Collaborative Research: A GPS Network to Determine Crustal Motions in the Bedrock of the West Antarctic Ice Sheet: Phase I-Installation

该奖项由极地计划办公室的南极地质和地球物理计划提供，支持一项合作研究计划，以启动全球定位系统（GPS）网络，测量南极西部冰盖（WAIS）周围和下面基岩的地壳运动。评估WAIS基岩的构造运动和冰致地壳运动的作用是理解WAIS过去、现在和未来的动力学及其在未来全球变化情景中的潜在作用的关键目标，也是提高我们对南极洲在全球板块运动中的作用的理解的关键目标。南极洲西部活跃构造活动的程度很大程度上是推测性的，因为很少有数据限制其地理分布、方向或变形速率。最近的地球物理资料表明，活跃的冰下火山作用和沉积盆地对冰流的控制，突出了活动构造作用和基岩对西洋带的影响。基岩地壳运动对西洋带及其未来动力学的影响是一个基本问题。现有的GPS项目仅位于冰盖的边缘，不涉及区域情况。重要的是，要开始在WAIS周围和内部的基岩上进行基线GPS测量，以便为探测变化奠定基础。为了测量地壳运动，该项目将在2001-2002年南极野外季节开始的两年时间里，在西南极洲内部（大约相当于美国从落基山脉到太平洋海岸的面积）建立一个至少有15个GPS站点的西南极洲GPS网络（WAGN）。规划的网络使用多模态占用策略（MOST）设计，其中少数独立的GPS“巡回”接收器在每个站点相对较短的时间内对连续的GPS站网络进行差分测量。这一试验策略已在加利福尼亚、南美、西南太平洋和中亚的一些项目中成功实施，它最大限度地减少了后勤需求，这是在WAIS基岩的分散和偏远露头地区应用GPS大地测量学的基本要素。WAGN项目将与通过斯科舍弧连接南极半岛和南美洲的GPS网络（斯科舍弧GPS项目（SCARP））相结合。它还将与目前测量罗斯湾运动的台站以及南极研究科学委员会（SCAR）大地测量学和地理信息系统工作组（Working Group on Geodesy and geographical Information Systems）在整个大陆范围内的GIANT项目进行对接。GPS网络将建立在坚固的岩石露头上的永久性纪念碑上，这些纪念碑对漫游GPS位置的设置误差接近于零，当未来的技术使整个南极洲西部的自主操作和卫星数据链接既可靠又经济时，这些纪念碑可以直接转换为连续的GPS站点。规划的网络是对现有和规划的连续网络的补充和依赖。由于成本和物流的原因，目前用连续站点网络或传统活动来完成本文提出的测量是不现实的。提出的WAGN将通过填补构成西南极洲的几个离散地壳块之间的主要覆盖空白来补充现有的GPS项目，这是一个潜在基岩运动的关键区域。如果地壳运动相对缓慢，有意义的结果只能在单个资助项目最长的五年时间内开始出现。因此，该建议仅用于启动网络并在最关键的站点测试精度和速度。然而，一旦建立起来，随着时间的推移，网络将产生越来越有意义的结果。事实上，利率越慢，尽早开始测量就越重要。预计该项目的结果将启动一个反复的过程，该过程将逐步解决对板块旋转以及由冰川消融和冰块变化引起的粘弹性和弹性运动的贡献的理解。从最初重新占用最关键地点获得的速度将决定在可探测到的运动发生时重新占用整个网络的后续建议的时间。

0003861BevisThis award, provided by the Antarctic Geology and Geophysics Program of the Office of Polar Programs, supports a collaborative research program to initiate a Global Positioning System (GPS) network to measure crustal motions in the bedrock surrounding and underlying the West Antarctic Ice Sheet (WAIS). Evaluation of the role of both tectonic and ice-induced crustal motions of the WAIS bedrock is a critical goal for understanding past, present, and future dynamics of WAIS and its potential role in future global change scenarios, as well as improving our understanding of the role of Antarctica in global plate motions. The extent of active tectonism in West Antarctica is largely speculative, as few data exist that constrain its geographic distribution, directions, or rates of deformation. Active tectonism and the influence of bedrock on the WAIS have been highlighted recently by geophysical data indicating active subglacial volcanism and control of ice streaming by the presence of sedimentary basins. The influence of bedrock crustal motion on the WAIS and its future dynamics is a fundamental issue. Existing GPS projects are located only on the fringe of the ice sheet and do not address the regional picture. It is important that baseline GPS measurements on the bedrock around and within the WAIS be started so that a basis is established for detecting change.To measure crustal motions, this project will build a West Antarctica GPS Network (WAGN) of at least 15 GPS sites across the interior of West Antarctica (approximately the size of the contiguous United States from the Rocky Mountains to the Pacific coast) over a two-year period beginning in the Antarctic field season 2001-2002. The planned network is designed using the Multi-modal Occupation Strategy (MOST), in which a small number of independent GPS "roving" receivers make differential measurements against a network of continuous GPS stations for comparatively short periods at each site. This experimental strategy, successfully implemented by a number of projects in California, S America, the SW Pacific and Central Asia, minimizes logistical requirements, an essential element of application of GPS geodesy in the scattered and remote outcrops of the WAIS bedrock.The WAGN program will be integrated with the GPS network that has been established linking the Antarctic Peninsula with South America through the Scotia arc (Scotia Arc GPS Project (SCARP)). It will also interface with stations currently measuring motion across the Ross Embayment, and with the continent-wide GIANT program of the Working Group on Geodesy and Geographic Information Systems of the Scientific Committee on Antarctic Research (SCAR). The GPS network will be based on permanent monuments set in solid rock outcrops that will have near-zero set-up error for roving GPS occupations, and that can be directly converted to a continuous GPS site when future technology makes autonomous operation and satellite data linkage throughout West Antarctica both reliable and economical. The planned network both depends on and complements the existing and planned continuous networks. It is presently not practical, for reasons of cost and logistics, to accomplish the measurements proposed herein with either a network of continuous stations or traditional campaigns.The proposed WAGN will complement existing GPS projects by filling a major gap in coverage among several discrete crustal blocks that make up West Antarctica, a critical area of potential bedrock movements. If crustal motions are relatively slow, meaningful results will only begin to emerge within the five-year maximum period of time for an individual funded project. Hence this proposal is only to initiate the network and test precision and velocities at the most critical sites. Once built, however, the network will yield increasingly meaningful results with the passage of time. Indeed, the slower the rates turn out to be, the more important an early start to measuring. It is anticipated that the results of this project will initiate an iterative process that will gradually resolve into an understanding of the contributions from plate rotations and viscoelastic and elastic motions resulting from deglaciation and ice mass changes. Velocities obtained from initial reoccupation of the most critical sites will dictate the timing of a follow-up proposal for reoccupation of the entire network when detectable motions have occurred.