青岛地震台2020年5月-2021年5月体应变趋势异常分析

Analysis of the abnormal trend of volumetric strain at Qingdao Seismic Station from May 2020 to May 2021

2020年5月至2021年5月,青岛地震台体应变观测数据年漂移量明显小于往年同期变化,基于周边监测环境、同场地其他观测手段、气象因素、其他台站测项数据、青岛GPS观测站数据、潮汐因子和超限率等进行分析,结果发现:①台站附近小学建设地下车库进行基坑开挖,有可能对体应变观测造成影响;②体应变异常为地下应变的真实反映;③体应变年漂移量减小非气象因素所致,且非区域性变化;④经小波分析,表明钻孔体应变数据变化趋势正常。采用midas GTS软件,基于有限元模型,模拟计算基坑开挖对体应变的影响量,结果显示,体应变仪探头处体应变变化量约为-1.7×10^(-5),而实际漂移量差值约为-0.53×10^(-5),二者量级一致,仅数值稍有差别。综合判定认为,青岛地震台体应变年漂移量变小与台站附近地下车库的基坑开挖有关。

From May 2020 to May 2021,the annual drift of the volumetric strain data at the Qingdao Seismic Station was significantly smaller than the changes observed in previous years during the same period.Based on the surrounding monitoring environment,other observation methods at the same site,meteorological factors,other station monitoring data,Qingdao GPS observation data,tidal factors,and overrun rate analysis,the analysis showed that:①The excavation of an underground garage for a nearby elementary school may have an impact on the volumetric strain observation;②The volumetric strain anomaly is a true reflection of underground strain;③The decrease in the annual drift of the volumetric strain is not due to meteorological factors,and the change is not regional;④The wavelet analysis showed that the trend of the borehole volumetric strain data was normal.Using midas GTS software and finite element models,we simulated the impact of foundation pit excavation on the volumetric strain and found that the volumetric strain variation at the volumetric strain probe was around-1.7×10^(-5),which was consistent with the actual drift difference of around-0.53×10^(-5),only with a slightly different numerical value.Based on the comprehensive judgment,we believe that the decrease in the annual drift of the volumetric strain data at the Qingdao Seismic Station is related to the excavation of the foundation pit near the station.