Ground Motion Simulation and Topographic Site Effect of Luding Earthquake
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摘要: 2022年9月5日四川省甘孜州泸定县境内发生MW 6.6地震，地震造成93人死亡、25人失联，423人受伤，给人民群众生命财产安全造成重大损失。本次地震震中位于青藏高原东部边缘，高山峡谷地貌形态突出，由此引发的地震动地形效应不容忽视。本文基于谱元方法模拟了泸定地震近断层地震动，并分析了地形场地效应的影响。在有效模拟频带范围内，得到如下结论：（1）相较于平面自由场，山谷地震动持时会增加约2倍左右，且在破裂方向上会更加明显；（2）山谷台站的三分量合成加速度峰值（PGA）放大系数普遍大于三分量合成速度峰值（PGV）放大系数，最大不超过2；（3）山谷地形使得地震动的累计绝对速度（CAV）增大2～4倍。地形能够引起地震动持时的放大，在重大工程紧急处置参数确定中应当考虑地形场地效应的影响。Abstract: An MW 6.6 earthquake occurred in Luding County, Ganzi Prefecture, Sichuan Province on September 5, 2022. This earthquake caused 93 deaths, 25 loss of contact and 423 injuries, causing major losses to the safety of people’s lives and property. The epicenter of this earthquake is located at the eastern edge of the Qinghai-Tibet Plateau, with prominent mountains and valleys. The topographic site effects cannot be ignored. In this paper, the near-fault ground motion of the Luding earthquake is simulated based on the spectral element method, and the influence of topographic site effects is analyzed. Within the effective frequency range, there are the following conclusions: (1) The duration of ground motion of the valley site is about 2 times of that in the far free field site, and it is more obvious along the strike; (2) The amplification factor of the three-component synthetic PGA (Peak Ground Acceleration) of the valley site is generally greater than that of the PGV (Peak Ground Velocity), but the maximum is not exceed 2; (3) The valley topography makes the CAV (Cumulative absolute velocity) of the ground motion increased by 2 to 4 times. The topography can lead to the amplification of ground motion duration, and the influence of topographic site effects should be considered in determining emergency response parameters for major projects.
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图 1 泸定地震震中与台站位置分布
Figure 1. The epicenter and stations location distribution of the Luding earthquake
图 6 断层面在地表的投影及PGA、PGV和PGD的空间分布
Figure 6. Projection of fault plane on the surface and the spatial distribution of PGA, PGV and PGD
图 9 12个台站的观测记录与模拟记录对比
Figure 9. The comparisonof observation records and simulation records for 12 stations
图 10 模拟记录与观测记录的偏差
Figure 10. The bias between the simulated data and the observed data
图 11 地形台站与平面台站PGA、PGV、Td、IA2、IV2和CAV及其对应比值
Figure 11. PGA, PGV, Td, IA2,IV2,CAV and their ratios for topographic stations and flat free-field stations
图 12 V2201台站地形场地记录与平面场地记录对比
Figure 12. Comparison between topographic site records and flat site records of station V2201
表 1 泸定地震震源参数
Table 1. Source parameters of the Luding earthquake
震源位置 震源机制 长度/km 宽度/km 矩震级MW 经度/(°E) 纬度/(°N) 深度/km 走向/(°) 倾角/(°) 滑动角/(°) 102.109 29.524 5.76 167.37 72 — 30 16 6.59 注：相关震源参数参考韩炳权等（2023）。 
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表 2 台站信息
Table 2. Information of stations
台站名 经度/(°E) 纬度/(°N) 震中距/km 震中方位角/(°) 备注 V2411 102.09 29.61 2.0 202.4 预警烈度台 V2204 102.13 29.64 6.9 220.5 预警烈度台 V2201 102.19 29.58 10.4 275.5 预警烈度台 V2271 102.18 29.53 11.6 306.9 预警烈度台 T2471 102.23 29.37 28.3 329.1 预警烈度台 V2203 102.20 29.83 28.5 204.2 预警烈度台 XXXJ 102.08 29.73 16.0 178.6 预警强震台 SMCK 102.14 29.42 19.9 343.6 预警强震台 CNXJ 102.21 29.76 22.3 212.5 预警强震台 VL002 102.25 29.76 24.3 221.2 预警强震台 51 LDJ 102.21 29.69 16.2 228.4 传统强震台 51 LDL 102.23 29.79 26.1 213.6 传统强震台
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