Correlation between changes in groundwater levels and surface deformation from GPS measurements in the San Gabriel Valley, California

Abstract

Changes in groundwater levels cause water‐bearing basins to deform. Here we provide a detailed history of horizontal surface displacements in the San Gabriel Valley, California, which we show are highly correlated with the water level changes measured at a nearby well: correlation coefficient of 0.96 ± 0.01. We use the surface response from a one year period during which water level change in the nearby well was over 16 m, to monitor the deformations over a 14 year period from 1998 to 2011. The water level changes lead surface deformation by 21 days, but the significance of the offset is only weakly supported (p‐value = 0.129). The projection method can be used as a real‐time monitoring or detection system for deformation caused by a variety of mechanisms such as fluid injection and removal (groundwater development, oil production, carbon sequestration), and by seismic and volcanic activity.

Tracking Groundwater Levels Using the Ambient Seismic Field

“…GPS stations recorded more than 40 mm of uplift in the central part of the SGV (Ji & Herring, 2012;King et al, 2007). Groundwater levels rebounded in the winter of 2004-2005 due to 1 m of total precipitation, the highest amount of rainfall in 100-years in Los Angeles.…”

“…Compounding this is the role of climate change, which has lead to more frequent and pronounced dry and hot years, along with stronger extreme precipitation events in places like California (Dettinger et al, 2011;Swain et al, 2016;Teng & Branstator, 2017). Surface displacements measured by GPS provide high temporal but sparse spatial resolution of groundwater level changes (Bawden et al, 2001;Ji & Herring, 2012;King et al, 2007), while those measured by Interferometric Synthetic-Aperture Radar bring high spatial resolution but limited temporal resolution (Chaussard et al, 2017;Galloway & Hoffmann, 2007;King et al, 2007). Surface displacements measured by GPS provide high temporal but sparse spatial resolution of groundwater level changes (Bawden et al, 2001;Ji & Herring, 2012;King et al, 2007), while those measured by Interferometric Synthetic-Aperture Radar bring high spatial resolution but limited temporal resolution (Chaussard et al, 2017;Galloway & Hoffmann, 2007;King et al, 2007).…”

Episodic inflation events at Akutan Volcano, Alaska, during 2005–2017

“…We have developed an efficient monitoring and detection technique, called the Targeted Projection Operator (TPO) [Ji and Herring, 2012;Ji et al, 2013], which is a kind of matched filter. Moreover, detecting anomalous deformation signals could provide timely alert for impending eruptions and thus reduce volcanic risks.…”

“…Moreover, detecting anomalous deformation signals could provide timely alert for impending eruptions and thus reduce volcanic risks. TPO has been successfully applied to monitor volcanic activity in Long Valley Caldera, California [Ji et al, 2013] and groundwater activity in the San Gabriel Basin, California [Ji and Herring, 2012]. With GPS data, the TPO detects a spatial pattern of surface deformation similar to a predefined (or targeted) pattern, using a simple projection method.…”

Analysis of systematic differences from GPS-measured and GRACE-modeled deformation in Central Valley, California

“…Based on the theory, simulations of groundwater induced surface motions have been validated to be useful by comparing with GPS and InSAR data. Groundwater rise will uplift the surface, whereas groundwater depletion will induce land subsidence (Galloway et al, 1999;Bawden et al, 2001;King et al, 2007;Ji et al, 2012;Galloway et al, 2013), which means GPS observations keeps consistent with the groundwater variation. Figure 7 is a conceptualization of this process.…”