Minor Earthquake North Of St. Lucia Felt On Island

At 11:48 PM Friday 23rd April 2021, a (reviewed) minor Magnitude 3.5 (Mt) earthquake occurred approximately 20.70 KM NNW of Castries, St. Lucia, 48.31 KM S of Fort-de-France, Martinique and 120.97 KM N of Kingstown, St. Vincent and the Grenadines. This event was located at 61.10°W and 14.19°N, at a depth of 15.99 Kilometers.

This event has been reported felt across parts of St. Lucia. You can submit felt reports to the University of the West Indies Seismic Research Centre.

U.W.I. Seismic Research Centre reviewed solution for the M3.5 earthquake North of St. Lucia.
U.W.I. Seismic Research Centre reviewed solution for the M3.5 earthquake North of St. Lucia.

The above information has been reviewed by a seismologist from the U.W.I. Seismic Research Centre, the authority for seismic and volcanological information in the Eastern Caribbean.

There is no tsunami threat.

There are four conditions necessary for an earthquake to cause a tsunami:

  1. The earthquake must occur beneath the ocean or cause material to slide in the ocean.
  2. The earthquake must be strong, at least magnitude 6.5.
  3. The earthquake must rupture the Earth’s surface and it must occur at shallow depth – less than 70 KM below the surface of the Earth.
  4. The earthquake must cause vertical movement of the seafloor (up to several meters).

These conditions were not met.

Note that different seismic monitoring agencies use different methods, or several methods, for processing quake parameters across the globe. Each method has its limitations and will likely produce different results within the ranges of the data’s uncertainty. This is generally accepted within the scientific community.

RéNaSS' seismometers recording the quake north of St. Lucia on Friday night. (RéNaSS)
RéNaSS’ seismometers recording the quake north of St. Lucia on Friday night. (RéNaSS)

The French National Seismic Surveillance Network (RéNaSS) also recorded this quake in a similar location and depth, at 16 kilometers but a smaller magnitude at 2.7.

Based on the location and depth of this quake, it is tectonic in origin and occurred within the overriding Caribbean Plate. In this area, the South American plate is beginning to descend into the Earth’s mantle.

In this location, the subducting slab is at approximately 80 kilometers depth. Within 20 kilometers of the epicenter of this earthquake, since the 1960s, there have been over 330 recorded events with varying depths – from 0 KM to 168 KM, with the majority of quakes occurring below a 25-kilometer depth. The largest of these was a magnitude 4.6 (Md) quake on December 8th, 1966.

Earthquakes *cannot* be predicted – meaning the precise time, date, magnitude, depth, etc. cannot be known ahead of time based on current research and technology.

Earthquakes *cannot* be predicted – meaning the precise time, date, magnitude, depth, etc. cannot be known ahead of time based on current research and technology.

Generally, across the Eastern Caribbean, a seismically active area, earthquakes of this magnitude, up to M8.0 and greater, are possible and this statement has been repeated by seismologists at the U.W.I. Seismic Research Centre for decades.

Each year, over 2,200 seismic events are recorded in the Eastern Caribbean. On average, the Eastern Caribbean has seen a pattern of major (M7.0-M7.9) quakes every 20 to 30 years. That pattern has stayed true. The last major (M7.0-7.9) quake occurred north of Martinique in 2007. 

Historical patterns indicate great quakes (M8.0+) on the Richter Scale have occurred every century or so in the region. The probability of another event at that level is high since the last >M8.0 earthquake occurred in 1843.

Now is the time to create or go over your earthquake preparedness plan and know what to do during, before, and after an earthquake.

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