蓟县台水管倾斜仪NS向加速北倾异常分析

蓟县水管倾斜仪NS向观测自2014-04-01开始出现加速北倾异常变化。通过观测系统检查、周边环境调查，开展了异常分析工作。结果表明：1）2014-03-31更换水管N端传感器对水管倾斜仪观测造成一定程度的影响。类似的变化在2009-04更换W端传感器后也出现过。2）04-01～11台站南侧于桥水库以高达50 m3/s的速率泄水也是导致异常的原因。对比发现，往年水库大速率泄水期间水管NS向相应地出现过短期加速北倾变化。3）利用三维集中载荷模型开展水库载荷变化影响理论分析，结果表明，04-01～11的平均泄水速率大幅超过库容变化临界速率理论计算值，并且期间倾斜水平方向变化理论值与同台的水管倾斜、垂直摆倾斜NS向观测实际变化量基本一致。从量化角度证实，水管倾斜NS向观测加速北倾变化确实含有水库大速率泄水的影响。4）04-11后库容增加，水管倾斜NS向观测仍呈加速北倾变化，5月中旬后逐步恢复，异常持续时间和幅度均超出了实际泄水时间和理论计算结果。因此，水管倾斜NS向2014-04-01以来出现的加速北倾变化，不仅含有更换N端传感器的影响，也受到了于桥水库大速率泄水的干扰，作为地震前兆异常的可能性不大。

Analysis of Acceleration Incline to North Direction of Water Tube Tilt-meter at Jixian Seismostation

In this paper, the environment around Jixian seismostation and instrument work state is investigated with respect to the water tube tilt-meter’s accelerated incline to north direction from 1st April. Results are as follows: (1) The sensor at the north end was replaced at 31st March in 2014. Similarly, the accelerated incline to western direction began after replacing the sensor at western end in April 2009, which confirms that replacement of the sensor will influence water tube measurement to some extent. (2) Yuqiao reservoir to the south of Jixian seismostation discharged from April 1st to 11th with a velocity as high as 50 m3/s, the maximum rate over the past years. Short term accelerated incline to the north began when reservoir discharged fast. (3) The average discharge rate drastically exceeds the reservoir threshold calculated using a 3D concentrated load model and the calculated incline data in a horizontal direction is consistent with the real change of water tube data and vertical pendulum tilt-meter at Xiaoxinzhuang cave, which confirms the influence of reservoir using quantitative method. (4) Water tube continued accelerated inclining to north until mid-May, though Yuqiao reservoir was storing after April 11th. Duration and range of anomaly exceed the real change time and calculated result. Therefore, the accelerated incline to the north direction from April 1st in 2014 reflects influence of sensor replacement and discharge of Yuqiao reservoir.