Acquisition of Long-Baseline Tiltmeters for Cascadia Slow Earthquakes

0320782墨尔本卡斯卡迪亚周期性慢地震是迄今为止利用GPS对俯冲带进行连续监测而探测到的最具地球物理意义的信号之一。然而，GPS测量值在解决瞬时蠕变过程的潜在物理问题方面存在局限性。特别是，GPS不能很好地解决垂直形变；每天平均几天的GPS解不能约束断层上非均匀滑动机制所预测的离散的、短期的滑动是否发生。这项重大研究仪器赠款支持安装五个长基线倾斜仪，以补充太平洋西北大地测量阵列(PANGA)内正在进行的GPS测量。这些仪器的空间和时间分辨率几乎比GPS高三个数量级，并将能够捕捉到伴随缓慢断裂事件的精细垂直运动和任何变形的时间变化。长基线倾斜仪将部署在普吉特湾北部地区，并与现有的庞加GPS站位于同一地点，在那里，已知的慢事件平均每14个月成核，大约1个月。第一台倾斜仪预计将于2003年秋季部署，随后将在接下来的两年内再安装四台。与正在进行的GPS测量相结合，倾斜仪的增加将使我们在位置和滑动持续时间上的分辨率分别从~50公里和几天增加到不到一公里和几十分钟。

0320782MelbournePeriodic slow earthquakes in Cascadia constitute one of the most geophysically interesting signals detected to date with continuous GPS monitoring of subduction zones. However, the GPS measurements are limited in what they can resolve about the underlying physics of the transient creep process. In particular, the vertical deformation is poorly resolved with GPS; daily GPS solutions averaged over several days cannot constrain whether slip occurs in discrete, short-lived episodes predicted by heterogeneous slip regimes on faults. This Major Research Instrumentation grant supports installation of five long baseline tiltmeters in order to supplement ongoing GPS measurements within the Pacific Northwest Geodetic Array (PANGA). These instruments have almost three orders of magnitude higher spatial and temporal resolution than GPS, and will be able to capture fine scale vertical motion and any temporal variations in deformation that accompany the slow faulting episodes. The long baseline tiltmeters are to be deployed within the Northern Puget Sound region and co-located with existing PANGA GPS stations, where the slow events are known to be nucleating on average every 14 months, give or take 1 month. The first tiltmeter is expected to be deployed in the autumn of 2003, followed by four additional installations over the following two years. In conjunction with ongoing GPS measurements, the addition of the tiltmeters will increase our resolving power in location and duration of slip from ~50 km and several days to less than a km and tens of minutes, respectively.