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81.
82.
Attenuation of Coda Waves at the Changbaishan Tianchi Volcanic Area in Northeast China 总被引:2,自引:0,他引:2
21 earthquakes recorded by a temporary seismic network in the Changbaishan Tianchi volcanic area in Northeast China operated
during the summer of 2002 and 2003 were analyzed to estimate the S coda attenuation. The attenuation quality factor Qc was estimated using the single scattering attenuation model of Sato (1977) in the frequency band from 4 to 24 Hz. All the
events studied in this paper occurred at depths from 2 to 6 km with ML of 1.4–2.8. The epicentral distances are less than
25 km. For all events which occurred near the Tianchi Lake (caldera), the Qc patterns obtained at the stations near the lake are similar, and the Qc values are relatively small. At the stations located about 15 km east of the Tianchi Lake, however, the average Qc is significantly higher. For an event which occurred 25km from the lake to the west, Qc patterns derived at the stations near the lake are quite similar to the above mentioned Qc for stations located in the east. Further study shows that Qc value in the north and central areas of the volcano is relatively lower than that in the surrounding area. Compared to other
volcanic areas in the world, the average Qc of the Changbaishan Tianchi volcanic area is obviously lower. The deep seismic sounding and teleseismic receiver function
studies indicated more than one lower velocity layer in the crust. The MT studies suggested the presence of high conductive
bodies beneath the area. We interpret the strong attenuation of coda waves near the Changbaishan Tianchi volcano as being
possibly related to high temperature medium caused by shallow magma chambers. 相似文献
83.
岫岩5.4级地震前后尾波振动持续时间比的演化特征 总被引:1,自引:0,他引:1
本文在前人工作的基础上,从地震波的动力学特性出发,利用尾波振动持续时间比τH/τv方法,对1999年11月29日岫岩Ms5.4地震前后地震活动的演化特征进行了详细研究。结果发现在岫岩Ms5.4地震前,距震中相对较近台站记录到的尾波振动持续时间比一rH/TV存在一定程度的异常显示,而距震中较远外围地区的台站记录到的一τH/τv震前无明显的异常反应。认为尾波振动持续时间比τH/τv从统计意义上提供了研究介质物理性质的较好方法,对短临地震预报具有一定的参考意义。 相似文献
84.
Juin-Fu Chai Tsung-Jen Teng Chin-Hsiung Loh 《Soil Dynamics and Earthquake Engineering》2004,24(7):527-536
The objective of this paper is to identify the first mode ground period Tg, at each interesting site along Taiwan High Speed Rail (THSR) route, and further, to determine the site-dependent design response spectrum for particular sites with Tg larger than 1 s. In this paper, a linear model of shear wave propagating in a multi-layered half-space is developed to identify the first mode ground period Tg of an interesting site on the basis of the field bore hole data. Furthermore, for each one of the strong ground motion observation stations within the Chiayi-Tainan area, the first mode ground period Tg was identified by either coda waves or pre-event ambient vibrations from the seismograms. In addition, the site-specific parameter Cv in defining the normalized response spectrum was also determined based on the observed strong ground motions at the specified observation station, and hence the empirical function between Tg and Cv can be regressed for this interesting area. Therefore, for a particular site along THSR route within the Chiayi-Tainan area, the site-specific parameter Cv can be determined from the regressed empirical function by the identified first mode ground period Tg, and further, used to develop the site-dependent design response spectrum. 相似文献
85.
基于Aki单次散射模型,利用江苏数字地震台网记录的地震数字波形资料开展了江苏地区尾波Q值特征研究。结果表明,江苏地区总体上属于高Q值地区,但不同地区存在明显差异,总体呈现出南高北低的特点。本文对台站相对密,地质构造特点明显、尾波Q0计算结果较为集中的四个区域分区进行了研究,获得了江苏四个区域的Q值与频率的特征关系。苏南至长江口和茅山断裂带附近为江苏的高Q值地区,苏中至沿岸为江苏的低Q值地区,苏北连云港及附近处于Q值中等水平地区。对照江苏四个Q值不同分区的构造及地震活动分析,Q值、地壳运动和地震活动性之间存在一定的相关关系。 相似文献
86.
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88.
Attenuation of coda waves in the Northeastern Region of India 总被引:1,自引:0,他引:1
Coda wave attenuation quality factor Qc is estimated in the northeastern region of India using 45 local earthquakes recorded
by regional seismic network. The quality factor Qc was estimated using the single backscattering model modified by Sato (J
Phys Earth 25:27–41, 1977), in the frequency range 1–18 Hz. The attenuation and frequency dependence for different paths and the correlation of the
results with geotectonics of the region are described in this paper. A total of 3,890 Qc measurements covering 187 varying
paths are made for different lapse time window of 20, 30, 40, 50, 60, 70, 80, and 90 s in coda wave. The magnitudes of the
analyzed events range from 1.2 to 3.9 and focal depths range between 7 and 38 km. The source–receiver distances of the selected
events range between 16 and 270 km. For 30-s duration, the mean values of the estimated Qc vary from 50 ± 12 (at 1 Hz) to
2,078 ± 211(at 18 Hz) for the Arunachal Himalaya, 49 ± 14 (at 1 Hz) to 2,466 ± 197 (at 18 Hz) for the Indo-Burman, and 45
± 13 (at 1 Hz) to 2,069 ± 198 (at 18 Hz) for Shillong group of earthquakes. It is observed that Qc increases with frequency
portraying an average attenuation relation for the region. Moreover, the pattern of Qc − 1 with frequency is analogous to the estimates obtained in other tectonic areas in the world, except with the observation that
the Qc − 1 is much higher at 1 Hz for the northeastern region. The Qc − 1 is about 10 − 1.8 at 1 Hz and decreases to about 10 − 3.6 at 18 Hz indicating clear frequency dependence. Pertaining to the spatial distribution of Qc values, Mikir Hills and western
part of Shillong Plateau are characterized by lower attenuation. 相似文献