El Salvador, Nicaragua Shaken by 7.3 Magnitude Quake

According to catastrophe modeling firm AIR Worldwide, on Monday night at 9:51 p.m. local time, a powerful M7.3 earthquake struck off the coast near the border of El Salvador and Nicaragua. The earthquake was the result of normal faulting in the Central America subduction zone at a depth of 40 km, either within the subducting oceanic Cocos plate, or in the overlying Caribbean plate. The quake was felt widely across the region, with shaking reported in Guatemala, southern Belize, El Salvador, Honduras, Nicaragua, Costa Rica, western Panama, and far southeastern Mexico. Based on the limited amount of reported damage thus far and low earthquake insurance penetration in the region, AIR does not expect significant insured losses from this event.

“The quake occurred along a seismically active portion of the Middle America subduction zone, where the last major ruptures were the 2012 M7.3 and 2001 M7.7 earthquakes,” said Dr. Claire Pontbriand, scientist at AIR Worldwide. “The devastating 2001 earthquake was also a result of normal faulting, and occurred at a depth of 40–60 km within the Caribbean plate. The 2001 earthquake triggered more than 16,000 landslides and was responsible for at least 844 deaths, 4,723 injuries, and more than 150,000 damaged buildings.”

A tsunami warning was initially issued, prompting the evacuation of residents in many coastal communities, but it was later downgraded to an alert. No damaging tsunami has been reported.

In El Salvador, the earthquake caused minor damage to at least 12 homes in the department of Usulutan and landslides were reported as well (moderate to heavy rain was falling across the country at the time of the earthquake). Power to the city of San Miguel was temporarily lost. In Nicaragua, at least 10 homes are reported damaged.

Dr. Pontbriand commented, “Central America is a tectonically active plate boundary region, where the Cocos plate subducts northeastward underneath the North American plate and the Caribbean plate along the Middle America Trench. The rates of tectonic plate convergence increase from north to south. Earthquakes occur at all depths along the subduction zone. Shallow earthquakes are primarily concentrated along the trench system, usually within the overriding Caribbean plate. Some of the region’s most intense earthquakes, large magnitude ‘megathrust’ earthquakes, occur along the subducting slab of the Cocos plate and are capable of producing tsunamis.”

According to AIR, in the affected region, masonry is the main construction type and wood is also commonly used for residential and commercial buildings, especially low-rise structures. High-rise buildings are generally constructed of steel and reinforced concrete. Across Central America, the commercial building stock is quite heterogeneous, and varies from poorly constructed low-rise masonry structures to well-maintained steel buildings.

After a M6.3 earthquake in 1965, El Salvador developed a seismic design code for buildings, the first seismic code in Central America. The code was updated in 1989, and again in 1994. The last update involved a probabilistic assessment of seismic hazard in El Salvador, as well as regulations to cover a wide range of practices, such as geotechnical works and guidance on construction using adobe.

According to AIR, Nicaragua implemented the country’s first seismic code, called the “Reglamento de Construcción que regirá el Territorio Nacional” (Construction Regulation that will govern in the National Territory) in 1983. The code takes into account the country’s soil profiles, as well as building design and analysis procedures. Despite more recent seismic events that have revealed flaws in the existing seismic hazard map of the country (such as the 1992 earthquake and tsunami that struck Rivas, a region thought to have low-to-moderate hazard), Nicaragua’s code has not been further updated. It has also been reported that the implementation of this code is not consistently used across building types. For instance, it is reported that the code is not regularly enforced for private residential buildings.

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 are the major factors that exacerbate building vulnerability in these countries.

Source: AIR Worldwide