Recognizing Signatures of Slow Slip in Plate Boundary Observatory Borehole Pore Pressure Data

在过去的15-20年里，人们发现，在几天到几周（而不是几秒钟）内滑动的不寻常的大地震，在俯冲带断层上反复发生。虽然这些慢滑地震不会产生地震震动，但认识到它们的发生是很重要的，因为它们会影响到常规地震和海啸的可能性。这些慢滑地震有时与极其安静的地震隆隆声有关，但通过连续的全球定位系统监测，可以发现在专用站点发生的小运动。本研究的目的是评估一种潜在的补充方法，通过使用地下水压力数据来识别这些事件。当断层滑动时，它会像海绵一样挤压和松弛地下的水饱和岩石。利用井/钻孔内的灵敏仪器，有时可以观察到由此产生的水压变化。该项目旨在通过结合对美国西北太平洋地区卡斯卡迪亚俯冲带现有监测设施的地下水压力数据的分析，提高检测慢滑地震的能力和速度。该项目将研究和确定与断层滑动相关的水压变化，并将支持研究生进行研究，作为项目的一部分。研究结果将通过发表论文和公开演讲的方式传播。该项目将探测和分析隐藏在Earthscope板块边界观测台钻孔阵列连续孔隙压力记录中的俯冲带慢滑的可疑特征。这门科学的动机是为了提高我们对俯冲带内慢滑的时空分布的理解。断层滑动行为的水文地质特征可以为大规模慢滑动提供额外的约束，而不仅仅是地震震动检测或连续定位测量中的瞬态。然而，断层滑动的可疑孔隙压力特征必须与不相关的局部水文地质扰动和气象影响区分开来。本研究通过分析已知大规模慢滑事件中现有的井眼孔隙压力数据，并利用各种数据类型的信号处理和统计技术来提高对可疑信号的鲁棒性识别和区分，从而解决了这些问题。研究结果有望提高我们对断层滑动的水文地质响应的理解，有助于进一步评估大规模慢滑事件的时间和程度，并有可能提供一种独立于连续定位数据或地震观测的实时统计慢滑检测算法。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Within the past 15-20 years, large unusual earthquakes that slip over the course of days to weeks, rather than seconds, have been discovered to repeatedly occur along subduction zone faults. Although these slow slip earthquakes do not create seismic shaking, recognizing their occurrence is important because they can influence the potential of regular earthquakes and tsunamis. These slow slip earthquakes are sometimes associated with extremely quiet seismic rumblings, but are otherwise identified through continuous Global-Positioning-System monitoring that reveals small motions occurring at dedicated stations. The aim of this study is to evaluate a potential complementary method for identifying these events through the use of groundwater pressure data. As a fault slips, it squishes and relaxes the water saturated rocks below the ground like a sponge. With sensitive instruments within wells / boreholes, the resulting water pressure changes can sometimes be observed. This project seeks to improve the ability and speed at which slow slip earthquakes are detected by incorporating the analysis of groundwater pressure data from existing monitoring facilities along the Cascadia subduction zone within the United States Pacific Northwest. The project will study and robustly identify water pressure changes associated with fault slip and will support graduate students to conduct research as part of the project. The results will be disseminated through published papers and public presentations.This project will detect and analyze suspected signatures of subduction zone slow slip hidden within continuous pore pressure records from Earthscope's Plate Boundary Observatory borehole array. The science is motivated by an aim to improve our understanding of the temporal and spatial distribution of slow slip within subduction zones. Hydrogeologic signatures of fault slip behavior can provide an additional constraint on large-scale slow slip beyond seismic tremor detections or transients in continuous positioning measurements. Suspected pore pressure signatures of fault slip, however, must be differentiated from unrelated local hydrogeologic disturbances and meteorological effects. This study addresses these issues by analyzing existing borehole pore pressure data during known large-scale slow slip events and uses signal processing and statistical techniques with a variety of data types to improve the robust identification and discrimination of suspected signals. The results are expected to improve our understanding of the hydrogeologic response to fault slip, help further assess the timing and extent of large-scale slow slip events, and potentially provide a real-time statistically-based slow slip detection algorithm independent of continuous positioning data or seismologic observations.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.