Collaborative Research: Making the San Andreas Fault at the Mendocino Triple Junction: Part II

合作研究：在门多西诺三重连接处制造圣安德烈亚斯断层：第IIA部分部署了密集的宽带地震仪阵列，以调查门多西诺三重连接处的结构，门多西诺三重连接处是加利福尼亚州著名的圣安德烈亚斯断层系统的最北端。研究区域从加利福尼亚州-俄勒冈州海岸延伸到西经120度，从北纬37度延伸到43度。门多西诺三重结合部是北美、太平洋和戈尔达板块的交汇点，相对于固定的北美参考框架，随着时间的推移向北迁移。与迁徙的门多西诺三联结有关的一系列相互作用过程，从地表延伸到软流层(100公里深)，将北美岩石圈从戈达俯冲带的俯冲杂岩改造到圣安德烈亚斯转换板块边界。地幔通过控制板块强度和运动学以及从软流圈到北美板块的热量和质量通量，对MTJ附近发生的过程进行了主导控制。戈尔达地壳和上面的沉积物俯冲，并与卡斯卡迪亚俯冲带的增生地体合并，随着这些块体流入新兴的转换边缘，并构造成圣安德烈亚斯走滑系统。与此同时，戈尔达板块南面的板块缝隙开口导致软流圈上升和减压熔融，这神奇地使圣安德烈亚斯断层附近的北美板块下沉。再加工和膨胀的岩石圈增厚，形成了一个小型的门多西诺角造山高原，而侵蚀则沿着受构造控制的北向河流将上地壳的大部分流向俯冲带。在东部，戈尔达-胡安德富卡俯冲导致了喀斯喀特火山，这有助于大陆地壳的生长、分离和再循环。1993-94年广泛的活动震源研究结果在MTJ地区提供了很好的地壳控制。目前部署的宽带地震仪阵列将保留到2009年4月，以提供一个数据集，使我们能够对MTJ地区和最南端的喀斯喀特地区的地幔和下地壳的结构、组构以及地震和无地震变形进行成像。使用各种分析技术，我们将产生地壳和上地幔的三维地震速度模型，该模型将被包括在加利福尼亚州北部和俄勒冈州南部的事件和强地面运动描述中，这两个地区可能发生毁灭性的大地震。

Collaborative Research: Making the San Andreas Fault at the Mendocino Triple Junction: Part IIA dense array of broadband seismographs have been deployed to investigate the structure of the Mendocino Triple Junction, the northernmost terminus of California's famed San Andreas fault system. The study area extends from the California-Oregon coast to 120o W longitude, and from 37 degrees to 43 degrees North latitude. The Mendocino Triple Junction, the site where the North America, Pacific and Gorda plates meet, migrates northward with time relative to a fixed North American reference frame. A set of interacting processes associated with the migrating Mendocino Triple Junction, extending from the surface to asthenospheric levels ( 100 km depth), act to modify North America lithosphere from a subduction complex at the Gorda subduction zone to the San Andreas transform plate boundary. The mantle imparts a dominant control on the processes occurring near the MTJ through its control on plate strength and kinematics and the flux of heat and mass from the asthenosphere to the North American plate. Gorda crust and overlying sediment subduct and become incorporated with accretionary terranes from the Cascadia subduction zone as this mass flows into the emerging transform margin and becomes structured into the San Andreas strike-slip system. Simultaneously, slab gap opening south of the Gorda slab causes asthenospheric ascent and decompression melting, which magmatically underplates North America near the San Andreas fault. The reprocessed and inflated lithosphere thickens to create a small Cape Mendocino orogenic plateau, while erosion fluxes large fractions of the upper crust back to the subduction zone along tectonically controlled north-trending rivers. To the east, Gorda-Juan de Fuca subduction results in the Cascade volcanoes, which contribute to continental crust growth, segregation and recycling. Results of an extensive active source seismic study in 1993-94 provide excellent crustal control in the MTJ region. The broadband seismograph array now deployed will remain in place through April 2009, to provide a dataset that will enable us to image the structure, fabric, and seismic and aseismic deformation of the mantle and lower crust in the MTJ region and the southernmost Cascades. Using a variety of analysis techniques we will produce a 3-D seismic velocity model of the crust and upper mantle that will be included in event and strong ground motion characterization for northern California and southern Oregon, a site of potentially devastating great earthquakes.