青海玛多M_(S)7.4地震安西站VP宽频带倾斜仪数据特征分析

Data Characteristics Analysis of VP Broadband Tiltmeter of the Anxi Station to the M_(S)7.4 Earthquake in Maduo,Qinghai

青海玛多M_(S)7.4地震前甘肃省安西县地震监测站VP宽频带倾斜仪出现明显异常变化且记录到该地震的同震波形。结合CTS-1地震计进行融合分析可知,2套仪器同震波形的震相到时基本同步,表明2套仪器具有可靠性和一致性,但震相记录特征存在差异。2021-04-17 VP宽频带倾斜仪数据打破原有倾斜趋势,年变向西北方向倾斜,05-13恢复为向西南方向倾斜,震前记录到倾角急剧增大的方位与震中至台站的方位一致,倾斜旋转变化方向与区域构造应力方向一致。在同时段时均值数据时频谱中,异常时段存在(1.085~4.340)×10^(-6)Hz(周期为64~128 h)的低频信号。此次地震中2套仪器的优势频率和时频变化特征存在显著差异,这种差异可能与2套仪器不同的机械结构、频段宽度、采样频率有关。

Before the Qinghai Maduo M_(S)7.4 earthquake,the VP broadband tiltmeter of Anxi seismic station in Gansu province showed obvious abnormal changes and recorded co-seismic waveforms.Combined with the CTS-1 seismometer for fusion analysis,the phase of co-seismic waveforms changed in the same time,showing that the records of two sets of instruments are reliable and consistent,but the characteristics of seismic phase differ.The annual change is broken and tilts to the northwest on April 17,2021,when analyzing the data of the VP broadband tiltmeter,and the original northwest tilt is restored to the southwest tilt on May 13.The azimuth of sharp increase of dip angle recorded before the earthquake is consistent with that from the epicenter to the station,and the change of tilt rotation is consistent with the direction of regional tectonic stress.The time-frequency spectrum of hour data show low-frequency signals from 1.085×10^(-6) to 4.340×10^(-6) Hz(period 64~128 h).There are significant differences in the dominant frequency and time-frequency variation characteristics of the two sets of instruments in the earthquake,which may be related to the different mechanical structures,frequency band widths,and sampling frequencies of the two sets of instruments.