摘要
喜马拉雅东构造结是研究青藏高原构造演化的关键地区,地震活动频繁。文中基于地震矩平衡理论,利用GPS资料与历史地震目录分析东构造结地区的地震矩亏损,继而评估该区未来的地震活动。结果表明:研究区总体的地震矩累积率高于青藏高原的平均水平,近200a内的累积总量达(1.15±0.03)×10^22N·m,明显高于地震矩的释放总量(5.50±2.54)×10^21N·m。而地震矩亏损量最高的主前缘断裂不丹段具备发生MW8.1以上地震的可能,那加山断裂及嘉黎断裂通麦段则不排除未来发生震级大于MW7.5与MW7.3地震的可能,其余断层发生强震(MW7.1以上)的概率相对较低。而对于米什米断层与主前缘断层东段,虽然察隅MS8.6地震发生于此,但这2条断层未来的地震危险性仍不容忽视,且无论察隅地震发生于哪条断层,其复发周期均为660~1030a。
The Eastern Himalayan Syntaxis(EHS)is a critical region for studying the tectonic evolution of Tibetan plateau,which was affected by the intense seismic activities.We use the theory of moment balance,GPS velocities and historical earthquake records to analyze the moment deficits in the EHS,assess the future seismicity and further to predict the recurrence interval of the 1950 Chayu MS8.6 earthquake.We first collected multiple sets of GPS velocity fields and combined them to reduce the systematic bias.Then a micro-blocks model,constrained by GPS velocities,was built by TDEFNODE software to simultaneously invert the fault elastic strain parameters and rigid motion parameters based on the grid research and simulated annealing methods.The long-term slip rates on the faults were further estimated by the differential motions between the neighboring blocks.The results show that the nearly NS dextral strike-slip faults,Naga Fault and Sagaing Fault,slip with the average rates of^10.6 and^16.6 mm/a,which are consistent with the lateral extrusion in the Tibetan plateau.However,the Main Frontal Thrust shows a distinguished sinistral strike-slip feature(6~10 mm/a),possibly caused by the NNE pushing from the Indian plate to the Eurasian plate.On the other hand,because the EHS is located in frontal area of the collision between Indian and Eurasian plate,most faults show thrusting feature.The most obvious one is the Mishimi Fault,slipping with the rate of23.3 mm/a,implying that the convergence rate of the Indo-European plates is largely absorbed by this fault.The moment accumulation rate in the EHS is higher than the average rate in the Tibetan plateau and the total moment accumulation is(1.15±0.03)×10^22 N·m in the last 200 a.About 59.7%and21.6%of the moment accumulation rate concentrate on the Main Frontal Thrust and Mishimi Fault.Second,we selected the earthquake records occurring on the upper crust since 1800 AD to analyze the moment release in the EHS based on the data from the International Seismological Centre,United States Geological Survey,and catalogue of historical strong earthquakes in China and some other previous studies.In addition,the Global Centroid Moment Tensor Project and linear regression method were adopted to estimate the relationship between body wave magnitude(mb),surface wave magnitude(MS),local magnitude(ML)and the moment(M0).Then we further estimated the total fault moment release in the EHS,(5.50±2.54)×10^21 N·m,which is significantly lower than the total moment accumulation.About 79.2%of the moment release occurs on the Mishimi Fault,this is because the 1950 MS8.6 Chayu earthquake is assumed to have ruptured on this fault.Finally,the present-day moment deficits on the faults in the EHS were calculated by the differences between the moment accumulation and release,which represent the possibility to produce earthquakes on the upper crust faults in the future.The largest moment deficit was found on the Main Frontal Thrust near Bhutan,which is able to rupture with MW8.1+.Similarly,earthquakes with MW7.5+and MW7.3+have the potentials to occur on the Naga Fault and the Jiali Fault near Tongmai.However,the future earthquake scales may be less than MW7.1 on the remaining faults.Moderate minor earthquakes are the main activity in the area near the Yarlung Zangbo Suture zone and the southern Sagaing Fault.Although the Chayu MS8.6 earthquake occurred near the Mishimi Fault and the eastern MFT,the earthquake risk on those two faults cannot be ignored.Meanwhile,no matter which fault produced the Chayu earthquake,its recurrence will likely be 660 a to 1030 a.
作者
田镇
杨志强
王师迪
TIAN Zhen;YANG Zhi-qiang;WANG Shi-di(School of Geology and Geomatics,Chang'an University,Xi'an 710054,China;Shaanxi Earthquake Agency,Xi'an 710068,China)
出处
《地震地质》
EI
CSCD
北大核心
2020年第1期33-49,共17页
Seismology and Geology
基金
中央高校基本科研基金(310826175032)资助。
关键词
GPS
滑动速率
地震矩亏损
地震复发周期
东构造结
GPS
fault slip rates
moments deficit
earthquake recurrence period
Eastern Himalayan Syntaxis
