The recent devastating earthquake in Haiti has raised concerns and questions in other earthquake-susceptible parts of the world: “What should we do to prepare for a potential earthquake?”; “If we do experience an earthquake, what should we do to reduce our chances or injury or death?”

I don’t want to frighten anyone, especially potential visitors to the beautiful country of Costa Rica (the chances of being murdered or killed in a car accident in the United States are astronomically higher than the chances of being injured in an earthquake in Costa Rica).  However, that said, the reality is that Costa Rica is one of the most earthquake-prone countries in the world.

Just off the west coast is the Middle America Trench, where a section of the seafloor called the Cocos Plate dives beneath Central America, generating powerful earthquakes and feeding a string of active volcanoes. This type of boundary between two converging plates of the Earth’s crust is called a subduction zone–and such zones are notorious for generating the most powerful and destructive earthquakes.

Moon Costa Rica explains it as follows:

Costa Rica lies at the boundary where the Pacific’s Cocos Plate–a piece of the earth’s crust some 510 km wide–meets the crustal plate underlying the Caribbean. The two are converging as the Cocos Plate moves east at a rate of about 10 cm a year. It is a classic subduction zone in which the Caribbean Plate is forced under the Cocos–one of the most dynamic junctures on earth. Central America has been an isthmus, a peninsula, and even an archipelago in the not-so-distant geological past. It has therefore been both a corridor for and a barrier to landward movements, and it has been an area in which migrants have flourished, new life forms have emerged, and new ways of life have evolved. Yet a semblance of the Central America we know today became recognizable only in recent geological history. In fact, Costa Rica has one of the youngest surface areas in the Americas–only three million years old–for the volatile region has only recently been thrust from beneath the sea.

In its travels eastward, the Cocos Plate gradually broke into seven fragments, which today move forward at varying depths and angles. This fracturing and competitive movement causes the frequent earthquakes with which Costa Ricans contend. The forces that thrust the Cocos and Caribbean Plates together continue to build inexorably.

From insignificant tremors to catastrophic blockbusters, most earthquakes are caused by the slippage of masses of rock along earth fractures or faults. Rocks possess elastic properties, and in time this elasticity allows rocks to accumulate strain energy as tectonic plates or their component sections jostle each other. Friction can contain the strain and hold the rocks in place for years. But eventually, as with a rubber band stretched beyond its breaking point, strain overcomes frictional lock and the fault ruptures at its weakest point.

Suddenly, the pent-up energy is released in the form of an earthquake–seismic waves that radiate in all directions from the point of rupture, the “focus.” This seismic activity can last for a fraction of a second to, for a major earthquake, several minutes. Pressure waves traveling at five miles per second race from the quake’s epicenter through the bedrock, compressing and extending the ground like an accordion. Following in their wake come waves that thrust the earth up and down, whipping along at three miles per second.

For Costa Ricans, the bad news is that the most devastating earthquakes generally occur in subduction zones, when one tectonic plate plunges beneath another. Ocean trench quakes off the coast of Costa Rica have been recorded at 8.9 on the Richter scale and are among history’s most awesome, heaving the sea floor sometimes scores of feet. These ruptures often propagate upward, touching off other, lower-magnitude tremors. This is what happened when the powerful 7.4 quake struck Costa Rica on 22 April 1991. That massive quake, which originated near the Caribbean town of Pandora (112 km southeast of San José), left at least 27 people dead, more than 400 injured, 13,000 homeless, and more than 3,260 buildings destroyed in Limón Province. The earthquake caused the Atlantic coastline to rise permanently–in parts by as much as 1.5 meters. In consequence, many of the beaches are deeper, and coral reefs have been thrust above the ocean surface and reduced to bleached calcareous skeletons.

In 2009, “the Cinchona Earthquake” occurred at 1:21:34 pm local time (19:21:34 UTC) on January 8, 2009. The epicenter of the 6.1 Mw earthquake was in northern Costa Rica, 30 kilometres (19 mi) north-northwest of San José. The earthquake was felt all over Costa Rica as well as in southern central Nicaragua.

The earthquake took at least 34 lives, including at least three children, left about 64 people missing, and injured at least 91. Hundreds of people were trapped and two villages had been cut off.  Most of the victims died when a landslide occurred near the La Paz waterfall by the Poás Volcano, and 452 people including 369 tourists were evacuated from the area in helicopters.  1,244 people were displaced, and 1,078 people are living in shelters.  In addition, a hotel, houses, roads, and vehicles were damaged, and several bridges were also destroyed.  The town of Cinchona was heavily hit, and all of the buildings there were heavily damaged. Power was temporarily disrupted in San José.

(Read the rest of this post to see Episode 14 of Pilot Season).

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