The South Fossa Magna, Japan, revealed by high-resolution P- and S-wave travel time tomography
The South Fossa Magna, Japan, revealed by high-resolution P- and S-wave travel time tomography
复制标题
通过高分辨率 P 波和 S 波走时断层扫描揭示日本南麦格纳窝
DOI：
10.1016/0040-1951(92)90436-a
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发表时间：
1992
期刊：
影响因子：
2.9
通讯作者：
M. Ukawa
中科院分区：
文献类型：
--
作者：
J. Lees;M. Ukawa
菲律宾海北缘与欧亚板块碰撞带的详细层析图像揭示了由地震活动推断的构造特征与P波和S波速度结构之间的高度相关性。线性层析反演覆盖了以伊豆半岛北部为中心的南大窝区150×150×60公里的区域。33个三分量台站位于目标区，从NRIESDP的地震目录中选择了3,823个高质量地震，产生了53,593个P波和50,059个S波的相位到达。模型参数化为60×60×10个直线段，每边水平2.5公里，深度5~10公里。通过最小化旅行时间残差的平方失配，得到了一维NRIESDP分层模型的三维摄动。通过在水平层内约束模型的二维拉普拉斯算子，采用正则化方法来减少噪声数据的影响。采用共轭梯度算法LSQR对大型稀疏矩阵进行求解。P波和S波的反演失配度分别降低了50%和57%，P波和S波的反演值具有很高的相关性。在5-15公里的深度范围内，两个3D图像都显示了从Suruga Bay到Mt.西北的藤川河以西向北的低速异常。富士。伊豆半岛以北有一片广阔的高速带。这些结果与之前观测到的布格重力异常相关联。从5公里深度开始，佐伽米湾下方的一个高速、向北倾斜的异常被推测为浅俯冲的PHS板块。在北面，P波反演在东山梨震群附近(深度15-32公里)观察到明显的高速带，S波反演观测到的极速带程度较小。由于该地区地震活动强烈，我们推测这就是小灵通板块向西北掠过欧洲板块的区域，高速异常代表了一个大尺度的凹凸体。在西面，在山下。在富士地区，在15到32公里的深度内观测到了广泛的低速。我们解释说，地震活动很少的深部低速构造，要么是火山弧的俯冲，要么是与热岩浆上升有关的高温区域。在伊豆半岛东部边缘的震群区附近，无论是P波还是S波的反演都在地表附近观察到了低速异常。沿伊豆半岛东部，S波像在10~20公里处有一个明显的低速异常，而P波反演的低速异常不太明显。
Detailed tomographic images of the collision zone between the northern edge of the Philippine Sea and the Eurasian plates reveal a high correlation between tectonic features inferred from seismicity and P- and S-wave velocity structures. The linear tomographic inversion covered a 150 × 150 × 60 km region in the South Fossa Magna centered on the northern Izu Peninsula. Thirty-three three-component stations were located in the target region and 3823 high-quality earthquakes were selected from the catalogues of the NRIESDP, giving rise to 53,593 P- and 50,059 S-wave phase arrivals used in the inversion. The model was parameterized by 60 × 60 × 10 rectilinear blocks, measuring 2.5 km per side horizontally and 5–10 km varying thicknesses in depth. Three-dimensional perturbations from the one-dimensional, NRIESDP, layered model were derived by minimizing the squared misfit of the travel-time residuals. Regularization was employed to reduce the effects of noisy data by constraining the two-dimensional Laplacian of the model, within horizontal layers, to be small. The large sparse matrix was solved using the conjugate gradient algorithm LSQR. Reduction of misfit was 50% for the P-wave inversion and 57% for the S-wave inversion.There is a high correlation between the P- and S-wave inversions. Between 5–15 km depth both 3D images indicate low velocity anomalies trending northward in the west along the Fujikawa, from Suruga Bay to northwest of Mt. Fuji. North of Izu Peninsula there is a broad high-velocity zone. These results correlate with Bouguer gravity anomalies previously observed. Starting at 5 km depth, a high-velocity, northeast-dipping anomaly beneath Sagami Bay is inferred to be the shallow subducting PHS plate. To the north, a high-velocity zone in the vicinity of the East Yamanashi seismic swarm (15–32 km depth) is clearly observed on the P-wave inversion and to a lesser extent on the S-wave inversion. Because of the high seismicity in this region, we speculate this is the zone where the PHS plate is grazing the EUR plate to the northwest, and the high-velocity anomaly represents a large-scale asperity. To the west, below thMt. Fuji area, a broad low velocity is observed between 15 and 32 km depth. We interpret the deep, low-velocity structure, which exhibits little seismicity, to be either the subduction of the volcanic arc, or a region of elevated temperature associated with hot rising magma. Near the swarm area on the eastern edge of Izu Peninsula, low-velocity anomalies are observed near the surface on both P- and S-wave inversions. Along the eastern part of Izu Peninsula a prominent low-velocity anomaly is observed between 10 and 20 km on the S-wave image but is less pronounced on the P-wave inversion.