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本文的主题是,研究是否可由尾波测得特定场地的S波响应。我们使用了南加州4个TERRA地学透镜台(PAS,PFO,SVD和GSC)观测到的1992年兰德斯和大熊地震的余震的记录。由于TERRA地学透镜仪的大动态范围,所记录的S波具有宽频带响应,而尾波的持续时间也长。我们研究了震级从3.3至5.4的65次地震的共708个三分量波形。上述4个台中只有SVD台位于第四纪)中积层上,其余各台均位于白垩纪岩石上。我们首先用频谱比方法(Mayeda等,1991;Koyanagi等,1992)估算了中心频率为0.75,1.0,1.5,2.0,3.0,4.0和6.0Hz,发震时刻70s后的尾波的场地放大因子。我们发现,径向分量的场地放大因子与横向分量的相似。这种相似性是在预料中的,因为尾波包括由各个方向到台站的反向散射波,所得到的是一种各个方向平均了的场地响应。然后,我们用同样资料组中的直达S波部分进行反演(Andrews,1986),以估算S波的场地放大因子。我们发现,尾波场地响应与S波场地响应相当一致,两者之比不超过1.5。这一发现支持了Tsujiura(1978)的相同的发现,并且证明了尾波可用于测定特定场地对S波的放大作用。正如Aki(1992)和Zeng(1993)理论上所指出的那样,如果我们假定尾波是由S波所支配的,则这种S波的场地响应与尾波的场地响应的一致是可以理解的。
The topic of this paper is to investigate whether the S-wave response at a particular site can be measured by the wake wave. We used the records of aftershocks of the 1992 Landes and Big Bear earthquakes observed by four TERRA geodetic lens platforms in Southern California (PAS, PFO, SVD and GSC). Due to the large dynamic range of the TERRA geodetic lens, the recorded S-wave has a broadband response and the coda has a long duration. We studied a total of 708 three-component waveforms for 65 earthquakes of magnitude 3.3 to 5.4. Only the SVD stations in the above four Taichung stations are located in the Quaternary) and the remaining stations are all located on Cretaceous rocks. We first estimate the field amplification factor of the coda at a center frequency of 0.75, 1.0, 1.5, 2.0, 3.0, 4.0 and 6.0 Hz and 70 seconds after the occurrence of the seismogenic event by using the spectral ratio method (Mayeda et al., 1991; Koyanagi et al., 1992) We find that the field amplification factor of the radial component is similar to the horizontal component. This similarity is expected because the coda wave contains the backscattered waves from all directions to the station, resulting in an averaged site response in all directions. Then, we invert the direct S-wave part of the same data set (Andrews, 1986) to estimate the field amplification factor of the S wave. We find that the response of the tailwave site is quite consistent with that of the S-wave site, with the ratio between the two not exceeding 1.5. This finding supports the same findings of Tsujiura (1978) and demonstrates that coda waves can be used to determine the amplification of S waves at specific sites. As pointed out by Aki (1992) and Zeng (1993), if we assume that the coda is dominated by the S wave, it is understandable that the correspondence of the S-wave’s field response to the coda’s field response .