【摘要】 高频S波随着传播距离的增大其均方根(RMS)包络逐渐变宽,我们把这种现象称为S波包络展宽现象.S波传播路径上随机分布的非均匀体对S波的多次前向散射和绕射作用是导致S波包络展宽现象的主要原因,因此可用S波包络展宽现象来研究介质非均匀性.本文采用S波包络峰值延时来对S波包络展宽现象进行量化.S波包络峰值延时定义为S波初至与其均方根包络峰值最大值之间的时间差.本文选用长白山天池火山区的小震记录,运用S波包络峰值延时对长白山天池火山口地区的介质非均匀性进行了评价.结果发现长白山天池火山区呈现强烈的介质非均匀性,在0-2 km深度范围内介质非均匀性表现出南部强北部弱的空间分布特征;在2-5 km深度范围内介质非均匀性的空间分布特征与频率具有相关性;天池火山区介质非均匀性具有明显的多尺度特性;强弱非均匀性接触带,往往是地震频发地带.根据地震与非均匀体在空间分布的相对位置,我们认为火山区介质非均匀性可能反映了火山早期喷发堆积物介质结构的差异.更多还原

【Abstract】 High-frequency S-wave seismogram envelopes of microearthquakes are broadened with increasing travel distance, which is called S-wave envelope broadening. Multiple forward scattering and diffraction induced by random inhomogeneities along seismic ray path are the main reasons to cause the S-wave envelope broadening, so the phenomena of S-wave envelope broadening can be used to study the medium inhomogeneity. The peak delay time of S-wave, which is defined as the time lag from the direct S-wave onset to the maximum amplitude arrival of its envelope, was accepted to quantify the phenomena of S-wave envelope broadening. The medium inhomogeneity of crust in Changbaishan Tianchi volcano area, based on analyzing small local earthquakes waveform, was studied by the peak delay time of S-wave envelope broadening method. The results show that the medium of Changbaishan Tianchi volcano area presents strong inhomogeneity, the spatial distribution characters of inhomogeneous medium in the south are stronger than that in the north region of Changbaishan Tianchi volcano area at the depth of 0-2 km, and the spatial distribution characters of inhomogeneous medium at the depth of 2 - 5 km depend on frequency. The medium inhomogeneity in Changbaishan Tianchi volcano area presents multi-scale character. Earthquakes usually occur around the contact band of the strong and the weak inhomogeneity. We believe that the medium inhomogeneity of crust in Changbaishan Tianchi volcano area may reveal the difference of early erupted material properties according to the relative spatial position of earthquakes and inhomogeneities.更多还原