Seismicity in Zemuhe fault zone based on dense seismic array
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摘要:
利用2019—2021年布设在则木河断裂带的20个宽频带流动测震台和周边6个固定台站的波形数据，对连续波形记录进行P和S震相识别、震相自动关联和初步定位，并应用传统的绝对定位技术得到了研究区绝对地震目录，再运用双差定位法对检测出的1 075个地震事件进行重定位。结果表明：① 研究区地震活动分布不均匀，多数地震沿着深大断裂带呈条带状分布，显示出断裂在地表的展布形态； ② 研究区地震的震源优势深度范围为5—15 km，说明本区地震发生在中上地壳；③ 地震在各个剖面深度的分布特征显示出断裂在深部的构造特征。从重定位后的震中空间分布可见，则木河断裂带中段存在倾向为60°左右的NW向小震密集带，分析认为研究时期以来小震活动频繁，该地区的局部应力较高，构造活动较强。
Abstract:Based on the continuous waveforms of twenty portable broadband seismic stations deployed in the Zemuhe fault and six local stations in the surrounding areas of the fault zone in the period of 2019−2021, we performed automatic earthquake detection with an integrated event detection system called PAL, and then obtained the absolute earthquake catalogue in the study area by using traditional absolute positioning technology, finally relocated 1 075 detected seismic events by the double-difference positioning method. The results show that: ① The seismic activity in the study area is unevenly distributed, and most of the earthquakes are distributed in strips along the deep-large fault zones, showing the distribution pattern of the fault on the surface; ② The focal depth of the earthquakes in the study area ranges 5−15 km, which indicates that the earthquake occurred in the middle to upper crust; ③ The distribution characteristics of earthquakes at the depth of each section show the structural characteristics of faults in the deep. It can be seen from the spatial distribution of the epicenters after relocation that there is a small earthquake dense zone with dip of 60° in the middle section of the Zemuhe fault zone. The analysis shows that the small earthquakes have been frequent since the study period, the local stress in this area is high, and the tectonic activity is strong.
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Keywords:
- Zemuhe fault /
- PALM /
- double-difference location /
- depth distribution
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图 1 研究区主要断裂展布和地震台站分布（断层数据来自邓起东等，2003）
Figure 1. Distribution of main faults and seismic stations in study area （the fault data is from Deng et al，2003）
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图 2 不同时窗长度的检测到时变化 （2020年3月22日）
Figure 2. Variation in detection time for different time window lengths （March 22，2020）
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图 6 基于Hypoinverse的一维地震定位误差分析
Figure 6. Error distribution of 1D earthquake location from Hypoinverse
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图 7 最小完备震级Mc，b值（a）和震级-频度图（b）
Figure 7. The minimum magnitude of completeness Mc，b value （a） and magnitude-frequency （b）
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图 8 重定位前后2019—2021年则木河地区地震震中分布图
（a） 震相关联初始事件震中分布；（b） 震相人工核查后绝对定位震中分布；（c） 基于绝对定位震相报告的双差定位结果
Figure 8. Distribution of earthquake hypocenters in Zemuhe area from 2019 to 2021 before and after relocation
（a） Initial epicentral distribution；（b） Hypoinverse epicentral distribution after manual inspection；（c） HypoDD epicentral distribution
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图 9 重定位前后震源深度分布
（a） 初始震中分布；（b） 重定位后震中分布
Figure 9. Distribution of earthquake hypocenters before and after relocation
（a） Initial epicentral distribution；（b） Epicentral distribution after relocation
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图 10 研究区重定位后的震中分布图（a）及地震震中沿剖面AA′ （b），BB′ （c）和CC′ （d）剖面线两侧0.2°范围的分布
Figure 10. Distribution of earthquake epicenters after relocation （a） and cross-section of earthquakes along the profiles AA′ （b），BB′ （c） and CC′ （d） each side of 0.2° distance
表 1 本文使用计算的R量规函数表
Table 1 Rcalibration functions in this study
震中距Δ/km R 震中距Δ/km R 震中距Δ/km R 震中距Δ/km R 0—5 2.0 40 2.8 85 3.3 150 3.7 10 2.0 45 2.9 90 3.4 160 3.7 15 2.1 50 3.0 100 3.4 170 3.8 20 2.2 55 3.1 110 3.5 180 3.8 25 2.4 60 3.2 120 3.5 190 3.9 30 2.6 70 3.2 130 3.6 20 3.9 35 2.7 75 3.3 140 3.6 210 3.9 
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