共查询到19条相似文献，搜索用时 125 毫秒
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云南地区中短期前兆场异常与强震关系研究 总被引：2，自引：0，他引：2
通过对云南地区观测连续、稳定的近200个台项前兆资料全时空的中短期异常信息分析研究,发现有规律的前兆变化只是一种理想的模式 .在强区域应力场的作用下,会导致观测环境发生变化,使观测值的规律性发生变化(这类变化通常发生在强震前后),从而异常的判别标准需有变化,才能提高预报效能.由于常常存在多个应力集中点,用前兆预测地点很难达到现行预报要求的精度,但用场上的群体特征判别云南地区的活动水平,有较好的预测预报效能.云南强震前前兆的群体异常特征很显著 ,当有40%以上的前兆观测项目出现异常,可能有7级地震发生.笔者认为目前观测到的大部分异常是区域应力场增强的结果,是场上的信息,而不完全是震源的应力集中引起的.在区域应力场的作用下,一定范围内可以有多个应力集中点,这些点中因结构和介质的不同, 有的积累了应变,逐渐发展成震源,有的以应力应变的形式表现出来,被前兆仪器观测到就成了人们认为的异常,地震和异常都是区域应力场增强的结果,二者是伴生关系,而不是因果关系. 相似文献
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本文用平面应变有限元方法,模拟了西南地区1970年—1976年5次大于7级地震的蕴育过程中,介质性质变化对区域应力场的影响,给出了各次地震蕴育影响场的分布图象和影响场的基本特征。由计算结果与大震前的地震活动、前兆观测资料对比得到,地震前的异常与影响场的应力变化有关。 相似文献
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北部湾6.1,6.2级地震的前兆异常 总被引：1，自引：0，他引：1
通过对北部湾６．１，６．１级地震前的震兆分析，认为地震是在区域地震活动出现中期异常背景的情况下发生的，前兆观测的趋势异常较为突出，但短临异常极少，地震活动性和前兆观测手段的趋势异常变化具有稳定性和准同步性，反映了震前区域应力场的变化。 相似文献
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本文通过对京津地区十个重点井孔水氡资料的处理分析,发现唐山地震前,京津地区水氡异常场有几个显著的特征。京津唐一带区域性水氡的升高变化,是该区构造应力场加强的结果,当观测区域受力达到线应变为10-6—10-5数量级的状态时,可以观测到水氡明显的异常变化。水氡中短期异常的扩散现象及临震突跳的收缩现象,是与震源应力场直接有关联的前兆变化。水氡异常的机理是复杂的,是多种作用的综合 相似文献
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Before 2013 Lushan MS7.0 earthquake, the bedrock ground temperature in Kangding station, the cross-fault deformation and the borehole strain in Guza station all show that regional stress changes possibly occurred along the Xianshuihe Fault. In this paper, further analysis is made on the observation data of bedrock ground temperature in the three stations in the Xianshuihe fault zone, and the results are compared with borehole strain, seismometry and cross-fault deformation data. Stress temperature in the three stations dropped suddenly synchronously a few days before the Lushan earthquake, indicating the enhanced tension characteristics of the regional stress in the Qianning-Kangding zone. High-frequency components of bedrock temperature in the three stations also showed synchronous changes in the 80 days before the Lushan earthquake, with an estimated stress change range of 0.98~1.96MPa, an average of about 1.47MPa, which is close to the seismometry results. Besides, tensional mutation in borehole strain is consistent with the enhanced tensional characteristics of regional stress revealed by bedrock ground temperature. Comparison with cross-fault deformation shows that the stress change was different in different active segments of the Xianshuihe Fault in different time periods before the Lushan earthquake, but the regional stress change did appear along the Xianshuihe fault zone before the Lushan earthquake. 相似文献
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The borehole strain meter at Wushi station recorded obvious anomaly before Jiashi M s=6.8 earthquake occurred on February 24, 2003. Its features are as follows. (1) Anomaly types are complete. The trend anomaly, short-term anomaly, short-imminent anomaly and exponential anomaly appeared 19 months, 56 days, 4 days, and more than 1 month before the event, respectively; (2) Anomaly is large in magnitude. The maximal magnitude of strain anomaly is 1.7×10?5, which is rare in the past 20-year observation records at Wushi station; (3) Strain rate fluctuates sharply with obvious alternation of tension and compression. According to the magnitude of strain anomaly, time of exponential anomaly appearance and regional features of recorded anomaly, we could predict the magnitude, occurrence time and potential region to a certain degree. 相似文献
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The borehole strain meter at Wushi station recorded obvious anomaly before Jiashi M
s=6.8 earthquake occurred on February 24, 2003. Its features are as follows. (1) Anomaly types are complete. The trend anomaly,
short-term anomaly, short-imminent anomaly and exponential anomaly appeared 19 months, 56 days, 4 days, and more than 1 month
before the event, respectively; (2) Anomaly is large in magnitude. The maximal magnitude of strain anomaly is 1.7×10−5, which is rare in the past 20-year observation records at Wushi station; (3) Strain rate fluctuates sharply with obvious
alternation of tension and compression. According to the magnitude of strain anomaly, time of exponential anomaly appearance
and regional features of recorded anomaly, we could predict the magnitude, occurrence time and potential region to a certain
degree. 相似文献
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China is one of the earliest countries to start borehole strain observation aiming to predicting earthquake.YRY-4 and other borehole strain instruments developed by China have reached the world advanced level,with a resolution of 10-10 and can work stably.In order to capture the tectonic stress signals and analyze the relationship with seismicity,it is firstly necessary to identify and exclude the non-structure stress signals (caused e.g.by rainfall,pressure change,groundwater level fluctuation,river fluctuation etc).Annual strain change signals have been observed by YRY-4 borehole strain instrument at some stations (e.g.Guzan station in Dadu River valley).The signal is on the wave crest in spring and trough in autumn.Up to now,no relative papers have interpreted the physical mechanism causing such strain signals.In this paper,we manage to explain the physical mechanism by using numerical simulation.Considering the terrain factor of Dadu River valley,we set up a 3D finite-lement thermoelastic coupling model to compute the heat stress caused by annual change of surface temperature.The computing results are in good accordance with observation values,which illustrates that the annual change of strain signals is caused by annual change of surface temperature.We suggest that high-resolution borehole strain instrument (e.g.YRY-4 strain instrument) should avoid installing in a terribly undulate area,but choose a flat one.Although the strain signal with an annual change is a noise signal,to a certain extent,the signal illustrates that the current borehole strain instrument has a high resolution.This gives us more confidence to use this instrument to measure the structural strain. 相似文献
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INFLUENCE OF PUMPING ON FOUR-COMPONENT BOREHOLE STRAIN AT TAI'AN SEISMIC STATION AND ITS INTERFERENCE MECHANISM 
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下载免费PDF全文 JIA Yuan GAN Wei-jun LI Jie ZHU Cheng-lin YIN Hai-tao LU Shuang-ling JU Jia-bin 《地震地质》2019,41(6):1429-1443
Four-component borehole strainmeter (FCBS) is one kind of high-precision borehole strain observation instruments invented in China. As a kind of near-surface deformation observation instrument, FCBS is also easily disturbed by the external environment factors. As a common factor, pumping has significant influence on FCBS observation. Existing studies mostly identify the pumping interference from the perspective of observation curve morphology, relatively few studies focus on its interference mechanism. In order to truly capture earthquake precursor information, it is necessary to study the interference mechanism. In recent years, RZB-3 type FCBS at Tai'an seismic station has been seriously affected by pumping, so it is necessary and also feasible to study the interference mechanism of pumping. Since the influence of pumping interference on borehole strainmeter is common, this work would be very practical and be used for reference by other borehole strain observation stations.
We find that the original observation curves and observed surface strain, shear strain from RZB-3 type FCBS at Tai'an seismic station have the characteristics of synchronous change with the borehole water level, in which the linear correlation coefficient between the two observed shear strain curves and borehole water level reached 0.70 and 0.82 respectively. We further find that the principal strain direction of borehole and borehole water level after normalization meet the nonlinear function as y=1.217arctan(x)0.224-0.284. The above phenomenon indicates that the observation of RZB-3 type FCBS at Tai'an seismic station is significantly affected by the borehole water level, and the influence is more obvious and the gradient is larger at the stage of low water level. Pumping interference often appears in low water level stage and changes the rock pore pressure state. Statistics show that pumping interference affects the borehole strain state.
To investigate the interference mechanism of pumping to RZB-3 type FCBS at Tai'an seismic station, we take a known pumping as an example, in which we study the principal strain state of the borehole in three periods of normal pumping, interruption of pumping and resuming pumping respectively. During each period, we solve 3 parameters of the principal plane strain state, i.e. the maximum principal strain rate, the minimum principal strain rate and the maximum principal strain direction from four observation equations of FCBS by nonlinear iterative least squares algorithm. On the other hand, concentrated load model (CLM) is used to simulate the mechanical mechanism of pumping. Firstly, the depth of FCBS relative to pumping source and the concentrated load at pumping source are inversed, then, the strain state surrounding the pumping well, including the state at RZB-3 borehole, is simulated by forward modeling. By comparing these results, we find that:
(1)The concentrated load at pumping source inversed by CLM during periods of normal pumping and resuming pumping are both located at or near the bottom of the pumping well, which is consistent with the actual situation, indicating that mechanism and degree of the influence of pumping on borehole strain are well simulated by CLM.
(2)The observed strain state is consistent with the simulation result of pumping interference by forward modeling, indicating that the principal strain state of borehole calculated based on observation of FCBS reflects the true strain state of borehole under different pumping states.(3)The inversed concentrated load at pumping source during pumping periods is significant greater than the load of the pumped water, indicating that the pumping process has more significant influence on the pore pressure of rocks than the load of the pumped water.
Even though CLM is an approximate simulation since it's based on some elastic assumptions, the interference mechanism of pumping on RZB-3 type FCBS at Tai'an seismic station is well explained, which is maybe very helpful for studying the influence of pumping interference on other deformation instruments, locating the unknown pumping source and studying the characteristics of pore pressure of rocks. 相似文献
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