用小波-超限率分析提取宁陕台汶川地震体应变异常

姑咱台观测的汶川地震应变异常变得越来越显著.同时,在龙门山断裂带的另一端,原来不好判别的宁陕台钻孔体应变观测异常也逐渐清晰起来.利用小波分解和改进的超限率分析方法,可以将细微的地震异常变化精细地提取出来.一般地,小波分解得到的某个带通信号,可以分为正常背景和异常"坏点"两部分.通过对这两部分界线划分的研究,找到了客观、惟一确定超限率分析的阈值的方法.分析结果表明:沿整个汶川地震发震构造带,应变异常影响范围比我们以前知道的大很多;特别是,这种异常变化明显受固体潮影响,这对进一步揭示其机制提供了新的重要线索.

Extracting anomaly of the Wenchuan Earthquake from the dilatometer recording at NSH by means of Wavelet-Overrun Rate Analysis

The observed strain anomaly at station GZ has become quite evident.At the other end of Longmenshan Fault,an initially unseen anomaly at station NSH is more and more obvious in the dilatometer recording as the time lapses.By means of wavelet decomposition and the help of a modified Overrun Rate Analysis(ORA),the tiny anomaly can be extracted from the raw data.Generally,a band-passed signal obtained with wavelet decomposition can be divided into two parts: normal "background" and abnormal "bad points".An approach to locate the objective as well as exact distinction between the two parts has been developed for the determinate threshold of ORA.According to the analysis,the extent of strain anomaly along the seismic fault of the Wenchuan Earthquake is much larger than previously recognised.The anomaly is characterized by small pulses in consistence with peaks of Earth Tide,providing a clue to search for its mechanism.