【摘要】 巨幅地倾斜异常既可能是地震前兆异常信息,也有可能是仪器问题或环境干扰所致的异常信号.有效地厘清其性质,对地震前兆异常的及时识别与科学判定至关重要.陕西韩城台金属水平摆EW分量自2010年以来连续两次出现巨幅东倾和西倾异常,幅度分别约达140″和180″,该巨幅地倾斜异常产生的根源至今尚未被厘清.鉴于此,本研究依据韩城台所在区域的水文、构造和地震活动等特征,提出并分析了地下水动力变化、韩城断裂慢滑移和地壳应力场变动等3种可能的成因机制.结果表明,第一种成因机制难以有效地解释巨幅地倾斜异常,第二和第三种成因机制则具有一定的可能性,但证据还不够充分.因此,更可靠的物理解释尚需更多的观测和更深入的研究.尽管本文未能给出该巨幅异常的真正成因,但所采取的分析方法可为今后巨幅地倾斜异常性质的判定工作提供有益的参考.更多还原

【Abstract】 The remarkable tilt anomalies could be the earthquake precursors,but may also be caused by instrumental factors and environmental disturbances. Thus,the question arises on how to distinguish the earthquake precursors from the non-tectonic factors,which is very important to effectively and reasonably detect earthquake precursors. Since 2010,two remarkable tilt anomalies have been recorded by metallic horizontal pendulums in E-W component at the Hancheng observatory in Shannxi Province,and the amount of east-and west-ward tilt approximately reach up to 140″ and 180″,respectively,but these two remarkable tilt anomalies have not been reasonably and clearly interpreted till now. Here,we propose and compare three different causal mechanisms possibly responsible for these anomalous phenomena according to the regional hydrological,tectonic and seismicity characteristics,i.e.(1) hydrodynamicsinduced surface tilt,(2) a long-term slow slip event on the northeastern segment of the Hancheng fault,and(3) variations of the regional tectonic stress field during the anomalous period. We then theoretically calculated the poroelastic deformation and the fault slip amount,and finally inversed the focal mechanism solutions of 85 earthquakes(2.0≤ML≤4.8) that occurred between2008 and 2015 with the aim of determining the regional stress field changes(35°N—36°N,110°E—111°E) in the crust. Our results show that the first possibility can be shown unlikely,but it is difficult to rule out the second and the third possibility according to the current evidence. To further prove and confirm the causal relationship between deformation of tectonic origin and the anomalies,more comprehensive tilt and crustal deformation measurements are necessary in the Hancheng region in the future,furthermore,more intensive researches are also needed to reveal and determine the causal mechanisms of these anomalies. Unfortunately,we fail to find the real causal mechanism,but the approaches used in this study could be helpful to investigate the causal origin of remarkable anomalies recorded by tiltmeters in the near future.更多还原