1970年通海 M s7.7地震中通海盆地地震动模拟

Simulation of ground motion in the Tonghai Basin during the 1970 Tonghai M s7.7 earthquake

1970年通海M s7.7地震是云南省近百年来发生的震级最大且烈度最高的一次强烈地震。通海盆地在此次地震中出现了IX~X度烈度异常区,震害严重。基于通海盆地新生界厚度和浅层速度结构等资料,建立了包含1970年通海地震发震断层和通海盆地的三维计算模型。采用凹凸体位于断层面不同深度的多个震源模型和三维谱元法模拟通海地震的地震动场。根据模拟地表速度峰值(peak ground velocity,PGV)分布与烈度对比,以及盆地内剖面时程,分析了地震动分布及通海盆地烈度异常区产生的原因。研究表明:通海地震近断层极震区的棒锤型分布,可能是由近断层的破裂方向性效应引起,断层地表迹线东北侧山峰对地震动有较明显的放大作用。通海盆地的显著放大区域主要位于盆地西南IX度烈度异常区对应的凹陷区域,不同震源模型在该区域模拟的PGV均明显大于盆地其他区域。凹凸体位于地下10~16 km的震源模型模拟的烈度异常区明显大于调查烈度,凹凸体位于地下2~8 km的震源模型则比较接近。烈度异常区产生的主要原因为盆地内体波和面波的叠加所致。凹凸体的深度不同,引起的盆地放大主频和倍数差异显著,凹凸体较浅的模型引起的盆地最深处的放大倍数约为凹凸体较深模型的2倍。

The 1970 Tonghai M s7.7 earthquake is the strongest and the most intensity earthquake in Yunnan Province in the last 100 years.The Tonghai Basin experienced an abnormally high intensity ranging from IX to X degrees,resulting in severe damage.Based on data such as the thickness of the Neogene strata and shallow velocity structure of the basin,this study establishes a three-dimensional model that includes the 1970 Tonghai seismogenic fault and the Tonghai Basin.Multiple source models with asperities at different depths on the fault plane and the three-dimensional spectral element method are used to simulate the seismic ground motion of the Tonghai earthquake.By comparing the simulated distribution of peak ground velocity(PGV)with intensity and analyzing the strong motion distribution,as well as the generation of intensity anomaly zones,the reasons behind them are examined.The study indicates that the hammer-like distribution of the near-fault strong ground motion in Tonghai earthquake may be caused by the rupture directivity effect,and the mountain on the northeast side of the fault surface has a significant amplifying effect on the ground motion.The prominent amplification area in the Tonghai Basin is mainly located in the depressed area corresponding to the intensity anomaly zone of IX degree in the southwest of the basin.The PGV simulated by different source models in this area is significantly higher than that in other areas of the basin.The intensity anomaly zone simulated by the source model with asperities at depths of 10~16 km is significantly larger than that of the observed intensities,while the source models with asperities at depths of 2~8 km are relatively closer.The main cause of the intensity anomaly zone is the superposition of body waves and surface waves within the basin.The different depths of the asperities result in significant differences in the dominant frequency and amplification factor within the basin,with the shallowest asperities model causing amplification at the deepest part of the basin approximately twice of that of the deeper asperities model.