Collaborative Research: Lithospheric Evolution in Response to Triple Junction Migration: Seismic Images of the Mendocino Triple Junction Region

美国北方加州从北纬38度开始的沿海地区 到41 oN代表了一个区域， 突然从俯冲转变为 门多西诺三重结（MTJ）。 因为三联点是 沿着北美海岸向北迁移 地壳和上地幔结构的变化将提供 深入了解整个美国西海岸的构造演化 大陆边以及全世界其他收敛边。 该项目包括一个综合地震实验， 地壳和上地幔的结构， 在MTJ通过之后。 这项研究代表了一个重要组成部分， 一个长期的，多学科的努力， 研究人员利用这个定义明确的系统作为一个原位 实验室研究相关的物理和化学过程 地幔上涌、熔体分离和迁移、构造 加积作用和地壳变形的转换和会聚作用 构造环境，并评估这些影响 大陆的生长和演化。 该研究包括两个领域的季节。 一个赛季涉及 采集8个多道地震剖面， 对地壳深部结构进行成像：1）Pt.竞技场盆地 安德烈亚斯断层，以及MTJ南部的灭绝海沟; 2） 门多西诺转换断层; 3）鳗鱼河流域和卡斯卡迪亚 俯冲带以北的MTJ。 剖面与威尔斯井相交 以提供地层控制。 海底水听器也将记录MCS剖面 和地震仪，以及部署在岸上的REFTEK地震仪， 提供互补的大孔径数据。 另一季 包括获取三个陆上爆炸源折射 剖面，其中两个向北延伸的陆上/海上断面 和南部的MTF，以跨越弧前和无板 窗口 第三折射剖面将遵循 方济各会为了穿越戈尔达的南部边缘 板块，绘制地壳结构可能的沿走向变化 并将两个主要的陆上-海上剖面连接在一起。 所有 三个土地剖面将使用REFTEK进行密集测量， SGR地震仪。

The coastal region of northern California from latitude of 38o to 41oN represents a region in which the present tectonic regime changes abruptly from subduction to transform motion at the Mendocino Triple Junction (MTJ). Because the triple junction is migrating north along the coast of North America, an understanding of the crust and upper mantle structure in this region will provide insights into the tectonic evolution of the entire U.S. west coast continental margin as well as other convergent margins worldwide. This project involves an integrated seismic experiment to image the structure of the crust and upper mantle immediately before and after passage of the MTJ. This study represents an important part of a long-term, multi-disciplinary effort on the part of many investigators to exploit this well defined system as an in-situ laboratory to study physical and chemical processes associated with mantle upwelling, melt segregation and migration, tectonic accretion, and crustal deformation in both transform and convergent tectonic settings, and to evaluate the implications of these processes for continental growth and evolution. The study encompasses two field seasons. One season involves acquisition of eight multichannel seismic (MCS) profiles designed to image deep crustal structure beneath: 1) Pt. Arena basin, San Andreas fault, and extinct trench south of the MTJ; 2) the Mendocino Transform fault; and 3) the Eel River basin and Cascadia subduction zone north of the MTJ. The profiles intersect wells both north and south of the MTJ to provide stratigraphic control. The MCS profiles will also be recorded on ocean-bottom hydrophones and seismographs and on REFTEK seismographs deployed onshore to provide complementary large aperture data. The other season involves acquisition of three onshore explosive-source refraction profiles, two of which extend onshore/offshore transects shot north and south of the MTF, in order to cross the fore-arc and slabless window. The third refraction profile will follow the trend of the Franciscan terrane in order to cross the southern edge of the Gorda plate, map possible along-strike variations in crustal structure and tie together the two primary onshore-offshore profiles. All three land profiles will be densely instrumented with REFTEK and SGR seismographs.