联合地震波和大地测量数据反演2015年皮山M_W6.4地震的同震破裂分布

GEODETIC AND TELESEISMIC CONSTRAINTS ON SLIP DISTRIBUTION OF 2015 M_W6.4 PISHAN EARTHQUAKE

2015年7月3日在西昆仑推覆构造带前缘发生了M_W6. 4新疆皮山地震,是近40a以来该区域发生的最大的一次中强地震。文中利用近场大地测量数据,包括4个高精度GPS点和一景高空间分辨率ALOS-2 In SAR干涉数据,联合IRIS/USGS提供的25个远震台网P波数据,基于有限断层理论,采取多参数非线性模拟退火算法反演了此次地震的同震破裂模型。联合反演的断层滑移模型显示皮山地震的主破裂区深度集中于9～16km,最大滑移量为95cm,释放的矩能量相当于M_W6. 42,且沿断层走向N302°W单侧破裂,与余震分布吻合。通过与单一数据源反演结果进行对比分析,文中采用的多源数据可以同时约束地震矩能量和断层破裂分布,有效解决了远震台网波形数据模型空间分辨率低(尤其对中强地震而言)和近场大地测量数据在地震矩评估方面不够精确的问题。

On July 3 rd,2015,a M_W6. 4 earthquake occurred on Pishan County,Xinjiang,located in the front of western Kunlun thrust belt,which is the largest earthquake( M_W6. 0 ~ 7. 0) in the past 40 years in this region. In this study, we collected both the near-filed geodetic coseismic deformation observations including 4 GPS sites and one high-resolution ALOS-2 In SAR imagery,and far-field teleseismic P waveforms from 25 stations provided by IRIS/USGS,to invert the fault parameters( strike and dip) and coseismic rupture model of 2015 M_W6. 4 Pishan earthquake. Using the finite fault theory,a non-linear simulated annealing algorithm was employed to resolve our joint inversion problem. The strike( 120° ~ 130°) and dip angle( 35° ~ 40°) of optimal models are different from that of some previous studies,and the dip change is strongly constrained by combined data than that of strike. In fixing the geometric parameters of optimal fault model,we also considered data weight( 5)( geodetic data/teleseismic P waveforms) and constrained weight from moment and smooth factor( 2. 5). Clearly,our results indicate that the slip distribution mainly concentrates in the depth range from 9 to 16 km and a length range of 20 km along the strike direction,which is similar to the spatial distribution of the relocated aftershocks. The maximum slip is ~ 95 cm. The seismic moment release is5. 45×1018 N·m,corresponding to M_W6. 42. Compared with the single data set,geodetic data or teleseismic waveform,our joint inversion model could simultaneously constrain the seismic moment and slip distribution well,thus avoiding effectively a lower-resolution rupture distribution determined by teleseismic-only inversion and a bias released moment estimated by the geodetic-only inversion.Importantly,we should consider both the near-field geodetic data and far-field teleseismic data in retrieving the rupture model for accurately describing the seismogenic structure of active fault in western Kunlun region.