In 2023, the West Coast experienced an extraordinary weather phenomenon with the arrival of more than a dozen atmospheric rivers. Despite the significant rainfall in the first three months of the year, California's aquifers saw minimal recharge. Groundwater, which provides about one-third of Los Angeles' water supply, remains insufficiently replenished. Within this period, Southern California, including the Los Angeles area, received over 90 billion gallons of water. However, this immense deluge only restored about 25% of the water lost from aquifers since 2006.
The state saw precipitation levels well over double the 20th-century average, further amplified by Hurricane Hilary's rains in August 2023. Despite these substantial figures, the impact on aquifer recharge was notably limited. Researchers have identified a promising technique to assess this water infiltration impact using seismic waves.
William Ellsworth and his team at Stanford University spearheaded a study employing seismic waves to evaluate how water affects aquifers. The method allows researchers to observe changes caused by water infiltration up to hundreds of meters below the surface. By analyzing how water influenced the speed of seismic waves through permeable rock, they aimed to identify shifts in aquifer conditions.
"free information, which is there in the earth every day," – William Ellsworth
Ellsworth's approach relies on what he describes as seismic noise, which offers valuable insights into subsurface changes. It enables researchers to develop a three-dimensional understanding of water storage dynamics over time.
"Getting a 3-D picture of water storage in aquifers over time is pretty exciting," – Roland Bürgmann
Despite its potential, implementing this technique on a broader scale faces challenges due to the lack of sufficient seismic instruments in many regions. Nonetheless, this innovative approach provides a new perspective on understanding aquifer health and groundwater management.
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