且末地震台记录特定地区地震的震相特征

A preliminary analysis of the characteristics of special seismic phases of earthquakes in a specific region recorded by Qiemo Seismic Station

对于特定区域(79.70°—88.75°E,34.05°—36.25°N)内发生的近震,新疆且末国家数字地震台的数字波形记录显示的震相特征与其他区域不同。以该区发生的31个近震(震中距200—600 km)波形为研究对象,对比分析原始波形与短周期仿真波形的震相特征,并运用MATLAB软件,对波形记录进行短时傅里叶变换(STFT),分析时频变化特征。结果表明:特定区域的近震波形具有明显的远震面波特征;与P波相比,S波列的周期、振幅明显较大;S波发育不完整,能量衰减快;S波列及S波尾波以低频信号为主,频率分布范围在0.15—0.5 Hz。研究发现,该研究区近震波形出现的震相特征,与该区地质构造背景有关:地处青藏高原北缘,构造破碎;存在地表低速带,对高频信号具有吸收、过滤作用。

For near earthquakes that occurred in a specific region(79.70°-88.75°E,34.05°-36.25°N),the waveform records of Qiemo national digital seismic station in Xinjiang show different seismic phase characteristics from other regions.The waveform of 31 near earthquakes that occurred in this area(epicenter distance 200-600 km)is studied in this paper.A comparative analysis is carried out for the phase characteristics of the original waveform and simulated short-period waveform.By using the MATLAB software,the Short Time Fourier Transform(STFT)is used to analyze the time-frequency characteristics of waveform records.The results show that the waveforms of near earthquakes in the specific area show obvious characteristics of teleseismic surface wave;compared with P wave,the period and amplitude of S wave train are obviously larger.The development of S wave is incomplete and energy attenuation is fast;S wave train and S wave coda are mainly low-frequency signals,and the frequency distribution ranges 0.15-0.5 Hz.The study finds that the special seismic phases that appeared in the near seismic waveform in the study area are related to the geological structure background of the area.It is located in the northern margin of the Qinghai-Tibetan Plateau with broker geological structures;there is a low-velocity zone near the surface,which absorbs high-frequency signals.