Numerical Simulation on Strong Earthquake Dynamics Process of Bayan Har Block of the Qinghai-Tibetan Plateau
|School||Lanzhou Institute of Seismology , China Seismological Bureau|
|Keywords||Qinghai-Tibetan plateau Bayan Har Block Finite element strongearthquake numerical simulation|
The Qinghai-Tibetan plateau, having been recognized as one of the six “level Iactive blocks” within the continents of China, is also considered as the strongestseismic active blocks in China. In the past decades, a sequence of large earthquake(Ms≥7) occurred along the boundary of Bayan Har Block. And, this arouses lots ofGeologists’ attention, they are eager to find out the correlation among those largeearthquakes, typically, once a large earthquake happened, what impacts it would haveon the following ones. In this paper, we build two finite element models individually,one is elastic shell element and the other is3D viscoelastic, to simulate the dynamicprocess of strong earthquake on the periphery of Bayan Har BlockIn this paper, we built elastic shell element finite element model, to simulate theimpact on Bayan Har Block and its adjacent area, which is due to the Indian plate’severlasting northward propulsion. By reducing the element elastic modulus in theearthquake location, we made a series of numerical simulations for the strongearthquakes (Ms≥7.0) after1900, to calculate the influence about the former strongearthquakes on the later ones.The results showed that:1) the background stressdistribution is that the equivalent stress is high in the west, and decreased graduallyfrom west to east; as to the middle and west part of the block, the equivalent stressdecreased gradually from south to north; and the equivalent stress is comparativelylow in the east;2) of the14simulated earthquakes, there are eight earthquakesoccurred in the area that has increased equivalent stress triggered by the previous ones,one is in the transition section, three in the area with decreasing equivalent stress andone is uncertain after the first earthquake;3) from the stress interaction between thestrong earthquakes before and after1970, we can conclude that the Alan lakeMs7.0earthquake on April19,1963has no effect on Luhuo Ms7.6earthquake onFebruary6,1973, the historic earthquakes triggered the Yijitaicuo Ms7.3earthquakeon July14,1973, the Mani Ms7.5earthquake on November8,1997, Kunlun MountainPass Ms8.1earthquake on November14,2001; the influence on the Wenchuanearthquake from the Kunlun Mountain Pass is less, and the effect on the Yushuearthquake caused by the Wenchuan earthquake is unobvious. The simulation of thepast14large earthquakes shows that strong earthquake sequence happened resultstrong equivalent stress increased in the process in the northeastern margin of BayanHar Block, where has a higher risk for disastrous earthquake in the future.Thesimulation of the past14large earthquakes shows that as a result of the strongearthquake sequence happened previously, the north-eastern margin of Bayan HarBlock is in the accumulation process of strong equivalent stress, may form higher riskof disastrous earthquake in the future.In this paper, we built the3D viscoelastic finite element model to simulate the present displacement velocity field and tectonic stress field of the Qinghai-Tibetanplateau. And combined with GPS observation data and stress field data, we analyzedcharacteristics of the displacement velocity field and tectonic stress field of theQinghai-Tibetan plateau’s main area.1) The direction of the displacement field of thewest part of the Bayan Har Block is northward with a deflection to the east, themiddle part’s is north-eastward, and the west is horizontal with a deflection to thenorth. Near the Longmenshan fault, the direction of the displacement field isapproximate to horizontal and the value is small. Generally it forms the eastwardflowing zone of crustal material with the north of Qiangtang block as its center, and inthe eastern part, it circles the east tectonic of Himalayan in the clockwise direction.The characteristics of the displacement are basically identical to the GPS measureddata.2) The direction of the main press stress of the west part of the Bayan Har Blockis northward with a deflection to the east, the middle part’s is north-eastward, and thewest is horizontal with a deflection to the south. The simulation results of the stressfields are basically identical to the work done previously. From the relationshipanalysis of the direction of the tectonic stress field and the rupture pattern of the activefaults, the characteristics of the stress field of north and south of the boundary ofBayan Har Block are inclined to inducing left-lateral strike-slip earthquake; the eastboundary is inclined to inducing right-lateral strike-slip earthquake. and theLongmenshan fault is inclined to inducing thrust and strike-slip earthquake.In the last part of the paper, we used the3D viscoelastic finite element model toanalyze the process of the adjustment of the viscoelasticity of the coseismicequivalent stress in the next50years, which were caused by the the KunLunMountain Ms8.1earthquake、 WenChuan Ms8.0earthquake and YuShu Ms7.1earthquake. And we mainly discussed the characteristics of the stress evolution of theQilian seismic belt and the southeast of Gansu Province. Hereby trying to do theexploratory experiment of judging risk area based on the characteristics of theadjustment of regional stress. The preliminary conclusion is that the adjacent zone ofthe southeast of Gansu Province and Qinghai Province and the adjacent zone of GansuProvince and Sichuan Province and the adjacent zone of Gansu Province are the riskarea with future strong earthquake.