3D Seismic Traveltime Tomography of the Central South Island, New Zealand
3D Seismic Traveltime Tomography of the
Central South Island, New Zealand
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3D 地震走时断层扫描
DOI：
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发表时间：
2010
期刊：
影响因子：
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通讯作者：
N. Brikke
中科院分区：
文献类型：
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作者：
N. Brikke
通过对新西兰南岛地球物理断面（SIGHT）地震资料的分析，采用一种新的三维层析成像反演方法FMTOMO，研究了新西兰南岛中部澳-太平洋边界的三维演化。通过对164，048个走时拾取的反演，构建了380 km长、350 km宽和56 km深的地壳和上地幔P波速度结构和界面几何形状的三维层析成像图像。拾取与测量几何体重合（共线）和倾斜（交叉线）。对走时拾取和测站高程分别进行静态校正和降低到基底水平，以消除反演过程中高度可变的沉积成分。对模型空间进行了综合测试，有助于解释解的模型特征，部分模型特征与前人的结果一致。在碰撞带的远端发现了地壳垂直速度（靠近地表为5.5 km/s，在地壳底部为6.3 km/s）。低速（5.7 km/s）侵入澳大利亚板块中地壳约20 km深处，这与澳大利亚板块的向下挠曲相一致，一个低速带（5.9 - 6.1 km/s）位于阿尔卑斯断层的东南部，这与阿尔卑斯断层低速带相一致。此外，在南岛西海岸和南阿尔卑斯山脉主分水岭之间加厚地壳上方的上地壳顶部10公里处观察到一个高速体（6.3公里/秒）。该岩体被解释为较干燥、较坚硬的片岩体。在上述高速体的东南部立即观察到低速区（5.8 km/s，达到8 km深度）。这一特征被解释为一个背剪切断层结构，通过它流体向地表逃逸。对澳大利亚板块沿着视线01的表观挠曲剖面进行挠曲分析，得出挠曲参数a为89 km，弹性厚度Te为14 km，挠曲刚度D为1.5：10^（23）N.m.。这些结果与视线02 W的弯曲分析结果一致[Harrison 1999]。随着地震波速度向南增加，上永久各向异性有明显的梯度，两个主要的SIGHT断面之间的莫霍界面的几何形状明显平滑。该项目中使用的层析成像方法证明是对该地区其他粗尺度和细尺度地震研究的补充，因为它显示了这些研究所没有看到的特征。尽管界面反演过程在软件中仍有待完善，但速度反演产生了令人满意的解模型。
The three-dimensional (3D) evolution of the Australian-Pacifi c late boundary in the central South Island of New Zealand is investigated by analysing seismic data from the South Island GeopHysical Transect (SIGHT) project and by using a novel 3D tomography inversion method, FMTOMO. A 380 km-long, 350 km-wide and 56 km-deep 3D tomography image of the P-wave velocity structure and interface geometry of the crust and upper-mantle is constructed by inverting for 164,048 traveltime picks. The picks are both coincident (in-line) and oblique (cross-line) to the survey geometry. The traveltime picks and station elevations were static corrected and reduced to basement level, respectively, to eliminate the highly variable sedimentary component of the inversion process. Synthetic testing of the model space was carried out to help the interpretation of the solution model features. Some model features are consistent with previous results. Usual crustal velocities (5.5 km/s close to the surface and 6.3 km/s at the bottom of the crust) are found at distal ends of the collision zone. Lower velocities (5.7 km/s) intrude the mid-crust of the Australian plate to depths of about 20 km, which is consistent with the downward flexure of the Australian plate. A low velocity zone (5.9 - 6.1 km/s) is situated to the southeast of the Alpine fault, which is consistent with the Alpine fault low velocity zone. Furthermore, a high-velocity body (6.3 km/s) is observed in the top 10 km of the upper-crust immediately above the thickened crust between the west coast of the South Island and the Main Divide of the Southern Alps. This body is interpreted as a drier, more rigid body of schist. A zone of low velocity (5.8 km/s reaching 8 km depth) is observed immediately to the southeast of the aforementioned high velocity body. The feature is interpreted as a back-shearing faulting structure through which fluid escape towards the surface. A flexural analysis of an apparent flexure profile of the Australian Plate along SIGHT line 01 yielded a flexural parameter, a, of 89 km, an elastic thickness, Te, of 14 km and a flexural rigidity, D, of 1.5 : 10^(23) N.m. These results are consistent with results of a flexural analysis of SIGHT line 02W [Harrison 1999]. The following features are derived from the solution model. An apparent gradient in uppermantle anisotropy is observed with seismic velocities increasing towards the south of the model. Also, the geometry of the Mohorovicic discontinuity is apparently smooth between the two main SIGHT transects. The tomography method used in this project proves to be complementary to other coarser-scale and finer-scale seismic studies of the region in that it brings out features that were not seen by them. Notwithstanding that the interface inversion process remains to be perfected in the software, the velocity inversion produced a satisfactory solution model.