Costa Rica Earthquakes
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.
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.
