巴颜喀拉块体周缘强震间应力作用与丛集活动特征初步分析

摘要

Since 1997,several major earthquakes occurred around the Bayan Har block in the Tibetan plateau,providing an opportunity to further understanding the mechanism of intraplate earthquakes. What is the effect of interactions among these events on the earthquake occurrence pattern is an issue to be addressed.In this article,we use the visco-elastic Coulomb stress changes model to calculate the stress interactions among the historical events close to or large than MS7.0 since 1893 in the Bayan Har block.We apply the relationships between the slip rate and stress accumulation rate to transform the Coulomb stress changes into the influenced time.Then we remove such influence time from the occurrence years,and analyze the effects of the earthquake interactions on the clustering patterns of the historical earthquakes in the Bayan Har block.The results show that the major earthquakes in the Bayan Har block are characterized by a quasi-period of about 16 years from 1893 to 1973 and a clustering occurrence time period from 1997 to present following a relatively long quiescence period. The Bayan Har block is still in the active period with high probabilities of major quakes.We calculate the conditional probabilities of the rupture segments that did not rupture since 1893 of the boundary faults of the Bayan Har block in the next 30 years.The following faults or fault sections seem to be of major risk:The Maqin segment and the Maqu fault of the East Kunlun fault zone,the Awanang fault, the Luocha segment of the Tazhong fault,the Moxi segment of the Xianshuihe fault,and the Dangjiang fault.Other Fault segments in the Bayan Har block without seismic events since 1893 probably also have hazard of MS7 earthquakes in the future.%巴颜喀拉块体是近年来青藏高原内部板内强震高发地带,对于该块体强震发生时空模式的研究可为大范围板内地震的深入研究提供基础;而断层间的相互作用在强震发生模式中的意义也需要深入研究.文中使用了黏弹性库仑应力模型,计算了1893年以来巴颜喀拉块体边缘和内部7级左右及以上历史地震破裂之间的黏弹性库仑应力相互影响,并使用强震所在断层的滑动速率将这一应力影响值转换为影响时间,并在历史地震发生时间中减去该影响值,比较历史地震影响值对于丛集现象的影响情况,从而分析历史地震间的相互作用对于巴颜喀拉块体内部历史地震丛集特征的影响.从结果看,巴颜喀拉块体的强震自1893年以来存在着前期相隔16a左右的准周期活动,然后经过相对较长时间平静后大约在1997年后发生丛集现象,目前巴颜喀拉块体仍然位于这一强震丛集活动中,仍存在着发生强震的危险;计算出的未来30a 强震发生条件概率显示,危险程度较高的断层包括玛沁断裂、玛曲断裂、阿万仓断裂、塔藏断裂罗叉段、鲜水河断裂带磨西段、当江断裂,其他破裂段也存在发生 MS7.0左右强震的危险.