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

北加州沿海地区北纬39oN ~ 42oN是Mendocino三联结（MTJ）活动构造体制从俯冲到转换运动突然转变的区域。对这一地区的地壳和上地幔结构的了解，与板块构造史、地质结构、地震活动、热流入的时间和程度以及随之而来的地表火山活动的信息相结合，对控制大陆生长和演化的过程产生了限制。由于三重连接点一直沿着北美海岸向北迁移，对该地区地壳结构和演化的了解将有助于了解整个美国西海岸大陆边缘的地质历史，并有助于更好地评估以卡斯卡迪亚俯冲带和北部圣安德烈亚斯断层系统为代表的地震危险性。1993年和1994年，主要研究人员收集了一个大孔径地震剖面网络，对加利福尼亚北部和邻近大陆边缘的地壳和上地幔结构进行成像。这些数据包括大约650公里的陆上地震折射/反射数据，2000公里的海上多通道地震（MCS）反射数据，以及同时记录陆上和海上MCS气枪源以获得大孔径数据。来自超过12个机构的科学家参与了数据采集，由来自俄勒冈州立大学、里海大学、赖斯大学和斯坦福大学以及美国地质调查局的主要研究人员组成的团队领导。该合同为大陆动力项目提供了第四年的支持，允许主要研究人员完成数据分析和展示。还提供了一个研讨会的支持，在此期间，他们将与对地质、地质动力学和与北美西部边缘板块相互作用有关的自然灾害问题感兴趣的地球科学家更广泛的社区讨论他们的地震学结果。＊＊＊

9527001 Trehu The coastal region of northern California from latitude 39oN to 42oN represents a region in which the active tectonic regime changes abruptly from subduction to transform motion at the Mendocino Triple Junction (MTJ). Knowledge of the crustal and upper-mantle structure in this region, when combined with information on the plate-tectonic history, geologic structure, seismic activity, and timing and extent of heat influx and consequent surface volcanism, places constraints on the processes that control continental growth and evolution. Because the triple junction has been migrating north along the coast of North America, an understanding of crustal structure and evolution in this region will provide insights into the geologic history of the entire U.S. west coast continental margin and will contribute to better assessments of the seismic hazards represented by the Cascadia subduction zone and northern San Andreas Fault system. In 1993 and 1994 the principal investigators collected a network of large-aperture seismic profiles to image the crustal and upper- mantle structure beneath northern California and the adjacent continental margin. The data include approximately 650 km of onshore seismic refraction/reflection data, 2000 km of offshore multichannel seismic (MCS) reflection data, and simultaneous onshore and offshore recording of the MCS airgun source to yield large-aperture data. Scientists from more than 12 institutions were involved in data acquisition, which was led by a team of principal investigators from Oregon State, Lehigh, Rice, and Stanford Universities and from the U.S. Geological Survey. This award provides a fourth year of support from the Continental Dynamics program to permit the principal investigators to complete data analysis and presentation. Support for a workshop is also provided during which they will discuss their seismological results with the broader community of earth scientists interested in geological, geod ynamic, and natural hazard issues associated with plate interactions in along the western margin of North America. ***