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基于四川区域地震台网记录的波形资料,利用CAP波形反演方法,同时获取了2013年4月20日芦山M7.0级地震序列中88个M≥3.0级地震的震源机制解、震源矩心深度与矩震级,进而利用应变花(strain rosette)和面应变(areal strain)As值,分析了芦山地震序列震源机制和震源区构造运动与变形特征.获得的主要结果有:(1)芦山M7.0级主震破裂面参数为走向219°/倾角43°/滑动角101°,矩震级为MW6.55,震源矩心深度15km.芦山地震余震区沿龙门山断裂带走向长约37km、垂直断裂带走向宽约16km.主震两侧余震呈不对称分布,主震南西侧余震区长约27km、北东侧长约10km.余震分布在7~22km深度区间,优势分布深度为9~14km,序列平均深度约13km,多数余震分布在主震上部.粗略估计的芦山地震震源体体积为37km×16km×16km.(2)面应变As值统计显示,芦山地震序列以逆冲型地震占绝对优势,所占比例超过93%.序列主要受倾向NW、倾角约45°的近NESW向逆冲断层控制;部分余震发生在与上述主发震断层近乎垂直的倾向SE的反冲断层上;龙门山断裂带前山断裂可能参与了部分余震活动.P轴近水平且优势方位单一,呈NW-SE向,与龙门山断裂带南段所处区域构造应力场方向一致,反映芦山地震震源区主要受区域构造应力场控制,芦山地震是近NE-SW向断层在近水平的NW-SE向主压应力挤压作用下发生逆冲运动的结果.序列中6次非逆冲型地震均发生在主震震中附近,且主震震中附近P轴仰角变化明显,表明主震对其震中附近局部区域存在明显的应力扰动.(3)序列整体及不同震级段的应变花均呈NW向挤压白瓣形态,显示芦山地震震源区深部构造呈逆冲运动、NW向纯挤压变形.各震级段的应变花方位与形状一致,具有震级自相似性特征,揭示震源区深部构造运动和变形模式与震级无关.(4)不同深度的应变花形态以NW-NWW向挤压白瓣为优势,显示震源区构造无论是总体还是分段均以NW-NWW向挤压变形为特征.但应变花方位与形状随深度仍具有较明显的变化,可能反映了震源区构造变形在深度方向上存在分段差异.(5)芦山地震震源体尺度较小,且主震未发生在龙门山断裂带南段主干断裂上,南段长期积累的应变能未能得到充分释放,南段仍存在发生强震的危险.
Based on the waveform data recorded by the Sichuan regional seismograph network and utilizing the CAP waveform inversion method, the focal mechanism solutions of 88 M≥3.0 earthquakes in the Lushan M7. 0 earthquake sequence on April 20, 2013 are obtained. The source centroid Depth and moment magnitude, and then use the strain rosette and areal strain As values to analyze the focal mechanism and the tectonic movement and deformation features of the Lushan earthquake sequence.The main results obtained are as follows: (1) Lushan M7 The parameters of rupture plane of grade 0 mater strike are 219 ° / dip angle 43 ° / 101 ° slip angle, moment magnitude MW6.55 and focal depth of center of concentric axis 15km. The Lushan earthquake aftershock zone is about 37km long along the Longmen Shan fault zone, The aftershocks of the fault zone are about 16 km wide.The aftershocks on both sides of the main shock show an asymmetric distribution.The aftershocks on the south west side of the main shock are about 27 km in length and about 10 km on the north east side.The aftershocks are distributed in the depth of 7 ~ 22 km with a dominant distribution depth of 9 ~ The average depth of the sequence is about 13 km, most of the aftershocks are distributed in the upper part of the main shock.The coarsely estimated focal volume of the Lushan earthquake is 37 km × 16 km × 16 km. (2) The statistical results of surface strain As indicate that the Lushan earthquake sequence is dominated by thrusting Absolute advantage, accounting for more than 93%. The sequence is mainly subject to dumping NW and dip angle of about 45 ° near the NESW thrust control; part of the aftershock occurred in the main fault with seismogenic fault nearly vertical SE thrust thrust fault; Longmenshan fault zone before the fault may be involved in part of the aftershock activity.P The NW-SE direction is nearly horizontal and the NW-SE direction is consistent with the tectonic stress field in the area where the southern segment of the Longmen Shan fault is located. This indicates that the focal region of the Lushan earthquake is mainly controlled by tectonic stress field. The Lushan earthquake is near NE-SW The result of thrusting movement under the NW-SE compressive stress near the horizontal strike of the fault is that the 6 non-thrust earthquakes occurred near the epicenter of the main epicenter and the P-axis elevation angle near the epicenter of the main epicenter changed Obviously, it indicates that the main shock has obvious stress disturbance on the local area near the epicenter. (3) The strain of the whole and different magnitudes of the sequence shows a NW-treaded white petal shape, indicating that the deep structure of the Lushan earthquake focal zone is thrusting , NW to the pure extrusion deformation.The strain azimuth and shape of each magnitude segment is consistent with the feature of magnitude self-similarity, revealing that the deep tectonic movement and deformation mode in the source area have nothing to do with magnitude. (4) -N WW is the advantage of compressing the white petals, which shows that the structure of the source area is characterized by NW-NWW extrusion deformation both in general and in sections.But the azimuth and shape of the strain flower still have obvious changes with depth, which may reflect the source (5) Lushan earthquake focal body scale is small, and the main shock does not occur in the main fault of southern Longmenshan fault, the long-term accumulated strain energy in the southern section can not be fully obtained Released, there is still the danger of strong earthquakes in the southern section.