Venezuela earthquake: A series of terrible earthquakes shows the dangers of California

The first earthquake, measuring 7.2, struck Venezuela on Wednesday evening with terrifying force. But just 39 seconds after we started, an even stronger 7.5 storm struck, causing an even bigger disaster.

The seismic one-two punch, which seismologists call a “doublet,” has added to concerns about what could be one of the Western Hemisphere’s worst earthquakes in years.

Although little known to the general public, double earthquakes have long been studied by seismologists. Several have occurred in California, including the 1992 twin earthquakes in Southern California that prompted officials to issue an unprecedented public warning.

“Obviously it’s not a very common occurrence with an earthquake, but it’s certainly not an unusual physical event,” said Julian Lozos, associate professor of geophysics at Cal State Northridge.

The widespread devastation in Venezuela – with more than 500 buildings dead and countless flattened – is expected to focus on the earthquake situation and how to make buildings and infrastructure stronger.

Turkey and Syria were devastated just three years ago, when an earthquake with an average magnitude of 7.8, struck 220 miles on the East Anatolian fault, followed nine hours later by a 7.5 earthquake in the Cardak region, struck 100 miles more, according to the US Geological Survey.

The twin earthquakes, and a staggering number of aftershocks, were catastrophic, killing more than 50,000 people.

Scientists in California have been looking at what destructive doublet sequences might look like.

In Southern California, researchers with the USGS simulated a hypothetical earthquake scenario, where 52 miles of the Newport-Inglewood fault – which runs along the coast of Orange County and passes through Long Beach, South LA, would explode with a 7.25 magnitude earthquake, which would be followed a few hours later by a 70 magnitude earthquake.

Doublets don’t necessarily need to stop in two swings. There was a quadruple earthquake sequence – all measuring 6.3 – in western Afghanistan in 2023. The first two earthquakes were separated by about four hours on October 7, and were followed by more earthquakes on October 10 and Oct. to follow at the meeting of the American Geophysical Union in 2024.

There is no universally accepted definition of what constitutes a doublet. A relatively loose definition involves an earthquake followed by another earthquake of similar magnitude within minutes, hours or days after the initial shock. Seismologist Lucy Jones has a smaller definition, where two earthquakes in the same seismic sequence are within 0.4 magnitude units of each other.

“It’s a little thing sometimes, like I know some people see Ridgecrest as a doublet, and some people don’t,” Lozos said, referring to the sequence of 2019 earthquakes that shook LA in the Mojave Desert.

In that sequence, a magnitude 6.4 on the morning of July 4 was followed about 34 hours later by a more damaging earthquake of 7.1. The China Lake Naval Air Weapons Station, the Navy’s largest base for building and testing military weapons, suffered millions of dollars in damage, and the fact that the second quake was more frightening than the first shocked many Californians.

There are several reasons why doubling is possible. “In fact, it’s clear how much he’s ready for all the near misses,” said Lozos. The eruption of a single fault may cause a nearby fault – which is likely already ruptured – to go into shock. Another example involves a system of faults that all start to erupt, but there is some delay in the second part of the fault eruption.

An aftershock isn’t the only type of aftershock that could cause concern or cause more damage.

A 2008 USGS report, called ShakeOut, said that a 7.8-magnitude aftershock felt south of the San Andreas fault, between the Salton Sea and Los Angeles County, and included a 6.95-magnitude tremor that would shake Sacramento and Modesto, the largest earthquake in three days. maintaining flood control and water flow from the northern Sierra Nevada to cities throughout the region.

Jones is working to update the ShakeOut scenario, and one concrete scenario he plans to study is a magnitude 7.8 earthquake in the San Andreas followed by a larger earthquake — perhaps as large as magnitude 7 — on the Hollywood and Raymond faults, which run beneath the heart of Hollywood and extend east into the San Gabriel Valley.

It is not certain that the USGS will stick to its initial declaration that the earthquake in Venezuela involved two, given that the gap between the first earthquakes was less than a minute. And even then, the first 7.2 quake would last for half a minute, which means that the first shock waves could have been felt as well as the second. Zhongwen Zhan, director of the Caltech Seismological Laboratory, said data from Venezuela’s earthquake sensor showed “continuing” tremors.

“The two earthquakes may be merged together, so we can expect that there may be some classification later,” Zhan said.

“I’m sure what happened in Caracas was a very long earthquake. Maybe someone who was able to stay still to see what was happening would have been able to hear it diminish for a few seconds,” Jones said. “If you ask people how long Northridge lasted, you’ll find a lot of them think it lasted a really long time,” but that may be a reflection of the short pause between the main shock and the aftershock, which came within a minute.

The fact that there are doubles is a reminder that people should be aware that a large earthquake can be followed by an aftershock. It is worth noting, too, that buildings damaged by the first earthquake may not be able to withstand aftershocks.

“It should be noted that this building could be seriously damaged by an earthquake,” said Maria Mohammed, president of the Structural Engineers Assn. from Southern California.

It is a warning that is not easily forgotten. A number of people died in Christchurch, New Zealand, due to the collapse of buildings caused by a 6.1 magnitude earthquake in 2011, despite the fact that the buildings were already damaged, which earthquakes can cause.

Small earthquakes can also lead to big ones. Moderate earthquakes of about 6.1 and 5.6 in Monterey County preceded the megaquake on the San Andreas fault in 1857, estimated at 7.9 magnitude, which struck the fault between Monterey and LA counties.

That earthquakes can cause other earthquakes has been shown before.

Scientists believe that the 6.1 Joshua Tree earthquake of April 22, 1992, resulted in an aftershock that continued to move north. Finally they started on June 28 the 7.3 Landers earthquake in the Mojave desert – strong enough to cause an earthquake in Denver – and, hours later, the 6.3 earthquake in Big Bear.

The government issued a strong warning urging citizens to prepare for strong tremors after the earthquake, and urged residents to stay off highways if possible. Jones, then with the USGS, created a “warfare,” where, if an earthquake of 6.5 or greater occurred somewhere in the San Andreas, it would trigger an automatic response that included calling the National Guard.

In the end, there were no more major earthquakes that day.