摘要
采用基于三维速度模型的定位方法,测定了九寨沟M_s7.0级地震的主震位置,震中为103.806°E,33.201°N,震源深度为20.4 km.使用最近一个强震台(51JZB)的S-P到时差,估算了主震初始破裂点的深度不浅于14.3 km.利用流动观测获得定位精度较高的余震,对早期余震位置进行校正,并采用双差方法对震后一个月的余震进行了重定位,获得了3030个地震的位置.余震呈北西西向的条带状分布,长约42 km,余震北临塔藏断裂,南接虎牙断裂北端.主震位于余震带的中央,其两侧各有长约20 km的余震带,西北侧有一长约5 km的余震稀疏段.西北段余震深度较浅,余震带宽度约6 km;东南段余震深度较深,余震带较窄,约4 km.余震震源深度的优势分布范围在4~20 km之间.发震断层倾角较陡,平均值约为84°.断层倾向和倾角沿走向方向有明显变化,断层在浅部向西南倾斜,深部略向北东倾斜.主震初始破裂点深度大于矩心深度和余震平均深度,地震破裂由深向浅传播.余震沿断层走向有明显的时空扩展特征,震源区可能存在余滑.
An earthquake of Ms7.0 struck Jiuzhaigou Country in Sichuan Province on 8 August 2017. It occurred at the northeastern boundary of the Bayan Har block. The Jiuzhaigou earthquake was one of the largest earthquakes in continental China since the 2013 Ms7.0 Lushan earthquake, and it was widely felt across Sichuan and adjacent provinces. The earthquake left 25 dead and up to 500 injured. Because the Jiuzhaigou earthquake did not produce obvious surface ruptures, the causative fault of this event was much debated. The shape of the seismogenic fault, the focal depth of the mainshock and the characteristics of the aftershock sequence were also not very clear. The Sichuan earthquake administration deployed 6 temporary seismic stations around the source region within 4 d of the mainshock. In this study, we collected seismic waveform data and phase arrival data recorded by permanent and temporary stations. We present a systematic investigation about the location of the Jiuzhaigou earthquake sequence with high precision. These results provide new constraints for refining earthquake rupture process, constructing seismogenic models, and evaluating regional earthquake risks. The mainshock of the Jiuzhaigou Ms7.0 earthquake was relocated using a 3D velocity model. The procedure takes station elevation, topography and the Earth＇s ellipticity into consideration. The location of the mainshock was found to be 103.806°E, 33.201°N, and the focal depth to be 20.4 km. The depth of the initial rupture point of the mainshock was estimated to be below 14 km with S-P arrival time difference recorded at the nearest strong motion station. The locations of early aftershocks were corrected with latter aftershocks recorded using dense temporary seismic stations. A double difference algorithm was used to relocate 1-month aftershock sequence of the Jiuzhaigou earthquake. The locations of 3030 aftershocks were here determined. The average location error was found to be 0.16, 0.15, and 0.18 km in the E-W, N-S, and UoD directions, respectively. The relocation results showed that the aftershocks spread approximately 42 km, trending NWW. The aftershock zone was found to connect the Tazang fault to the north and to the Huya fault to the south. The mainshock is located at the center of the aftershock zone, with similar aftershock length at the both sides. There is a ~5 km sparse aftershock segment to the NW of the mainshock which is consistent with large coseismic slip area. This phenomenon can be explained due to the large amount of stress released during the mainshock rupture. The depth of the aftershock in the northwest end was relatively shallow, and the aftershock zone was about 6 km wide. The depth of aftershock in the southeast section was deeper and the area was narrower, about 4 km. The predominant distribution of the focal depth is 4-20 km. The dip angle of the seismogenic fault is steep, with an average value of about 84~, and changes obviously along the strike direction. The seismogenic fault inclined to the southwest in the shallow part and to the northeast in the deep part. The complex fault shape should be considered when constructing seismogenic model and inverting earthquake rupture process. The depth of the initial rupture point of the mainshock is deeper than the centroid depth and average depth of the aftershock sequence, indicating that the earthquake rupture spreads from deep space to shallow. We find that the aftershocks migrated in the along-strike direction with logarithmic time since the mainshock. The length of the aftershock area expanded from 25 to 42 km in 2 d. The rate of spread was approximately 1.3 km/log（s）, consistent with aftershock expansion caused by propagating afterslip. There may be afterslip in the source area of the Jiuzhaigou earthquake.
作者
房立华
吴建平
苏金蓉
王毛毛
蒋策
范莉苹
王未来
王长在
谭夏露
Lihua Fang1,2, Jianping Wu1,2, Jinrong Su3, Maomao Wang4, Ce Jiang5, Liping Fanl, Weilai Wang1, Changzai Wang1 ＆ Xialu Tan1(Institute of Geophysics, China Earthquake Administration, Beijing 100081, China; Key Laboratory of Seismic Observation and Geophysical Imaging, China Earthquake Administration, Beijing 100081, China; Sichuan Earthquake Administration, Chengdu 610041, China; College of Oceanography, Hohai University, Nanjing 210098, China; Guangdong Earthquake Administration, Guangzhou 510070, Chin)
出处
《科学通报》
EI
CAS
CSCD
北大核心
2018年第7期649-662,共14页
Chinese Science Bulletin
基金
国家自然科学基金(41774067
41774102)
中国地震局"四川省九寨沟7.0级地震科学研究"项目资助
关键词
九寨沟地震
余震序列
双差定位
震源深度
发震断层
Jiuzhaigou earthquake, aftershock sequence, double difference location, focal depth, seismogenic fault
