M6.5 Parrita Earthquake, Costa Rica, 2017
11/13/2017 9:24:00 AM
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First Posting 11/13/2017 9:24:00 AM 
Posting Date: 11/13/2017 9:24:00 AM

An M6.5 earthquake shook the Central Valley of Costa Rica at 8:28 p.m. local time Sunday night (02:28:24 UTC today), causing minor damage in the lightly populated Puntarenas region of the Pacific Coast. The epicenter was located 16.8 km (10.4 miles) southeast of the beach resort of Jacó, and shaking was felt briefly in Costa Rica's capital, San Jose, 100 km (60 miles) to the northeast. The event occurred at a depth of about 20 km according to the USGS, and was followed by at least two aftershocks.

Hazard and Exposure

Central America, an isthmus that extends from Guatemala and Belize in the northwest to Panama in the southeast, is a highly active, complex seismic environment. The region is sandwiched between the large North American and South American plates. It is connected to the Caribbean plate on the east and bordered by the Cocos plate on the west. The southern region is a little more complicated. In the southeast, there is the Panama block, an independent tectonic unit comprising southern Costa Rica and Panama that fits between the Caribbean and South American plates. The Nazca plate borders the Panama block to the southwest, wedged between the Cocos and South American plates.

Costa Rica is at significant risk of exposure to earthquakes due to the country’s subduction and volcanic environment. It is important to note that the seismic performance of buildings in Central America is greatly influenced by local construction practices. Notwithstanding the existence of seismic codes, poor detailing and workmanship; inadequate materials; and a lack of rigorous inspection and quality control procedures for building construction exacerbate building vulnerability in the region.

In Costa Rica, the primary construction type for residential buildings is masonry. The choice of masonry is chiefly influenced by wind design considerations, rather than by seismic considerations. Confined masonry is the most popular type of masonry construction practice in Central America and it performs better than plain masonry in earthquakes. In addition to masonry, wood and adobe buildings are common in residential properties.  For commercial buildings aside from masonry, steel and reinforced concrete are also very common especially for mid- and high-rise buildings.

In view of seismic activity, Costa Rica has put in practice seismic design requirements and has made several amendments to its seismic code. In 1974, Costa Rica became the second Central American country to implement an official modern seismic code.  The code was updated in 1986, 2002 and 2010. 

Reported Damage
The earthquake was experienced most severely in the provincial districts of Quepos, Parrita, and Garabito. In the resort of Jacó, which has a population of about 10,000 and few tall buildings, at least one structure has been reported evacuated because of apparent damage. Elsewhere, there are reports of fallen walls and of landslides blocking highways, including the road between Jacó and Tárcoles to the north. Fallen utility poles and brief power outages have also been noted, and there are widespread reports of artwork falling from walls and objects from shelves. Hospitals are functioning normally, and there are no reports of significant damage to infrastructure.


ShakeMap for the M6.5 earthquake that struck near Jacó, Costa Rica, at 2:28 UTC on November 13, 2017. (Source: USGS)

Deadly Earthquake on IranIraq Border

Just hours before the Parrita event, the deadliest earthquake of 2017, a massive M7.3 temblor, struck the border region of Iran and Iraq late on Sunday, November 12 (18:18:17 UTC). The epicenter of this earthquake was located 32 km south of Halabjah, Iraq (220 km northeast of Baghdad). According to the USGS, the temblor was the result of oblique-thrust faulting at mid-crustal depth (~25 km). The number of casualties in Iraq is not yet clear, but at least 480 have died in Iran and many more have been injured; these numbers are likely to increase as recovery efforts advance.

Iran’s western Kermanshah Province, a rural area in the Zagros Mountains, appears to have experienced the worst impact. Power outages and multiple collapsed buildings are reported. The main hospital in the Iranian town of Sarpol-e Zahab in Kermanshah, for example, was severely damaged according to state television. Reports on social media indicate that shaking was felt as far afield as Armenia, Azerbaijan, Georgia, Israel, Jordan, Kuwait, Turkey, and the United Arab Emirates.

M6.5 Parrita Earthquake, Costa Rica, 2017
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