| Popis: |
An MS 7.4 earthquake occurred in Maduo County, Guoluo Tibetan Prefecture, Qinghai Province at 02:04 on May 22, 2021(Beijing time), which is the largest one in China after the 2008 Wenchuan MS 8.0 earthquake. Finding out the distribution and characteristics of its coseismic surface rupture in time is of great significance for the identification of seismogenic structure, regional earthquake prevention and disaster reduction. Combining the post-earthquake field investigation with the results from the interpretation and analysis of high-resolution satellite remote sensing images, aftershock data and UAV low altitude photogrammetry, we got a preliminary judgment on the characteristics of six typical seismic surface ruptures. Firstly, the surface rupture caused by the Maduo earthquake is mainly distributed along the southeastern segment of the known South Branch of the East Kunlun fault zone, the kunlunshankou-Jiangcuo fault. It indicates that the Jiangcuo fault should be the seismogenic fault of the earthquake. Secondly, the western segment of the coseismic rupture with an overall strike of 275°~300°, is mainly manifested as an inclined combination of compressive bulges and echelon tensile fractures. There is a significant vertical displacement of 1.4~0.8 m between the Jiangcuogongma section and the Jiangduocun section, indicating that the western segment may have obvious normal fault components. The huanghexiang section in the middle is mainly composed of a series of NW-trending P shear fractures with left-order oblique and NE-trending tensile fractures with right-order en echelon, with small strike slip displacements. The Changma reach of the North Branch is mainly composed of a series of en echelon fractures, with the overall strike of 260°, The strike of the fault is obviously different from that of the western segment of the fault. Thirdly, the maximum left lateral displacement caused by the earthquake occurred in the Cuoerjiala rapture section of the western segment, about 2.8 m, indicating that the strike slip displacement of the surface fracture zone of the earthquake is mainly characterized by unilateral expansion attenuation from west to East. The fact that the Maduo earthquake occurred in the Bayan Har block on the south side of the East Kunlun main fault demonstrate the possibility of earthquake with magnitude 7 or above in this block. Therefore the seismogenic conditions and mechanism of strong earthquake activity in the Bayan Har block should be a scientific issue that needs further attention. |
