| 利用主动震源监测地下介质衰减特性变化 |
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| 引用本文： | 陈海潮,葛洪魁,王宝善,宋丽莉,王伟涛.利用主动震源监测地下介质衰减特性变化[J].地震学报,2012,34(6):804-817. |
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| 作者姓名： | 陈海潮 葛洪魁 王宝善 宋丽莉 王伟涛 |
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| 作者单位： | (中国北京100081中国地震局地球物理研究所) |
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| 基金项目： | 地震行业专项，国家自然科学基金，国家科技支撑计划"汶川地震断裂带科学钻探——主动震源探测及发震断裂的走时变化监测"共同资助 |
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| 摘 要： | 监测地下介质物性动态变化对于研究地震的孕育发生过程具有重要意义. 汶川地震发生后, 在汶川地震主断裂带东北端的陕西省宁强县, 建立了一套主动震源观测系统,利用电动落锤作震源对断裂带开展了近一个月的连续监测实验. 利用主动震源激发波形的高度可重复性, 用谱比法计算了浅层地下介质衰减参数t*随时间的变化, 并与波速和大气压变化进行了对比分析. 结果显示, 由未固结的沉积层和破碎岩石组成的断裂带地震波衰减强,品质因子为10左右；衰减参数t*与大气压的变化有很好的相关性, 并与波速随大气压的变化趋势一致, 可能是由于大气压变化导致浅层介质的裂隙密度变化引起的；强余震引起显著的t*的同震变化及震后各接收台站的不同变化趋势. 野外实验表明, 主动震源是一种监测地下介质物性变化的有效方法.
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| 关 键 词： | 汶川地震 主动震源 地震波衰减 随时间变化 大气压 |
Monitoring temporal variation of subsurface wave attenuation using active source |
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| Chen Haichao
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Ge Hongkui
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Wang Baoshan
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Song Lili
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Wang Weitao.Monitoring temporal variation of subsurface wave attenuation using active source[J].Acta Seismologica Sinica,2012,34(6):804-817. |
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| Authors: | Chen Haichao Ge Hongkui Wang Baoshan Song Lili Wang Weitao |
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| Institution: | (Institution of Geophysics, China Earthquake Administration, Beijing 100081, China) |
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| Abstract: | Monitoring subsurface medium properties is essential for understanding earthquake evolution process. After the occurrence of Wenchuan MS8.0 earthquake, a 1-month field experiment was conducted in Ningqiang County, Shaanxi Province, to monitor subsurface medium property variation. The experiment site is located at the northeast end of the main fault ruptured during the devastating Wenchuan earthquake. An electric drop hammer was used for highly repeatable excitation of elastic waves. We extracted small temporal variations of the attenuation parameter t* of subsurface medium using spectral ratio method, and investigated the correlation between the attenuation, wave velocity and atmospheric pressure. The result shows that the shallow fault zone, which is generally composed of sedimentary cover and unconsolidated rocks, exhibits strong attenuation with a quality factor Q of about 10; the temporal variation of t* is strongly correlated with the variation of atmospheric pressure and is conformable to seismic velocity change with atmospheric pressure, which is probably caused by the opening and closing of compliant microcracks associated with pressure variation; apparent co-seismic change, as well as different post-seismic variation patterns across different seismic stations, of t* associated with a moderate aftershock is identified. Our field experiment shows that it is feasible to monitor subsurface medium properties using active source. |
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