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91.
利用2011年至2013年上海及邻近地区的常熟地震台、金泽地震台、佘山地震台记录的ML2.0以上地震波资料,基于Sato模型,采用不同的流逝时间,计算该区域的尾波Q值。结果表明:该区域为低Q值、高频率依赖性区域;不同流逝时间下同一个地震的Q值是不同的,流逝时间越长Q值越大;在2012年7月20日江苏宝应ML5.0级地震发生前,尾波Q值存在增大现象。 相似文献
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93.
Qin Jiazheng Liu Zuyin and Long Xiaofan Seismological Bureau of Yunnan Province Kunming China 《中国地震研究》1996,(2)
Using the theoretical model of coda scattering from local earthquakes, we have studied the features of time-space variations of the attenuation rate β of coda amplitude and coda Qc-1 values before and after the Qina earthquakes (MS5.4 and MS5.1) in Dec. 1992 in West Yunnan Earthquake Prediction Study Area (WYEPSA). The study results show that the attenuation rate of coda amplitude has remarkable regional inhomogeneity in the near-field (△ <50 km) around the main shock: β = 0.0076 s-1 and Qc-1 = 0.0056 during the main shock while (3 = 0.0209 s-1 and Qc-1 = 0.0153 during the aftershock. The Qc-1 value shows an approximate 3-foid variation before and after the main shock. We have also obtained the regional averages of β = 0.0235 s-1 and Qc-1 = 0.0153, which show that the coda attenuation in surrounding areas (△ > 50 km) far away from the epicenter of the main shock did not change much before and after the main shock. The evolution of Qc-1 values of the main seismic sequence with time has passed throug 相似文献
94.
Raúl R. Castro Giancarlo Monachesi Luca Trojani Marco Mucciarelli Massimo Frapiccini 《Journal of Seismology》2002,6(1):43-59
We studied spatial and temporal characteristics of seismic attenuation inCentral Italy using S- and coda- waves recorded by the MarchesanSeismograph Network from earthquakes located in the epicentral area ofthe 1997 Umbria-Marche sequence. The amplitude decay of the S waveswith distance was defined calculating empirical attenuation functions at 15frequencies between 1 and 25 Hz. We analyzed separately foreshocks andaftershocks and we found the same attenuation functions, suggesting thatthe possible temporal variations could be confined in a small area. Thefrequency dependence of Q
S was approximated by the equation Q
S=18 · f
2.0between 1 and 10 Hz. At higher frequencies (10–25 Hz), the frequencydependence of Q
s weakens, having an average value of Q
S=990. We also estimated Q from coda waves (Q
C) using the single-scattering models of Aki andChouet (1975) and Sato (1977). We found that Q
C=77 · f
0.6, (between 2 and 20Hz) at the western side of the mountain chain, using either foreshocks oraftershocks. This relation is consistent with previous estimates of Q
Creported for the Central Apennines. For a volume sampling the Colfioritobasin, the Apennines and the Marche region we found that Q
C=55 · f
0.8,indicating highattenuation below the mountain belt. To detect small temporal changes ofQ, we calculated spectral ratios of 5 temporal doublets located in theepicentral area and recorded at the closest station. We found temporalchanges of Q that vary from 27% to 56%, depending on the locationof the doublets. This variability suggests that the temporal change ofattenuation may depend on the spatial variation of Q and perhaps on thespatial distribution of tectonic stress in the epicentral area. 相似文献
95.
EXPERIMENTAL STUDY ON THE CHANGES OF ULTRASONIC CODA WAVE AND ACOUSTIC EMISSION DURING ROCK LOADING AND DEFORMATION
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YANG Hai-ming CHEN Shun-yun LIU Pei-xun GUO Yan-shuang ZHUO Yan-qun QI Wen-bo 《地震地质》1979,42(3):715-731
The coda wave propagation path has received extensive attention as it is more sensitive to small changes in the medium than the direct wave. During the process of loading, the wave velocity, medium or source changes may cause the coda wave to change. The physical mechanism of change in the ultrasonic coda wave varies during different deformation stages. Meanwhile, there exist local damages in the rock sample during the deformation, and it will be accompanied by acoustic emission. Combining the ultrasonic coda wave and acoustic emission is beneficial to characterize the coda wave characteristics and damage degree of the sample at different deformation stages. In this paper, three kinds of rocks, including granodiorite, marble and sandstone with the sizes of 50mm×50mm×150mm, are used to carry out observations of ultrasonic coda wave and acoustic emission during the whole process of loading so as to study characteristics of the coda wave at different deformation stages. The major results are given below: 1)There is a good correspondence between the coda wave variation and the acoustic emission evolution process. When the acoustic emission frequency increases, the coda wave changes accordingly. In particular, the coda wave changes in the early stages of increased acoustic emission frequency, which indicates that the early damage information of rock can be obtained by analysis of the coda wave. 2)The physical mechanism of the coda wave change is different in different deformation stages. At the initial stage of loading, there are obvious scatterer changes in the coda wave change; then, in the linear elastic deformation stage, the wave velocity change is dominating; in the late-stage of loading, the scatterer change increases and coexists with the wave velocity change, the scatterer change effect is related with the rock micro-fracture degree, the rock will locally be damaged before rupturing, and the role of the scatterer will be enhanced. 3)With the increase of loading, the amplitude of increase of the wave velocity generally decreases gradually, which is basically consistent with the understanding obtained through the direct wave. The interference of acoustic emission can be eliminated because of the Kaiser effect when analyzing the coda wave. The consistency of the wave velocity change and stress loading and unloading is further verified. 4)The micro-fracture generated during rock deformation will change the physical mechanism of the coda wave change, and the scatterer effect will be significantly enhanced. At the same time, the acoustic emission waveform will cause interference to the ultrasonic coda wave. This means that attention needs to be paid when analyzing rock damage using only coda wave data. In short, the ultrasonic coda wave and acoustic emission can reflect the damage inside the rock, and the change mechanism of the coda wave in different deformation stages is different. The joint observation of the two can play a mutual verification role, which is conducive to improving the reliability of the observation results. 相似文献
96.
The authors apply soil response estimation techniques employing accelerograms for fifteen earthquakes recorded at the Yokohama Strong Motion Network and its vertical array of nine sites, plus microtremor data recorded at all 150 sites. Assessment of the reliability of surface to reference site spectral ratios, and horizontal to vertical spectral ratios of S‐waves, coda, and microtremors, relied on cross‐validation with both surface to borehole spectral ratios, and theoretical soil response functions for vertically incident SH plane waves calculated from the vertical array recordings and logging data, respectively. The results indicate the following: (1) the reference site method provides more accurate soil response estimations; (2) the H/V of microtremors provides relatively better soil response estimations than its S‐wave and coda counterparts; and (3) the H/V of microtremors provides coincident soil response estimations at two‐thirds of the sites when considering no more than ±30% mismatch in the determination of the predominant periods. The matching of parameters obtained from the analysis of microtremors, combined with their relatively low economic cost and the possibility of recording without strict spatial or time restrictions turns microtremors into a particularly appealing approach. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
97.
收集了昆明台1990~2000年间大于4.0级的地震宽频记录资料,以及分布在云南境内的23个昆明数字化台网1999~2000年的资料,使用单台叠加谱比方法处理了280个Lg尾波信号. 在假定Lg尾波Q与频率f有Q =Q0fη关系的基础上,计算出各射线1Hz时的Q值及频率相关因子η. 在此基础上,运用反投影技术反演得到云南及周边地区0.5°×0.5°网格内的Q0和η的分布图像. 结果表明:云南及周边地区的Q0在150~300之间变化,滇东地区的Q0明显高于滇西地区;η的变化范围在0.3~0.8之间,绝大部分地区η的变化范围为0.5~0.6. 相似文献
98.
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