1976 Guatemala earthquake

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1976 Guatemala earthquake
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UTC  time1976-02-04 09:01:46
ISC  event 717474
USGS-ANSS ComCat
Local dateFebruary 4, 1976 (1976-02-04)
Local time03:01:43
Magnitude7.5 Mw
Depth5 kilometres (3 mi)
Epicenter 15°19′N89°06′W / 15.32°N 89.10°W / 15.32; -89.10 Coordinates: 15°19′N89°06′W / 15.32°N 89.10°W / 15.32; -89.10
Fault Motagua Fault
Type Strike-slip
Areas affected Guatemala
Max. intensity IX (Violent) [1]
Casualties23,000 fatalities, 76,000 injured

The 1976 Guatemala earthquake struck on February 4 at 03:01:43 local time with a moment magnitude of 7.5. The shock was centered on the Motagua Fault, about 160 km northeast of Guatemala City at a depth of 5 kilometers (3.1 mi) near the town of Los Amates in the department of Izabal. [1]

The moment magnitude scale is a measure of n earthquake's magnitude based on its seismic moment, expressed in terms of the familiar magnitudes of the original "Richter" magnitude scale.

Motagua Fault

The Motagua Fault is a major, active left lateral-moving transform fault which cuts across Guatemala, continuing offshore along the southern Pacific coast of Mexico, returning onshore along the southernmost tip of Oaxaca, then continuing offshore until it merges with the Middle America Trench near Acapulco. It forms part of the tectonic boundary between the North American Plate and the Caribbean Plate. It is considered the onshore continuation of the Swan Islands Transform Fault which runs under the Caribbean Sea.

Guatemala City City in Guatemala, Guatemala

Guatemala City, locally known as Guatemala or Guate, officially Nueva Guatemala de la Asunción, is the capital and largest city of Guatemala, and the most populous in Central America. The city is located in the south-central part of the country, nestled in a mountain valley called Valle de la Ermita. It is estimated that its population is about 1 million. Guatemala City is also the capital of the Municipality of Guatemala and of the Guatemala Department.

Contents

Cities throughout the country suffered damage, and most adobe type houses in the outlying areas of Guatemala City were destroyed. The earthquake struck during the early morning (at 3:01 am, local time) when most people were asleep. This contributed to the high death toll of 23,000. Approximately 76,000 were injured, and many thousands left homeless. Some of areas went without electricity and communications for days.

Adobe Building material made from earth and organic materials

Adobe is a building material made from earth and organic materials. Adobe is Spanish for mudbrick, but in some English-speaking regions of Spanish heritage, the term is used to refer to any kind of earth construction. Most adobe buildings are similar in appearance to cob and rammed earth buildings. Adobe is among the earliest building materials, and is used throughout the world.

Electricity physical phenomena associated with the presence and flow of electric charge

Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. In early days, electricity was considered as being not related to magnetism. Later on, many experimental results and the development of Maxwell's equations indicated that both electricity and magnetism are from a single phenomenon: electromagnetism. Various common phenomena are related to electricity, including lightning, static electricity, electric heating, electric discharges and many others.

The main shock was followed by thousands of aftershocks, some of the larger ones causing additional damage and loss of life. [2]

An aftershock is a smaller earthquake that follows a larger earthquake, in the same area of the main shock, caused as the displaced crust adjusts to the effects of the main shock. Large earthquakes can have hundreds to thousands of instrumentally detectable aftershocks, which steadily decrease in magnitude and frequency according to known laws. In some earthquakes the main rupture happens in two or more steps, resulting in multiple main shocks. These are known as doublet earthquakes, and in general can be distinguished from aftershocks in having similar magnitudes and nearly identical seismic waveforms.

Seismic data

The quake's epicentre was located near the town of Los Amates, in the eastern part of the Motagua Fault, a left-lateral strike-slip fault that forms the tectonic boundary between the North American plate and the Caribbean plate. [1] Ground shaking was felt during approximately 39 seconds, and caused visible rupturing over 230 km along the Motagua fault, while the inferred length of faulting—based on aftershock registration—was estimated at 300 km. Average horizontal displacement along the Motagua fault was 100 cm, with a maximum displacement of 326 cm. [1]

Los Amates Municipality of Guatemala in Izabal Department

Los Amates is a municipality in the Izabal department of Guatemala. The population is about 56,000. The mayor is currently Marco Tulio Ramirez Estrada. Los Amates is located on the Motagua River, 6 kilometres (3.7 mi) from the ruins of the ancient Maya city of Quiriguá.

Maximum seismic intensity (MM IX) was located in the Mixco area, some sections of Guatemala City and in Gualán. A seismic intensity of MM VI covered an area of 33,000 km². [1] Soil liquefaction and sand boils were observed in several locations with high seismic intensity. The main quake activated secondary fault zones, including the Mixco fault, located in a densely populated area just north-west of Guatemala City.

Mixco Place in Guatemala, Guatemala

Mixco is a municipality in the Guatemala department of Guatemala.

Gualán is a municipality in the Guatemalan department of Zacapa. It is located in the Eastern part of the country about 165 Kilometers from Guatemala City on route CA-9.

Soil liquefaction

Soil liquefaction occurs when a saturated or partially saturated soil substantially loses strength and stiffness in response to an applied stress such as shaking during an earthquake or other sudden change in stress condition, in which material that is ordinarily a solid behaves like a liquid.

Victims and damage

The most heavily affected area covered some 30,000 km², with a population of 2.5 million. Some 23,000 people were reported dead and 77,000 wounded. Approximately 258,000 houses were destroyed, leaving about 1.2 million people homeless. 40% of the national hospital infrastructure was destroyed, while other health facilities also suffered substantial damage. [3]

International reaction

Very soon after the earthquake, the then president Kjell Eugenio Laugerud García invited most of the foreign ambassadors to tour the affected regions by helicopter, which prompted them to quickly ask for help in their home countries. For example, the United States of America rebuilt most of the roads, and the Canadians and Belgians each rebuilt a village.[ citation needed ]

Aftershocks

Several heavy aftershocks, ranging from 5.2 to 5.8 Mw caused additional casualties and hampered relief efforts.

DateOrigin TimeCoordinatesLocationDepthMagnitude
Feb. 04 197609.30.28.3 14°42′N90°36′W / 14.7°N 90.6°W / 14.7; -90.6 7 km NNE of Mixco 5 km5.8 Mw
Feb. 06 197604.11.03.3 14°36′N91°06′W / 14.6°N 91.1°W / 14.6; -91.1 6 km SSE of San Lucas Tolimán 5 km4.8 Mw
Feb. 06 197618.11.59.2 14°18′N90°12′W / 14.3°N 90.2°W / 14.3; -90.2 11 km ENE of Cuilapa 5 km5.2 Mw
Feb. 06 197618.19.17.7 14°42′N90°36′W / 14.7°N 90.6°W / 14.7; -90.6 5 km ENE of San Pedro Sacatepéquez 5 km5.8 Mw
Feb. 08 197608.13.51.9 15°42′N88°30′W / 15.7°N 88.5°W / 15.7; -88.5 13 km SE of Puerto Barrios 5 km5.7 Mw
Feb. 09 197611.44.46.7 15°18′N89°06′W / 15.3°N 89.1°W / 15.3; -89.1 30 km WSW of Morales 5 km5.1 Mw
Feb. 10 197606.17.43.0 15°00′N89°42′W / 15.0°N 89.7°W / 15.0; -89.7 18 km WNW of Zacapa 5 km4.7 Mw
Mar. 07 197602.54.05.4 14°54′N90°54′W / 14.9°N 90.9°W / 14.9; -90.9 14.5 km SW of Joyabaj 5 km4.8 Mw
Mar. 07 197603.15.40.3 14°42′N90°30′W / 14.7°N 90.5°W / 14.7; -90.5 Chinautla (9 km North of Guatemala City)5 km4.9 Mw
Source: Wayerly Person, William Spence, and James W. Dewey. Main event and principal aftershocks from teleseismic data. In: Guatemalan Earthquake of February 4, 1976, A Preliminary Report.

See also

Notes

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References