From the near-field records of aftershock of Datong earthquakes in October 1989 and March 1991,an extra phase between P and S arrivals is found. High-precision epicenter location shows that some of these records are o...From the near-field records of aftershock of Datong earthquakes in October 1989 and March 1991,an extra phase between P and S arrivals is found. High-precision epicenter location shows that some of these records are obtained with the incidental angle less than the critical angle. This excludes the possibility that the extra wave phase is a refractive wave from ground surface. Particle motion analysis shows that the characteristic of the extra wave is similar to that of wave, so it is possible that the extra phase is an S to P convert wave from the bottom of sediment basin. Suppose a low velocity layer covers a high velocity basement. Successful simulation by the synthetic seismogram confirms that the extra phase is an S-P convert wave from the interface of the basin bottom. Modifying the depth of interface at each ray path to match the waveform, we obtain an interface distribution in space. In this way, a brief bottom image could be shown, and the Datong basin has a 'V' shaped bottom.展开更多
利用远震初至波穿越地壳、上地幔等速度界面时产生的一系列PS型透射转换波,测定远震PS转换波与初至P波的到时差Δ t PS = t PS - t P随时间的变化特征,有可能监测孕震区转换界面以上有限的地层空间内介质物性的变化。选取2001—2012年...利用远震初至波穿越地壳、上地幔等速度界面时产生的一系列PS型透射转换波,测定远震PS转换波与初至P波的到时差Δ t PS = t PS - t P随时间的变化特征,有可能监测孕震区转换界面以上有限的地层空间内介质物性的变化。选取2001—2012年作为研究时段,通过四川地震台网的YZP和JJS 2个台站记录到的兴都库什、苏门答腊南部地区2组震中距变化<3°的远震数据,得到2个台站在2008年5月12日汶川MS8.0地震前后记录的PS转换波与初至P波到时差Δ t PS 的变化特征。结果表明,在2006年以前Δ t PS 有一个缓慢增大的过程;汶川地震前约2a内Δ t PS 出现明显的降低过程,最大降幅达0.2~0.3s,超过测量误差4~5倍;震前2~3个月低值有一定程度的回返。文中讨论了可能引起Δ t PS 变化的原因,分析表明文中提出的远震转换波法在地震监测中有很好的应用前景,值得进行进一步实验研究。展开更多
基金State Key Basic Research Development and Programming Project (95-13-05-02) the Federal Institute for Geosciences and Natural Resources, Germany.
文摘From the near-field records of aftershock of Datong earthquakes in October 1989 and March 1991,an extra phase between P and S arrivals is found. High-precision epicenter location shows that some of these records are obtained with the incidental angle less than the critical angle. This excludes the possibility that the extra wave phase is a refractive wave from ground surface. Particle motion analysis shows that the characteristic of the extra wave is similar to that of wave, so it is possible that the extra phase is an S to P convert wave from the bottom of sediment basin. Suppose a low velocity layer covers a high velocity basement. Successful simulation by the synthetic seismogram confirms that the extra phase is an S-P convert wave from the interface of the basin bottom. Modifying the depth of interface at each ray path to match the waveform, we obtain an interface distribution in space. In this way, a brief bottom image could be shown, and the Datong basin has a 'V' shaped bottom.
文摘利用远震初至波穿越地壳、上地幔等速度界面时产生的一系列PS型透射转换波,测定远震PS转换波与初至P波的到时差Δ t PS = t PS - t P随时间的变化特征,有可能监测孕震区转换界面以上有限的地层空间内介质物性的变化。选取2001—2012年作为研究时段,通过四川地震台网的YZP和JJS 2个台站记录到的兴都库什、苏门答腊南部地区2组震中距变化<3°的远震数据,得到2个台站在2008年5月12日汶川MS8.0地震前后记录的PS转换波与初至P波到时差Δ t PS 的变化特征。结果表明,在2006年以前Δ t PS 有一个缓慢增大的过程;汶川地震前约2a内Δ t PS 出现明显的降低过程,最大降幅达0.2~0.3s,超过测量误差4~5倍;震前2~3个月低值有一定程度的回返。文中讨论了可能引起Δ t PS 变化的原因,分析表明文中提出的远震转换波法在地震监测中有很好的应用前景,值得进行进一步实验研究。
