汶川M_S 8.0地震断层与地震灾害初步分析

AN ANALYSIS ON M_S 8.0 WENCHUAN EARTHQUAKE FAULT AND SEISMIC DISASTER

对于特大地震近断层地震场的空间分布的复杂性学术界一直很关注,由于样本地震数量和资料的不足,至今还没有非常清晰的结论。通过参加汶川MS8.0地震的应急科学考察,对震中区和高烈度区断层破裂带附近的地震灾害情况进行了现场调查。文中以典型事例为主线介绍了现场考察的结果,结合既往的研究成果和汶川地震的震源特性,分析讨论了地表破裂带、地震动以及建筑物震害之间的关系。结果表明:1)地震断层发生强变形和地表破裂对建筑物的损害现象非常明显,对具有大震级发震危险的断裂带,今后应该考虑进行一定宽度的破裂避让或采取针对性的必要措施。2)初步探讨了紧邻断裂带的建筑物没有倒塌的可能机理,第一,出现地表破裂的大部分区域为基岩或坚硬的场地,场地条件相对较好;第二,存在导致地表破裂的浅部有效应力降和破裂速率相对较低,导致了1s附近的地震动相对低下的可能性。

Complex spatial distribution of seismic motion near faults has always been a concern to scientists, and it still remains as an uncertain problem due to insufficiency of events and information. The paper presents the main cases of seismic disaster by field investigations of Ms 8.0 Wenchuan earthquake, analyzes and discusses the relationship among earthquake fault, ground motion and earthquake disaster near the fault fractured zone, based on previous research of source rupture processes and source inversion of Wenchuan earthquake. Intensive deformation and ground surface rupture along the earthquake fault have caused obvious damage to buildings, so it is necessary to introduce the safety distance away from active fault and other measures. Possible reasons for buildings near surface rupture zone having withstood the strong earthquake are as follows ： other than their performance of seismic resistance, firstly, most of them locate at hard sites or on bedrock in the surface rupture zone, and secondly, the effective stress drop and low rupture velocity may exist in the shallow asperities, resulting in a relatively lower ground motion at the period about 1 sec.