阿拉善左旗5.8级地震前地脉动信号特征分析
Characteristics of Ground Pulse Signals before the 2015 Alxa Left Banner M5.8 Earthquake

本文针对2015年4月15日发生在南北地震带北端的阿拉善左旗5.8级地震，利用乌海台、东升庙台、石嘴山台的连续数字地震波形资料，采用快速傅里叶变换对三个台站的2015年4月1日00时—4月15日23时波形数据进行分析，并持续跟踪0~0.25 Hz包络幅值极大值的变化形态。结果显示：（1）在5.8级地震前，震中附近的乌海地震台、东升庙地震台、石嘴山地震台记录的地震波形均出现频谱向低频偏移的现象；（2）三个台站出现低频异常的包络幅值极大值跟踪形态不一致，其中只有乌海台在震前出现明显的持续不稳定异常，异常持续时间约120 h；（3）三个台站距离震中由近及远包络幅值极大值的跟踪形态差异明显。
Considering the Alxa Left Banner M5.8 earthquake that occurred on April 15, 2015, the continuous digital seismic waveform data recorded by Wuhai, Dongshengmiao, and Shizuishan seismic stations from 00:00 April 1 to 23:00 April 15, 2015 were analyzed using Fourier transform, and the variation of maximum envelop amplitude within 0~0.25 Hz was tracked. The results reveal the following. (1) Before the M5.8 earthquake, the seismic waveform recorded by Wuhai, Dongshengmiao, and Shizuishan stations near the epicenter all show that the frequency spectrum shifts to low frequency. (2) The tracking forms of maximum envelop amplitude with low frequency anomaly in the three stations are different. Before the earthquake, only the tracking form in Wuhai station shows obvious continuous unsteady anomaly, which continues for about 120 hours. (3) The tracking forms of maximum envelop amplitude in the three stations are quite different with their distance from epicenter.