Measuring Sea Floor Motion: New Technology for Continental Margin Geodesy

2004年（苏门答腊）和2011年（日本）的大地震和海啸给我们敲响了警钟，我们估计未来地震震级和海啸潜力的能力很弱。在这种具有挑战性的环境中，测量海上应变积累的困难是一个促成因素。本研究将为浅海陆架环境下的海底运动和变形测量提供新技术，包括在俯冲带浅海关键区域的应变积累和释放。如果成功，这项拟议中的技术可以加强目前在太平洋西北部卡斯卡迪亚俯冲带的陆地监测，这是美国的一个关键优先事项，因为未来这里可能发生大地震和海啸。现有的海底大地测量技术在灵敏度、漂移和成本方面存在局限性，限制了精确、长期、连续和空间密集的观测。在浅层大陆架环境中尤其如此，因为海洋的盐度和温度变化意味着水中的声速变化很大，这对声学测距技术提出了挑战，而且海洋瞬变现象可能会混淆对海底压力记录的解释。我们建议开发一种适用于浅层（小于200米）大陆架环境的新型海底大地测量系统。我们的概念是基于一个成功的意大利设计，将高精度GPS安装在半刚性结构上，系泊在海底。该系统已在一座活火山侧面水深100米的地方进行了测试。这种仪器网络在经济上是可行的（船舶操作只需要初始安装和定期维护，不需要数据检索），并承诺精确、准确、连续、实时的变形测量，其保真度几乎相当于陆基GPS网络。本研究将开发并演示这样一个系统。

The giant earthquakes and tsunamis of 2004 (Sumatra) and 2011 (Japan) were wake up calls that our ability to estimate future earthquake magnitude and tsunami potential is weak. The difficulty of measuring offshore strain accumulation in this challenging environment is a contributing factor. The proposed research will lead to new technology for measurement of sea floor motion and deformation in the shallow continental shelf environment, including strain accumulation and release in the critical shallow offshore region of subduction zones. If successful, the proposed technology could augment current on-land monitoring in the Cascadia subduction zone in the Pacific Northwest, a key US priority because of the likelihood of a major earthquake and tsunami here in the future. Existing technology for sea floor geodesy has limitations in terms of sensitivity, drift, and cost, limiting precise, long term, continuous, and spatially dense observations. This is especially true in the shallow continental shelf environment, where salinity and temperature variations in the ocean mean that the speed of sound in water is highly variable, challenging acoustic ranging techniques, and where oceanographic transients can confuse interpretation of sea floor pressure records. We propose to develop a new type of sea floor geodetic system, suitable for the shallow (less than 200 m) continental shelf environment. Our concept is based on a successful Italian design that uses high precision GPS mounted on a semi-rigid structure, moored to the sea floor. The system has been tested at 100 meters water depth on the flank of an active volcano. A network of such instruments would be economically feasible (ship operations are only required for initial installation and periodic maintenance, not data retrieval) and promises precise, accurate, continuous, real time deformation measurements, with fidelity nearly equivalent to land-based GPS networks. This research will develop and demonstrate such a system.