利用数字地震波资料研究新疆天山中东段地区的介质衰减特征
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摘要
利用新疆数字地震台网记录的155条地震波形资料,根据S波记录得到观测振幅谱,采用遗传算法联合反演的方法研究了新疆天山中东段地区(乌鲁木齐—乌苏—库尔勒地区)的几何衰减模型、介质非弹性衰减模型。结果表明:在500 km震源距范围内,研究区地震波的几何衰减满足三段衰减模型;研究区非弹性衰减Q值随频率f的关系为:Q(f)=344f~(0.55)。本研究为今后在该研究区利用数字地震观测资料开展震源谱的恢复和强地面运动的模拟等地震学、工程地震学研究奠定了基础。
Based on 155 horizontal-component digital seismograms of 23 earthquakes recorded by 7 stationsof Urumqi Digital Tele-seismic Network and the Kuerle regional station, which have been formally runsince 2001, the inelastic attenuation, geometric spreading pattern of the central and eastern Tianshan re-gion, as well as the site response of each station were investigated. Firstly, the signals were corrected forinstrumental responses. Then, we adopted a lag-window spectral technique to obtain a stable Fourier spec-trum of the signals and noises. By subtracting the noise spectrum from the signal spectrum, the noise-cor-rected Fourier amplitude of displacement was obtained. Assuming a hinged tri-linear geometrical spreadingmodel directly following Atkinson, we corrected the spectra, and furthermore used the joint-inversion todetermine the inelastic attenuation co-efficiency C(f) and Q(f) by performing regression iteratively. Final-ly, the tri-linear geometrical spreading pattern were obtained. When hypocenter distance, R, is less than68 km, which corresponds to attenuation of the direct-wave, the wave attenuated with R~(-1). When R is be-tween 68 and 113 km, which corresponds to a transition zone as the direct-wave is joined by post-criticalreflections from mid-crustal interfaces and Moho discontinuity, the energy of S almost does not attenuate.When R is greater than 113 km, which corresponds to attenuation of multiply reflected and refracted Swaves, the wave attenuated with R~(-0.5). The frequency-dependent Q in this region is estimated as Q(f)=344·f~(0.55), which is consistent with the seismic activity in this area, characterized by frequently small tomoderate earthquakes but lack of large earthquakes. This study pays the way for the future seismologicalresearches in this area, including recovering the real source spectrum, modeling the ground motion,etc.
Based on 155 horizontal-component digital seismograms of 23 earthquakes recorded by 7 stationsof Urumqi Digital Tele-seismic Network and the Kuerle regional station, which have been formally runsince 2001, the inelastic attenuation, geometric spreading pattern of the central and eastern Tianshan re-gion, as well as the site response of each station were investigated. Firstly, the signals were corrected forinstrumental responses. Then, we adopted a lag-window spectral technique to obtain a stable Fourier spec-trum of the signals and noises. By subtracting the noise spectrum from the signal spectrum, the noise-cor-rected Fourier amplitude of displacement was obtained. Assuming a hinged tri-linear geometrical spreadingmodel directly following Atkinson, we corrected the spectra, and furthermore used the joint-inversion todetermine the inelastic attenuation co-efficiency C(f) and Q(f) by performing regression iteratively. Final-ly, the tri-linear geometrical spreading pattern were obtained. When hypocenter distance, R, is less than68 km, which corresponds to attenuation of the direct-wave, the wave attenuated with R~(-1). When R is be-tween 68 and 113 km, which corresponds to a transition zone as the direct-wave is joined by post-criticalreflections from mid-crustal interfaces and Moho discontinuity, the energy of S almost does not attenuate.When R is greater than 113 km, which corresponds to attenuation of multiply reflected and refracted Swaves, the wave attenuated with R~(-0.5). The frequency-dependent Q in this region is estimated as Q(f)=344·f~(0.55), which is consistent with the seismic activity in this area, characterized by frequently small tomoderate earthquakes but lack of large earthquakes. This study pays the way for the future seismologicalresearches in this area, including recovering the real source spectrum, modeling the ground motion,etc.
引文
[1] 黄玉龙,郑斯华,刘杰,等.广东地区地震动衰减和场地响应的研究[J].地球物理学报,2003,46(1) :54-61
[2] Hasegawa. H. Lg spectra of local earthquakes recorded by the Eastern Canada Telemetered Network and spectral scaling[J]. Bull. Seism. Soc. Am., 1983, 73(4) : 1041-1061
[3] Hasegawa, H. Attenuation of ground motion in the Canada shield[J]. Bull. Seism. Soc. Am., 1985, 75(6) : 1569-1582
[4] Chun, K, G West, R Kokoski, C Samson. A novel technique for measuring Lg attenuation: result from eastern Canada between 1 to 10 Hz[J], Bull. Seism. Soc. Am., 1987, 77(2) : 398-419
[5] Shin T, R Herrmann. Lg attenuation and source studies using 1982 Miramichi data[J]. Bull. Seism. Soc. Am., 1987, 77(2) : 384-397
[6] Singh, S K, M Ordaz, R S Dattarayam, et al. A Spectral analysis of 21 May 1997, Jabalpur, India, Earthquake (M_W=5． 8) and estimation of ground motion from future earthquakes in the Indian shield region[J]. Bull. Seism. Soc. Am., 1999, 89(6) : 1620-1630
[7] Burger, R, P Somerville, J Barker, et al. The effect of crustal structure on strong ground motion attenuation relations in eastern North America [J]. Bull. Seism. Soc. Am., 1987, 77(2) :420-430
[8] Ou, G, R Herrmann. A statistical model for peak ground motion from local to regional distances [J]. Bull. Seism. Soc. Am., 1990, 80(6) : 1397-1417
[9] Atkinson, G M, R F Mereu. The shape of ground motion attenuation curves in Southeastern Canada[J]. Bull. Seism. Soc. Am., 1992, 82(5) : 2014-2031
[10] 刘杰,郑斯华,黄玉龙.利用遗传算法反演非弹性衰减系数、震源参数和场地响应[J].地震学报,2003,25(2) :211-218
[11] Jin A, Aki K. Spatial and temporal correlation between coda Q-1 and seismicity and its physical mechanism[J]. Geophys. Res., 1989,94: 14041-14059
[12] Singh S, Herrmann R B. Regionalization of crustal coda Q in the continental United States[J]. Geophys. Res. 1983, 88: 527-538
[13] 秦嘉政.澜沧-耿马地震后尾波衰减的区域特征[J].地震学报,1992,14(1) :71-82
[14] 秦嘉政,刘祖荫,龙晓帆.滇西实验场两次中强地震前后尾波衰减的区域特征分析[J].中国地震,1995,11(3) :212-221
[2] Hasegawa. H. Lg spectra of local earthquakes recorded by the Eastern Canada Telemetered Network and spectral scaling[J]. Bull. Seism. Soc. Am., 1983, 73(4) : 1041-1061
[3] Hasegawa, H. Attenuation of ground motion in the Canada shield[J]. Bull. Seism. Soc. Am., 1985, 75(6) : 1569-1582
[4] Chun, K, G West, R Kokoski, C Samson. A novel technique for measuring Lg attenuation: result from eastern Canada between 1 to 10 Hz[J], Bull. Seism. Soc. Am., 1987, 77(2) : 398-419
[5] Shin T, R Herrmann. Lg attenuation and source studies using 1982 Miramichi data[J]. Bull. Seism. Soc. Am., 1987, 77(2) : 384-397
[6] Singh, S K, M Ordaz, R S Dattarayam, et al. A Spectral analysis of 21 May 1997, Jabalpur, India, Earthquake (M_W=5． 8) and estimation of ground motion from future earthquakes in the Indian shield region[J]. Bull. Seism. Soc. Am., 1999, 89(6) : 1620-1630
[7] Burger, R, P Somerville, J Barker, et al. The effect of crustal structure on strong ground motion attenuation relations in eastern North America [J]. Bull. Seism. Soc. Am., 1987, 77(2) :420-430
[8] Ou, G, R Herrmann. A statistical model for peak ground motion from local to regional distances [J]. Bull. Seism. Soc. Am., 1990, 80(6) : 1397-1417
[9] Atkinson, G M, R F Mereu. The shape of ground motion attenuation curves in Southeastern Canada[J]. Bull. Seism. Soc. Am., 1992, 82(5) : 2014-2031
[10] 刘杰,郑斯华,黄玉龙.利用遗传算法反演非弹性衰减系数、震源参数和场地响应[J].地震学报,2003,25(2) :211-218
[11] Jin A, Aki K. Spatial and temporal correlation between coda Q-1 and seismicity and its physical mechanism[J]. Geophys. Res., 1989,94: 14041-14059
[12] Singh S, Herrmann R B. Regionalization of crustal coda Q in the continental United States[J]. Geophys. Res. 1983, 88: 527-538
[13] 秦嘉政.澜沧-耿马地震后尾波衰减的区域特征[J].地震学报,1992,14(1) :71-82
[14] 秦嘉政,刘祖荫,龙晓帆.滇西实验场两次中强地震前后尾波衰减的区域特征分析[J].中国地震,1995,11(3) :212-221
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