芦山Ms7．0级地震余震序列重新定位及构造意义

Relocation of the Lushan M_s7.0 earthquake sequence and its tectonic implication

利用四川省地震台网的震相数据和双差定位方法对芦山慨7．0级地震及其余震序列进行了精确定位，根据余震分布确定了发震断层的位置和断层面的几何特征，并对余震活动进行了分析．结果显示，芦山Ms7．0级地震的震中位于30．28°N、102．99°E，震源深度为16．33km．余震沿发震断层向主震两侧延伸，主要分布在长约32km、宽约15～20km、深度为5～24km的范围内．地震破裂带朝西南方向扩展范围较大，东北方向略小，余震震级随时间迅速衰减．震源深度剖面清晰地显示出发震断层的逆冲破裂特征，推测发震断层为大川一双石断裂东侧约10km的隐伏断层．该断层走向217°、倾向北西，倾角约45°，产状与大川一双石断裂相比略缓，它们同属龙门山前山断裂带的叠瓦状逆冲断层系．受发震断裂影响，部分余震沿大川一双石断裂分布，西北方向的余震延伸至宝兴杂岩体的东南缘，与汶川地震的破裂带之间存在50km左右的地震空区，有可能成为未来发生强震的潜在危险区．

Using travel time data from the Sichuan Seismic Network and the double difference relocation algorithm, we determined accurate locations of the Lushan MsT. 0 earthquake and aftershocks. The aim is to determine seismogenic faults and to place constraints on geometry of the fault plane according to the aftershock distribution, and also to analyze aftershock activities. The results indicate that the epicenter of the Lushan MsT. 0 main shock is located at 30.28°N, 102.99°E and its focal depth is 16.33 km. The aftershocks are distributed within a region 32 km long and 15-20 km wide, with depths ranging 5-24 kin. The seismic rupture extends relatively longer to the southwest of the main shock epicenter than that to the northeast. Magnitudes of the aftershocks decrease rapidly with time. Focal depth distributions show a clear thrust rupture within the crust, which is a hidden fault about 10 km east of the Dachuan-Shuangshi fault zone. We estimate that the fault plane has a strike of 217~ and dips to the northwest at 45~ angle, almost parallel to the Dachuan-Shuangshi fault zone only with a gentle dipping angle. Both of them belong to the imbricate thrust system of the Longmengshan range-front fault zone. Affectedby this fault, extend to the zone to the so gap, which is the aftershocks also occurred on the Dachuan-Shuangshil fault zone, parts of which southwestern margin of the Baoxing massif in the northwest. From Baoxing massif uthern end of the Wenchuan Ms8.0 earthquake rupture zone is a 50 km long seismic considered to have a potential risk of a large earthquake in the future.