Double trouble: What is a seismic doublet?
The phenomenon has no strict definition, but involves similarly sized earthquakes occurring close together. The deadly quakes in Venezuela in June were considered an earthquake doublet.
Days after major earthquakes struck Venezuela, video continues to show unbelievable levels of devastation, especially in the area of La Guaira.
Two earthquakes struck off the Northern California coast within 44 seconds of each other Wednesday evening: a seismic event known as a doublet.
The first, a magnitude 3.8 earthquake, struck at about 6:24 p.m. PDT roughly 15 miles west of Petrolia in Humboldt County, according to the U.S. Geological Survey. Less than a minute later, a magnitude 3.6 earthquake struck near the same location.
What is a seismic doublet?
Doublets are two earthquakes of similar magnitude that happen close in time and proximity, according to the USGS.
William Yeck, a research geophysicist at the National Earthquake Information Center at the USGS, told AccuWeather that double earthquakes do not need to meet set criteria to be defined as a doublet.
“For example, the earthquakes in Venezuela this year were termed doublets, and [they] occurred about 30 seconds and 150 kilometers apart,” Yeck told AccuWeather. “Another recent example was the 2024 Turkey earthquakes that occurred nine hours and about 100 kilometers apart.”
Rescue teams search for people as cranes remove debris from destroyed buildings in Antakya, southeastern Turkey, Friday, Feb. 10, 2023. Rescuers pulled several earthquake survivors from the shattered remnants of buildings Friday, including some who lasted more than 100 hours trapped under crushed concrete after the disaster slammed Turkey and Syria. (AP Photo/Hussein Malla)
While Wednesday night’s Northern Californian earthquakes can be considered a doublet, they are not equivalent to those events, Yeck said. Earthquakes in the magnitude 3 range are common, and the region is seismically active.
Yeck explained that doublets are uncommon, but not rare, with a notable doublet occurring every few years. In addition to the 2026 Venezuela earthquakes, Herat, Afghanistan, experienced four magnitude 6.3 earthquakes in the same area over about a week in 2023.
When was the last doublet?
As Yeck noted, the most recent seismic doublet occurred in Venezuela in June. On the evening of June 24, a magnitude 7.2 earthquake struck near San Felipe. About 30 seconds later, a magnitude 7.5 earthquake hit northern Venezuela, west of Caracas. The double earthquake caused more than 6,000 deaths and over 16,500 injuries, according to official reports.
U.S. rescue teams conduct search operations for survivors following two powerful earthquakes, measuring 7.2 and 7.5 on the Richter scale, that struck La Guaira, Venezuela, on June 30. (Photo Credit: U.S. Department of State/UPI | License Photo)
Northern Venezuela also experienced a doublet in September 2025, when a sequence of magnitude 6.2 and 6.3 earthquakes struck, the USGS noted. The event caused at least one death, more than 110 injuries and structural damage across Lara and Zulia.
What is the difference between a doublet and an aftershock?
An aftershock is smaller than the mainshock of an earthquake, Yeck explained. In the case of a doublet, there is no clear mainshock since both earthquakes are of similar sizes.
A road is damaged from an earthquake Thursday, July 4, 2019, in Trona, Calif. A strong earthquake rattled a large swath of Southern California and parts of Nevada on Thursday, rattling nerves on the July 4th holiday and causing some damage in a town near the epicenter, followed by a swarm of aftershocks. (AP Photo/Matt Hartman)
Aftershocks also occur in the same general area as the larger earthquake, known as the “mainshock,” and can continue for days to years after the main earthquake, according to the USGS.
“As a general rule, aftershocks represent minor readjustments along the portion of a fault that slipped at the time of the mainshock,” the agency said. “The frequency of these aftershocks decreases with time. Historically, deep earthquakes (>30 kilometers) are much less likely to be followed by aftershocks than shallow earthquakes.”
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