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汶川地震前一年多开始,位于龙门山断裂带西南端的姑咱台钻孔应变仪,记录到异常应变变化.这种异常变化以短周期(数分钟至数小时)的“毛刺”形态为特征.在全国100多个钻孔应变台中,姑咱台距震中最近,也只有该台记录到这种异常变化.该台钻孔应变观测的良好的自检结果,说明了观测应变变化的可靠性.这种持续出现的异常变化与季节变化明显不同步,不是环境干扰因素造成的.异常变化与长期趋势变化以及同震阶跃变化的一致性,进一步说明这种异常应该是构造运动的表现.超限率分析结果显示:这种异常变化在汶川地震主震前逐渐增大,震时特别剧烈,震后逐渐衰减,显示了与该地震相当密切的相关性.这种变化的机制可能是当地附近的小尺度岩石破裂.2008年2月27日康定Ms4.5地震造成最大的典型“毛刺”.小波分解结果表明:主震前,比较长周期的异常成分出现得比较晚,这是破裂尺度在增大的表现.姑咱台的观测应变变化与唐山地震前观测到的应力变化有相似之处。
More than a year before the Wenchuan earthquake, the Guansai drilling borehole strain gauge located at the southwestern end of the Longmenshan fault zone recorded anomalous strain changes that occurred in a “glitch” pattern of short duration (minutes to hours) .There are more than 100 borehole strain tables in the country, only the Taiwan station has recorded the abnormal change recently since the epicenter.The good self-test results of the borehole strain observation show that the observed strain changes This persistent anomalous change is clearly out-of-sync with the seasonal change, not due to environmental disturbances, and the anomalous change is consistent with the long-term trend change and the co-seismic step change, which further indicates that this anomaly should be tectonic movement The results of the overrun rate analysis show that this anomaly change gradually increases before the Wenchuan earthquake and the earthquake time is extremely intense, and gradually decays after the earthquake, indicating a fairly close correlation with the earthquake. Is the local small-scale rock near the rupture.The February 27, 2008 Kangding Ms4.5 earthquake caused the largest typical “glitch.” The wavelet decomposition results show that: before the main shock, the relatively long period of anomalous components appear to be more than Late, which is broken scale in increased performance. Regardless of the strain changes observed before we table the Tangshan earthquake observed stress similarities.