Ten kilometer vertical Moho offset and shallow velocity contrast along the Denali fault zone from double-difference tomography, receiver functions, and fault zone head waves
Ten kilometer vertical Moho offset and shallow velocity contrast along the Denali fault zone from double-difference tomography, receiver functions, and fault zone head waves
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DOI：
10.1016/j.tecto.2017.09.003
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发表时间：
2017-11
期刊：
影响因子：
2.9
通讯作者：
A. Allam;V. Schulte‐Pelkum;Y. Ben‐Zion;C. Tape;N. Ruppert;Z. Ross
中科院分区：
文献类型：
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作者：
A. Allam;V. Schulte‐Pelkum;Y. Ben‐Zion;C. Tape;N. Ruppert;Z. Ross
我们利用双差断层扫描、纵波接收函数以及断层带头波分析（空间分布和时差）来检查地壳和上地幔中德纳利断层系统的结构。三种方法灵敏度互补；层析成像对 3D 地震速度结构敏感，但平滑尖锐边界，接收器函数对（准）水平界面敏感，断层带头波对（准）垂直界面敏感。结果表明，莫霍洛维奇不连续面沿成像区域德纳利断层中部 600 公里垂直偏移 10 至 15 公里，北侧莫霍面深度较浅，约为 30 公里。自动相位选择器算法用于识别约 1400 个仅在近断层站产生断层带头波的事件。在震源距离较短的情况下，在断层北侧的台站观测到头波，而较长的传播距离和更深的事件在断层南侧产生头波。这些结果表明速度对比极性随深度的反转，我们通过分别计算断层北部和南部的平均一维速度模型来证实这一点。使用 M ≥ 5.1 的远震事件，我们获得 31,400 个 P 接收器函数并应用公共转换点叠加。使用派生的 3D 断层扫描模型将结果迁移到深度。成像界面与断层扫描模型一致，显示了沿着德纳里断层中央以及亚平行海因斯溪断层（向北 30 公里处的缝合带边界）的莫霍面偏移。在东部，这个偏移是沿着托春达断层（在 2002 年 M7.9 地震期间破裂），而不是德纳利断层本身。综合结果表明，迪纳利断层带将两个不同的地壳块体分开，托奇达河段和海因斯河段是断层和白垩纪缝合带结构的重要组成部分。
We examine the structure of the Denali fault system in the crust and upper mantle using double-difference tomography, P-wave receiver functions, and analysis (spatial distribution and moveout) of fault zone head waves. The three methods have complementary sensitivity; tomography is sensitive to 3D seismic velocity structure but smooths sharp boundaries, receiver functions are sensitive to (quasi) horizontal interfaces, and fault zone head waves are sensitive to (quasi) vertical interfaces. The results indicate that the Mohorovičić discontinuity is vertically offset by 10 to 15 km along the central 600 km of the Denali fault in the imaged region, with the northern side having shallower Moho depths around 30 km. An automated phase picker algorithm is used to identify ~ 1400 events that generate fault zone head waves only at near-fault stations. At shorter hypocentral distances head waves are observed at stations on the northern side of the fault, while longer propagation distances and deeper events produce head waves on the southern side. These results suggest a reversal of the velocity contrast polarity with depth, which we confirm by computing average 1D velocity models separately north and south of the fault. Using teleseismic events with M ≥ 5.1, we obtain 31,400 P receiver functions and apply common-conversion-point stacking. The results are migrated to depth using the derived 3D tomography model. The imaged interfaces agree with the tomography model, showing a Moho offset along the central Denali fault and also the sub-parallel Hines Creek fault, a suture zone boundary 30 km to the north. To the east, this offset follows the Totschunda fault, which ruptured during the M7.9 2002 earthquake, rather than the Denali fault itself. The combined results suggest that the Denali fault zone separates two distinct crustal blocks, and that the Totschunda and Hines Creeks segments are important components of the fault and Cretaceous-aged suture zone structure.