AIR Analyzes Powerful Honduran Quake; Report 6 Dead

May 29, 2009

According to catastrophe risk modeling firm AIR Worldwide, a powerful 7.1 magnitude earthquake struck off the coast of Honduras early Thursday morning. AIR said “the earthquake hit at 3:24 a.m. local time (08:24 UTC) 39 miles (64 km) northeast of Roatan, the largest of Honduras’s three Bay Islands. Homes and other buildings have been toppled in several locations, and damage has also been reported in neighboring Guatemala and other Central American countries.

“The earthquake, which had a relatively shallow focal depth of 8.7 miles (14 km), briefly triggered a tsunami alert for much of Central America’s Caribbean coast. According to the most recent news reports at least six people were killed by the quake, a number have been injured, and significant property damage in some areas has been confirmed.

The bulletin noted, however, that “because the event occurred well offshore and the majority of affected properties are not insured against earthquake risk, AIR expects insured losses will be minimal.”

Dr. Peeranan Towashiraporn, Senior Engineer at AIR Worldwide, explained that the ” tremor took place along the Swan Fracture zone, which separates the North American and Caribbean plates and extends from the Caribbean Sea westward into Southern Guatemala. The two plates slide past each other here at a rate of about 18mm per year. Thursday’s earthquake was the largest offshore quake to strike along the fracture zone since a 6.0 magnitude temblor hit there in 2002.”

AIR’s bulletin added: “The Caribbean-North America plate boundary fault is seismically very active. Most notably, on February 4th, 1976, a magnitude 7.6 quake struck about 180 miles west of the current earthquake. A century earlier, in 1856, an earthquake of magnitude about 7.7 occurred in the same area as Thursday’s quake, probably rupturing the same segment or a nearby segment of the Swan fracture zone. Earthquakes of similar magnitude also took place along two landward extensions of the Swan fracture zone in 1785, 1812, and 1921.”

“Honduras is the only country in the region where there are no official seismic provisions for design codes,” Dr. Towashiraporn. stated: “Construction has been strongly influenced by historical connections with Spain and Britain. Perhaps 15 percent of total building stock is unreinforced masonry, which is among the construction types most vulnerable to ground shaking.”

The earthquake shook the area for more than 30 seconds and according to rescue officials, knocked out power and caused minor damage to buildings on Roatan. Houses also collapsed in Puerto Cortes on the north coast of the country, and in Santa Barbara, further inland, where the ceiling of an old colonial church caved in. Fires broke out in the northern business city of San Pedro Sula, where workers were evacuated from factories that exhibited cracked walls. The city’s connection to the rest of the country, Democracy Bridge, which spans Honduras’s largest river, the Ulua, also collapsed. San Pedro Sula is the country’s second-largest city.

In Honduras, about one quarter of all residential construction is estimated to be of adobe, about one third of wood, and over 40 percent to be of masonry. Commercial construction consists about equally of one third masonry and one third adobe, less than ten percent concrete and steel, and the remainder of wood.

Source: AIR Worldwide

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