相似矩震级下地震近断层强地面运动的差异性比较

Differential energy radiation and characteristics of strong ground motion in the near-fault from two Earthquakes with similar moment magnitude

2010年1月12日海地(Haiti)地区发生Mw 7.0地震,最终造成约31万人遇难,同年4月4日墨西哥南加州Baja地区发生Mw 7.2地震,2人遇难.Haiti地震的矩震级与Baja地震的矩震级相当,人员伤亡却远大于后者,其原因只是Haiti地区经济不发达,建筑物抗震设防标准低、抗震性能差吗?地震造成建筑物倒塌及人员伤亡程度并非仅仅取决于建筑物的抗震程度,一方面与其释放的地震波辐射能相关,另一方面则主要与发震后造成的强地面运动的大小有关.目前尚无两个地震完整的强震观测记录,尤其是Haiti地震,针对二者构建几何尺度相同的动态复合震源模型(DCSM),选取两个地震中分别主要人员伤亡的城市太子港及Mexicalia城作为强地面运动模拟的特征城市,对比其近断层强地面运动的差异.模拟结果表明,Haiti地震近断层区域强地面运动显著高于Baja地震的强地面运动,两个地震模拟的烈度特征分布图也显示出了明显的强地面运动的差异性.因此,Haiti地震造成发震区域内建筑物损毁程度及人员伤亡情况均严重于Baja地震,重要原因之一在于Haiti地震地震波辐射能大且造成的强地面运动强.

The January 12, 2010, MW 7.0 Haiti, earthquake occurred in the boundary region separating the Caribbean plate and the North America plate, and more than 310,000 people were killed in the Port-au-Prince area and in much of southern Haiti. The April 4, 2010, MW 7.2 Baja, earthquake occurred at shallow depth along the principal plate boundary between the North American and Pacific plates, and two people were killed in the Mexicalia area. International media reports of such kind of disasters by Haiti earthquake is resulted from poor building structure design comparing with Baja area. In fact, although the moment magnitude of Haiti event is similar to the Baja event, the radiated seismic energy from the dynamic rupture process of Haiti earthquake is almost 15 times of the Baja earthquake, resulting stronger near-fault ground motions. In this paper, two special finite fault models, dynamical composite source model （DCSM）, with the same size in fault length and width are constructed to simulate the near-fault strong ground motion for comparison reason. The fault slip distributions on both faults are generated based on the DCSM in which the subevent-source-function is described by Brune＇s pulse. Our results show that the near-field peak ground accelerations （PGAs） and peak ground velocities （PGVs） in Port-au-Prince from Haiti event are more than ten times as that in Mexicalia city from Baja event. Moreover, the simulated distribution in our results also show that the strong ground motion from Haiti event are almost 3 to 5 times as that from Baja event. The simulated PGA in the normal, parallel and vertical directions are 682 cm/s2, 306 cm/s2, 327 cm/s2 at Port-au-Prince, respectively, and the PGA in the normal, parallel and vertical directions are 34 cm/s2, 44 cm/s2 and 51 cm/s2 at Mexicalia city, respectively. Therefore, the radiated seismic energy plays a significant role in determining the levels of strong grounds in which stronger ground accelerations usually could cause much more property damages on the ground. Based on the results of strong ground motion in the near-fault, we have simulated the intensity distribution of the two events. It is encouraging that simulated intensity distributions are all show much identity with ShakeMap from USGS. The numerical modeling developed in this study has a potential application in ground motion estimation/prediction for earthquake engineering purpose.