January 8, 2009, M6.1 Earthquake

Available Information


News Summary: M6.1 Cinchona, Costa Rica, Earthquake of January 8, 2009
Contributed by Guillermo Santana, LANAMME, University of Costa Rica


Map of epicentral region
Fig.1 Map of epicentral region
(click to enlarge)

The M6.1 Costa Rica earthquake of January 8, 2009, was caused by a strike-slip fault segment that is perpendicular to the much greater deformation belt that crosses Costa Rica roughly west to east, connecting to the subduction zone in the Pacific to the west and continuing east to northern Columbia. The belt constitutes the north boundary of a microplate that stretches south to the Nazca and Cocos plates. Recent activity in the portion of the microplate includes the 1990-1991 earthquake sequence that concluded with the 7.6 Limon, Costa Rica earthquake. The earthquake epicenter (Figure 1) was located in an area that borders the northern limit of the Central Valley (major city San Jose, 2 million inhabitants, approximately 30 km NNW) just east of the Poas Volcano, at a depth of 5 km, according to the USGS. The town of Cinchona (300 inhabitants), nearest to the epicenter, was completely destroyed. The closest strong-motion record obtained to date indicates a peak acceleration of slightly less than 0.25g and a duration of about 25 seconds with accelerations higher than 0.05g. This record was obtained at a SB type site in the township of Alajuela, some 20 km south of the epicenter at a recording station operated by the University of Costa Rica ( More accelerograms will be forthcoming from the university’s network, which has over 10 stations located in and around the city of San Jose.

Damage is widespread in the epicentral region. This area consists of a mountainous terrain with plenty of rain forests and waterfalls. The area had experienced sustained economic growth due especially to the tourist industry. The next economic activity in importance is agriculture: dairy and strawberry farms. To date the National Emergency Commission ( reports 33 people dead, 7 missing, 2,326 displaced individuals, 91 seriously injured, 267 single-family dwellings damaged, 251 destroyed, and losses estimated in US$ 100 million in an area that covers 180 square km.

Cariblanco Power Generating Station
Fig 2 Cariblanco Power Generating Station
(click to enlarge)

Major failures are both critical lifelines. The first is the hydroelectric power station located within 10 km of the epicenter (Figure 2). This station consists of a system of several reservoirs that altogether generated approximately 100 MW and was operated by the state-run power company. The plant was taken out of operation by the earthquake and constitutes a loss of about 10% of the national energy production capacity. It was overtaken by a mudflow that reached over two meters in several locations. All equipment in the powerhouse has been rendered inoperative.

The second critical lifeline is Route 126, a national road that crosses the epicentral region from north to south through most of the seriously affected rain forests. The road does not comply with modern highway design standards. It is actually a refurbished 160+ year-old road used to connect San José to the Caribbean coast at the mouth of the San Juan River, which serves as the international border between Costa Rica and Nicaragua. Another highway through another corridor further east, opened in 1980, is currently used for that purpose. The damaged bridges are narrow one- or two-lane bridges with simply supported spans of 20 meters or less and ADT of less than 1,000. Five days after the earthquake, at least three of the small bridges have been replaced with prefabricated truss structures (Bailey bridges). Several segments of the highway collapsed due to terrain failure. Altogether more than 3 km of highway have disappeared.

There is probably much to be learned from this earthquake in the areas of landslides, highway failure, environmental impact, power lifelines, power plant generation response, and vulnerability of single-family dwellings.