Two Quakes Hit Southern Costa Rica

Two moderately strong earthquakes hit Costa Rica’s Southern Zone on Wednesday. The first, a magnitude 5.7 quake, struck at 11:24 a.m. near the mouth of the Golfo Dulce, and the second, magnitude 5.9, occurred at 3:04 p.m. and was centered a few kilometers farther north in the gulf, according to U.S. Geological Survey preliminary reports.

The Red Cross and the National Emergency Commission (CNE) reported no injuries and only very limited structural damages. Airline representatives in Puerto Jiménez said the airport was unaffected.

“The tremor was a bit strong, but we didn’t have any damages,” said Isai Venegas, assistant manager at the Danta Corcovado Lodge, located near Golfo Dulce. Venegas, an OsaPeninsula native, added the quake was the second strongest he has ever experienced.

Although the area sits just off a major fault line, Wednesday’s quakes were both shallow – less than 30 km in depth – and likely the local fault line activity.

Local instruments, though, registered different numbers for the first quake. The National Seismological Network recorded a magnitude 5.5, and the Volcanological and Seismological Observatory of Costa Rica (OVSICORI), magnitude 6.3.

Geophysicist Bruce Presgrave at the USGS’ National & InternationalEarthquakeCenter in Golden, Colorado, said all the readings were accurate, and simply measuring separate aspects of the quakes.

“(Earthquakes) don’t send out the same amount of energy in the same directions.” He said the ranges measured were typical in his experience.

Julie Dutton, another USGS geophysicist, said the different magnitude readings are normal, however, called the difference between local readings on the first quake a “fairly large discrepancy.”

The National Seismological Network, a division of the University of Costa Rica, and OVSICORI, based at the NationalUniversity in Heredia, use readings from local instruments, while USGS readings come information received from stations all over the world. These stations pick up waves from the tectonic movements and send the information to USGS satellite, which in turn relays the information to USGS Colorado offices, where it is compiled.

“It’s a matter of triangulation: If you have more spread out information, your results are going to be more precise,” said Dutton.

But Presgrave insisted on the accuracy of all the readings. “I wouldn’t say (local institutes’) solutions are wrong; they’re different.”

Dutton said stations as far-flung as Uzbekistan, Antarctica and Japan will pick up readings from waves generated by Wednesday’s quakes in Costa Rica. Undulations from the recent temblors, for example, would take about seven to 10 minutes to reach Japan, she estimated.

In Costa Rica, USGS gets readings out of OVSICORI’s monitoring station in Juntas de Abangares in the northwest province of Guanacaste. They also have stations near BarraColoradoIsland in Panama and just outside Tegucigalpa, Honduras, among others.

On Jan. 8, a magnitude 6.1 earthquake hit Costa Rican territory, centered right by the Poas Volcano, a couple dozen kilometers northwest of San José, killing 23 people.

Costa Rica sits over a conflux of various tectonic plates, what seismologists qualify as a “highly seismic” territory.

Tico Times reporters Vanessa I. Garnica and Patrick Fitzgerald contributed reporting.