The 1969 Portugal earthquake struck western Portugal and Morocco on February 28 at 02:40 UTC

Coordinated Universal Time

Coordinated Universal Time is the primary time standard by which the world regulates clocks and time. It is one of several closely related successors to Greenwich Mean Time. Computer servers, online services and other entities that rely on having a universally accepted time use UTC for that purpose...

. Originating west of the Strait of Gibraltar

Strait of Gibraltar

The Strait of Gibraltar is a narrow strait that connects the Atlantic Ocean to the Mediterranean Sea and separates Spain in Europe from Morocco in Africa. The name comes from Gibraltar, which in turn originates from the Arabic Jebel Tariq , albeit the Arab name for the Strait is Bab el-Zakat or...

, the earthquake registered a magnitude

Moment magnitude scale

The moment magnitude scale is used by seismologists to measure the size of earthquakes in terms of the energy released. The magnitude is based on the seismic moment of the earthquake, which is equal to the rigidity of the Earth multiplied by the average amount of slip on the fault and the size of...

 of 7.8 and the maximum felt intensity was VII (Very Strong) on the Mercalli intensity scale

Mercalli intensity scale

The Mercalli intensity scale is a seismic scale used for measuring the intensity of an earthquake. It measures the effects of an earthquake, and is distinct from the moment magnitude M_w usually reported for an earthquake , which is a measure of the energy released...

. In total, thirteen people died. Far more people sustained minor injuries.

Tectonic setting

The epicenter

Epicenter

The epicenter or epicentre is the point on the Earth's surface that is directly above the hypocenter or focus, the point where an earthquake or underground explosion originates...

 of the earthquake

Earthquake

An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...

 lies within a diffuse zone of seismicity known as the Azores-Gibraltar seismic belt

Azores-Gibraltar Transform Fault

The Azores-Gibraltar Transform Fault, also called the Azores-Gibraltar fault zone , is a major geologic fault which runs eastward from the eastern end of the Terceira Rift in the Azores, extending through the Strait of Gibraltar and into the Mediterranean Sea. It forms part of the tectonic boundary...

, that marks the boundary between the African Plate

African Plate

The African Plate is a tectonic plate which includes the continent of Africa, as well as oceanic crust which lies between the continent and various surrounding ocean ridges.-Boundaries:...

 and the Eurasian Plate

Eurasian Plate

The Eurasian Plate is a tectonic plate which includes most of the continent of Eurasia , with the notable exceptions of the Indian subcontinent, the Arabian subcontinent, and the area east of the Chersky Range in East Siberia...

. The deformation at this plate boundary is transpressional in style, with dextral (right lateral) strike-slip 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. The earthquake was located within the Horseshoe Abyssal Plain where active reverse faulting has been imaged on seismic reflection

Reflection seismology

Reflection seismology 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 seismic source of energy, such as dynamite/Tovex, a specialized air gun or a...

 data.

Damage and casualties

At magnitude 7.8, the earthquake was considered very powerful. The resulting damage killed thirteen people (11 in Morocco and 2 in Portugal) and injured about a further 1,000. Damage to local buildings was "moderate", according to the United States Geological Survey

United States Geological Survey

The United States 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, and the natural hazards that threaten it. The organization has four major science disciplines, concerning biology,...

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

Characteristics

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