11:55 AM – Light Earthquake North of Tobago

At 11:55 AM Tuesday 12th May 2020, a light (preliminary) Magnitude 4.5 (Md) earthquake struck 89 km N of Scarborough, Trinidad, and Tobago, 101 km E of St. George’s, Grenada and 138 km SSE of Kingstown, Saint Vincent, and the Grenadines.

UWI SRC’s preliminary solution for the M4.5 earthquake at 11:55 AM Tuesday 12th May 2020

This event occurred at a preliminary depth of 10 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 Grenada (St. Andrew’s, Mt. Moritz), Canouan of St. Vincent and the Grenadines, and Scarborough, Tobago as a small jolt, lasting no longer than 5 seconds with weak to light shaking. You can submit felt reports to the University of the West Indies Seismic Research Centre and the United States Geological Service.

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.

Though the University of the West Indies Seismic Research Centre’s solution remains preliminary, it’s the authoritative information for our region. The Centre not only as access to other seismic networks in the area, but their own dense network of seismometers and accelerometers to determine more precise and accurate quake parameters for seismic events in our region.

Nearly all international seismic monitoring agencies do not receive seismic data from FUNVISIS or UWI SRC. This means that in most cases, with reporting stations mainly north of T&T, the epicenter of quakes nearly always have a northward bias when it comes to latitude and longitude of a quake. It is also important to note that there is no exact location of a quake, as these seismic events occur due to a slip across a fault.

No matter how dense the seismic network is, there is always uncertainty which by the density of stations is reduced but never eliminated. When a solution is produced, the longitude and latitude are generated. All processing algorithms also provide the small and big axis of the eclipse with that location in the center, hence the location of an earthquake is not one point on the earth, but an area defined by those axes.

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.

USGS’ reviewed solution for this morning’s earthquake.

The United States Geological Survey (USGS) also recorded this quake, at a reviewed Magnitude 4.3 (ML) further south and west of the UWI SRC’s preliminary solution. According to the USGS, this quake occurred at a deeper depth of 45.0 kilometers.

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 51 kilometers depth, but based on the depths provided by UWI SRC and the USGS, this quake occurred within the overriding Caribbean Plate. The USGS’ solution has this quake occurring near the Wadati–Benioff zone, where the subducting slab (South American Plate) interacts with the overriding slab (Caribbean Plate).

Seismograph between 5:00 AM and 1:00 PM Tuesday 12th May 2020 from Grenada showing the main shock of the earthquake North of Tobago.

Within 20 kilometers of the epicenter of this earthquake, since 1952, there have been 42 recorded events with varying depths – from 0 KM to 144 KM, with the majority of quakes occurring below a 75-kilometer depth.

Based on records going back to the 1950s, if the location of this quake doesn’t drastically change, this will be the third strongest quake within the 20-kilometer radius in recent, recorded history. The largest quake that occurred in this area was recorded as magnitude 5.4 (Md) quakes, occurring on May 31st at 12:21 PM. 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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