地震研究

基于2009年1月1日至2013年5月6日四川地震台网、重庆地震台网记录的龙门山断裂带南段587个地震的5 012个P波到时数据,利用最小一维速度模型方法反演了龙门山断裂带南段地壳一维P波速度模型及台站校正值,并将其应用到龙门山地区地震重定位中。结果表明,台站校正值表征出龙门山断裂带南段地表速度结构的横向不均匀性,青藏高原的彭灌杂岩体及宝兴杂岩体在近地表表现为高速异常,而四川盆地的第四纪沉积表现为低速异常。重定位后地震震源在北西向的剖面上呈明显的条带状并向北西倾斜,该地震带与宝兴杂岩下方的滑脱带延伸趋势一致。此外,该地震带上方分布着一条反冲地震带,两地震带呈“y”型分布,这可能是宝兴杂岩上方的岩层为调节逆冲过程受阻而产生的反冲运动所致。

Using 5 012 P wave arrival times of 587 earthquakes occurred at the south segment of Longmenshan Fault recorded by Sichuan and Chongqing Seismic Network from Jan.1, 2009 to May.6, 2013, we obtained the P wave velocity model and station correction value by the minimum 1D velocity model method, which are applied in earthquake relocation in Longmenshan area. The result shows that the station correction value represents the lateral heterogeneity of surface velocity structure in the south segment of Longmenshan Fault. There appeared the high velocity anomaly in the near surface of Pengguan and Baoxing complex rock bodies in Tibet plateau, whereas obvious low velocity anomaly in Quaternary deposit of Sichuan basin. The distribution of epicenter after relocation shows an obvious banding and dips to NW in NW profile, which is corresponding to the extending trend of slip band below Baoxing complex rock body. Above the NW dipping seismic belt, there is a recoil seismic belt, and these two seismic belts distribute in “y” type, which may due to the recoil movement generate from that the rock stratum above Baoxing complex rock body blocked in the process of adjusting the thrusting.

引言
1 计算方法
2 数据资料与反演计算
3 结论

图1 研究区域内地震、台站及二维射线分布图<br/>Fig.1 Distribution of earthquakes,stations and two-dimensional ray path in the study area

图1 研究区域内地震、台站及二维射线分布图
Fig.1 Distribution of earthquakes,stations and two-dimensional ray path in the study area

图2 震相走时曲线<br/>Fig.2 Travel time curve of seismic phase

图2 震相走时曲线
Fig.2 Travel time curve of seismic phase

图3 初始震源深度分布<br/>Fig.3 Distribution of the initial focal depth

图3 初始震源深度分布
Fig.3 Distribution of the initial focal depth

图4 初始一维速度模型<br/>Fig.4 Initial 1D velocity model

图4 初始一维速度模型
Fig.4 Initial 1D velocity model

图5 一维输出速度模型<br/>Fig.5 1D output velocity model

图5 一维输出速度模型
Fig.5 1D output velocity model

图6 速度模型对应地震走时均方根残差(RMS)变化<br/>Fig.6 The corresponding variation of travel time root mean square residuals(RMS)to velocity model

图6 速度模型对应地震走时均方根残差(RMS)变化
Fig.6 The corresponding variation of travel time root mean square residuals(RMS)to velocity model

表1 初始模型与最小一维模型速度值对比<br/>Tab.1 The contrast between the initial velocity model and minimum 1D velocity model

表1 初始模型与最小一维模型速度值对比
Tab.1 The contrast between the initial velocity model and minimum 1D velocity model

图7 最小一维速度模型稳定性检验<br/>Fig.7 Test on the stability of minimum 1D velocity model

图7 最小一维速度模型稳定性检验
Fig.7 Test on the stability of minimum 1D velocity model

表2 台站校正值<br/>Tab.2 Station correction value

表2 台站校正值
Tab.2 Station correction value

图8 研究区域重定位前后地震分布图及震源深度分布直方图(a)重定位前后震中分布;(b)重定位前后震源在经度方向的投影;(c)重定位前后震源在纬度方向的投影; (d)震源深度分布直方图<br/>Fig.8 Distribution of hypocenter before and after relocation and the histogram of focal depth in the study area (a)distribution of hypocenter before and after relocation;(b)projection of hypocenter on longitude direction before and after relocation;(c)projection of hypocenter on latitude direction before and after relocation;(d)the histogram of focal depth

图8 研究区域重定位前后地震分布图及震源深度分布直方图(a)重定位前后震中分布;(b)重定位前后震源在经度方向的投影;(c)重定位前后震源在纬度方向的投影; (d)震源深度分布直方图
Fig.8 Distribution of hypocenter before and after relocation and the histogram of focal depth in the study area (a)distribution of hypocenter before and after relocation;(b)projection of hypocenter on longitude direction before and after relocation;(c)projection of hypocenter on latitude direction before and after relocation;(d)the histogram of focal depth

图9 A-AA(a)及B-BB(b)剖面上震源深度分布图<br/>Fig.9 Distribution of epicentre depth at profiles of A-AA(a)and B-BB(b)

图9 A-AA(a)及B-BB(b)剖面上震源深度分布图
Fig.9 Distribution of epicentre depth at profiles of A-AA(a)and B-BB(b)

图10 使用模型6(a)及最小一维速度模型(b)重定位后走时均方根残差(RMS)分布直方图<br/>Fig.10 Histogram of travel time root mean square(RMS)residual distribution after relocating using Model 6(a)and minimum 1D velocity model(b)

图10 使用模型6(a)及最小一维速度模型(b)重定位后走时均方根残差(RMS)分布直方图
Fig.10 Histogram of travel time root mean square(RMS)residual distribution after relocating using Model 6(a)and minimum 1D velocity model(b)

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备注

引言

1 计算方法

2 数据资料与反演计算

3 结论

期刊信息