Pattern of Earthquakes Following Heavy Rain Raises Concern Over Possible Impending Tremors in California

Devastating earthquakes have a pattern of occurring after extended periods of heavy rain, as seen in history. This prompts worries about the possibility of tremors in California.

Parts of California have experienced one of the wettest seasons since the 1800s as a result of the recent torrential downpours.

Additionally, the National Weather Service reported that some other areas, including San Francisco, had received more than 12 inches of rain in the previous 15 days.

Storm and Earthquake Link in History

But the question is, could this torrential downpour trigger an earthquake?

The San Andreas Fault, which forms the boundary between two enormous tectonic plates beneath the Earth's surface, is the reason why the state is extremely tectonically active. Since these plates are comparatively static, heavy pressures gradually build up and can occasionally trigger extremely destructive earthquakes.

Additionally, in other parts of the world, heavy rain has in the past caused earthquakes.

After evaluating connections between storms and earthquakes in 2010, Shimon Wdowinski, a professor in the Department of Earth and Environment at Florida International University, conducted extensive research on the subject.

Haiti. This interest was sparked by the devastating earthquake that shook Haiti in 2010, that is, about 18 months after the area experienced torrential rainfall as a result of a series of hurricanes and protracted heavy rain.

According to UN News, a 7.0 magnitude earthquake that hit Haiti on January 12, 2010, completely destroyed Port-au-Prince, and claimed 220,000 fatalities, including 102 United Nations employees.

Taiwan. When an earthquake struck Taiwan in 2009, it happened seven months after a typhoon.

According to PhysOrg, the strongest earthquake to shake the island in 2009 struck off the coast of eastern Taiwan on Saturday night with a magnitude of 6.4. Buildings in the northern part of the island's capital Taipei shook for about 20 seconds, but there weren't any immediate reports of serious injuries or significant property damage.

Wdowinski's study, which concentrated on Taiwan, discovered that massive earthquakes were five times more probable to occur after severe storms.

China. Researchers from the Chinese Academy of Meteorological Sciences discovered a strong link between earthquakes with a magnitude greater than 6 and rainfall in a study that was published in 2021. It was discovered that in China, 74.9% of earthquakes were accompanied by rainfall.

However, Wdowinski told Newsweek that while torrential downpours can cause earthquakes, this only happens in specific tectonic environments and not everywhere.

Kartsified Limestone: Rain, Earthquake, Then Erosion

Erosion is the main risk associated with rainfall and earthquakes. These faults may loosen and cause an earthquake if rainfall is sufficiently intense to start eroding them.

According to Raymond Russo, an Associate Professor in the Department of Geological Sciences at the University of Florida, there is very little chance that an earthquake will occur as a result of recent heavy rains. But there are circumstances in which it might happen.

A plausible scenario, according to Russo, is when rainwater seeps into a fault zone that is on the verge of failing and reduces the normal stress on the fault. If the fault is already primed and ready to go, a reduction in the normal stress across it could cause failure and seismic slip.

If there is an increase in seismicity caused by these heavy rains, these are the only places in California where there is karstified limestone.

According to Stephen A. Miller, a professor at the University of Neuchâtel in Switzerland's Centre for Hydrogeology and Geothermics, rain itself has little effect on the origin of earthquakes unless it is karstified limestone because it carbonates.

He continued, saying that torrential downpours could fill these networks and significantly raise the hydraulic head, or height of the water column. In this situation, as fluid pressure rises, the high fluid pressure from the bottom of the water column may be transmitted to depth and result in earthquakes.

This could also be dangerous because it adds to the load on the subsurface when reservoirs are filled, according to Miller.

Rain-Induced Seismic Activities

As per Miller, if there is an increase in seismicity brought on by rain in California, it will be concentrated in carbonate-rich areas or near reservoirs.

Wdowinski, however, claimed that rainfall-induced earthquakes mainly happened in convergent tectonic environments, where two tectonic plates were moving in the same direction and lifting the crust, as it is in Taiwan.

According to Wdowinski, in this situation, a lot of rain can cause a significant amount of surface erosion, which can alter the stresses in the crust and alter when earthquakes will occur. This is not the situation in California, where the Pacific and North American tectonic plates move in a horizontal direction in relation to one another.

He added that in such a setting, crustal stresses would not be significantly impacted by erosion. As a result, it is unlikely that there is a direct physical link between the rain and seismic activity, Newsweek reports.