Does heavy rain from a storm like Hillary cause an earthquake?

As I write this, the USGS is reporting a magnitude 5.1 earthquake 7 km southeast of Ojai, California. This report comes in Tropical Storm Hillary It moves through the area and produces heavy rain. Heavy rain will continue to be a problem for Southern California and the Southwest through Sunday evening. And here I ask the question: Is the Southern California earthquake related to the rainfall from the tropical storm?

To be clear, I have absolutely no evidence to say “yes” to this question, and to do so would be entirely guesswork. Scientifically, it would also be irresponsible. However, I thought it would be useful to check out the scientific studies in the literature on this topic, such as the 2006 Stady in Geophysical Research Letters Entitled “Evidence of earthquake activity caused by precipitation.” The researchers found that seismic activity was significantly related to pore pressure changes associated with precipitation diffusion. The physics gets a little complicated, but there is a discussion about directing rainwater into open fractures and precipitation into a finite number of open fractures. These processes lead to hydraulic changes that can be linked to earthquakes.

The US Geological Survey has also weighed in on this topic. that it website He says, “A seismic hazard is unlikely to be affected by precipitation. This makes sense because rainwater cannot easily percolate several kilometers below the earth’s surface to the depths where most earthquakes occur… Periods of heavy rainfall or drought may indirectly affect the earthquake-prone faults. She says such changes can affect stresses on faults and, in turn, rates of earthquakes.

Researchers at Stony Brook University have also zeroed in on this topic. The USGS website continues to note, “Using computer models, they have shown that annual pressure differences over the California faults are greatest during years of unusually heavy or dry rainfall.” This 2021 study focused on California, but another 2021 focus Stady also found associations between precipitation and earthquakes in China.

Obviously, this is speculative and ongoing research but it’s also a teachable moment.