Despite repeated heavy rains in California in 2023, they hardly helped to recharge aquifers that were pulled down by decades of drought and human pumping, new research reveals I’m doing it.
About a third of Los Angeles’ water supply is susceptible to long, dry spells and comes from underground water. However, in the first three months of 2023, a long, narrow weather system filled with water vapor caused rainfall on the West Coast. Then, in August, Hurricane Hillary started raining in Southern California. The statewide, rainfall in the year was well above the average of twice the 20th century. Overall, the August precipitation of January added over 90 billion gallons of water to water reservoirs in the Los Angeles area.
That moisture has almost completely recharged aquifers near the surface of the area.. However, Stanford seismologist William Ellsworth and his team report on February 13th, the deeper water-containing layers rarely received relief. Science.
To make that assessment, Ellsworth and his colleagues saw how water that had penetrated previously dry layers of permeable rocks affected the velocity of seismic waves moving them. . Previous teams have used constantly existing seismic noise, both from small earthquakes and human causes such as traffic activity, to map faults and other underground characteristics.
What many researchers consider as seismic noise is “free information, and it’s on Earth every day,” says Ellsworth. “It’s really exciting to be able to do something with that.”
By analyzing vibrations at different frequencies, Ellsworth and his team can identify changes caused by water infiltration as hundreds of meters below the surface.
Overall, the team points out that only about 25% of the water lost from local aquifers since 2006 was replenished by the 2023 storm.
“It’s extremely exciting to take 3D photographs of aquifer reservoir storage over time,” says Roland Bürgmann, a geophysicist at the University of California, Berkeley. This technique is promising, but many regions lack the large, dense network of seismic instruments that California performs. However, in these areas, researchers may be able to extract useful information from underground fiber optic networks with appropriate sensors.
