One-Dimensional qP-Wave Velocity Model of the Upper Crust for the West Bohemia/Vogtland Earthquake Swarm Region
One-Dimensional qP-Wave Velocity Model of the Upper Crust for the West Bohemia/Vogtland Earthquake Swarm Region
复制标题
西波希米亚/沃格特兰地震群区上地壳一维 qP 波速度模型
DOI：
10.1007/s11200-005-0024-2
复制
发表时间：
2005
影响因子：
0.9
通讯作者：
J. Janský
中科院分区：
文献类型：
--
作者：
J. Málek;J. Horalek;J. Janský
波希米亚地块西部（西波希米亚/沃格特兰地区）的特点是板内地震群相对频繁地重现，以及过去到最近地球动力学活动的其他表现。在这项研究中，我们推导出了一维各向异性qP波模型的上地壳在孕震西波希米亚/Vogtland地区的两个独立的数据集-旅行时间从控制炮和到达时间从WEBNET地震记录提取的联合反演。我们还推导了简单的一维P波和S波各向同性模型。导出这些模型的原因是：（a）到目前为止，只导出了该地区的简化地壳速度模型，均匀半空间或一维各向同性层状模型;（B）最近通过S波分裂表明该地区上地壳具有显著的有效各向异性。我们的各向异性qP波和各向同性的P波和S波速度模型都被限制在具有恒定速度梯度的四个层中。弱各向异性的P波假设。各向同性模型由9个参数表示，各向异性模型由24个参数表示。在联合反演中采用了一种新的稳健有效的优化算法-等距算法。采用两步反演算法。在第一步，各向同性的P-和S-波速度模型推导。在第二步中，它被用作一个背景模型和各向异性的参数seeed. We的一维模型是足够的上地壳在西波希米亚/Vogtland群区的深度为15公里。qP波速度模型显示出5%的各向异性，水平方向上的最小速度对应于170°的方位角。各向同性模型表明VP/VS比值随深度的变化。根据导出的各向同性和各向异性模型的震源位置之间的差异被发现是几百米。
The western part of the Bohemian Massif (West Bohemia/Vogtland region) is characteristic in the relatively frequent recurrence of intraplate earthquake swarms and in other manifestations of past-to-recent geodynamic activity. In this study we derived 1D anisotropic qP-wave model of the upper crust in the seismogenic West Bohemia/Vogtland region by means of joint inversion of two independent data sets - travel times from controlled shots and arrival times from local earthquakes extracted from the WEBNET seismograms. We derived also simple 1-D P-wave and S-wave isotropic models. Reasons for deriving these models were: (a) only simplified crustal velocity models, homogeneous half-space or 1D isotropic layered models of this region, have been derived up to now and (b) a significant effective anisotropy of the upper crust in the region which was indicated recently by S-wave splitting. Both our anisotropic qP-wave and isotropic P-and S-wave velocity models are constrained by four layers with the constant velocity gradient. Weak anisotropy for P-waves is assumed. The isotropic model is represented by 9 parameters and the anisotropic one is represented by 24 parameters. A new robust and effective optimization algorithm - isometric algorithm - was used for the joint inversion. A two-step inversion algorithm was used. During the first step the isotropic P- and S-wave velocity model was derived. In the second step, it was used as a background model and the parameters of anisotropy were sought.Our 1D models are adequate for the upper crust in the West Bohemia/Vogtland swarm region up to a depth of 15 km. The qP-wave velocity model shows 5% anisotropy, the minimum velocity in the horizontal direction corresponds to an azimuth of 170°. The isotropic model indicates the VP/VS ratio variation with depth. The difference between the hypocentre locations based on the derived isotropic and anisotropic models was found to be several hundreds of meters.