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                      Earth Science and Ecology

Costa Rica Earthquakes

Information about Rainforest Animals, Environment and Earth Science in Costa Rica

Seismograph Costa Rica
Earthquake Magnitude

Moment Magnitude is the measure of total energy released by an earthquake. Moment magnitude is the measurement and term generally preferred by scientists and seismologists to the Richter scale because it is more precise.

It is not based on instrumental recordings of an earth quake, but on the area of the fault that ruptured in the quake. It is calculated in part by multiplying the area of the fault's rupture surface by the distance the earth moves along the fault.

Recent Seismic Activity

A map showing the recent earthquake activity worldwide

Worldwide data with seismograms from the Wilbur II seismic stations.

Imaging the seismogenic zone along the Middle America Trench, Costa Rica


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Earthquakes and Geology in Costa Rica

All of us have felt the earthquakes that occur occasionally in Costa Rica. Depending on your level of understanding of the geologic processes which caused these earthquakes, you may have been a little frightened, or you may have thought it was a little fun and exciting. To a geologist, these little earthquakes are a good sign, Mother Earth letting go of her forces a little at a time.   § continued below ...

Costa Rica Geology

Geology and Earthquakes Costa Rica
Plate Tectonics

The oceanic Cocos Plate and the continental Caribbean Plate are converging (moving toward each other) at the rate of about 80mm/year.  Continental plates are made up of rock materials that are less dense (lighter) than oceanic plates. At the margin of the collision, the continent "floats" and the oceanic crust "sinks", causing a deep trench along the boundary, which is slightly offshore and parallel to our coast.

As the oceanic plate sinks (subducts), it continues to move inland deep underground, until it sinks deep enough to melt into magmas and lavas.  The string of volcanoes trending through central Costa Rica are the heat and pressure relief valves of this melted oceanic rock.  Between the offshore trench and the onshore volcanoes lies a zone of continental rocks sliding over oceanic rocks deep underground.  This zone is not smooth, and the roughness of the zone causes large chunks of earth to collide, push against each other, and sometimes break. On the surface, we feel the tremors and vibrations of these many underground collisions as earthquakes. §

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Predicting Large Earthquakes

The Nicoya Seismic Gap is an area which has not experienced a large earthquake in over 50 years.  Large earthquakes, of magnitude 7 or higher, have occurred in this gap in 1853, 1900 and 1950.   Scientists from all over the world have been studying the geology of this special area for years, and most are predicting that this area is well overdue for a large earthquake to relieve the stresses and strains of the earth that is moving beneath us.  Marino Protti, Director of OVISCORI (Observatorio Volcanológico y Sismológico de Costa Rica) has stated that "the Nicoya gap has the potential to generate an earthquake with moment magnitude above 7.5".

Magnitude comparisons are on a logarithmic scale, so a magnitude 6 earthquake would be 10 times more destructive than a magnitude 5.  Then a magnitude 7 would be 100 times more destructive, and a magnitude 8 would be 1000 times more destructive.  So what has been predicted by OVISCORI, a 7.5, is the type of earthquake that leaves very few buildings standing and causes fissures in the ground. It would be something like the energy released by 100 hydrogen bombs, or about 500 times more destructive than what we typically feel during the recent !!  §

Costa Rica Geology

Middle America Trench Costa Rica  Earthquakes are Red Dots

Middle America Trench and the Nicoya Seismic Zone

An Early Warning System in Costa Rica

In the early to mid 1990's, the Ocean Drilling Program of Texas A&M University conducted an extensive study of the Middle American Trench, just offshore of the Nicoya Peninsula. Their findings spurred several other worldwide agencies to study the Nicoya Seismic Gap as a possible testing site for an earthquake early warning system.  Over the last decade, OVSICORI, together with cooperating agencies from around the world, has implemented a system of GPS receivers to measure the earth's movement, and a system of seismic receivers to measure and record tremors and earthquakes on the Nicoya Peninsula.

Since radio waves travel faster than seismic waves, the theory behind the early warning system is that when a large earthquake occurs, radio transmissions can give San Jose about 30 seconds of warning before the earthquake waves demolish the city.  San Jose is the major metropolitan center, where the greatest loss of  life and property can be expected.

On the Nicoya Peninsula, however, there will be no prior warning.  The Costa Rican government is also implementing an emergency response procedure to deal with the aftermath of large natural disasters, such as the predicted large earthquake. What can we do?  Hope for more small earthquakes on the Nicoya peninsula, like the ones in January, to relieve the underground stresses that have been building up for years.  §

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