文安地震前后首都圈分区波速比时变特征
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摘要
2006年7月4日在首都圈数字地震台网的中南部发生了河北文安MS5.1地震.此次地震为该数字地震台网2002年投入运行以来发生的最强地震事件.本文利用多台和达法,分析处理了首都圈107个数字地震台站2002—2007年判读的大量震相数据.为提高波速比计算的精度和稳定性,对波速比计算环境和条件进行了多方面限定.例如,地震发生位置相对集中,台站选取范围有限,参与计算到时数据在5个以上,以及线性拟合精度高、误差低等.经这些限定条件后的研究发现,文安地震前,在文安和唐山附近地区地震波速比出现正常—降低—恢复—发震的异常演变过程.震前1年,出现波速比较明显降低过程,异常持续时间1年左右;同期邢台、京西北、京西南、京津和北京地区波速比的变化则基本平稳.文安地震发生后,文安和唐山地区的波速比恢复正常的平稳变化状态.通过波速比计算结果的误差和稳定性分析认为,文安地震前在文安和唐山附近地区地震波速比异常是可信的.
On July 4, 2006, an earthquake of MS5.1 took place in Wen’an, Hebei Province, just in the south part of China’s Capital area digital seismograph network. It is the strongest event recorded ever since the network went into operation in 2002. We processed the large amount of phase data yielded by the 107 digital seismic stations during 2002—2007 using the Wadati method. In order to improve the precision and stability of shear and compressional wave velocities (vP/vS) estimation, we imposed a number of restrictions on the computation condition, e.g., the earthquakes are densely distributed, selected stations are in limited area, the number of stations involved in the computation is more than 5, and the linear fitting featuresa high precision. Under these restrictions, the study shows that vP/vS in and around Wen’an and Tangshan underwent a normal-low-normal variation process before the Wen’an earthquake: one year before the quake, vP/vS became obviously low and the low ratio lasted for about one year, meanwhile, little variation of vP/vS was seen in Xingtai, northwest of Beijing, southwest of Beijing, Beijing-Tianjin and Beijing; after the quake, the vP/vS returned to normal in Wen’an and Tangshan. Error and stability analysis of the calculated vP/vS shows that the vP/vS anomalous variation appeared in and around Wen’an and Tangshan before the Wen’an earthquake is convincible.
On July 4, 2006, an earthquake of MS5.1 took place in Wen’an, Hebei Province, just in the south part of China’s Capital area digital seismograph network. It is the strongest event recorded ever since the network went into operation in 2002. We processed the large amount of phase data yielded by the 107 digital seismic stations during 2002—2007 using the Wadati method. In order to improve the precision and stability of shear and compressional wave velocities (vP/vS) estimation, we imposed a number of restrictions on the computation condition, e.g., the earthquakes are densely distributed, selected stations are in limited area, the number of stations involved in the computation is more than 5, and the linear fitting featuresa high precision. Under these restrictions, the study shows that vP/vS in and around Wen’an and Tangshan underwent a normal-low-normal variation process before the Wen’an earthquake: one year before the quake, vP/vS became obviously low and the low ratio lasted for about one year, meanwhile, little variation of vP/vS was seen in Xingtai, northwest of Beijing, southwest of Beijing, Beijing-Tianjin and Beijing; after the quake, the vP/vS returned to normal in Wen’an and Tangshan. Error and stability analysis of the calculated vP/vS shows that the vP/vS anomalous variation appeared in and around Wen’an and Tangshan before the Wen’an earthquake is convincible.
引文
刁桂苓,周仕勇,刘杰,张学民,李晓峰,张民.2005.岫岩地震序列的平均波速比前兆异常[J].华北地震科学,23(4):1--5.
冯德益.1981.地震波速异常[M].北京:地震出版社:7,11--14,33,168--178.
冯德益,顾谨萍,王周元.1978.我国西部地区一些强震及中强震前后波速异常得初步研究(三):和达曲线得曲率变化[J].地球物理学报,21(4):292--309.
冯德益,谭爱娜,王克芬.1974.近震地震波波速异常与地震预报[J].地球物理学报,17(2):84--97.
冯锐,庞庆衍,傅征祥.1976.海城地震前后地震波速比地变化[J].地球物理学报,19(4):295--305.
黎明晓,张晓东.2004.应用多台法测定华北地区地壳的平均波速比[J].地震,24(1):163--169.
黎明晓,刘杰.2006.云南地区地震序列的波速比(vP/vS)异常的研究[J].地震,26(1):26--34.
李善邦.1981.中国地震[M].北京:地震出版社:522--532,566--568.
张爱香.2005.安阳及邻区中强地震前波速比时空演化特征分析与研究[J].防灾技术高等专科学校学报,7(1):40--45.
张小涛,吕坚,马广庆,靳玉科,张建国.2006.九江—瑞昌地震序列的波速比特征研究[J].华北地震科学,24(4):36--40.
张学民,刁桂苓,束沛镒.2004a.华北地区地下介质波速比值(vP/vS)研究[J].地震地质,26(2):305--317.
张学民,刁桂苓,束沛镒,刘素英.2004b.鄂尔多斯快体及其东南缘剪切速度结构与波速比研究[J].中国地震,20(1):53--63.
张学民,张天中,李永红,李霞,刁桂苓.2007.山东地区多台波速比研究[J].地震地质,29(1):95--104.
赵明淳,刁桂苓,张学民.2005.首都圈平均波速比分析[J].西北地震学报,27(3):245--254.
邹振轩,李金龙,俞铁宏.2006.应用多台和达法测定温州珊溪水库地区地震的平均波速比[J].地震,26(4):133--137.
Hauksson E,Haase J.1994.Three-di mensionalvP/vSvelocity model of the Los Angels basin and central TransverseRanges,California[J].J Geophys Res,102:5423--5453.
Kanamori H,Fuis G.1976.Variation of P wave velocity befor and after the Gal way Lake earthquake(ML=5.2)andGoat Moumtain earthquake(ML=4.7),in the Mojave desert,California[J].Bull Seism Soc Amer,66:2027--2037.
Korneev V A,McEvilly T V,Karageorgi E D.2000.Seismological studies at Parkfield.VIII:Modeling the observedtravel-ti me changes[J].Bull Seismol Soc Amer,90:702--708.
Li Y G,Vidale J E,Aki K,Xu F,Burdette T.1998.Evidence of shallowfault zone healing after the1992M7.5Lan-ders,California,earthquake[J].Science,279:217--219.
McEvilly T V,Johnson L R.1974.Stability of P and S velocities fromcentral California quarry blasts[J].Bull SeismSoc Amer,64:343--353.
Nakamura A,Hasegawa A,Hirata N,Iwasaki T,Hamaguchi H.2002.Temporal variations of seismic wave velocity as-sociated with1998M6.1Shizukuishi earthquake[J].Pure Appl Geophys,159:1183--1204.
Nur A.1972.Dilatancy,pore fluids and premonitory variations oftS/tPtravel ti mes[J].Bull Seism Soc Amer,62(5):1217--1222.
Schaff D P,Beroza G C.2004.Coseismic and postseismic velocity changes measured by repeating earthquakes[J].J Geo-phys Res,109:B10302,doi:10.1029/2004JB003011.
Walck MC.1988.Tree-di mensionalvP/vSvariations for the Coso region,California[J].J Geophys Res,93:2047--2053.
冯德益.1981.地震波速异常[M].北京:地震出版社:7,11--14,33,168--178.
冯德益,顾谨萍,王周元.1978.我国西部地区一些强震及中强震前后波速异常得初步研究(三):和达曲线得曲率变化[J].地球物理学报,21(4):292--309.
冯德益,谭爱娜,王克芬.1974.近震地震波波速异常与地震预报[J].地球物理学报,17(2):84--97.
冯锐,庞庆衍,傅征祥.1976.海城地震前后地震波速比地变化[J].地球物理学报,19(4):295--305.
黎明晓,张晓东.2004.应用多台法测定华北地区地壳的平均波速比[J].地震,24(1):163--169.
黎明晓,刘杰.2006.云南地区地震序列的波速比(vP/vS)异常的研究[J].地震,26(1):26--34.
李善邦.1981.中国地震[M].北京:地震出版社:522--532,566--568.
张爱香.2005.安阳及邻区中强地震前波速比时空演化特征分析与研究[J].防灾技术高等专科学校学报,7(1):40--45.
张小涛,吕坚,马广庆,靳玉科,张建国.2006.九江—瑞昌地震序列的波速比特征研究[J].华北地震科学,24(4):36--40.
张学民,刁桂苓,束沛镒.2004a.华北地区地下介质波速比值(vP/vS)研究[J].地震地质,26(2):305--317.
张学民,刁桂苓,束沛镒,刘素英.2004b.鄂尔多斯快体及其东南缘剪切速度结构与波速比研究[J].中国地震,20(1):53--63.
张学民,张天中,李永红,李霞,刁桂苓.2007.山东地区多台波速比研究[J].地震地质,29(1):95--104.
赵明淳,刁桂苓,张学民.2005.首都圈平均波速比分析[J].西北地震学报,27(3):245--254.
邹振轩,李金龙,俞铁宏.2006.应用多台和达法测定温州珊溪水库地区地震的平均波速比[J].地震,26(4):133--137.
Hauksson E,Haase J.1994.Three-di mensionalvP/vSvelocity model of the Los Angels basin and central TransverseRanges,California[J].J Geophys Res,102:5423--5453.
Kanamori H,Fuis G.1976.Variation of P wave velocity befor and after the Gal way Lake earthquake(ML=5.2)andGoat Moumtain earthquake(ML=4.7),in the Mojave desert,California[J].Bull Seism Soc Amer,66:2027--2037.
Korneev V A,McEvilly T V,Karageorgi E D.2000.Seismological studies at Parkfield.VIII:Modeling the observedtravel-ti me changes[J].Bull Seismol Soc Amer,90:702--708.
Li Y G,Vidale J E,Aki K,Xu F,Burdette T.1998.Evidence of shallowfault zone healing after the1992M7.5Lan-ders,California,earthquake[J].Science,279:217--219.
McEvilly T V,Johnson L R.1974.Stability of P and S velocities fromcentral California quarry blasts[J].Bull SeismSoc Amer,64:343--353.
Nakamura A,Hasegawa A,Hirata N,Iwasaki T,Hamaguchi H.2002.Temporal variations of seismic wave velocity as-sociated with1998M6.1Shizukuishi earthquake[J].Pure Appl Geophys,159:1183--1204.
Nur A.1972.Dilatancy,pore fluids and premonitory variations oftS/tPtravel ti mes[J].Bull Seism Soc Amer,62(5):1217--1222.
Schaff D P,Beroza G C.2004.Coseismic and postseismic velocity changes measured by repeating earthquakes[J].J Geo-phys Res,109:B10302,doi:10.1029/2004JB003011.
Walck MC.1988.Tree-di mensionalvP/vSvariations for the Coso region,California[J].J Geophys Res,93:2047--2053.
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