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.
See also
*
List of earthquakes in 1969
This is a list of earthquakes in 1969. Only magnitude 6.0 or greater earthquakes appear on the list. Lower magnitude events are included if they have caused death, injury or damage. Events which occurred in remote areas will be excluded from the ...
*
List of earthquakes in Portugal
This list documents major earthquakes affecting Portugal.
See also
* List of earthquakes in the Azores
References
{{Europe topic, List of earthquakes in
Earthquakes in Portugal
Portugal
Portugal, officially the Portuguese Republic ...
*
List of earthquakes in Morocco
This is a list of significant earthquakes that either had their epicentres in Morocco or had a significant impact in the country.
Seismicity in Morocco
Northern Morocco lies close to the boundary between the African Plate and the Eurasian Plate, t ...
*
1761 Portugal earthquake
The 1761 Lisbon earthquake and its subsequent tsunami occurred in the north Atlantic Ocean and south of the Iberian Peninsula. This violent shock which struck just after noon on 31 March 1761, was felt across many parts of Western Europe. Its di ...
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