EAPSI:Aquifer System Storage Response to Canterbury Earthquake Sequence using Satellite Radar and Observation Well Time Series Data

Miller Megan M, Tempe AZ

Investigators

Abstract

The 2010-2011 Canterbury, New Zealand earthquake sequence prompted a significant hydrologic response in the form of groundwater level variations due to ground shaking. It is important to understand the extent to which the storage capacity of aquifers is affected, given the reliance of local populations on groundwater for drinking water supply. This award funds research to investigate the spatial extent and amplitude of the change in aquifer storativity due to the seismic activity. The research will be conducted in collaboration with Dr. Simon Cox, Principal Scientist at GNS Science and renowned expert in structural and hydrogeology. By analyzing seasonal patterns in ground uplift and well head levels, the fellow will estimate and compare elastic aquifer storativity before, during, and after the seismic sequence. This project will use the abundant satellite radar and well data available for the region, which acts as a natural laboratory to study aquifer-earthquake interactions. The findings will impact other earthquake prone regions with active groundwater usage, including Southern California and Tennessee, to enhance water management plans following major seismic events. Understanding the spatiotemporal extent of the interaction between aquifer systems and seismic faults is a key factor for mitigating hazards associated with liquefaction and enhancing water management plans. To this end imaging surface deformation with sufficient precision, spatiotemporal resolution, and spatial accuracy is integral to this effort. The fellow will use Interferometric Synthetic Aperture Radar (InSAR) datasets from two SAR satellites, ENVISAT and TerraSAR-X, in both ascending and descending acquisition geometries. The overlapping areas allow for calculating the vertical and horizontal displacement time series, capturing pre-, co-, and post-seismic deformation in two dimensions including both tectonic and hydrological signals. In addition, observation wells with dense temporal measurements are abundant in the Canterbury and Christchurch region. The elastic storage coefficient is estimated by comparing the isolated seasonal component of the vertical displacement and the observation well time series. To isolate these seasonal components in the signals, wavelet power spectra analysis is applied, and the desired seasonal time series is identified, isolated and reconstructed. To determine if any increase or decrease in storativity occurred during the earthquake sequence, a best-fit linear value relating the inputs is chosen within a 95% confidence interval. This study will use Christchurch and the Canterbury Plains as a case study that will ultimately help other regions prone to seismic hazards that rely on groundwater resources. This award under the East Asia and Pacific Summer Institutes program supports summer research by a U.S. graduate student and is jointly funded by NSF and the Royal Society of New Zealand.