Abstract：Based on 24 years′ observation of 4-component borehole strainmeter in Tianshan Mountains，Xinjiang Uygur Autonomous Region，China，the low frequency strain waves prior to major earthquakes are analyzed. Among the 144 earthquakes with M≥4.0，it is found that the low frequency strain waves appeared obviously prior to 39 earthquake events. The major findings about the characteristics of the strain waves can be summarized as follows：(1) The range of the strain wave period is 3–16 days，centered at 3–7 days；(2) The amplitudes of the strain waves are between 10－7 and 10－5，with a majority at 10－6；(3) With the increase in the magnitude of the earthquake，a series of characteristics of the strain wave could present as follows：① more complicated waveforms；② increased percentage of strain wave record，from 17% for magnitude ranging from 4.0 to 4.7，to 100% for magnitude greater than 7.7；③ increased epicentral distance of strain wave record；④ longer duration of strain wave，from several days prior to small earthquakes to several years prior to great events；⑤ longer precursory interval prior to the pending earthquake. Comprehensive understanding of the characteristics of the low frequency strain wave prior to major earthquake provides the practical significance for disastrous earthquake forecasting.
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2011, Vol. 30 
