【作者】 赵凌云；

【导师】 刘小凤；

【作者基本信息】 中国地震局兰州地震研究所 ， 固体地球物理， 2008， 硕士

【摘要】 近年来,随着矿山快速发展和甘肃省数字化测震台网的优化改造及省内小震监测能力的提高,一些大型矿山开采地区小震活动频次明显增大,例如平凉华亭煤矿、金川镍矿、镜铁山铁矿、天祝石膏矿等地区的小震活动增强现象突出。以平凉华亭煤矿为例,2001年以来发生1023次ML1.0级以上地震,最大为2005年10月2日ML4.2级地震,造成了一定的经济损失和人员伤亡。因此开展大型矿山区域地震研究很有意义,本文将以平凉地区煤矿中小地震地震活动为研究对象,对这一地区的地震展开深入研究,探究其发震机理。根据平凉地区地震时空分布特征和震相特征,通过遗传算法重新定位深度,利用矩张量反演方法反演震源机制解,最后综合推断平凉地区地震发震机理。得出如下结论:1.平凉地区地震增强活动的时间始于2001年12月,至2005年3-8月达到最高值,小震月频度达到20次。地震活动在空间上十分集中,基本丛集在30-40公里的范围内。地震活动强度以ML1.0-3.9级地震为主,ML3.0级以上地震主要集中在西部的华亭及附近地区,而ML1.0-2.9级地震丛集在东部的崇信及附近地区。2.经过与爆破、天然地震震相异同分析研究可判断:平凉地区中小地震震相具有矿震波形特征:主要震相有(?)波、(S|—)波,周期较大,波形较光滑,且比较单一、规则,频率低,台站记录波形衰减速度较快; P波初动时间与峰值时间很接近,S波较发育。3.利用遗传算法对平凉地区及其西侧六盘山地区地震进行了重新定位,结果显示,这些地震的空间位置定位前后差异较小,但平凉地区震源深度定位前后差异较大,其中,平凉地区震源深度一般为5公里以内,而六盘山地区震源深度一般为10-30公里。4.采用矩张量反演求解了平凉地区及其西侧六盘山地区地震震源机制解,平凉地区震源类型以挤压逆冲居多,正断层、走滑次之,类型混合。主压应力(P)轴的优势方向为北西向,优势倾角15o-20°,主张应力(T)轴优势方向北东向,优势倾角为30°-60°。西侧六盘山地区地震震源机制类型大多是走滑型,主压应力(P)轴优势方向为北东向,优势倾角50°左右,主张应力( T)轴优势方向为北东东,优势倾角60°-80°5.发震机理初步分析结果根据地震时空强分布特征、地震波形特征、震源深度、震源机制解等分析结果初步分析认为,平凉地区地震活动可能的发震机理为:(1)2001-2007年共发生1023次ML1.0级以上地震,其中,1.0-1.9级481次为煤体(压缩)矿震。发生的机理:它是煤岩结构在压性载荷作用下而失稳破坏的动力现象。地下开采后,由于应力集中,在采煤工作面煤壁或巷道周边附近,应力超过强度极限,煤岩材料变成了应变软化的非稳定材料,而深部受采动影响较小的区域仍处于硬化或,随着开采范围扩大,煤岩体进入峰值强度后变形的区域加大,应变软化程度的加深,使得煤岩结构由稳定的平衡向非稳定平衡过渡。当成为非稳定平衡时,在外部扰动下,系统的原有平衡状态失稳而发生矿震。(2)平凉地区2.0-2.9级493次为顶板拉伸型矿震。.顶底板拉伸矿震机理:也就是极值点失稳理论,当一个初始稳定的平衡路径随着载荷的增长,载荷达到一个局部最大值,在这载荷作用下,结构将丧失稳定性。(3)平凉地区3.0-3.9级48次,4.0-4.9级1次,最大为2005年10月2日ML4.2级地震,为断层矿震。发生的机理:断层矿震可看成是断层带介质和围岩组成的系统在采矿活动诱发扰动下的变形失稳问题。断层矿震的直接原因是煤层的开采,在未开采之前,断层与煤岩组成了一个平衡(动态平衡)系统,开采对这一系统的扰动导致了断层应力的重新分布。更多还原

【Abstract】 In rencently years,with the quickly development of mine , the optimizational renovation of digital seismograph network and the enhanced monitoring ability of small earthquake,the activity of small earthquake increases obviously in large scale mine ,such as Pingliang coal mine,Jinchuan nickel minerals,Jingtieshan iron ore,Tianzhu gesso mine.Take the coal mine at Huating in Pingliang area as example,since 2001, the earthquakes over ML1.0 have happened more than1023,the biggest is ML4.2 on Oct.2 2005,and brought some losses of wealth and people.Therefore,it is very necessary to do reseach in large scale mine.In this article , taking the increasing seismicity of small -moderate in PingLiang area as object,we do the further study in order to find seismicity mechanism in this area.We definited focal depth by locating method based on genetic algorithm, calculated focal mechanism by moment tensor inversion, according to seismic spatiotemporal distribution,seismic phase and regional geological structural environment, finally, we deduced the seismic mechanism in PingLiang area.We get following conclusions:The seismicity in PingLiang area increases form Dec.2001,reaches the maximum during March to August and the monthly frequence arrives at about 20. The seismicity appears densely in space and the earthquakes are located 30~40km area,The structure of magnitude is primarily composed of ML1.0-3.9,the earthquakes over ML3.0 distribute in Huating and its surroundings in the west,the earthquakes between ML1.0-2.9 distribute in Chongxin and its surroundings in the east.After the comparison of seismic phase with blasts,earthquakes,we reached a conclusion that seismic phase of the small-morderate earthquake in Pingliang area are similar with the mining-induced earthquake .The mainly phase is (?)、(S|-),the period is very long,the wave shape is very smooth ,single and regular, the frequece is lower,and the weakening speed is very quickly; the time of P wave first motion is nearly with peak value,the S is full. We definited focal depth in Pingliang area and the western region- Liu pan mountain by locating method based on genetic algorithm ,the results showed that the localization in space keeped unchangeable,but the focal depth changed obviously,the focal depth in pingliang area is mostly inside 5km and the focal depth in Liupan mountain is mainly between 10-30km.We calculated focal mechanism in Pingliang area and the western region- Liu pan mountain by moment tensor inversion ,the types of focal mechanism is mainly compressional-thrust fault , others are the normal slip fault and the strike-slip fault ,and the types is mixed.The dominant direction of principal compression axis is NW, the dominant inclination angle is 15o-20°, the dominant direction of tensile compression axis is NE, and the dominant inclination angle is 30°.The types of focal mechanism in the western region- Liu pan mountain is mainly strike-slip fault.The dominant direction of principal compression axis is is NE, the dominant inclination angle is about 50°, the dominant direction of tensile compression axis is NEE, the dominant inclination angle is60°-80°.Based on the characters of space-time seismicity , seismic phase,focal depth, focal mechanism,the possible seismic mechanism in Pingliang area are as the follows:(1)Among 1023 earthquakes more than ML1.0 from 2001 to 2007, there were 481 earthquekes between 1.0-1.9 which were mining-induced earthquakes by coal body. The kinds of initial mechanism is the dynamic phenomenon that coal structure losed the stability and destructed under thecompression load.After the underground mining,duing to the concentrative strain, the strain exceed the strength limit near the coal wall on coal face,the coal material become unstable under strain softing,but the deep area which have seldom influences by mining keeped flexible stage.With the mining area enlarging ,the deformed area is largening after coal mass get into peak strength, the strength of strain softing intensified,and the coal structure transform from stable to unstable.When they became unstable ,the system lost the stability and destructsed under the external force. (2) There were 493 earthquekes between 2.0-2.9 which are mining-induced earthquakes by work face .The kinds of initial mechanism ,that is lose the stability at extreme value point, with the load increasing , the balanceable route t is firstly steaty , when the load arrived at local maximum.the structure will loss the stability .There were 48 earthquekes between 3.0-3.9,1 earthquake between 4.0-4.9 which are mining-induced earthquakes by fault rockburst. The kinds of initial mechanism is the system whice made up by fault media and wall rock loss the stability under the mining activity.The direct reason is the coal mining, ,the fault and wall rock are dynamic balanced system before the mining,and the coal mining reduce to the fault strain distributes again.更多还原