Could Heavy Rainfall From A Storm Like Hilary Trigger An Earthquake?

As I write this, the U.S. Geological Survey has reported a Magnitude 5.1 earthquake 7 km southeast of Ojai, California. This report comes as Tropical Storm Hilary is moving through the region and producing extreme rainfall. Heavy rainfall will continue to be a problem for southern California and the Southwest through Sunday evening. Herein, I pose the question – “Is the southern California earthquake linked to rainfall from the tropical storm?

To be clear, I have absolutely no evidence to say “yes” to that question and to do so would be completely speculative. Scientifically, it would als be irresponsible. However, I thought that it would be informative to make you aware of scientific studies in the literature on the topic. A 2006 study published in Geophysical Research Letters was entitled, “Evidence for rainfall-triggered earthquake activity.” They found that seismic activity was highly correlated with pore pressure changes associated with diffusing rainwater. The physics get a bit complicated, but there is discussion of rainwater channeling into open fractures and precipitation into a limited number of open fractures. These processes lead to hydraulic changes that could be linked to earthquakes.

The U.S. Geological Survey has also weighed in on the topic. Their website says, “….It’s unlikely that seismic hazard is affected by precipitation. This makes sense as rainwater cannot easily percolate several kilometers below the earth’s surface to the depths where most earthquakes occur…..periods of heavy precipitation or of drought might indirectly affect earthquake-prone faults.” They say that such changes could cause changes to stresses on faults, and therefore rates of seismicity.

Researchers at Stony Brook University have also weighed in on the topic. The USGS site goes on to note, “Using computer models, they demonstrated that annual variations in stress on California’s faults are larger during years of unusually heavy precipitation or drought.” That 2021 study focused on California, but another 2021 study also found correlations between rainfall and earthquakes in China.

This is obviously speculative and ongoing research but also a teachable moment.

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