微地震波在煤矿岩层中的传播特征研究

 在塔山矿8103工作面微地震监测中，测到距离震源远的底板孔检波器比距离震源近的顶板孔检波器先接收到微地震波的异常现象。研究表明，微地震波的直达波和透射直达波两种传播模式是造成这一异常现象的主要原因。在性质相近的介质中，微地震波是按直达波模式传播，现场监测到的“顶板断裂产生震动波—顶板—顶板检波器”的路径是典型的“直达”传播模式。而在性质差异较大介质的界面处，微地震波在入射界面上的入射点将形成新的震源点，并以新震源点为起始点，再按直达波模式传播，从而形成“透射–直达”传播模式，现场监测到的“顶板断裂产生震动波—综放支架—底板—底板检波器”的路径是典型的“透射–直达”传播模式，这是造成微地震监测中“远点先达”现象的重要原因。根据微地震波在煤矿岩层中的传播特征可以确定合理的定位方法和验证震源定位的准确性。实践证明，在性质差异较大的介质中定位震源时，需将性质相近介质中的检波器信号放在一起定位，这样可以减弱“透射–直达”传播模式造成“远点先达”现象的影响，提高定位精度。

RESEARCH ON SPREAD CHARACTERISTICS OF MICRO-SEISMIC WAVE IN MINE STRATA

In the sublevel caving longwall face 8103 of Tashan coal mine，an abnormal phenomenon that time of micro-seismic wave transmitting to bottom hole geophones far from the hypocenter was shorter than that to roof hole geophones near hypocenter. According to classical model of micro-seismic wave transmission，the energy consumption and transmitting time of micro-seismic wave induced by roof through separation layers and coal seam to bottom hole geophones must be larger. In order to explain the phenomenon，it was assumed that new hypocenter was formed at the interface between bottom floor and coal seam when micro-seismic waves induced by immediate roof or main roof passed through the entrance interface of coal seam and bottom vertically. Transmission direct assumption explained the phenomenon that remote point reached first on the basis of sufficient research on stress history and support effort，etc.. In-situ experiment of calibration blasting confirmed that obtained time difference according to the assumption was equal to true reach time difference approximately. So transmission direct assumption could be used in hypocenter localization and checking. It also could be used for improving location precision.