2013-12-16巴东MS5.1地震前后波速比异常特征

利用2008～2021年地震观测报告提取巴东周边小震纵横直达波走时数据，分别采用单台多震、单震多台和达法计算波速比，分析波速比在2013年巴东M_S5.1地震前后的时空演化特征。结果表明：1）巴东地震前震中东西两侧8个台站的单台波速比出现不同程度的下降-回升异常变化；2）巴东地震周边地区多台波速比在震前经历了2 a下降-2 a回升的变化过程，与单台波速比结果相似；3）多台波速比空间演化图像显示，巴东地震前2 a波速比低值集中分布在震中周边区域，震后该区波速比回升至高值。

The Abnormal Variations of Wave Velocity Ratio before and after December 16, 2013, Badong MS5.1 Earthquake

From the seismic observation report from 2008 to 2021, we extract the travel time data of direct P and S waves of small earthquakes near Badong area. We calculate the wave velocity ratio by the Wadati method of single earthquake and multi-station and single station and multi-earthquake, respectively. We analyze the temporal and spatial evolution characteristics of wave velocity ratio before and after the Badong M_S5.1 earthquake in 2013. We conclude: 1) the wave velocity ratio of 8 stations on the east and west sides of the epicenter before the Badong earthquake changed abnormally in varying degrees with decline-rising process. 2) The wave velocity ratio of multiple stations in the surrounding area of Badong earthquake experienced the change process of two years decline-two years rise before the earthquake, which is similar to the result of single station wave velocity ratio. 3) The spatial evolution images of the Wadati method of single earthquake and multi-station show that the low value of wave velocity ratio in the first two years of Badong earthquake are concentrated around the epicenter, and the wave velocity ratio rises to the high value after the earthquake.