Improvement and case test of linear method for single event seismic location
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摘要: 根据大震速报和快速预警实际需要,首先对Inglada线性单事件定位方法进行了适当的改进, 使其在仅有P波到时数据的情况下也能快速定位,且求解过程仅需简单迭代而不用奇异值分解; 其次, 尝试将改进后的方法从单层均匀模型引入到分层均匀模型中的近源台网定位情形,并通过单层均匀和分层均匀两种不同模型的理论实验讨论了该方法的可行性和适用范围; 最后整合了质量高且分布较好的距离2008年汶川MS8.0地震震中最近的强震、微震, 以及川西流动台阵等观测记录资料,对汶川MS8.0主震初始破裂点的时空参数进行了多种模型的定位实验. 结果表明, 改进后的线性单事件定位方法简单、快捷、易用,可广泛应用于近源地震定位,尤其是用于无法得到S波到时的中强以上直至巨大地震的速报、地震现场流动台网的快速定位以及地震的快速预警等.Abstract: Under the necessity of earthquake rapid reporting and early warning systems, we improve the Inglada linear method for single event seismic location. After this improvement, locating easily uses a simple iteration and mean algorithm instead of a complex singular value decomposition, and only four arrival times of P wave are essential. We also try to theoretically test this method from homogeneous velocity model to layered homogenous velocity model, so as to expand the application scope of the method. Combining with the 31 high-quality arrival times of direct P waves recorded at the near-field stations in Sichuan strong motion network, Sichuan regional seismic network, western Sichuan mobile array and Zipingpu reservoir seismic network, we practically relocate the main shock of Wenchuan MS8.0 earthquake, and report the new parameters for this earthquake based on different velocity models. Theoretical tests show that this improved linear method is a simple, rapid and practical procedure for local earthquake location using a single-layer homogeneous crust model. It could be used for large earthquake rapid report, mobile seismic network fast location, and earthquake early warning for local earthquakes.
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图 1 龙门山地区区域构造、所用台站及其空间分布图 图中各种空心符号代表虽有台站,但其时间服务有明显错误或GPS故障子台,本文中其时间资料均未被采用
Figure 1. Regional tectonic background and distribution of strong motion stations(black triangle),broad-b and stations(grey square),mobile stations(black cross) and reservoir seismic stations(diamond)in Longmenshan area. Hollow symbols indicate the stations that time service is bad. Black star is the epicenter of Wenchuan MS8.0 earthquake given by this paper
图 2 分层均匀速度模型与折合单层均匀速度模型理论走时差与震源深度h、台站震中距Δ、台站海拔高程的关系(图中拐点为实际台站海拔高程影响)
Figure 2. Theoretical travel time difference between the layered homogeneous velocity model and its approximate single-layer homogenous velocity model related to focal depth h,epicentral distance Δ,and elevation of stations(see the inflexions of the curves)
表 1 文方法与Geiger法在单层均匀速度模型中理论检验结果的比较(全部31台)
Table 1 Comparison of theoretical test results between the improved linear method in this paper and the Geiger method for single event seismic location in a single-layer
表 2 龙门山断裂带的4种P波平均速度模型
Table 2 Four P-wave velocity models in Longmenshan fault zone
表 3 本文方法在分层均匀速度模型中的理论检验结果(h=18.66 km)
Table 3 Theoretical test result of the improved linear method in this paper for single event seismic location in a layered homogenous crust model(h=18.66 km)
表 4 本文方法在分层均匀速度模型中的理论检验结果(h=9.50 km)
Table 4 Theoretical test result of the improved linear method in this paper for single event seismic location in a layered homogenous crust model(h=9.50 km)
表 5 不同研究机构及团队给出的汶川MS8.0主震震源参数
Table 5 Focal parameters of Wenchuan MS8.0 main shock given by different institutions and authors
表 6 基于不同模型利用本文方法与Geiger法给出的汶川MS8.0主震的定位结果
Table 6 Relocation results of Wenchuan MS8.0 earthquake based on different velocity models using the improved linear method in this paper for single event seismic location
表 7 基于不同模型定位结果的走时残差与其方均根误差比较
Table 7 avel time residuals and their root-mean-square errors derived from different location results based on several velocity models
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田玥. 2001. 一种新的线性单事件地震定位方法[G]//北京大学政学者论文集. 北京: 北京大学: 266-276. Tian Y. 2001. A new linear method for single event seismic location[G]//Series of Selected Papers from Chun-Thsung Scholars, Peking University. Beijing: Peking University: 266-276 (in Chinese).
中国地震局监测预报司. 2009. 汶川8.0级地震科学研究报告[M]. 北京: 地震出版社: 1-2. Department of Monitoring and Prediction, China Earthquake Administration. 2009. Scientific Research Report of M8.0 Wenchuan Earthquake[M]. Beijing: Seismological Press: 1-2 (in Chinese).
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期刊类型引用(1)
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