天山地壳低频应变波特征研究

 依据新疆天山地区24 a的分量式钻孔应变观测资料,分析144个M≥4.0级地震的应变波记录数据。研究发现,在39个地震前出现明显应变波,其特征如下：(1) 周期为3～16 d,以3～7 d为主;(2) 应变波振幅为10－7～10－5,以10－6居多;(3) 随震级由小到大应变波有下列特征：① 应变波图像从简单到复杂;② 仪器记录应变波的比例逐步增强,从17%逐渐提高到100%;③ 仪器记录应变波的距离由近而远,并呈指数分布特点;④ 应变波持续时间逐步延长,从小震的几天到巨震的几年;⑤ 应变波出现、结束、最大幅度出现到地震发生时间间隔由短到长。应变波最重要的特征是出现在震前,与地震时才出现的地震波截然不同,这对灾害性地震预测有实际意义。

STUDY OF CHARACTERISTICS OF LOW FREQUENCY CRUSTAL STRAIN WAVES RECORDED IN TIANSHAN MOUNTAINS

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.