【作者】 郭斌；

【导师】 蒋骏；

【作者基本信息】 华中科技大学 ， 理论物理， 2016， 硕士

【摘要】 在对中国大陆宽频带数字地震信号连续波形数据的分析中,发现其中普遍存在有一种非常低频的微弱地震信号,通常湮没在地震观测的背景信号中。该信号的周期范围在30-120s之间,持续时间数小时至十几小时;信号的时空变化具有一定程度的规律;信号在水平方向的表现较强,而垂直方向较弱。这与国际上所提到的俯冲带地区的VLFEs(Very Low-Frequency Earthquakes)有着明显区别,频率更低,频带更宽,我们称其为甚低频地震信号(VLFS,very low-frequency seismic signal)。本文针对川滇构造地区的甚低频地震信号,进行了多方面的详细分析研究。首先对其主要特征进行综合性的描述,运用多种时频分析处理方法,包括傅里叶变换等对长时间段内秒采样地震资料进行分析研究,通过数字带通滤波、小波变换等技术手段对初始数据进行滤波处理,其频谱主要成分在小波分层处理的细节部分d5和d6中,相当于周期范围在30-120s的部分,在对信号的分析中通过与当地普通地震信号比对,跟远震、海洋、重力波以及大规模气象活动如风暴和气旋等产生的地震信号不一致。针对其特征表现,我们提取其主要周期部分。通过比对川滇地区多个台站在长时段下甚低频地震信号的表现,我们发现在长时段内它们表现出一定的重复性,通常情况下出现频次高,每次持续的时间长达数个小时;并且在多个台站的出现时段上具有一致性,前后时间相差不大。在此基础上我们尝试对甚低频地震信号的产生源位置进行探索,以获得对甚低频地震信号更深入的认识。考虑到甚低频地震信号是一种持续时间较长的低频率弱信号,并且信号到时确定相对困难,在观测范围比较大、台网密度稀疏的条件下,基于震源扫描算法,我们采用多种数据处理手段,有效提取了特征“震相”,对川滇地区的连续波形数据进行实际定位和研究。我们采用不同的扫描波速,对川滇地区多个台站周期在60-120s的甚低频地震信号源进行扫描定位。定位结果表明,这些甚低频地震信号源自台站附近地区的可能性较大。更多还原

【Abstract】 In the analysis of continuous waveform data of China mainland broadband digital seismic signal, a very weak low-frequency seismic signal can be universally observed, usually lost in the background signal. Period of the signal is between 30-120 s, and its duration is from several hours to ten hours; temporal change of the signal has a certain degree of regularity; the signal has strong horizontal component performance, but weak in vertical component. With lower frequency and wider band, it is obvious different from very low-frequency earthquakes mentioned internationally in subduction zone; we call it very low-frequency seismic signal(VLFS).This paper focuses on VLFS in Sichuan-Yunnan area and carries out a detailed analysis. Firstly, main features of VLFS are described. By a variety of time-frequency processing methods including FFT, 1 Hz sampling seismic data in long period has been analyzed. Through analysis with digital band-pass filtering and wavelet transform techniques, the result shows that its main spectral component is in the detail sections d5 and d6 of wavelet processing, which is equivalent passband in period of 30-120 s. In comparison to seismic signals generated by local regular earthquakes, teleseismic, oceans, gravity waves, large scale weather events such as storms and cyclones, it is different in lots of aspects. Considering the features of VLFS, the part containing main cycle is extracted. By comparing VLFS in several seismic stations, we found that they exhibit certain repetitive over a long period. Its frequency of occurrance is relatively high, with duration of several hours each time. And the consistency shows in several stations, with a little time difference. On this basis, we try to search the generating source of VLFS for a deep understanding. Taking into consideration that VLFS is weak low-frequency signal, and has long lasting time, and the arrival time is also relatively difficult to determine, in large observation area and sparse station network density conditions, based on the source scanning algorithm, we adopted multiple data processing methods, and effectively extracted feature ?seismic phases? of continuous waveform data recorded in Sichuan-Yunnan area for positioning research.We choose different wave propagation speed to scan Sichuan-Yunnan area with signals of period between 60-120 s in several stations. The result of locating indicates that the source of these VLFS is more likely from area near the stations.更多还原