While hurricanes are not directly responsible for causing earthquakes, the alignment of tropical rain with an earthquake occurrence northwest of Los Angeles has sparked curiosity about their potential connection.
Over the weekend, a magnitude-5.1 earthquake struck near Ventura, northwest of Los Angeles, followed by numerous aftershocks into Monday. Coincidentally, this seismic activity coincided with the approach of rain from Tropical Storm Hillary, which made landfall over the Baja Mexican peninsula later in the day.
This confluence of events has led to speculation about whether hurricanes could trigger earthquakes, leading to the coining of the term “hurriquake” by local Los Angeles television stations. However, it’s crucial to move beyond sensationalism and consider the insights from the US Geological Survey (USGS):
The USGS asserts that there is no discernible pattern in California where significant and damaging earthquakes occur more frequently during periods of heavy rainfall or drought. As such, the influence of precipitation on seismic hazards is considered unlikely. This conclusion is reasonable, given that rainwater cannot easily permeate the several-kilometer depth beneath the Earth’s surface where most earthquakes originate.
Earthquakes materialize when segments of the Earth’s crust slide past each other, liberating energy in the form of seismic events. This movement’s force can be measured using instruments. This tectonic plate movement can generate ground shaking of a magnitude that results in catastrophic destruction, particularly when magnitudes reach the range of 7 to 9.
Human activities are also capable of inducing earthquakes. Delicate equipment can detect minor tremors with magnitudes under 2, as exemplified by the vibrations recorded during massive gatherings like Taylor Swift concerts in Seattle.
The recent upswing in earthquake occurrences in the central United States is mainly attributed to the disposal of waste fluids stemming from oil production. The practice of hydraulic fracturing, or fracking, deliberately triggers small earthquakes with magnitudes below 1 as a byproduct of waste fluid disposal.
However, the question arises: could the weight of heavy rainfall exert an influence on geological shifts? During Hurricane Irma, an astonishing 2 trillion gallons of water fell across the St. Johns River watershed, equivalent to over 1.66 trillion pounds. Hurricane Harvey was even more substantial, depositing 34 trillion gallons of water. This resulted in a 1.8 cm subsidence in the ground in Houston, which persisted for about three weeks before the Earth’s crust returned to its original state.
It’s important to note that none of this substantial rain fell directly over fault zones, which are critical to seismic activity. Nevertheless, in theory, extended periods of intense rainfall or drought could indirectly impact fault lines that are susceptible to earthquakes. The USGS indicates that some studies suggest these circumstances might exert minor changes in stress on faults, potentially influencing the rate of seismic events.