资源环境科技发展态势分析平台

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.

Plain Language Summary Interaction between near-surface hydrological water and the solid Earth generates significant deformation in the shallow Earth. To better understand how hydrological process deforms the shallow Earth, we search hydro-related deformation recorded in the borehole strainmeters installed in Southern California and explore its physical mechanism. We observe a strong long-period (three to four years) underground deformation signal related to hydrological process at some strainmeter sites in Parkfield and Anza, California. The deformation signal exhibits compression from December 2010 to January 2011, extension till May 2011, and compression till 2014 to 2015. Similar long-period signals are also observed in rainfall, groundwater level, and soil moisture change in the same regions. At some sites with the deformation signal, similar pore pressure change is observed that correlates with the deformation signal in both time and shape, but no similar pore pressure change is also observed accompanying the deformation at other sites. These observations are explained well by a physical model in which surface hydrological water infiltrates into different depths and produces different pore pressure changes and strong hydro-related deformations, with those poroelastic responses intimately related to local hydrological properties and hydrological settings.