10:33 PM – Light Earthquake Felt Across Northwestern Trinidad

At 10:33 PM Thursday 12th August 2021, a (reviewed) light Magnitude 4.4 (Mt) earthquake occurred approximately 37.9 KM NW of Macuro, Venezuela, 38.6 KM NNE of Güiria, Venezuela and 78.5 KM WNW of Port of Spain, Trinidad and Tobago. This event was located at 62.180°W and 10.900°N, at a depth of 69.0 Kilometers.

This information has been reviewed by a seismic technician at the U.W.I. Seismic Research Centre, the authority for seismic and volcanological information in the Eastern Caribbean. This information may change when additional data is processed by a seismologist.

Information from the Venezuelan Foundation for Seismological Research concerning the M4.4 earthquake northwest of Trinidad.

The event was reported felt across Northwestern Trinidad with a short jolt, lasting no longer than 1-2 seconds. Some have reported hearing a rumble before the shaking. You can submit felt reports to the University of the West Indies Seismic Research Centre.

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).

None of these conditions occurred.

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.

The Venezuelan Foundation for Seismology also recorded this earthquake as a (preliminary) minor Magnitude 3.9 (Mw) approximately 35.8 KM NNE of Güiria, Venezuela, 43.0 KM NW of Macuro, Venezuela, 85.5 KM WNW of Port of Spain, Trinidad and Tobago. This event was located at 62.250°W and 10.890°N, at a depth of 35.8 Kilometers.

Information from the Venezuelan Foundation for Seismological Research concerning the M3.9 Earthquake northwest of Trinidad.
Information from the Venezuelan Foundation for Seismological Research concerning the earthquake northwest of Trinidad.
Seismic waves from the light earthquake were recorded at a seismometer in Grenville, Grenada. (IRIS)
Seismic waves from the light earthquake were recorded at a seismometer in Grenville, Grenada. (IRIS)

Based on the earthquake’s calculated location, this quake occurred in seismic zone 1, within the Paria Peninsula.

Seismic Zone 1: The Paria Peninsula
Seismic Zone 1: The Paria Peninsula

Seismic zone one is a complex, and without a doubt, the most seismically active area near Trinidad. Within zone one, the South American plate is beginning to rapidly descend into the Earth’s mantle as the detached oceanic lithosphere exists at depths between 50 to 300 kilometers. (Russo et al. 1993). This zone is one of the most active seismogenic sources in the Eastern Caribbean and has the potential to generate earthquakes up to Magnitude 8.0.

At shallower levels, the North Coast Fault Zone and the El Pilar Fault are part of the Boconó-San Sebastian-El Pilar Fault system, run across Zone 1. These fault systems compensate for the stress built up as the Caribbean plate slides past the South American plate. Hence, most of these earthquakes from these fault systems are shallow to moderate between 0 to 70 kilometers.

Within 20 kilometers of the FUNVISIS solution, over 775 seismic events have been recorded, the largest being a magnitude 6.3 on October 11th, 2013. Earthquakes in this area generally between 50 kilometers to 125 kilometers deep. Earthquakes in this location have occurred from near 0 depth to as deep as 129 kilometers.

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.

Why did I hear the earthquake?

The rumbling you hear before the shaking occurs is the P-Wave, a quake’s first seismic wave creating a sound wave.

The speed of sound in the air is 330 meters per second.  a single number can not describe the speed of seismic waves in the earth because it depends heavily on the material through which the waves are passing. 

It is well known that sound is created in air when an oscillating object is in contact with it. The sound really is oscillations in pressure, displacement, and speed of the air, in concordance with the object creating them. 

Now, the seismic waves themselves include oscillations of the earth’s surface, which is in contact with the air. Therefore, they cause oscillations in the air. However, the frequency of these oscillations is so low that we hear the least part of them as sound. Still, the frequency of the fastest waves, the P-waves, may be more than 30 Hertz and thus be audible as sound. The sound-induced by seismic waves in the air have been compared to the boom in underground stations when a train is approaching.

We normally sense P-waves as an earthquake to a lesser degree than, for instance, the S-waves following them. If an earthquake has not been very strong or we are reasonably far away from its center, we will not at all sense the P-waves as an earthquake but only hear the sound-induced by them in the air. Still, we may feel the S-waves quite clearly and then other waves, which often arrive later, especially at a distance.

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