Earthquake swarms are continuing just off the U.S. Pacific Northwest coast and the eastern Caribbean. While some earthquakes have been moderate, there is no threat of tsunami at this time. Scientists are exploring the cause of each new swarm; while they are happening at roughly the same time, they do not appear to be related.
More than 20 earthquakes struck off the coast of Oregon in the last 24 hours, including a 5.2 which struck a short time ago. Most of the earthquakes in the last 24 hours have ranged in intensity from 3.2 to 5.3 magnitudes. These earthquakes are part of a swarm that began two days ago on December 7. The first earthquake in the series was a 4.2 magnitude shaker which struck at 5:20 am local time. In the first 24 hours of the event, there were more than 55 earthquakes with a magnitude of 3.4 or greater. The greatest in the entire swarm was a 5.8 thus far.
There is no tsunami threat from the Pacific Northwest swarm at this time. USGS says, “Because these quakes are generally small to moderate in magnitude and have a strike-slip focal mechanism (lateral or horizontal motion, not vertical), they are unlikely generate tsunamis. However, if they become larger, they might cause some increased local waves.” In addition to USGS, the National Weather Service Tsunami Warning Center has also issued their own bulletins on the stronger quakes in the swarms, adding there’s no imminent threat of tsunami at this time.
According to USGS, the swarm is located roughly 200 miles west of the Cascadia Subduction Zone and is ongoing along the Blanco Fracture Zone, which is a strike-slip fault system on the edge of the Juan de Fuca plate.
This isn’t the first earthquake swarm to strike this region in recent times. In 2003, a swarm struck within 31 miles of today’s swarm. The 2003 swarm included a magnitude 6.3 earthquake along with 4 other earthquakes that had magnitudes of 5.1 – 6.7. The 2003 swarm only lasted 24 hours; scientists aren’t sure when the ongoing swarm, now in day three, will end.
According to USGS, an earthquake swarm is a sequence of small to moderate earthquakes within a relatively small area that don’t fit the pattern of a mainshock-aftershock sequence. Swarms are usually short-lived, but can continue for days, weeks, or sometimes months, and often recur at the same locations.
While USGS is studying the swarm off the coast of Oregon, scientists with the UWI Seismic Research Centre are also exploring a surge of moderate earthquakes impacting portions of the eastern Caribbean. Based at the University of the West Indies (UWI), the Seismic Research Centre there provides support for tsunami warning and public education and awareness on geological hazards that are present in the eastern Caribbean. “Our vision is to the leading agency in the Eastern Caribbean for earthquakes, volcano, and tsunami monitoring and for the dissemination of information to mitigate the negative impacts of these hazards,” UWI Seismic Research Centre states on their website.
Within the last 72 hours, several earthquakes have struck near Trinidad and Tobago, Grenada, and Barbados. The strongest was a 5.3 which struck southwest of the Port of Spain, Trinidad and Tobago. A 5.0 and 3.8, and 3.9 in the last 48 hours join other magnitude 3 and 4 events in the region over the last few weeks.
According to the UWI Seismic Research Centre, most of the earthquakes occurring in the Eastern Caribbean are either tectonic or volcanic in origin. Tectonic earthquakes are generated when plates move as accumulated strain energy is released. Volcanic earthquakes are generated by the movement of magma within the lithosphere; since magma is less dense than the surrounding rock, it rises to the surface, breaking the rock as it moves, creating earthquakes in the process. According to the UWI Seismic Research Centre, more than 75% of the world’s earthquakes occur at convergent plate boundaries, making the countries of the Eastern Caribbean highly susceptible to earthquakes.
Scientists will continue to monitor both areas for any change in seismic behavior; the Tsunami Warning Center will also monitor ongoing earthquake activity and will issue a tsunami advisory when needed.