Strong Hydro‐Related Localized Long‐Period Crustal Deformation Observed in the Plate Boundary Observatory Borehole Strainmeters

Abstract

Strong localized hydro‐related long‐period strain variations, with amplitude up to about 2,000 ns (nanostrain) (1–2 orders of magnitude larger than the tidal deformation), are observed in some Plate Boundary Observatory borehole strainmeters in Parkfield and Anza, California. The long‐period strain signals exhibit compression from December 2010 to January 2011, extension till May 2011, and compression till 2014 to 2015. The observed strain signals are accompanied by similar pore pressure change at some strainmeters and no pore pressure change at other strainmeters. Similar long‐period signals are also observed in rainfall, groundwater, and soil moisture in the same regions. Poroelastic simulations suggest that the observed long‐period strains and their relationships with rainfall and pore pressure could be explained by a rainfall–hydrological diffusion–poroelastic deformation mechanism. Our study indicates that poroelastic response to hydrological water would generate significant underground deformation, which is intimately related to local hydrological properties and settings.

Months‐Long Crustal Deformation Driven by Aseismic Slips and Pore Pressure Transients Triggered by Local and Regional Earthquakes

“…Based on the above modeling results, we propose a mechanism that the mainshock event instantly triggers an aseismic slip on a local fault and alters the hydrological conditions in the region; the change of hydrological condition likely involves removal of a barrier in the groundwater channel by the seismic waves and/ or coseismic stress changes of the mainshock (Text S5; Brodsky et al, 2003), and results in postseismic pore pressure changes that produce poroelastic deformation in the region, while the aseismic slip produces elastic deformation (Figure 4). Such mechanism is consistent with the results of our previous study on hydro-related strain at Anza which shows that underground pore fluid could produce significant poroelastic deformation (Lu & Wen, 2018). For the current study, additional supporting evidence for hydro-related strains includes: (a) Observation of the postseismic pore pressure change at the multiple strainmeters suggests a broad distribution of pore pressure change, which could produce poroelastic deformation in a broad region, (b) the significant differences of the postseismic pore pressure change observed among the strainmeters suggest a significant spatial variation of the pore pressure change, which would further promote the poroelastic deformation, and (c) the consistent correlations between pore pressure changes and postseismic strains observed after all the four earthquakes support the inference of a likely connection between the two observations.…”

“…Despite the point source simplification, the existence of the aseismic slip and the decomposition of the slip-related strain from the hydro-related strain are well resolved by the observed residual strain and pore pressure data. Second, we have assumed that the strain induced by the pore pressure change is proportional to the pore pressure change recorded at the site, while the strain should be related to the spatial and temporal changes of pore pressure in the region (Lu & Wen, 2018).…”

“…By contrast, postseismic deformation produced by pore fluid flow has been reported by only a few studies (e.g., Hughes et al., 2010; Jónsson et al., 2003; Peltzer et al., 1998), although significant changes in hydrological conditions have been reported after some earthquakes (Manga & Wang, 2007; Matsumoto et al., 2003; Roeloffs, 1998; C. Y. Wang et al., 2004) and crustal deformation related to hydrological process has been observed to be significant (Fu & Freymueller, 2012; Lu & Wen, 2018; Silverii et al., 2019; C. Y. Wang & Barbour, 2017; Zhan et al., 2017).…”

Results From a Decade of Optical Fiber Strainmeters at Piñon Flat Observatory

“…Records for the water table from the strainmeter borehole (named "GSD") as well as a nearby well (named "CIC") are displayed in the figure and suggest that there is a possible correlation between water table and vertical strain. While the correlation is not perfect, it is not unexpected to see such a relationship as it has been observed in multiple cases elsewhere (e.g., Barbour & Wyatt, 2014;Evans & Wyatt, 1984;Lu & Wen, 2018;Neely et al, 2021). The relationship is complex and depends on both the rheological and hydrological properties of the local material as well as the details of fractures and their connections to wells.…”

Muometric positioning system (μPS) with cosmic muons as a new underwater and underground positioning technique

“…Precise underwater and underground positionings are required for submarine 1 – 3 or submerged 4 , 5 volcano monitoring, slow slip observations 6 , coseismic displacement measurements 7 – 9 , and multiple engineering purposes 10 – 12 . These works have utilized the techniques of a combination of GPS and the acoustic positioning system, ocean bottom pressure gauges, autonomous-underwater-vehicles-based sonar bathymetry, Wi-Fi location technology, radio-frequency identification technology, strainmetry, and inertial navigation.…”