摘要
自唐山地区发生7.8级地震以来,古冶—滦县地区一直为唐山地震的余震频发区.该地区断裂和地质构造十分复杂,这些断裂的破碎程度有哪些差异?这是地震学家所关心的问题.本文使用在古冶—滦县地区布设的密集流动地震台网2020年8月—2021年7月近一年的波形记录,采用剪切波分裂原理通过对古冶—滦县地区上地壳各向异性研究来揭示这些问题.得到以下结论:(1)古冶—滦县地区快剪切波平均偏振方向为NE86.2°±27.8°,慢剪切波平均时间延迟为2.37±1.25 ms·km^(-1).快剪切波偏振第一优势方向为ENE向,与区域背景主压应力方向一致;第二优势方向为NE向,该方向揭示了研究区域断裂主要以NE向为发育的构造意义.(2)唐山断裂带附近台站快剪切波偏振方向均显示出NE向的第二优势方向,与断裂走向一致.断裂附近台站慢剪切波时间延迟较高,各台站时间延迟差异较小,表明区域各向异性程度较强,断裂沿NE向破碎程度较强且破碎均匀.(3)滦县—乐亭断裂和卢龙断裂附近台站快剪切波偏振方向显示出复杂性,表明两条活动断裂的交汇在地壳内部产生了复杂的地壳破裂裂隙结构.断裂附近台站慢剪切波时间延迟较高,各台站时间延迟差异较大,表明区域各向异性和断裂破碎程度较强,且破碎不均匀.(4)丰台—野鸡坨断裂和榛子镇断裂附近台站快剪切波偏振方向与区域主压应力方向接近,慢剪切波时间延迟最小,表明断裂对其附近台站快剪切波偏振方向影响大不,区域各向异性和断裂破碎程度较弱,断裂内部裂隙可能存在愈合的现象.另外,本文还针对1976年唐山M_S7.8地震后在唐山断裂带上出现的尖端效应是否对唐山断裂带北段应力场产生了影响做出了讨论.本研究结果不仅反映了断裂分布的复杂程度与地壳各向异性的关系,还揭示了地壳各向异性在不同破碎程度断裂上的差异.
Since the occurrence of the Tangshan MS7.8 earthquake, Guye—Luanxian area has been a frequently occurrence of aftershocks. The fault and geological structure are very complex in Guye—Luanxian area. What are the differences in the fragmentation degree of these faults? The problems are concerned by seismologists. To answer these questions, by using the waveform records of the mobile seismic network densely deployed in the Guye—Luanxian area from August 2020 to July 2021, we study the anisotropy of the upper crust in Guye—Luanxian area according to the principle of shear wave splitting. The following conclusions are obtained: (1) The average polarization direction of fast shear wave in Guye—Luanxian area is NE86.2°±27.8°, the average time delay of slow shear wave in this area is 2.37±1.25 ms·km-1. The first dominant polarization direction of fast shear wave is ENE, which is consistent with the direction of principal compressive stress of regional background, the second dominant direction is NE direction, which reveals the tectonic significance that the faults in this area are mainly developed in NE direction. (2) The polarization direction of fast shear wave near the Tangshan fault zone shows the second dominant direction in NE direction, which is consistent with the fault strike. The time delay of slow shear wave of stations near the fault is higher, and the difference of time delay in stations is smaller, which indicates that the regional anisotropy is stronger, and the fragmentation degree along the NE direction is stronger and homogeneity. (3) The polarization direction of fast shear wave near Luanxian—Leting fault and Lulong fault shows complexity, indicating that the intersection of two active faults produces a complex crustal fracture structure in the crust. The time delay of slow shear wave in stations near the fault is higher, and the time delay difference of each station is larger, which indicates that the regional anisotropy and fragmentation degree are stronger, and the fragmentation is heterogeneity. (4) The polarization direction of fast shear wave at stations near the Fengtai—Yejituo fault and Zhenzizhen fault is consistent with the direction of regional principal compressive stress. The slow shear wave time delay of stations near the fault is the smallest, indicating that the Fengtai—Yejituo fault and Zhenzizhen fault have no influence on the polarization direction of fast shear wave at nearby stations, regional anisotropy and fragmentation degree are weaker, and may be indicating closure of fracture internal cracks in the faults. Moreover, we also discussed whether the tip effect on the Tangshan fault after the 1976 Tangshan MS7.8 earthquake has an impact on the stress field in the northern segment of the Tangshan fault zone. The results of this study not only reflect the relationship between the complexity of fault distribution and crustal anisotropy, but also reveal the difference of crustal anisotropy on faults with different degrees of fragmentation.
作者
李枭
万永革
王晓山
吴鹏
张小涛
余海琳
LI Xiao;WAN YongGe;WANG XiaoShan;WU Peng;ZHANG XiaoTao;YU HaiLin(Institute of Disaster Prevention,Sanhe Hebei 065201,China;Hebei Key Laboratory of Earthquake Dynamics,Sanhe Hebei 065201,China;Hebei Hongshan Thick Sediment and Earthquake Disaster National Field Scientific Observation and Research Station,Longyao Hebei 055350,China;Hebei Earthquake Agency,Shijiazhuang 050021,China;Handan Earthquake Monitoring Center Station,Handan Hebei 056001,China)
出处
《地球物理学报》
SCIE
EI
CAS
CSCD
北大核心
2024年第3期1053-1068,共16页
Chinese Journal of Geophysics
基金
国家自然科学基金(42174074,41674055)
中央高校科研业务费专项(ZY20215117)
河北省地震科技星火计划项目(DZ20200827053,DZ20200827056)
河北省地震动力学重点实验室开放基金项目(FZ212105)联合资助。
关键词
古冶—滦县地区
地壳各向异性
剪切波分裂
构造应力
断裂破碎程度
Guye-Luanxian area
Crustal anisotropy
Shear-wave splitting
Tectonic stress
Fragmentation degree in the fault
