at depth and continuous, high-resolution observations of surface displacements in the future.
See the article:
Feng Y, Xiomg X, Shan B, Liu C. 2022. Coulomb stress changes due to the 2021 MS7.4 Maduo Earthquake and expected seismicity rate changes in the surroundings. Science China Earth Sciences, 65, https://doi.org/10.1007/s11430-021-9882-8
