The Analysis of Seismogenic Structure of Seismic Source Area of Qingzhou ML4.1 Earthquake in Shandong
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摘要: 2022年5月2日7时53分山东潍坊青州发生ML4.1地震，基于中国地震台网中心的地震观测报告和山东数字化台网的波形资料，采用双差定位法对潍坊青州地震序列进行重新精定位，利用 P波初动方法对其中11个ML2.0以上的地震求震源机制解。利用阻尼时空应力反演方法和MSATSI软件包反演震源区局部应力场特征。经过分析得到以下结论：青州地震序列往SN向展布、倾向N。主震震源机制显示为正断，其节面Ⅰ走向263°、倾角31°、滑动角−109°，节面Ⅱ走向106°、倾角61°、滑动角−78°，局部应力场最佳主压应力轴呈NWW-SEE向（−92.19°）低倾角（16.09°）挤压，最优主张应力轴呈SSE-NNW向（0.26°）近水平（8.45°）拉张。本文推断发震断层为走向EW的隐伏断裂。Abstract: The ML4.1 earthquake occurred in Qingzhou, Weifang, Shandong province,at 7:53 a.m., on May 2, 2022. Based on the earthquake observation reports from the China Earthquake Networks Center and the digitized waveform data from the Shandong Digital Network, the double-difference localization method was used to relocate the earthquake sequence in Qingzhou, Weifang, and the P-wave initial motion method was used to determine the source mechanism solutions for 11 of the earthquakes with magnitude above ML2.0. The damped spatial-temporal stress inversion method and MSATSI software package were used to invert the local stress field characteristics in the source area. The following conclusions were obtained from the analysis. The Qingzhou earthquake sequence is orientated in the SN direction tending to the North. The focal mechanism of mainshock shows a rupture in normal type with a 263° strike, 31° dip, and −109° rake for node I, and a 106° strike, 61° dip, and −78° rake for node II. The principal compressive stress axis is in the direction of the SSE-NNW(−92.19°) with a low plunge (16.09°), and the optimal extensional stress axis is the direction of the SSE-NNW(0.26°) with a horizontal plunge(8.45°). In this paper, we concluded that the seismogenic fault is a blind fault which is trended in the direction of the E-W.
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图 2 青州地震震中及震源机制解分布图
Figure 2. The distribution of epicenter and focal mechanism solutions of Qingzhou earthquake sequence
图 3 地震断层特征分布三元图
Figure 3. A ternary diagram representing the distribution of earthquake faulting characteristics
图 4 双差重定位地震分布图
Figure 4. The location distribution of earthquakes after double-difference relocation
图 5 青州地震震源区R值和局部应力场投影
Figure 5. R-values and regional stress fields in the source area of the Qingzhou earthquake
表 1 青州地震震群震源机制解
Table 1. The focal mechanism solutions of Qingzhou earthquake swarm
序号 发震时刻 经度/（°） 纬度/（°） 深度/km 震级ML 节面Ⅰ
str/dip/rake节面Ⅱ
str/dip/rakePaz/Ppl Taz/Tpl Baz/Bpl MDB P波初动 地震类型 1 2022-05-01
T07:23:57118.268 36.550 5.0 2.1 150/90/90 15/0/135 240/45 60/45 150/0 0.21 19 R 2 2022-05-01
T07:32:34118.268 36.540 4.6 2.9 320/0/0 50/90/ -90 320/45 140/45 50/0 0.19 26 N 3 2022-05-01
T08:01:00118.270 36.545 5.0 2.4 27/75/-132 280/44/-22 256/44 147/19 40/40 0.17 18 N-SS 4 2022-05-02
T07:53:27118.266 36.530 5.0 4.1 263/31/-109 106/61/-78 43/72 187/15 280/10 0.13 30 N 5 2022-05-02
T20:31:51118.267 36.542 5.0 3.4 100/90/90 325/0/135 190/45 10/45 100/0 0.18 22 R 6 2022-05-02
T20:36:35118.265 36.545 3.9 3.0 100/90/90 325/0/135 190/45 10/45 100/0 0.12 24 R 7 2022-05-03
T00:41:23118.265 36.535 5.1 2.4 206/53/115 348/44/60 278/5 176/69 100/20 0.25 24 R 8 2022-05-03
T19:58:37118.264 36.541 5.0 2.5 182/44/120 324/53/65 72/5 174/69 340/20 0.18 22 R 9 2022-05-03
T20:50:23118.266 36.541 5.0 2.4 191/36/126 329/ 62/67 75/14 198/ 65 340/20 0.18 20 R-SS 10 2022-05-12
T18:14:36118.266 36.552 4.9 2.7 300/70/-90 120/20/-90 210/65 30/25 120/0 0.20 15 N 11 2022-05-13
T22:13:16118.270 36.551 4.0 2.3 123/31/-109 326/61/ -78 263/72 47/15 140/10 0.19 16 N 注：str、dip、rake分别是震源机制的走向、倾角、滑动角；Paz/Ppl 、Taz/Tpl 、 Baz/Bpl分别代表P轴、T轴、 B轴的方位角和倾伏角；MDB表示矛盾比。 
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表 2 青州地震序列震源机制解反演使用的一维速度模型
Table 2. The 1-D velocity model used for focal mechanisms inversion of Qingzhou earthquake sequence
参数 序号 1 2 3 4 5 6 7 8 9 10 11 12 顶层深度/km 0.0 1.0 5.0 7.0 10.1 12.0 15.0 18.0 20.0 23.0 25.0 32.0 P波速度/（km·s-1） 2.25 3.80 5.10 5.20 5.40 5.60 5.80 6.00 6.20 6.50 7.20 8.13
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表 3 青州地震震源区应力场
Table 3. The stress field in seismic area of Qingzhou earthquake
R值 最优主压应力轴（σ1） 中间应力轴（σ2） 最优主张应力轴（σ3） 方位角/° 倾伏角/° 方位角/° 倾伏角/° 方位角/° 倾伏角/° 最优解 0.51 −92.19 16.09 116.99 71.72 0.26 8.45
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