Earthquake swarms continue off the Pacific and Caribbean northwest coast; No tsunami threat yet


Earthquakes continue to rock the Pacific Northwest Coast and the Eastern Caribbean today. Image: Weatherboy

Earthquake swarms continue just off the Pacific Northwest coast of the United States and the eastern Caribbean. Although some earthquakes have been moderate, there is currently no threat of a tsunami. Scientists explore the cause of each new swarm; although they happen around the same time, they don’t seem to be related.

More than 20 earthquakes have struck off the coast of Oregon in the past 24 hours, including a 5.2 that recently struck. Most of the earthquakes of the past 24 hours have ranged in intensity from 3.2 to 5.3 magnitudes. These earthquakes are part of a swarm that started two days ago on December 7. The first earthquake in the series was a magnitude 4.2 agitator that struck at 5:20 a.m. local time. During the first 24 hours of the event, there were over 55 earthquakes with a magnitude of 3.4 or greater. The largest of the whole swarm was 5.8 so far.

More than 70 earthquakes have hit the Oregon coast since the start of the ongoing earthquake swarm on December 7.  Image: USGS
More than 70 earthquakes have hit the Oregon coast since the start of the ongoing earthquake swarm on December 7. Image: USGS

There is no threat of a tsunami from the Pacific Northwest swarm at this time. The USGS says, “Because these earthquakes are generally of low to moderate magnitude and have a focal dropout mechanism (lateral or horizontal movement, not vertical), they are unlikely to generate tsunamis. However, if they get bigger, they could cause increased local waves. In addition to the USGS, the National Weather Service Tsunami Warning Center also published its own bulletins on the strongest earthquakes in swarms, adding that there is no imminent threat of a tsunami at this time.

According to the USGS, the swarm is located about 200 miles west of the Cascadia Subduction Zone and continues along the Blanco Fracture Zone, which is a stall fault system on the edge of the Juan Plate of Fuca.

This is not the first swarm of earthquakes to hit this region in recent times. In 2003, a swarm struck within 31 miles of today’s swarm. The 2003 swarm included an earthquake of magnitude 6.3 as well as 4 other earthquakes of magnitude 5.1 to 6.7. The 2003 swarm lasted only 24 hours; scientists don’t know when the current swarm, now on day three, will end.

According to the USGS, an earthquake swarm is a sequence of small to moderate earthquakes in a relatively small area that does not match the pattern of a main shock aftershock sequence. Swarms are usually short lived, but can last for days, weeks or sometimes months, and often breed in the same places.

Several earthquakes have also hit the eastern Caribbean in recent days, some as strong as the earthquakes that hit the Oregon coast.  Image: UWI Seismic Research Center
Several earthquakes have also hit the eastern Caribbean in recent days, some as strong as the earthquakes that hit the Oregon coast. Image: UWI Seismic Research Center

As the USGS studies the swarm off the coast of Oregon, scientists at the UWI Seismic Research Center are also exploring a wave of moderate earthquakes affecting parts of the eastern Caribbean. Based at the University of the West Indies (UWI), the Seismic Research Center provides support for tsunami warning and public education and awareness of the geological hazards that are present in the eastern Caribbean. “Our vision is that of the leading agency in the Eastern Caribbean for monitoring earthquakes, volcanoes and tsunamis and disseminating information to mitigate the negative impacts of these risks,” says the Center for UWI seismic research on its website.

Over the past 72 hours, several earthquakes have struck near Trinidad and Tobago, Grenada and Barbados. The strongest was a 5.3 which struck southwest of Port of Spain, Trinidad and Tobago. A 5.0 and 3.8 and 3.9 over the past 48 hours join other magnitude 3 and 4 events in the region in the past few weeks.

According to the UWI Seismic Research Center, most earthquakes that occur in the Eastern Caribbean are of tectonic or volcanic origin. Tectonic earthquakes are generated when the plates move when the accumulated strain energy is released. Volcanic earthquakes are generated by the movement of magma in the lithosphere; as the magma is less dense than the surrounding rock, it rises to the surface, breaking the rock as it moves, thus creating earthquakes. According to the UWI Seismic Research Center, more than 75% of earthquakes in the world occur at the borders of converging plates, making countries in the Eastern Caribbean very susceptible to earthquakes.

Scientists will continue to monitor both areas for any changes in seismic behavior; the Tsunami Warning Center will also monitor ongoing seismic activity and issue a tsunami warning when needed.

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