汶川地震破裂过程联合反演及高频辐射研究

发布时间：2018-09-07 09:26

【摘要】：汶川地震是发生在叠瓦状曲面断层上的一次复杂破裂过程,北川-映秀断层和灌县-江油断层以及与其垂直相交的小鱼洞断层均有地表破裂发生,已有动力学和运动学研究表明断层破裂扩展至三个断层相交处发生了重要的转换。因而,北川断层、彭灌断层和小鱼洞断层的破裂顺序是反演汶川地震破裂过程的关键。本文首先建立合理的三维复杂断层模型,采用3种可能的破裂方式,基于并行非负最小二乘法和多时间视窗技术,联合远场、近场、GPS和地表破裂资料,反演汶川地震精细破裂过程,给出了合理的破裂方式。进一步采用近场加速度记录和差分进化方法,反演断层面上高频辐射分布规律,对比分析高低频地震波辐射的差异。主要成果如下:1.综合考虑三维发震构造模型、余震分布和地表破裂调查,建立更符合实际的曲面断层模型;采用远场36个台站垂直向P波位移记录,利用并行非负最小二乘法结合多时间视窗技术,反演了汶川地震破裂过程。研究表明:(1)目前震源破裂过程反演广泛采用的单侧破裂,在北川断层虹口-映秀近地表区域不产生与地表破裂相符的位错。如果彭灌断层与小鱼洞断层相交处发生双侧破裂,则会在断层南段近地表处产生高达4m的位错,且在北川断层虹口-映秀近地表区域不产生位错,这与地表破裂矛盾。而北川断层浅部区域从与小鱼洞断层相交处发生双侧破裂,则会在虹口-映秀近地表产生与地表破裂相符的位错,明显优于单侧破裂。综合三种破裂方式的结果,本文认为北川断层在与小鱼洞断层相交处发生双侧破裂更符合汶川地震的实际情况。(2)北川断层南段和彭灌断层空间上接近,两者在远场台站的格林函数波形相似,基于远场记录的反演不能区分两者的位错,且北川断层南段位错分布的可靠性大于彭灌断层的位错分布。2.选用近场方位角覆盖较均匀的43个台站三分向速度记录,采用并行非负最小二乘算法结合多时间视窗技术,得到了汶川地震破裂过程。研究表明:(1)与远场记录反演结果相似,单侧破裂和彭灌断层在与小鱼洞断层相交处发生双侧破裂,北川断层虹口-映秀浅部都不产生位错。要使虹口-映秀区域发生与地表破裂吻合的位错,只有北川断层在与小鱼洞断层相交处发生双侧破裂才能满足,所以北川断层需发生双侧破裂。北川断层西南侧高倾角区域有明显的破裂停顿和二次破裂,部分区域破裂持时可达15s左右。(2)51MZQ、51SFB、51MXN和51MXT等台站水平向较大的PGV与断层面相邻区域的滑动速率具有很好的一致性。说明,断层面上发生较大滑动速率的区域,其临近台站往往伴随有较大的PGV产生。3.为了克服单一数据分辨率不足的缺陷,联合远场和近场资料以及联合远场、近场、GPS和同震位移观测资料反演了汶川地震破裂过程。研究表明:(1)联合远场和近场资料,提高了北川断层南段高倾角部分、PGF南半段区域以及北川断层北川附近滑动分布的识别能力。(2)反演中加入GPS资料能很好的控制断层浅部和北川断层北段的滑动分布。(3)联合反演结果显示,汶川地震破裂持续时间达100s,释放地震矩为1.058×10~(21)N·m,断层面上存在5个凹凸体,表明此次地震至少由5个子事件组成。滑动主要分布在北川断层上,说明北川断层是主要的破裂面。在北川断层南段上,龙门山镇下侧以及虹口-映秀近地表区域的位错以逆冲错动为主,最大滑动量达12m,位于虹口下侧;在岳家山到清平近地表附近错动以逆冲为主兼有走滑错动,最大滑动量约为10m。北川断层北段上,北川附近滑动以逆冲为主,最大滑动量10m;南坝到青川区域以走滑错动为主,最大滑动量10m。在彭灌断层上,白鹿下方区域的位错也以逆冲为主,断层深部位错达8m。4.利用芦山地震记录建立的加速度包络衰减关系和汶川地震近场30个台站的加速度包络,基于线源模型采用差分进化方法反演了汶川地震断层面上高频(1Hz)辐射区域分布。结果表明:(1)断层面上高频辐射分布很不均匀,辐射较强的区域主要位于:产生较大地表破裂的映秀、北川和南坝区域;映秀和北川等凹凸体的周边区域,包括震中东北侧60~90km区域、北川和南坝东北侧30km处;断层破裂停止的东北端约30km长的区域。其中,破裂贯穿到地表的映秀、北川和南坝是高频和低频辐射都很强的区域。(2)对于无观测记录场点,选择其临近且场地条件类似的台站加速度提取平稳随机过程,结合高频辐射分布和衰减关系得到的包络,合成了加速度时程,可为汶川地震结构震害分析提供地震动输入。
[Abstract]:The Wenchuan earthquake is a complex rupture process on imbricated curved faults. Both Beichuan-Yingxiu fault, Guanxian-Jiangyou fault and Xiaoyudong fault intersected vertically have surface ruptures. The existing dynamics and kinematics studies have shown that the rupture extends to the intersection of three faults and undergoes an important transformation. The rupture sequence of Beichuan fault, Pengguan fault and Xiaoyudong fault is the key to inverting the rupture process of Wenchuan earthquake.Firstly, a reasonable three-dimensional complex fault model is established. Based on the parallel non-negative least squares method and multi-time window technique, the method combines far-field, near-field, GPS and surface rupture data to invert Wenchuan earthquake. The high frequency radiation distribution on fault plane is inverted by using near field acceleration record and differential evolution method, and the difference between high frequency and low frequency seismic wave radiation is analyzed. A more realistic curved surface fault model is established, and the fracture process of Wenchuan earthquake is inverted by using the parallel non-negative least square method and multi-time window technique with the vertical P-wave displacement records of 36 stations in the far field. If the Pengguan fault and Xiaoyudong fault intersect, a dislocation of up to 4m will occur near the surface of the southern section of the fault, and no dislocation will occur near the surface of the Hongkou-Yingxiu area of the Beichuan fault, which is in contradiction with the surface rupture. Bilateral rupture occurs at the intersection of strata, and dislocations corresponding to surface rupture occur near Hongkou-Yingxiu, which is obviously superior to unilateral rupture. Faults are close in space, and the waveforms of Green's function are similar at the far-field stations. The inversion based on the far-field records can not distinguish the dislocations of the two stations, and the reliability of the dislocation distribution in the south section of Beichuan fault is greater than that of Pengguan fault. 2. 43 stations with uniform near-field azimuth coverage are selected and parallel non-negative velocity records are used. The results show that: (1) Similar to the inversion results from far-field records, the unilateral rupture and the Pengguan fault occur at the intersection of the Xiaoyudong fault and the dislocation does not occur at the Hongkou-Yingxiu shallow part of the Beichuan fault. Only when the Beichuan fault intersects with the Xiaoyudong fault can the dislocations of fissure anastomosis be satisfied. Therefore, the Beichuan fault needs to undergo bilateral rupture. The slip rate to the larger PGV is in good agreement with that to the adjacent area of the fault plane. It shows that the area where the larger slip rate occurs on the fault plane is often accompanied by the larger PGV produced by the adjacent stations. 3. In order to overcome the defect of insufficient resolution of single data, the far-field and near-field data as well as the far-field, near-field, GPS and co-seismic data are combined. The results show that: (1) the combination of far-field and near-field data can improve the recognition ability of slip distribution in the south part of Beichuan fault, the South half of PGF and the north part of Beichuan fault. (2) GPS data can control the slip in the shallow part of the fault and the north part of Beichuan fault. (3) The joint inversion results show that the rupture duration of the Wenchuan earthquake is 100 s, the release moment is 1.058 (21) N 65507 The dislocations on the lower side of Menshan Town and near the surface of Hongkou-Yingxiu are mainly thrusting, with the maximum slip of 12 m at the lower side of Hongkou and strike slip of 10 m at the vicinity of Yuejiashan to Qingping. In the area from Nanba to Qingchuan, the strike-slip dislocation is dominant, and the maximum slip is 10m. On Pengguan fault, the dislocation in the area below Bailu is also dominant, and the deep dislocation of the fault is 8m.4. The acceleration envelope attenuation relationship established by Lushan seismic record and the acceleration envelope of 30 stations in the near-field of Wenchuan earthquake are used based on the line source model. The regional distribution of high frequency (1Hz) radiation on the fault plane of Wenchuan earthquake is inverted by chemical method. The results show that: (1) the distribution of high frequency radiation on the fault plane is very uneven, and the regions with strong radiation are mainly located in Yingxiu, Beichuan and Nanba regions, which produce large surface ruptures, and the surrounding areas of concave-convex bodies such as Yingxiu and Beichuan, including 60-90km area in the north-east of the earthquake. Beichuan and Nanba are located at 30 km northeast of Beichuan and Nanba, and the northeast end of the fault rupture stops at about 30 km long. The envelope obtained from the relationship between frequency radiation distribution and attenuation synthesizes the acceleration time history, which can provide seismic input for the seismic damage analysis of Wenchuan earthquake structure.
【学位授予单位】：中国地震局工程力学研究所
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P315

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