10:54 AM – Light Earthquake Felt Across T&T, Grenada

At 10:54 AM Tuesday 7th April 2020, a light (preliminary) Magnitude 4.3 (Md or Mt) earthquake struck 67 km SW of St. George’s, Grenada, 118 km NW of Port of Spain, Trinidad and Tobago and 136 km NW of Arima, Trinidad and Tobago.

UWI SRC’s preliminary solution for the light earthquake north of T&T

This event occurred at a (preliminary) depth of 58 Kilometers. This information is preliminary from the U.W.I. Seismic Research Centre, the authority for seismic and volcanological information in the Eastern Caribbean. Quake parameters such as location, depth, and magnitude may change upon review from a seismologist at the SRC.

This event has been reported felt across parts of Trinidad, Tobago, Grenada and Northeastern Venezuela as a small jolt, lasting no longer than 5 seconds. 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).

These conditions were not met.

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

Based on the location and depth of this earthquake, it is tectonic in origin. In this area, 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).

In this location, the subducting slab is at approximately 50-80 kilometers depth. While this earthquake is some distance away from last night’s M5.3 (preliminary) event, this quake also occurred on the Wadati–Benioff zone, where the subducting slab (South American Plate) interacts with the overriding slab (Caribbean Plate).

Seismographs since 9:00 PM Monday 6th April 2020 from Grenada showing earthquake activity in our area, with at least 10 aftershocks since last night's quake.
Seismographs since 9:00 PM Monday 6th April 2020 from Grenada showing earthquake activity in our area, with at least 10 aftershocks since last night's quake.
Seismographs since 9:00 PM Monday 6th April 2020 from Grenada showing earthquake activity in our area, with at least 10 aftershocks since last night’s quake.

Within 20 kilometers of the epicenter of this earthquake, since 1960, there have been 129 recorded events with varying depths – from 0 KM to 166 KM.

Based on records going back to the 1960s, the largest quake that occurred in this area was recorded as a magnitude 5.0 (Md) quake, occurring on February 8th, 1976. All other quakes have registered below magnitude 5.0.

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. See here for more details.

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