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EARTHQUAKE OF 13 JANUARY 2001 IN EL SALVADOR

EARTHQUAKE OF 13 JANUARY 2001 IN EL SALVADOR

George Pararas-Carayannis

Introduction

On Saturday, 13 January 2001, a powerful earthquake struck El Salvador. This was the strongest earthquake to hit the country since October 1986. No destructive tsunami was generated.

The quake killed hundreds of people in San Salvador, the capital, as well as in Las Colinas and other towns and villages. Hundreds more were injured and thousands were left homeless. Many people were trapped beneath the rubble of collapsed buildings. The greatest damage to buildings occurred in Las Salinas. Eighty-seven churches were damaged or destroyed – including Our Lady of Guadalupe Church overlooking Las Colinas.

As of January 15, 2001, preliminary reports estimated that 2,000 were injured, 4,692 houses were destroyed and 16,148 were damaged. The death toll had not been finalized. Authorities estimated that more than 1,000 people were still missing. These estimates were expected to rise.

 

El Salvador, with geographic coordinates of 13 50 N, 88 55 W is located in the Middle of Central America, bordering the North Pacific Ocean, between Guatemala and Honduras on the CircumPacific Belt of Fire, a region characterized by intense seismic and volcanic activity.

Church destruction – Santa Ana

The capital of the country, San Salvador, is located in a valley at 2100 feet (640 meters) on the eastern flank of San Salvador Volcano about 20 miles (32 km) north of the coast of the Pacific Ocean. Near the eastern end of the city is the caldera of the Ilopango Volcano, now a deep lake. Due to the threat of earthquakes, the city’s houses tend to be low and surrounded by open areas.

Earthquake Epicenter, Origin Time, Magnitude and Aftershocks

The earthquake occurred at 17:33:29 UTC, Saturday, 13 January 2001. Its epicenter was at 12.83N, 88.79W, about 60 miles (100 km) SW of San Miguel and about 110 km SE of San Salvador, the capital. The quake’s magnitude was initially given as 7.6 on the Richter scale but later revised to 7.9. The depth of focus was estimated to be 39 km.

Earthquake Epicenter (USGS graphic)

As of January 15, 2001, there were 660 aftershocks, some of them quite strong. Most of the aftershocks were centered within a few miles of the capital. The largest aftershock, with magnitude 5.4, occurred late on Sunday afternoon (14 January 2001), causing widespread panic and forcing many residents of San Salvador to sleep in the streets or in cars.

The quake was felt throughout El Salvador with great intensity. It was also felt throughout Central America from Northern Panama to Central Mexico – a distance of more than 1,100 miles. In Mexico City buildings shook.

Recent Earthquakes and Volcanic Activity in El Salvador

Earthquakes, ranging from 6.5 to 7.9 on the Richter scale, have struck San Salvador 13 times over the last 400 years, all but destroying the city in 1854, 1873, 1917 and, most recently, in October of 1986. The 1986 earthquake killed 1400 people, injured 21,000, and left nearly 300,000 homeless.Of the volcanoes located within the metropolitan area, San Salvador Volcano last erupted in 1917 and Ilopango Volcano last erupted in 1879.

Tectonic Setting – Geological Instability of the Central American Region.

The earthquake of 13 January 2001, occurred on the Cocos tectonic plate, along one of the world’s most intense seismic zones where large destructive earthquakes occur with frequency. The regional tectonic setting and seismogenic coupling in this region are complex.

The geological instability of this region is caused by several tectonic interactions. The Cocos tectonic plate is being subducted beneath two overriding plates: North America to the North-West and the Caribbean to the South-East. Active subduction of the Cocos plate beneath the Caribbean plate is responsible for the formation of the Middle America Trench – which is the plate boundary.

The amount of seismogenic coupling in the region appears to be controlled by several other interacting factors such as the age and motion rate of the subducting Cocos plate, the width of the seismogenic layer, the rheology of the overriding plate, and the influence of the nearby Motagua-Polochic fault system. Segmentation of the subducting plate limits the amount of seismic moment release and therefore the size of potential earthquakes in the region. Therefore, maximum earthquake magnitudes may not exceed 7.9 on the Richter scale.

As a result of active interaction and movement of these tectonic plates, hundreds of earthquakes of all sizes are recorded every year throughout this region. Examples of recent large events in the region are the 7.9 magnitude earthquake of 13 January 2001 in El Salvador, the February 4, 1976 earthquake (Ms 7.5) in Guatemala, and the October 1986 earthquake in El Salvador.
The larger seismic activity results primarily from the active subduction and collision of the Cocos tectonic plate underneath the Caribbean plate. As a result of this active interaction and tectonic plate convergence, several depressions (horsts) and grabens have been also formed on the landward direction of the Middle America Trench, paralleling the Pacific coast. A chain of several active volcanoes has been formed on land. Also, secondary faults and other geological structures are responsible for a number of earthquakes of moderate size throughout this region.

Tsunami Was Not Generated

Although the earthquake of 13 January 2001 occurred along a subduction area known for its tsunamigenic potential, the reason that a destructive tsunami was not generated may be that the depth of focus of this particular event was rather deep at 39 km. The focal depth and epicenter location indicate that this earthquake was probably along the Benioff Zone rather than along the subducting boundary where shallow focus events cause large vertical displacements of the ocean floor. As more seismic data becomes available, a source mechanism study will be undertaken to determine why a significant tsunami was not generated and to understand better the seismotectonic coupling and tsunamigenesis of the Cocos tectonic plate in this particular region of Central America.

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