Research

My research focuses on the interaction of the solid earth and climate - I am working to understand how aquifers respond to drought using the Earth's ambient wavefield. Specifically, I calculate the change in seismic velocity of the subsurface, dv/v, from the cross-correlation of ambient seismic noise. dv/v scales linearly with changes in groundwater level. 

San Gabriel Valley Groundwater and dv/v

In our recent paper we showed that variations in groundwater levels can be mapped using perturbations in seismic velocity (dv/v). We measure dv/v in the San Gabriel Valley, California, from cross correlation of the ambient seismic field. dv/v reproduces the groundwater level changes that are marked by the multi‐year depletions and rapid recharges, typical of California's cycles of droughts and floods. dv/v correlates spatially with vertical surface displacements and deformation measured with GPS. Our results successfully predict the volume of water lost in the San Gabriel Valley during the 2012‐2016 drought and thus provide a new, complementary approach to monitor groundwater storage.

SGV GWL
Groundwater level change in San Gabriel Valley during most recent drought (Fall 2012 - Fall 2016). Seismic stations are shown as blue triangles, groundwater wells are shown as yellow circles and “key” groundwater wells are shown as green circles.

 

DVV GWL
Relating seismic wavespeed temporal perturbation to ground water levels. Observed dv/v stacked over all station pairs (black) with modeled dv/v due to thermo-elastic strain (dashed) removed compared with groundwater change (blue) in the Baldwin Park Key Well. Grey bars indicate lowest historical water levels of the Baldwin Park Key Well. Blue patches indicate times of drought.

Wells
Groundwater levels at five key wells (thick line) in the SGV and relative groundwater level changes derived from regionalization of dv/v (thin line) at location of each well. Relative groundwater estimates from dv/v regionalization are scaled by calibration constant β and plotted at mean groundwater elevation for each well.