Establishing a Long-Term Geodetic Network at the East Pacific Rise Ridge 2000 Integrated Studies Site

摘要世界上大部分板块边界都淹没在海洋之下，人们对这些边界如何适应月到年时间尺度上的板块运动知之甚少。在洋中脊，随着两个大洋板块的分离和岩浆从脊下的地幔上涌中流出，新的洋壳形成。 陆地上活火山下的岩浆运动已经用GPS和干涉合成孔径雷达等各种大地测量技术进行了跟踪，但是，迄今为止，在大洋中脊下提取岩浆的限制很少。 在地壳内部和壳幔边界都发现了熔融（岩浆）透镜体，在地壳岩浆透镜之下还发现了低地震速度浆（部分熔融）带。 在脊顶的喷发可能会进入这些熔体透镜体，但与脊顶下的岩浆运动有关的基本尺度仍然不清楚。在这项研究中要解决的问题包括：1）有多少体积的地壳熔体透镜是由一个爆发？熔融的透镜从上涌地幔中得到补充的速度有多快？喷发是否取决于浅岩脉中岩浆的水平迁移？2.）山脊的流变结构是什么，包括低粘度糊状区的宽度？ 火山爆发期间和之后地壳的力学行为是什么？3.）第三章当下面的岩浆透镜演化时，喷口是否会改变温度、化学物质流速和位置？我们计划通过监测2006年初发生的一次火山喷发附近的EPR上9degrees50'N海底的垂直位移来解决这些问题。 我们将在三次活动式勘测中使用移动的压力记录仪（MPR）测量不同海底位置之间的相对水压，以确定海底基准点相对高程的变化。 由于岩浆的浮力，地表变形直接反映了地表以下岩浆的运动。 我们希望跟踪岩浆在喷发和筑堤事件之间的逐渐运动。 我们计划比较这个快速扩张的山脊段下的过程，这是由一个连续的，线性的熔体，火山在其他地方，通常有一个集中的岩浆源。 岩浆房喷发后的补给的时间和空间尺度将取决于下面的糊状带的物理特性，并提供洞察周围地壳的流变学。 当与将于2007年2月部署的同位阵列底部压力记录仪（BPR）配对时，将提供幕式和长期变形信息，以每小时到每年的时间尺度跟踪岩浆运动。 这将使我们能够与其他研究人员合作，研究系统之间的关系，例如岩浆运动之间的相互作用，热液喷口系统的变化和微震活动。更广泛的影响这项工作将建立长期大地测量监测的基础设施，并开始积累大地测量时间序列。 洋脊系统的所有方面都受到地壳内岩浆运动的热量的影响或驱动，这使得这项工作对于理解所有洋脊系统和过程非常重要。从Zumberge博士那里借用仪器将促进我们两个机构之间的合作。 将通过同行评审的出版物和在科学会议、跨学科会议和其他大学的研讨会上的演讲来公开传播这项工作。 我们将与山脊2000教育和推广办公室合作，教育公众了解这个项目在理解山脊系统方面的重要性，以及这项工作如何融入更大的图景。

Abstract Most of the world's plate boundaries are submerged beneath the oceans, and little is known about how these boundaries accommodate plate motion on monthly to yearly time scales. At mid-ocean ridges, new oceanic crust is formed as two oceanic plates move apart and magma is tapped from mantle upwelling beneath the ridge. Magma movement beneath active volcanoes on land has been tracked using a variety of geodetic techniques such as GPS and InSAR, however, to date there are few constraints on magma extraction beneath mid-ocean ridges. Lenses of melt (magma) have been identified both within the crust and at the crust mantle boundary, as well as a low seismic velocity mush (partial melt) zone beneath the crustal magma lens. Eruptions at the ridge crests presumably tap into these melt lenses but the fundamental scales associated with magma movement beneath ridge crests remain obscure. The questions to be addressed in this study include 1) What volume of the crustal melt lens is tapped by an eruption? How quickly does the melt lens get replenished from upwelling mantle? Does an eruption depend on horizontal transport of magma in a shallow dike? 2.) What is the rheologic structure of the ridge, including the width of the low viscosity mush zone? What is the mechanical behavior of the crust during and after an eruption? 3.) Do vents change temperature, chemistry flow rates, and location as the underlying magma lens evolves?We plan to address these questions by monitoring the vertical displacements of the seafloor at 9degrees50'N on the EPR in the vicinity of an eruption that occurred in early 2006. We will use a Mobile Pressure Recorder (MPR) in three campaign style surveys to measure the relative water pressure between different seafloor locations to determine changes in the relative elevation of benchmarks placed on the seafloor. Due to the buoyancy of the magma, surface deformation directly reflects the movement of magma below the surface. We expect to track the gradual movement of magma between eruption and diking events. We plan to compare processes under this fast-spreading ridge segment, which is underlain by a continuous, linear body of melt, to that of volcanoes elsewhere, which typically have a focused magma source. The temporal and spatial scales of recharging of the magma chamber post eruption will depend on the physical characteristics of the underlying mush zone and provide insight into the rheology of the surrounding crust. When paired with the co-located array Bottom Pressure Recorders (BPR) to be deployed in February 2007, both episodic and long-term deformation information will be available, tracking magma movements with hourly to yearly time scales. This will allow us, in collaboration with other researchers, to examine system relationships, such as the interplay between movements of magma, changes in hydrothermal vent systems, and microseismicity.Broader impacts This work will establish the infrastructure for long-term geodetic monitoring and begin accumulating a geodetic time series. All aspects of the ridge system are influenced or driven by the heat from magma that moves within the Earth's crust, which makes this work important in understanding all ridge systems and processes. Borrowing an instrument from Dr. Zumberge will promote collaboration between our two institutions. Public dissemination of the work will take place through peer reviewed publications and presentations at scientific conferences, interdisciplinary meetings, and seminars at other universities. We will work with the Ridge 2000 Education and Outreach office to educate the public about the significance of this project in understanding ridge systems, and how this work fits into the larger picture.