Two powerful, deadly earthquakes struck Venezuela, just 39 seconds apart, on Wednesday.
But in addition to those temblors, two other strong earthquakes struck across the world in less than 24 hours. A 5.6-magnitude tremor hit Northern California at 8:10 a.m. Pacific time, with some reports of injuries and power outages, and a 6.9-magnitude quake off the coast of Japan, with no reports of serious damage, soon after the Venezuela quakes.
While that may seem like an unusual number of strong earthquakes in a short time, experts said there was no indication they had any relation to each other.
The quakes in Venezuela are “not a coincidence,” said William Barnhart, a geodesist with the United States Geological Survey. Large earthquakes can lead to more quakes, but only in the same region, and usually along the same fault line, he added.
Dr. Barnhart said the first magnitude 7.3 earthquake that struck in Venezuela was likely a foreshock, with the magnitude 7.5 earthquake being the main shock.
The quakes in Japan and California were “coincidental,” he said.
Neither earthquake in Japan nor California was close enough to transfer stress to the tectonic plates under Venezuela, said Martin Hudson, an expert in geotechnical engineering at the University of California, Los Angeles. But the strength of the first Venezuelan quake could have triggered the second.
“The shaking of the first earthquake increases the stress on a nearby fault,” he said. “If the other one was close to going off anyway, it wouldn’t take much to set it off.”
Scientists are increasingly recognizing that earthquakes can happen in pairs, like the ones in Venezuela on Wednesday, Prof. Hudson said.
“The ones that we’ve observed in the last 100 years, a lot of them have been single earthquakes followed by aftershocks. Now we’ve had enough time under our belts to observe one fault triggering an earthquake in a nearby fault,” he said.
The earthquakes in Venezuela were comparable to another pair that struck California in 1992, he said. Two earthquakes from two different faults along the Pacific and North American plates happened in such quick succession that they were recorded as a single quake with a magnitude of 7.3, known as the Landers earthquake.
Both the Landers and Venezuela earthquakes were triggered by the same motion between faults, the experts said. On Wednesday, the South American and Caribbean plates slipped past each other, which seismologists call a strike-slip earthquake, as opposed to thrust earthquakes like the one in Japan, when plates push together.
Dozens of aftershocks were reported in Venezuela overnight, including one with a magnitude of 2.6 that was recorded shortly after 1 a.m. local time Thursday near the port city of La Guaira, according to the country’s interior ministry.
Tremors were also felt in Curaçao, an island nation off the coast of Venezuela, according to the authorities.
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