用超限率分析法研究汶川地震的前兆应变变化

STUDY ON PRECURSORY STRAIN CHANGES OF WENCHUAN EARTHQUAKE WITH ORA METHOD

汶川地震前,姑咱台钻孔应变仪观测到频繁的周期从数分钟到数小时的脉冲变化,经过高通滤波,可看出姑咱台钻孔应变仪观测到的脉冲异常变化与汶川地震有明显的相关性。为了验证这种脉冲的异常变化与汶川地震的相关性,提出3条判断地震前兆的相关性特点,并用超限率分析法,对这种前兆异常进行了系统的、定量的分析。这种前兆现象与"地震前驱波"相去甚远,其统计特征与岩石破裂前的声发射现象类同。

Frequent pulses, whose period from minutes to hours, were recorded with the YRY-4 strainmeter at Guza station before the Wenchuan earthquake in 2008. Via high-pass filtering, strong correlation between the recorded pulses and the main shock is revealed. In order to prove, an Overrun Rate Analysis （ORA） is carried out for a systematic and quantitative examination of the abnormal changes, based on three criteria with respect to the periods for before, during and after the main shock, respectively. The phenomenon does not seem to be close to the so called precursory long-period wave preceding a macroquake but is similar to the acoustic emission prior to the fracture of rocks.