关键词: 玛多7.4级地震, 巴颜喀拉块体, 地震地表破裂, 左旋走滑, 发震构造

Abstract: At 2:4 on May 22, 2021, an earthquake with Ms7.4 occurred in Maduo County, Guoluo Tibetan Autonomous Prefecture, Qinghai Province. The epicenter of the earthquake was about 70km south of the East Kunlun Fault Zone on the northern boundary of Bayan Har block (34.59° N，98.34 ° E) The focal depth is 17km. The Maduo Ms7.4 earthquake is the largest in China after the 2008 Wenchuan Ms 8.0 Earthquake. The field geological investigation after the earthquake shows that the earthquake occurred in yematan area, more than 30 kilometers south of Machali town. The surface rupture of the earthquake is obviously segmented, which can be divided into 3-4 segments. From east to west, the rupture is distributed in left step, and gradually approaches to the middle of yematan basin. The nature of the fracture is mainly left lateral strike slip. The earthquake formed a large-scale and well-continuous surface rupture from the west of G214 to the south of Eling Lake. Its length is about 45km, and it strikes N95°-105°E. The surface rupture zone consists of a series of squeezing bulges and It is composed of echelon fractures, forming large-scale seismic bulges (beams), seismic cracks, left-handed displacement and other geomorphic features, and there are a large number of seismic geological disasters such as sandblasting and water, soft soil subsidence. From the east of G214 to Xueluodong, the rupture zone runs towards N100°E and consists of discontinuous small-scale tension-shear cracks and small bulges (beams). Near Xuema Village, Changmahe Township, there has developed a section of about 10km long, with a strike of N75°E, a large-scale, well-continuous tension-shear crack, seismic bulge (beam), etc. The earthquake caused left-handed displacement of geological bodies, water system gullies, roads, etc., and the formation of strike-slip scratches in the strata. Through measurement, the displacement of the rupture in the Langmajiaheri area was 1.5m, and the upper part of the Yema Beach was 1.3m. 1.1m west of Xuema Village. A 1.3m vertical fault ridge is formed in the western section. A large amount of sandblasting and water and earthquake subsidence have developed along the line. Analysis believes that the earthquake occurred inside the Bayan Har block and the seismogenic structure is the Jiangcuo fault. According to a comprehensive survey of the scale and length of the earthquake surface rupture and the damage of buildings, it is believed that the Langma Jiaheri area has large surface ruptures, good continuity of the rupture zone, and development of multiple types of seismic surface ruptures. The area can be preliminarily determined as The macroscopic epicenter, the geographical coordinates are: 34.736°N, 97.794°E.

Key words: Maduo7.4 Earthquake, Bayan Har block, Earthquake surface rupture, Sinistral strike-slip, Seismogenic structure