前郭MS5.8和松原MS5.7地震震源区地壳速度结构与孕震环境

为了解2013年11月23日吉林前郭M_S5.8和2018年5月28日吉林松原M_S5.7地震震源区的地壳速度结构及其孕震环境，本研究收集了东北地区CEA固定台站、NECESSArray流动台站和五大连池WAVESArrary流动台站的连续波形数据，使用背景噪声成像方法，获得了前郭地震和松原地震震源区地壳S波速度结构.结果显示，这两个地震主要发生在相对高波速异常区，而震源区下方存在明显低波速异常，且该低速层呈北北东走向，并有向北延展的趋势.结果表明，震源区相对高波速异常区易于积累能量孕育地震，而震源区下方的低波速异常可能代表了流体作用.这种流体作用会降低断层面有效正应力从而触发地震.这种流体作用可能和太平洋板块深俯冲至我国东北地区（包括前郭地震和松原地震震源区）下方的地幔转换内形成"大地幔楔"结构与动力学密切相关.在"大地幔楔"结构中，由于地幔转换带中滞留板块脱水作用和地幔角流作用，容易形成热湿物质上涌，进而导致松辽盆地中北部岩石圈物质拆沉、地幔流体入侵至中下地壳、然后作用于断裂带，从而导致了两个震源区中强度地震的发生.

Crustal velocity structure and seismogenic environment in the source areas of the Qianguo MS5.8 and Songyuan MS5.7 earthquakes

To understand the crust velocity and seismogenic environment of the 23 November 2013 Qianguo, Jilin, M_S5.8 earthquake and 28 May 2018 Songyuan, Jilin, M_S5.7 earthquake, we collect the continuous waveform data from CEA permanent seismic stations, NECESSArray portable seismic stations, and WAVESArray portable seismic stations, apply the ambient noise tomographic technique to infer the 3-D S-wave velocity structure of the crust both in the Songyuan and Qianguo earthquake source areas. The results show that these two earthquakes occurred in the relative high-velocity areas, and the source areas are underlain by an obvious low-velocity anomaly with a NNE-SSW orientation and a northward extension. These results suggest that the source areas with relative high velocities are easier to accumulate the energy and generate the earthquakes, whereas the low-velocity anomaly under the source areas may denote the influence of fluids. These fluids influence could be related to the big mantle wedge structure and dynamics due to the deep subduction of the Pacific slab down to the mantle transition zone under NE China including the Qianguo and Songyuan earthquake source areas. In the big mantle wedge structure, owing to the dehydration reaction of the stagnant slab in the mantle transition zone and corner flow, there exists hot and wet mantle upwelling which leads to the lithospheric delamination under the central-to-north Songliao basin, and the mantle fluids can intrude to the mid-lower crust and affect the fault zone. These processes could result in the generation of these two earthquakes.