乳山震群震源区地壳速度结构初步研究

运用距离乳山震群最近的乳山台2011-2014年远震波形资料，计算接收函数，确定震群震源区及邻近区域的地壳厚度和波速比。结果显示：乳山台下方各个方位的接收函数差异比较大，地壳速度结构呈现横向非均匀性；震源区与邻近区域存在明显差别，邻近区域的中、下地壳存在明显的高速区，震源区中下地壳中存在明显的低速区；震群中M_L3.0以上地震基本发生在高低速交界处。据此推断，乳山震群可能是由于中下地壳小范围内的物质的不均匀性导致上地壳破裂。

Preliminary Study of Crustal Velocity Structure in the Focal Region of the Rushan Earthquake Swarm

The M_L3.8 earthquake that occurred on October 1, 2013, in Rushan at 12:07 is located in Shandong Province''s northeast section. Then the earthquake swarm activity was formed. A total of 13 000 seismic records were obtained in the seismic network at Shandong so far. The largest earthquake on May 22, 2015, is M4.6. During 2011-2014 we collected the teleseismic waveform from Rushan station to calculate the receiver functions, then we calculated the crustal thickness and velocity ratio in the focal region and its adjacent regions. The results showed that the lateral heterogeneity of the crustal velocity structure in the study area is high, and the receptor functions observed differently in different azimuth. There is an obvious difference between the source area and the adjacent area. In the middle and lower crust of source area, there is an obvious low-velocity zone but high-velocity zone in the middle and lower crust of its neighboring areas. We used the receiver functions stacking method H-k to determine the crustal thickness and wave velocity ratio of the seismic source area and adjacent area. The results showed that the thickness of the crust is 31 km, and the wave velocity ratio is 1.74. Many earthquakes above M_L3.0 occurred in the high and low-velocity junction regions. It was inferred that the occurrence of the Rushan earthquake swarm may be due to the upper crust rupture caused by the heterogeneity of matter within a small scope.