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Cinchona

January 8, 2009, M6.1 Earthquake

Available Information

EERI REPORTS


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 (http://iniiserver.inii.ucr.ac.cr/lis/). 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 (www.cne.go.cr) 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.

Papua, Indonesia (offshore)

January 3, 2009; M7.7, 7.4 Earthquakes

Available Information

EERI REPORTS

The Papua Earthquakes of January 3, 2009

Map of West Papua earthquake epicenters
West Papua earthquake epicenters (click to enlarge)

On January 3, 2009 (Indonesian time), a M7.6 earthquake in the pre-dawn hours and a M7.4 earthquake three hours later, almost certainly triggered by the first event, shook the remote east Indonesian province of West Papua. The region nearest the epicenter is sparsely populated and attracts tourists thanks to its diving sites, wildlife, and spectacular scenery. The capital city of Manokwari is the nearest major city (population 161,000) and is located about 145 km and 85 km from the first and second large shocks respectively. Depths of the two events were 17 km for the M7.6 and 23 km for the M7.4.

A tsunami warning was issued and cancelled an hour later. Liquefaction was observed on beaches and in river banks. According to EERI Member Teddy Boen, these events and their aftershocks resulted in little damage to buildings and infrastructure. The Badan Geologi (Geological Agency) reported that in Manokwari, about 250 houses were lightly to heavily damaged with one collapse. Two people were killed and 74 injured. Numbers may have been two or three times larger throughout the entire province.

Widespread fleeing from homes occurred not because of damage but because of fears of tsunamis and additional large shocks. Upwards of 17,000 evacuees filled tent cities. Fear coupled with illness within these camps and rainy weather has impeded the populace’s return home.

The 2009 events were both associated with subduction of the Pacific plate beneath the Australian plate. Relative plate motion in this area is 12 cm/yr; the convergence rate on these two plates is probably a few cm per year on a plane dipping about 30 degrees south beneath the north shore of West Papua. The Sorong fault, a major onshore transform fault that could have a sliprate as high as 10 cm/yr, has not had a large event for at least 100 years and may have been stress-loaded during this recent activity. Therefore there is concern that these recent events may lead to another large earthquake on the Sorong fault, which is located much closer to the cities of Manokwari and Sorong. The original newsletter article can be read here.

 

OTHER REPORTS
Jan 4, 2009 by staff writers of TerraDaily.com

Two powerful earthquakes rattled Indonesia’s West Papua province early Sunday, triggering panic among residents but there were no immediate reports of any casualties or heavy damage.

The first 7.6-magnitude quake struck at 4:43 am (1943 GMT Saturday), about 150 kilometres northwest of the city of Manokwari, the US Geological Survey said, triggering a tsunami alert that was later withdrawn.

It was followed almost three hours later at 2233 GMT by a 7.5-magnitude aftershock, the US agency said.

Both quakes were fairly shallow, with the first hitting at a depth of 35 kilometres (22 miles) and the second at 45 kilometres.

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