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Terceira
Graciosa
São Jorge
Location of the epicenter of the 1980 Azores Earthquake
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| Date | January 1, 1980 |
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| Origin time | 15:43:39 UTC-1 |
| Magnitude | 6.8 Mw |
| Depth | 10 km |
| Countries or regions | Portugal Azores |
| Tsunami | A small tsunami was registered in Angra do Heroismo |
| Casualties | 59 confirmed dead 300 injured |
Striking the Autonomous Region of Azores on January 1, the 1980 Azores Island earthquake killed 61 people and injured over 400, causing severe damage on the islands of Terceira and São Jorge. Measuring 7.2 on the Richter scale, it also shook the islands of Pico and Faial. The earthquake was found to be, like other Azores earthquakes, ruptured in a strike slip motion.
In response to the earthquake, Portuguese president António Ramalho Eanes announced three days of national mourning. Relief efforts, initiated by local Air Force agents, were successful and were soon accompanied by government-supported agencies.
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In 1950, another strong earthquake had rocked the Azores Islands region, and this was the largest earthquake since.[1]
The Azores islands are volcanic in origin and lie in a tectonically complex area to the east of the Mid-Atlantic Ridge. They lie close to the boundary between the Eurasian and African plate but are generally considered to form their own microplate.[2] The 1980 earthquake was caused by movement on a northwest-southeast trending strike-slip fault.[2]
After aftershocks from the quake had concluded, examination took place, producing a focal solution to the small events. Movement of these shocks were similar to previous earthquakes around the Azores Islands. For these earthquakes, scientists had determined that the conjugate nodal plane was responsible, seeing fault shear on the right-lateral (dextral) side.[3] All faulting in this area is strike-slip-oriented, and on a rather large scale.[4] Because of this research, information now points towards Azores volcanism being controlled by earthquake movement.[3]
The earthquake struck the Azores Islands with a Richter scale magnitude of 7.2.[5] Causing considerable damage on three separate islands (Terceira, São Jorge, and Graciosa),[5] it destroyed several buildings.[6] According to local reports, roughly 70 % of the houses on Terceira were completely demolished, including the historic quarter of the-then island capital, Angra do Heroísmo.[1] In general, public buildings such as churches remained, in spite of several that caved in on themselves.[1] Public utilities such as electricity and water, were reported cut in several areas.[1]
Initial fatality numbers were set at 52,[6] this was later revised to 61.[2] Additionally, the injuries were set at 300[7] but this was revised to more than 400.[5] At least 20,000 people were left homeless.[8] Minor damage was recorded at Pico and Faial islands.[1]
No fatalities were recorded at the Lajes Field air base, nor any major damage.[1]
United States Navy and Air Force troops stationed at Lajes functioned as disaster relief workers,[1] sheltering as many as 150 families.[9] Portuguese Air Force members brought supplies to earthquake victims, while a João Coutinho class corvette navy ship transported medical officials to the island. The President António Ramalho Eanes flew in on a plane accompanied by medical personnel and supplies such as bedding.[1] Local officials including policemen and volunteer firemen cleared roads for relief supplies transportation. Responding to the situation, they were to look through rubble spawned from the earthquake for survivors.[1] Soon after, huts were built to replace the destroyed homes for 200 families of the islands. 100 huts were constructed by a People to People project fund.[9]
Three days of national mourning were declared by Eanes.[1] Nineteen seismograph stations have since been installed and are relied on by most of the islands' people. Eleven of them are used to monitor activity, while the other eight also record information on a geothermal area.[10]
The earthquake forced hundreds of people to leave the country for the United States. It occurred during a period of several major natural disasters in which many residents of the island left; in 1975, 8,000 residents left. In 1981, however, just 2,500 people left the island.[8]
Later studies of the events leading up to the tragedy found several factors contributing to the extent of the damage. A. Malheiro (2006) linked five major causes to damage from these earthquakes. The buildings most damaged by the earthquake were near fault lines on top of loosely packed soil. They tended to be of poor construction and did not conform to proper building code or had not been adequately addressed.[11]
The area around the Azores remains active. Threats from earthquakes and landslides remain.[11]