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Puerto Rico’s Earthquakes: The Science

Puerto Rico has been hit by more than 1,280 earthquakes in the past month. How severe have the quakes been, what has caused them, and will there be more?

What’s magnitude?

When we hear that Puerto Rico has experienced a 6.4 magnitude earthquake, what does that mean?

Earthquakes are measured according to the Richter scale, developed in 1935 by Charles F. Richter. This is a way of measuring the amount of energy released in an earthquake. This scale is logarithmic. This means that a 2.0 magnitude quake is not twice as strong as a 1.0 earrthquake, but 10 times as strong.

  • Nearly all the earthquakes that take place each year are microquakes — smaller than 2.0 magnitude. People usually can’t feel these quakes.
  • Most people will feel a 3.0 magnitude earthquake.
  • A 4.0 magnitude earthquake will usually cause damage, if it takes place in a populated area.
  • A 5.0 magnitude earthquake is considered a moderate earthquake.
  • A 7.0 magnitude earthquake is considered a major earthquake.
  • A 9.5 magnitude earthquake is the strongest quake ever recorded.

Puerto Rico has had some 1300 earthquakes since the series began in December, 2019. While most of these have been micro quakes, there have been several moderate quakes and at least one approaching the status of a major earthquake.

The amount of damage caused by an earthquake depends not only on its magnitude, but also on the population density, the strength of the infrastructure, and the kind of construction in use.

What caused the earthquakes?

Puerto Rico is squeezed between two tectonic plates. Tectonic plates are huge pieces of solid rock on which our land and water rest. Puerto Rico is between the North American and Caribbean tectonic plates, at a point where one of the plates slides under the other. The Caribbean plate moves very slowly past the North American plate, at about half the rate at which human fingernails grow.

Bathymetry of the northeast corner of the Caribbean plate. Image courtesy of the USGS.

The Island has had many significant earthquakes:

  • 1787: estimated magnitude 8.0
  • 1918: magnitude 7.3
  • 1922: magnitude 6.3
  • 1943: magnitude 7.8
  • 1946: magnitude 8.0
  • 1979: magnitude 6.1
  • 1981: magnitude 5.7

The US Geological Survey acknowledges that drilling for oil and fracking have caused earthquakes elsewhere, but they say firmly that there is no evidence of human activity around Puerto Rico that could have caused these earthquakes. They have concluded that the earthquakes are naturally occurring events.

Will there be more quakes in Puerto Rico?

Experts believe that the quakes and aftershocks are not over.

It is not possible to predict earthquakes. However, once an earthquake takes place, it is possible to use statistical modeling and information about the quakes taking place to predict whether the series has finished or is likely to continue.

Experts currently say they think the quakes are not yet over.

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