3:43 PM – Light Earthquake West of Antigua & Barbuda

At 3:43 PM Wednesday 21st April 2021, a (preliminary) light Magnitude 4.4 (Mt) earthquake occurred approximately 66.3 km NW of St. Johns, Antigua & Barbuda, 66.0 km ENE of Basseterre, St. Kitts and 163.0 km NNW of Point-à-Pitre, Guadeloupe. This event was located at 62.176°W and 17.531°N, at a depth of 10.0 Kilometers.

This event has been reported felt across parts of St. Kitts and Nevis, and Antigua and Barbuda. You can submit felt reports to the University of the West Indies Seismic Research Centre.

U.W.I. Seismic Research Centre preliminary solution for the M4.4 earthquake west of Barbuda.
U.W.I. Seismic Research Centre preliminary solution for the M4.4 earthquake west of Barbuda.

The above information is preliminary from the U.W.I. Seismic Research Centre, the authority for seismic and volcanological information in the Eastern Caribbean. Parameters may change as more data is received and reviewed by seismologists.

Seismic data from a seismometer stationed on Barbuda, capturing the M4.4 earthquake at 3:43 PM, seen by the large spike in amplitude at 19:44 (accounting for the delay in seismic waves to travel from the hypocenter to the seismic station) (IRIS)
Seismic data from a seismometer stationed on Barbuda, capturing the M4.4 earthquake at 3:43 PM, seen by the large spike in amplitude at 19:44 (accounting for the delay in seismic waves to travel from the hypocenter to the seismic station) (IRIS)

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.

United States Geological Survey's solution for the earthquake west of Barbuda.
United States Geological Survey’s solution for the earthquake west of Barbuda.

The United States Geological Survey (USGS) recorded this quake at a similar magnitude of 4.5 (mb) and in a similar location and depth.

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 North American plate is beginning to descend into the Earth’s mantle.

In this location, the subducting slab is at approximately 50 kilometers depth. Within 20 kilometers of the epicenter of this earthquake, since the 1960s, there have been over 440 recorded events with varying depths – from 0 KM to 151 KM, with the majority of quakes occurring below a 35-kilometer depth. The largest of these was a magnitude 5.4 (Md) quake on November 11th, 1983.

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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