Collaborative Research: Constraints on Interseismic Deformation Offshore Oregon from Calibrated Continuous Pressure Records

卡斯卡迪亚俯冲带位于太平洋西北海岸，具有科学和公共利益，因为它是灾难性地震的地点，类似于过去十年在日本，智利和苏门答腊发生的地震。在陆地上，仪器网络可用于测量卡斯卡迪亚俯冲带断层上的应变积累。为了更好地了解俯冲带的动力学，并对断层每隔几百年产生的地震和海啸施加更强的约束，需要在海上进行类似的观测。 该项目使用经过校准的海底压力传感器对俄勒冈州中部海岸外的六个地点的海底高程进行精确测量。 该项目将启动一项十年期研究，以测量海底海拔的变化，这种变化是由于俯冲带断层上的应变积累和潜在释放造成的。 这项研究将限制断层锁定部分的宽度，这些锁定部分将在下一次俯冲带大地震中破裂。该项目将有两名研究生参加，每次研究考察至少有四名本科生参加，将使用高质量的近海垂直大地测量数据提供一个基线，以解决卡斯卡迪亚俯冲带锁定造成的长期应变问题，并探测缓慢滑动事件。一些先前的研究表明，海底压力测量可以检测到慢滑事件，但海底压力传感器的漂移限制了其应用于测量长期应变。华盛顿大学（UW）和斯克里普斯海洋学研究所（SIO）合作建造并成功测试了SIO海底校准压力记录仪的活动版本，即绝对海底校准压力记录仪（ASCPR）。 该仪器测量绝对压力的精度相当于水深约1厘米。 将使用ASCPR对配备有连续记录海底压力计的稳定海底基准进行重复测量，以消除压力时间序列中的漂移，并能够测量长期应变。华盛顿大学和SIO已经在俄勒冈州中部海域部署了一个由6个基准和底部压力记录器组成的垂直于沟槽的剖面。该项目支持在两年内对每个基准点进行重复的重力式绝对压力测量，以充分表征ASCPR测量的可重复性，并启动测量长期应变所需的十年研究。通过利用稳定的、未受干扰的基准进行精确的绝对压力测量，这项工作可以改变我们在海上进行长期大地测量观测的能力。正在利用补充的大地测量和物理海洋学建模研究来进一步了解预期的大地测量信号，并制定更好的方法来区分压力的大地测量和海洋学组成部分。

The Cascadia Subduction zone lies off the coast of the Pacific Northwest and is of both scientific and public interest because it is the site of catastrophic earthquakes similar to those that have occurred over the last decade in Japan, Chile, and Sumatra. On land, networks of instruments are available to measure the build-up of strain across the Cascadia subduction zone fault. Similar observations are required offshore to understand the dynamics of the subduction zone better, and to place stronger constraints on the earthquakes and tsunamis the fault produces every few hundred years. This project uses calibrated seafloor pressure sensors to make accurate measurements of the elevation of the seafloor at six sites off the coast of central Oregon. The project will initiate a decadal study that will measure changes in seafloor elevation that result from the build-up, and potentially the release, of strain across the subduction zone fault. The study will constrain the width of the locked portion of the fault that will break in the next large subduction zone earthquake. The project will involve two graduate students, and include at least four undergraduates on each research expedition.High-quality offshore vertical geodetic measurements will be used to provide a baseline suitable for resolving secular strain caused by locking across the Cascadia subduction zone, and for detecting slow slip events. Several previous studies have shown that seafloor pressure measurements can detect slow-slip events, but the drift of seafloor pressure sensors has limited their application to measuring secular strain. The University of Washington (UW) and Scripps Institution of Oceanography (SIO) have collaborated to build and successfully test a campaign version of the SIO seafloor calibrated pressure recorder, the Absolute Seafloor Calibrated Pressure Recorder (ASCPR). This instrument measures absolute pressures to an accuracy equivalent to ~1 cm of water depth. Repeat measurements with the ASCPR on stable seafloor benchmarks equipped with a continuously recording bottom pressure gauge will be used to remove the drift from pressure time series and enable measurements of secular strain. The UW and SIO have deployed a trench-perpendicular profile of 6 benchmarks and bottom pressure recorders off central Oregon. This project supports repeat campaign-style absolute pressure measurements over two years on each benchmark to fully characterize the repeatability of ASCPR measurements and initiate a decadal study required to measure secular strain. By utilizing stable, undisturbed benchmarks to make accurate absolute pressure measurements, this effort could transform our capabilities for making long-term geodetic observations offshore. Complementary geodetic and physical oceanographic modeling studies are being used to further understand the expected geodetic signals and develop improved methods to separate geodetic and oceanographic components of pressure.