四川芦山7.0级地震及其与汶川8.0级地震的关系

The M7.0 Lushan earthquake and the relationship with the M8.0 Wenchuan earthquake in Sichuan,China

2013年4月20日在四川省雅安市芦山县发生M7.0级地震.根据四川省台网资料和收集的国内外相关资料,我们分析了芦山地震的基本参数、余震分布、序列衰减等特征.结果表明:芦山地震位于龙门山断裂南段,其震源力学机制显示为纯逆冲性质,与龙门山断裂构造特征相符合;芦山地震的余震较丰富,震后15天震区已发生7800多次余震,其中,5级以上余震4次,最大余震是4月21日17时5分芦山、邛崃交界M5.4级地震;余震分布形成的图形显示其长轴走向与龙门山断裂构造走向一致,余震分布显示密集区长轴约40km,短轴约20km.与汶川M8.0级地震在震源力学机制、破裂过程、余震空间展布以及地表破裂等对比分析后表明:芦山地震与汶川地震的震源错动类型、破裂过程、地表破裂以及余震活动等特征存在明显差异;芦山地震与汶川地震震中位置相距90km,两次地震的余震密集区相距50km;汶川8.0级地震造成龙门山断裂中北段较充分破裂,芦山7.0级地震则展布于龙门山断裂南段且破裂尺度有限;两者有发震构造上的联系,但两次地震是相对独立的地震事件.

On 20 April 2013 an M7.0 Lushan earthquake in the Sichuan of China occurred on the southern segment of the Longmenshan fault.According to the data of the telemeter seismographic network in Sichuan and the current correlative information from internal and overseas,we analyze the basic earthquake parameters,aftershock distribution,sequence attenuation characteristics.Our results show that the focal mechanisms of the Lushan earthquake result from a pure thrust and are consistent with the characteristics of Longmenshan fault structure.The Lushan earthquake is rich in aftershocks.More than 7800 aftershocks are logged since main-quake from 20 April to 5 May,2013.4 aftershocks of magnitude 5 or greater have occurred in the region.The largest aftershock is the M5.4 earthquake on April 21 at 17∶05 of Beijing time between Lushan and Qionglai counties.The long axis of aftershocks distribution ellipsoid is consistent with the Longmenshan fault structural trend.The lengths of the long and short axis of the aftershocks distribution ellipsoid are about 40 km and 20 km respectively.This indicates that the rupture scale of this earthquake is limited.From following aspects such as the focal mechanisms,the rupture process,aftershocks spatial distribution and the surface rupture,we compare the Lushan earthquake with the M8.0 Wenchuan earthquake and find that these two earthquakes are significantly different.The distance between the Lushan earthquake and the Wenchuan earthquake is about 90 km.The distance between two locations of the aftershock-intensive areas is 50 km.The Wenchuan earthquake made the middle-northern segment of the Longmenshan fault to rupture fully.The original location of the Lushan earthquake is in the southern segment of the Longmenshan fault.The rupture scale of the M7.0 event is limited.Although they are connected with each other on same seismogenic structure,they are two relatively independent seismic events.