晋冀鲁豫交界地区震源位置及震源区速度结构的联合反演
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摘要
利用邯郸数字台网记录到的2001—2008年间460次ML≥1.0地震的1 861条P波到时数据,采用震源位置和速度结构联合反演方法确定晋冀鲁豫交界地区(35.0°～38.0°N,113.0°～116.0°E)地震的震源位置分布和该区域的速度结构。结果表明:①经过重新定位后,P波走时的均方根残差(RMS)由反演前的1.35s降到反演后的0.45s。定位偏差在EW方向上平均为0.031km,在NS方向上平均为0.029km,在垂直方向上平均为0.060km。②邢台震区的中小地震明显呈NEE向分布,深度主要集中分布在7～14km范围内;磁县震区中小震分布相对复杂,具有NEE和NWW两个展布方向,震源深度主要集中在8～18km范围内,总体上晋冀鲁豫交界地区中小地震深度呈现北部浅南部深的趋势。③反演得到了晋冀鲁豫交界地区的速度结构,在邢台地震极震区下方7～14km处存在低速层,与1966年邢台7.2级地震的震源深度一致;在磁县地震极震区下方13～18km处也存在低速层与1831年磁县7.5级地震震源深度一致,且磁县震区下方的速度结构比邢台震区更为复杂。
Using 1861 P wave arrival times from 460 local earthquakes(ML≥1.0) recorded by the Handan Seismic Network from 2001 to 2008,we use the simultaneous inversion method to determine the hypocentral distribution and velocity structure in the juncture area(35.0°～38.0°N,113.0°～116.0°E) of Shanxi,Hebei,Shandong and Henan provinces.T④he results show that: ① After the simultaneous inversion of earthquake relocation and velocity structure,residual root mean square(RMS) of P wave travel time decreased from the 1.35 s to the 0.45 s,location error averaged 0.031 km in the EW direction,0.029 km in the NS direction,and average 0.060 km vertically.② Small and medium earthquakes spread in the NEE direction in the Xingtai hypocentral area,with focal depths varying from 7 to 14 km;seismicity displays two conjugated distributions in the directions of NEE and NNW in the Cixian hypocentral area with focal depths varying from 8 to 18 km.The focal depths become shallower form south to north in the juncture area.③ Low velocity layer exists in 7~14 km beneath the meizoseismal area of Xingtai earthquake,consistent with the focal depth of Xingtai M7.2 earthquake;low velocity layer also exists in 13~18 km beneath the meizoseismal area of Cixian earthquake,consistent with the focal depth of Cixian M7.5 earthquake.The velocity structure of Cixian hypocentral area is much complicated than that of Xingtai hypocentral area.
Using 1861 P wave arrival times from 460 local earthquakes(ML≥1.0) recorded by the Handan Seismic Network from 2001 to 2008,we use the simultaneous inversion method to determine the hypocentral distribution and velocity structure in the juncture area(35.0°～38.0°N,113.0°～116.0°E) of Shanxi,Hebei,Shandong and Henan provinces.T④he results show that: ① After the simultaneous inversion of earthquake relocation and velocity structure,residual root mean square(RMS) of P wave travel time decreased from the 1.35 s to the 0.45 s,location error averaged 0.031 km in the EW direction,0.029 km in the NS direction,and average 0.060 km vertically.② Small and medium earthquakes spread in the NEE direction in the Xingtai hypocentral area,with focal depths varying from 7 to 14 km;seismicity displays two conjugated distributions in the directions of NEE and NNW in the Cixian hypocentral area with focal depths varying from 8 to 18 km.The focal depths become shallower form south to north in the juncture area.③ Low velocity layer exists in 7~14 km beneath the meizoseismal area of Xingtai earthquake,consistent with the focal depth of Xingtai M7.2 earthquake;low velocity layer also exists in 13~18 km beneath the meizoseismal area of Cixian earthquake,consistent with the focal depth of Cixian M7.5 earthquake.The velocity structure of Cixian hypocentral area is much complicated than that of Xingtai hypocentral area.
引文
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[17]张小涛,吕坚,马广庆,等.双差地震定位法在邯邢地区地震精确定位中的初步应用[J].地震研究,2008,31(1):37-41.
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[23]刁桂苓,张四昌,赵军,等.用现今小地震研究历史强震的震源断层以1830年河北磁县7.5级地震为例[J].地震地质,1999,21(2):121-126.
[11]马宏生,张国民,周龙泉,等.川滇地区中小震重新定位与速度结构的联合反演研究[J].地震,2008,28(2):29-38.
[2]周仕勇,许忠淮,韩京,等.主地震定位方法分析及1997年新疆伽师震群高精度定位[J].地震学报,1999,21(3):258-265.
[3]Spencer C,Gubbins D.Travel time inversion for simultaneous earthquake location and velocitystructure determination in laterally varying media[J].Geophys J R Astron Soc,1980,63(1):95-116.
[4]Waldhauser F,Ellsworth W L.A double-difference earthquake location algorithm:Method and Ap-plication to the Northern Hayward fault[J].Bull Seis Soc Amer,2000,90(6):1 353-1 368.
[5]Aki K,Lee W H K.Determination of three-dimensional velocity anomalies under a seismic array u-sing P arrival times from local earthquakes.1.A homogeneous initial model[J].J Geophys Res,1976,81:4 381-4 399.
[6]刘福田,李强,吴华,等.用于速度图像重建的层析成像法[J].地球物理学报,1989,32(1):46-61.
[7]刘福田.震源位置和速度结构的联合反演理论和方法[J].地球物理学报,1984,27(2):167-175.
[8]Kissling E,Ellsworth W L,Eberhard-Phillips D,et al.Initial reference models in local earthquaketomography[J].J Geophys Res,1994,99:19 635-19 646.
[9]周龙泉,刘杰,张晓东.2003年大姚6.2级、6.1级地震前三维波速结构的演化[J].地震学报,2007,29(1):20-30.
[10]周龙泉,刘杰,马宏生,等.2003年大姚6.2级、6.1级地震序列震源位置及震源区速度结构的联合反演[J].地震,2009,29(2):12-23.
[11]Zhao D,Hasegawa A,Horiuchi S.Tomographic imaging of P and S wave velocity structure beneathnortheastern Japan[J].J Geophys Res,1992,97:19 909-19 928.
[12]邵学钟,张家茹,章思亚,等.邢台地震区深部构造背景的地震转换波探测和研究[J].地球物理学报,1993,36(5):609-619.
[13]祝治平,张先康,盖玉杰,等.邢台震源区及相邻地区地壳上地幔速度结构研究[J].地震学报,1995,17(3):328-334.
[14]Zhou H.Direct inversion of velocity interfaces[J].Geophys Res Lett,7:doi:10.1029/2003GL019318
[15]Paige C,Saunders M A.LSQR:Sparse linear equations and least squares problems[J].ACMTransactions on Mathematical Software,1982,8(2):195-209.
[16]顾梦林,刘保金,赵成斌,等.邢台地区深浅构造耦合关系的探测研究和几个值得思考的问题[J].地震学报,2000,22(1):385-394.
[17]张小涛,吕坚,马广庆,等.双差地震定位法在邯邢地区地震精确定位中的初步应用[J].地震研究,2008,31(1):37-41.
[18]河北省地震局.一九六六年邢台地震[M].北京:地震出版社,1986.
[19]徐锡伟,于贵华,王峰,等.1966年邢台地震群的发震构造模型新生断层形成?先存活断层摩擦粘滑?[J].中国地震,2000,16(4):364-367.
[20]李大鹏,林邦慧.地震剪切破裂的三维断裂力学有限元分析1966年邢台地震的数值模拟[J].中国地震,1997,13(2):151-163.
[21]林真明,邵学钟,陈学波.1966年邢台地震区地震测深资料再解释[J].华北地震科学,1990,8(3):55-65.
[22]江娃利,刘仲温,李咸业,等.1830年河北磁县强震区活动构造初步研究[J].华北地震科学,1994,12(1):21-27.
[23]刁桂苓,张四昌,赵军,等.用现今小地震研究历史强震的震源断层以1830年河北磁县7.5级地震为例[J].地震地质,1999,21(2):121-126.
[11]马宏生,张国民,周龙泉,等.川滇地区中小震重新定位与速度结构的联合反演研究[J].地震,2008,28(2):29-38.
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