Will Big Quake Soon Strike Nicoya?
THE ground undulated strongly, Evaristo Díaz said,curling and opening his fingers to show the effects of the1950 earthquake on the Nicoya Peninsula, a quake thatregistered a powerful 7.7 on the Richter scale.Díaz, 69, a retired grade-school teacher who has livedhis entire life in the town of Nicoya, pointed to the densedevelopment around the Central Park, the two- and three-story-cement buildings that have replaced the woodenhouses of his childhood.“Now it would be more dangerous,” he said.For years he and his neighbors have heard scientistspredicting another quake of similar magnitude – historicalpatterns suggest there is a 50-year lapse between the bigones – but nobody pays attention, he said.“They don’t give it any credence,” he said. “Nobodyhas prepared themselves.”THE expected earthquake, which scientists call a certainty,not a probability, and the Pacific peninsula’s seismicactivity in general have shined the international scientificcommunity’s limelight on the region.A fault lies under the entire Nicoya Peninsula, wherethe Cocos tectonic plate is plowing into and under theCaribbean plate with the sluggish but irresistible consistencyof geologic force. As it topples downward at a paceof roughly 88 millimeters per year, it is dragging the south- ern edge of the peninsula down with it.Some coastal communities have seentheir beach slowly sink until seawater islapping at their doorsteps.But every 50 years or so, according toscientists, the peninsula breaks free ofCocos’ grip and springs upward, like a divingboard. Record exists of a quake of largemagnitude in the region in 1853, another in1900 and the last in 1950.ACCORDING to Marino Protti of theVolcanological and Seismological Observatory(OVSICORI) at the UniversidadNacional (UNA) in Heredia, north of SanJosé, the area is in the midst of a seismicgap, a waiting period between powerfulquakes.“The very limited seismic sliding thathas occurred in Nicoya since 1950, therapid convergence of the Cocos andCaribbean plates and the size of the fault atthe subduction zone suggest Nicoya’s seismicgap has already reached its potential toproduce an earthquake with a magnitude ofnear 7.5,” Protti said.OVSICORI monitors a network of fourstations in Nicoya that record earthtremors, and five Global PositioningSystem (GPS) receptors, operated togetherwith scientists from the University ofMiami and the University of Tokyo, thatcontinuously transmit plate movement.GPS units are a relatively new additionto the arsenal of seismic detection technology,each linked to a cloud of 24 satellitescircling the earth in distinct orbits.Through receptors anchored to any pointon firm ground, the units can pinpoint themovement of the earth’s plates to the millimeter.OVSICORI plans to expand its GPScoverage on the peninsula to 12 receptorsthis year, Protti said. The U.S. NationalScience Foundation, through grants fromthe University of California at Santa Cruzand the University of Miami, will pay forthe new GPS units.TIMOTHY Melbourne, of the CentralWashington University in the U.S. state ofWashington, a visiting Fulbright professor atUNA, is studying the fault line off the coastof Nicoya as a miniature scale model of thefault line off the northwestern U.S. coast.“The subduction in Washington is 50times bigger than Nicoya,” he said. “Whenthe quake strikes there, it will be a Xeroxcopy of Sumatra (the quake that generatedlast year’s southeast Asian tsunamis).”To mount GPS units alongWashington’s fault, however, scientistswould have to drill into the sea floor milesoffshore.“What we don’t have in Washington isa Nicoya Peninsula,” he said. “That makesthis region very special in the world. It isright on the subduction zone, so it’s easy tomeasure the processes. These types ofpeninsulas are very rare – there are onlyabout three in the world as good as this,and this is the closest to the States.”EARTHQUAKES and resultingtsunamis have claimed about 8 millionlives in the last 1,000 years, Melbournesaid, about half of those in the last century.It is not that there are more or bigger earthquakesthese days, rather, there are muchhigher concentrations of people in earthquake-prone areas.In Nicoya, “The earthquake will happen,there’s no doubt,” he said.Most of its energy will be consumed onland, which will prevent it from creatingtsunamis, he said.While citizens of the town of Nicoyasay they are not prepared for such a quake,scientists are attempting to understand theforces at play to predict future quakes and,hopefully, save lives.“Seismic prediction is difficult, but notimpossible. It requires a lot of observationand registry of information that allows thefine-tuning of physical models to accelerateour understanding of the naturalprocesses that merge in the generation ofearthquakes,” Protti said. “This is an historicopportunity to document an earthquakeof large magnitude in Costa Ricaand contribute to the development and perfectionof seismic prediction.”
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