大地震引起的承压井水位变化作为探测活动构造的新途径

From the continental deep drilling on the newly slipped fault after earthquakes, scientist learned that fluid played significant roles (i.g., lubricant and weakening) on faulting during earthquake occurrednce. Fluid can lubricate the fault to make slip easily. High pore pressure inside the fault can reduce the intesity of the fault rocks. While high pore pressure (whcich can be transferred as water level ) also means high tectonic stress/strain state of the site. The fault activity is closely related to the fluid trapped in the fault. That is to say, we may infer the fault activity if we can observe the pore pressure(water level) of the fault. In this proposal, we try to investigate the relationship between activity of tectonic/fault and observed water level change of deep wells with confined aquifer system which was induced by strong earthquakes with magnitude more than 8 which had occurred inside and outside of Chinese Mainland since 1999. .Since Xingtai earthquake occurred in 1966, networks for monitoring water level changes and borehole strain changes aimed at earthquake prediction have been carried out and rebuilt as digital netorks since 2001 via programs in 9th five year plan and 10th five year plan. The digital networks has recorded large amount of co-seismic changes induced by local and distant strong earthquakes since 2001. The co-seismic step-like water level changes have been endowed with indicators of strain changes and tectonic activity by our former NSFC programs. The research experiences in this field, as well as the observation networks and the recently occurred strong earthquakes give us the unique background for this proposal. .In this proposal, we try to focus on specific well to invetigate the co-seismic water level changes difer with time and focus on specific event to investigate the spatial distribution of water level changes in different wells induced by that event. Then the following four topics are involved: (1) the methodology for inferring strain changes from observed water level changes, and their comparability with borehole volume strain changes; (2) the effects of static stress/strain changes (by rupturing) and dynamic stress/strain changes (by seismic wave propagation) on water level changes and active tectonic settings of Chinese Mainland; (3) the relationship between the spatial distribution of water level changes and the boundaries of tectonic blocks; (4) the parameters of Skempton's coefficient B and permeability before and after earthquakes and their changes with time, and their contributions to explainlation of active tectonic settings in Chinese mainland. .Through above researches we try to find a new approch to active tectonic invetigation, which also enrich the tectonic meanings of water level observation data aiming at earthquake prediction.

在全球不断开展的大陆钻探结果揭示断层活动与流体作用密切相关的背景下，本项目拟探索利用长期连续的承压井水位观测所记录到的同震水位变化作为新途径来探测中国大陆活动构造的理论与方法。以中国大陆地震观测台网所记录的由1999年来发生在中国大陆内部以及周边的8级以上地震所引起的井水位同震阶跃变化观测资料为主要研究对象，在孔隙弹性理论框架下，配合钻孔应变观测结果、地震波形分析结果与中国大陆的活动构造特征，本项目拟研究：（1）根据井水位变化反演同震应变的方法；（2）大地震引起的动/静态应力/应变变化对大陆构造活动与井水位变化的影响；（3）水位变化的空间分布特征与大陆活动地块分布格局的关系；（4）井水位变化前后含水层介质孔隙弹性参数变化特征及其地质解释技术。本项研究不仅拓宽了地震观测台网资料的应用领域，而且使用作地震预报的井水位观测资料在地震及其它灾害危险性评估中体现了物理与地质的含义。

本项目利用大地震引起的承压井水位变化作为切入口，通过分析引起水位变化的各种因素，来尝试建立水位变化与承压井所在区域的地地质与构造条件、水文地质条件等因素的关系，再通过地质构造条件、水文地质条件与活动构造之间的关联，搭建起井水位变化与活动构造之间的联系。由于全球大地震震较为普遍，大地震发生后引起我国大陆地震地下水观测台网井孔承压水位变化也是以忠普遍现象，因此，利用这样的方法来分析构造活动性是一条非常便捷的途径，尤其是分析活动构造当前的活动状态，是十分有意义的。通过执行项目的研究内容，建立并完善利用承压井水位变化作为探测活动构造新途径的理论与方法。潮汐和气压因素是本方法中需要借助的两项重要（影响）因素。Skempton系数B和渗透率是建立水位变化与构造活动性的桥梁。水位变化与应变变化的对比是本方法的物理基础。