The Independence Day earthquake in California’s Mojave Desert serves as a reminder that it’s not just the rift zone rubbed by the North American and Pacific tectonic plates that we need to concern ourselves with in this state.
Since the 4.0 foreshock on July 4 that led to the 6.4 Ridgecrest temblor about 30 minutes later, the ground literally hasn’t stopped moving in the region. The U.S. Geological Survey reported an average of 30 earthquakes an hour in the days following the first temblor, which was followed about 36 hours later by a magnitude 7.1 that shook the San Joaquin Valley and was reportedly felt in two neighboring states.
California’s San Joaquin Valley may be bordered on one edge by the San Andreas Fault, yet it’s rare when we feel earthquakes. Much of the time what we do feel are more of a fun conversation starter than something worrisome. If nothing else these earth tremors become a race to see who can tweet out the word “earthquake” the fastest.
The general area where this happened is ripe for big earthquakes. Several of California’s largest temblors on record have happened within a 100-mile radius of the big quakes that struck the Mojave Desert region the week of July 4. Those include a 7.9 earthquake in southern Kern County in 1857 that happened when 200 miles of the San Andreas Fault in central California suddenly lurched. A similarly sized quake in the nearby Owens Valley in 1872, and a 7.5 earthquake on a small fault near Arvin, Calif. in the summer of 1952 that killed 12 and created several large aftershocks are among the biggest quakes in state history.
That the Ridgecrest quakes are happening in the Coso Volcanic field and considering the relative proximity to other volcanic structures such as the Long Valley Caldera and Ubehebe Crater in Death Valley National Park makes questions about possible volcanic activity in the region relevant, particularly since over 1,000 of them have happened since July 4. The latest website information from the USGS says no volcanic activity has been detected and there is no imminent danger of an eruption.
Significant impacts to the adjacent San Joaquin Valley are unknown. A Friant Water Authority spokesperson did not know if the seismic shaking impacted segments of the Friant-Kern Canal already affected by ground subsidence.
Did this significant motion cause changes in our aquifers and what were they? Can we mitigate such impacts to our water supplies and conveyance systems? Do we have contingencies in place if the LA Aqueduct or California Aqueduct become severed by an earthquake?
Could events like this have a larger impact on nearby faults, causing them to lurch violently? We already understand the 200-mile segment of the San Andreas Fault that slipped during the 1857 Fort Tejon quake has not moved since, leading folks to believe it’s poised to unleash a catastrophic event we may be ill-prepared for.