The 1969 Portugal earthquake struck western Portugal and Morocco on February 28 at 02:40 UTC. Originating west of the

Strait of Gibraltar The Strait of Gibraltar ( ar, مضيق جبل طارق, Maḍīq Jabal Ṭāriq; es, Estrecho de Gibraltar, Archaic: Pillars of Hercules), also known as the Straits of Gibraltar, is a narrow strait that connects the Atlantic Ocean to the Medi ...

, the earthquake registered a

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

of 7.8 and the maximum felt intensity was VII (''Very strong'') on the

Mercalli intensity scale The Modified Mercalli intensity scale (MM, MMI, or MCS), developed from Giuseppe Mercalli's Mercalli intensity scale of 1902, is a seismic intensity scale used for measuring the intensity of shaking produced by an earthquake. It measures the eff ...

. In total, 13 people died and 80 sustained minor injuries. It is the largest earthquake to hit Portugal since the

1755 Lisbon earthquake The 1755 Lisbon earthquake, also known as the Great Lisbon earthquake, impacted Portugal, the Iberian Peninsula, and Northwest Africa on the morning of Saturday, 1 November, Feast of All Saints, at around 09:40 local time. In combination with ...

Tectonic setting

The

epicenter The epicenter, epicentre () or epicentrum in seismology is the point on the Earth's surface directly above a hypocenter or focus, the point where an earthquake or an underground explosion originates. Surface damage Before the instrumental pe ...

of the earthquake lies within a diffuse zone of seismicity known as the Azores–Gibraltar seismic belt, which marks the boundary between the

African Plate The African Plate is a major tectonic plate that includes much of the continent of Africa (except for its easternmost part) and the adjacent oceanic crust to the west and south. It is bounded by the North American Plate and South American Plat ...

and the

Eurasian Plate The Eurasian Plate is a tectonic plate that includes most of the continent of Eurasia (a landmass consisting of the traditional continents of Europe and Asia), with the notable exceptions of the Indian subcontinent, the Arabian subcontinent and ...

. The deformation at this plate boundary is

transpression In geology, transpression is a type of strike-slip deformation that deviates from simple shear because of a simultaneous component of shortening perpendicular to the fault plane. This movement ends up resulting in oblique shear. It is generally ve ...

al in style, with dextral (right lateral)

strike-slip In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

accompanied by slow convergence (4 mm/yr). Linear bathymetric features within this zone, such as the SW–NE trending Gorringe Bank, are thought to be a result of reverse faulting. Investigations using multibeam swathe bathymetry have revealed additional SW–NE trending reverse faults and fold axes and a set of WNW–ESE trending lineaments, interpreted as

strike-slip faults In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

. The earthquake was located within the Horseshoe Abyssal Plain, where active reverse faulting has been imaged on

seismic reflection Reflection seismology (or seismic reflection) is a method of exploration geophysics that uses the principles of seismology to estimate the properties of the Earth's subsurface from reflected seismic waves. The method requires a controlled seismi ...

data.

Damage and casualties

At magnitude 7.8, the earthquake was considered very powerful. The resulting damage killed 13 people (11 in Morocco and 2 in Portugal). Damage to local buildings was "moderate", according to the

United States Geological Survey The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, ...

. Overall, structures were prepared for the earthquake and responded well, sustaining slight, if any, damage.

Characteristics

The earthquake is interpreted to have resulted from movement on a southeast-dipping reverse fault.

References

External links

* {{Earthquakes in Africa Earthquakes in Portugal Portugal Earthquake, 1969 Earthquakes in Morocco

Earthquake An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, from ...

1969 in Morocco 1969 tsunamis

Tectonic setting

Damage and casualties

Characteristics

See also

References

External links