Simulation of ground motion in the Tonghai Basin during the 1970 Tonghai Ms 7.7 earthquake
The 1970 Tonghai Ms7.7 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.
1970 Tonghai earthquakeTonghai Basinthree-dimensional spectral element methodPGV distributionseismic intensity
万方数据
