汶川大地震宽带地震仪短临异常及成因初探

2008年5月12日8.1级汶川大地震发生后，我们对国家测震台网的40台宽频带地震仪在5月7日~5月13日的观测数据进行了分析.结果表明，汶川大地震前有明显的短临异常: 各台站在大地震发生前1~3天内不同程度检测到了低频异常颤动，颤动振幅逐渐增大，一直持续到大地震发生，信号周期范围为2~10 s.重力仪和倾斜仪也观测到了这类颤动信号.汶川大地震前的异常颤动信号几乎遍布中国大陆，但在西部较弱，东南部较强，尤其在华南地块靠近菲律宾板块的边界处颤动信号很强.因此我们的初步推测是：异常颤动产生的可能原因是地震爆发前华南地块可能开始了慢滑移，滑移时的摩擦产生低频颤动.

The short-term anomalies detected by broadband seismographs before the May 12 Wenchuan earthquake, Sichuan, China

We investigated broadband seismographic waveform data in 7~13 May 2008 from 40 seismic stations of the National Digital Seismograph Network of China(NDSN) after the 12 May 2008 Wenchuan earthquake,showing that obvious precursor was widely detected throughout China.The premonitory phenomena is that tremor amplitudes in the period band of 2~10 s have increased steadily within 1~3 days before the main shock rupture.Anomaly tremors can also be detected by gravimeters and tiltmeters.Tremor signals are widely detected in mainland China,but they are very strong in Southeastern China and weak in Western China.The possible slow slip of South China block before the great Wenchuan earthquake may be the cause of tremors,which is related to some frictional processes of the slow slip.