张北地震前小震活动和余震序列精确定位及主震破裂方向的讨论
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摘要
1970年至1998年1月10日张北地震前, 沿NWW向发生2级以上地震24次, 其分布相对集中, 呈条带状。对华北台网所记上述地震的到时数据全部重新查图核对, 并补充了内蒙古台网5个台的数据以改善用于定位的台站分布, 并采用主地震定位法重新定位, 除一个地震外, 其余地震更加集中, 形成一小震条带。1998年2月中国地震局地球物理勘探中心在张北震区架设10台短周期数字化地震仪, 记录了大量微震。作者采用P波和S波到时差重新进行了震源定位, 得到184次微震的定位结果, 连同1998年1~2月张北震区3级以上地震事件定位结果一起勾画出6.2级地震的震源破裂带。由张北地震震中向SEE向延伸存在由强震构成的张家口渤海地震带。根据精确定位结果, 结合修订后主震的震源机制、宏观烈度分布和层析成像资料, 讨论了张北地震和小尺度地震带(震源破裂带)、震前的中等尺度小震条带以及大尺度的张家口渤海强震带的关系。
Before the Zhangbei earthquake through the lst of Jan. 1970 to the 10th of Jan. 1998, 24 earthquakes with magnitude larger than M_L2.0 occurred in the NWW direction of Zhangbei earthquake, they were relatively concentrated along a belt. The arrival times of all the events are checked from the seismograms recorded at North China telemetric seismograph network. Additional data are used from other 5 stations of Inner Mongolia telemetric seismograph network to improve the distribution of stations used in location. Those earthquakes are relocated using the main event location approach. All events became more closely except one, forming a seismic belt. Many micro-earthquakes along Zhangbei seismic zone are recorded by 10 short period seismographs employed by Research Center of Exploration of Geophysics in February 1998. We relocated 184 micro-earthquakes using the arrival time difference between P and S waves. These micro-earthquakes together with the relocated earthquakes with magnitude large than 3.0 occurred along Zhangbei seismic zone in January 1998 outline a focal rupture belt of M6.2 earthquake. There is Zhangjiakou-Bohai rupture belt, where many strong earthquakes occurred in history, extended along the SEE direction of Zhangbei earthquake epicenter. In this paper, the results of accurate location together with the corrected focal mechanism and the distribution of macroscopic intensity are used to discuss the relationship between Zhangbei earthquake and small scale focal rupture belt and intermediate scale weak earthquake belt before the main earthquake and large scale Zhangjiakou-Bohai strong earthquake belt.
Before the Zhangbei earthquake through the lst of Jan. 1970 to the 10th of Jan. 1998, 24 earthquakes with magnitude larger than M_L2.0 occurred in the NWW direction of Zhangbei earthquake, they were relatively concentrated along a belt. The arrival times of all the events are checked from the seismograms recorded at North China telemetric seismograph network. Additional data are used from other 5 stations of Inner Mongolia telemetric seismograph network to improve the distribution of stations used in location. Those earthquakes are relocated using the main event location approach. All events became more closely except one, forming a seismic belt. Many micro-earthquakes along Zhangbei seismic zone are recorded by 10 short period seismographs employed by Research Center of Exploration of Geophysics in February 1998. We relocated 184 micro-earthquakes using the arrival time difference between P and S waves. These micro-earthquakes together with the relocated earthquakes with magnitude large than 3.0 occurred along Zhangbei seismic zone in January 1998 outline a focal rupture belt of M6.2 earthquake. There is Zhangjiakou-Bohai rupture belt, where many strong earthquakes occurred in history, extended along the SEE direction of Zhangbei earthquake epicenter. In this paper, the results of accurate location together with the corrected focal mechanism and the distribution of macroscopic intensity are used to discuss the relationship between Zhangbei earthquake and small scale focal rupture belt and intermediate scale weak earthquake belt before the main earthquake and large scale Zhangjiakou-Bohai strong earthquake belt.
引文
[1] 高景春,刁桂苓,张四昌,等.以震源精确定位结果分析张北地震序列的破裂特征[J].地震地质,2002,24(1):8189.
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[9] 周仕勇,许忠淮,韩京,等.主地震定位法分析以及1997年新疆伽师强震群高精度定位[J].地震学报,1999,21(3):258265.
[10] 白玲,张天中,张宏志.多重相对定位法和波形相关校正及其应用[J].地震学报,2003,25(6):591600.
[11] 刁桂苓,蔡华昌,刁建新,等.1998年张北6.2级地震宏观烈度[J].华北地震科学,2001,19(1):2330.
[12] 赖晓玲,李松林,张先康,等.张北震区三维构造特征[J].地学前缘,2002,9(4):383388.
[13] 刁桂苓,于利民,孙佩卿,等.1989年大同震群的体破裂特征[J].地球物理学报,1993,36(3):360368.
[14] 郑秀芬,丁晗,张宏志,等.张北尚义地震序列的空间分布、构造活动性初探[J].地震地磁观测与研究,1998,19(6):2427.
[2] 杨智娴,陈运泰,张宏志.张北尚义地震序列的重新定位和发震构造[J].地震学报,2002,24(4):366377.
[3] 刁桂苓,张四昌,朱艾斓.张北6.2级地震发生在小震条带上[J].华北地震科学,1998,16(3):3438.
[4] 张国民,张永仙.张北地震的科学问题及反思[A].中国地震局监测预报司.1998年张北地震[C].北京:地震出版社,1999.231232.
[5] FitchT J,MuirheadK J.Depths to larger earthquakes associated with crustal loading[J].GeophysJ R astrS,1974,37:285296.
[6] JacksonJ,FitchT J.Seismotectonic implications of relocated aftershock sequences inIran andTur key: an application of the master event technique[J].GeophysJ R astrS,1979,57:209229.
[7] 马秀芳.用相对定位法测定1973年安徽霍山震群的震源位置[J].地震研究,1982,5(1):99113.
[8] 章光月,王碧泉,许绍燮,等.1975年2月4日海城地震(M=7.3)的前震系列[J].地震学报,1983,5(1):114.
[9] 周仕勇,许忠淮,韩京,等.主地震定位法分析以及1997年新疆伽师强震群高精度定位[J].地震学报,1999,21(3):258265.
[10] 白玲,张天中,张宏志.多重相对定位法和波形相关校正及其应用[J].地震学报,2003,25(6):591600.
[11] 刁桂苓,蔡华昌,刁建新,等.1998年张北6.2级地震宏观烈度[J].华北地震科学,2001,19(1):2330.
[12] 赖晓玲,李松林,张先康,等.张北震区三维构造特征[J].地学前缘,2002,9(4):383388.
[13] 刁桂苓,于利民,孙佩卿,等.1989年大同震群的体破裂特征[J].地球物理学报,1993,36(3):360368.
[14] 郑秀芬,丁晗,张宏志,等.张北尚义地震序列的空间分布、构造活动性初探[J].地震地磁观测与研究,1998,19(6):2427.
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