Origin time 02:40:32 Depth 22 km Date 28 February 1969 | Magnitude 7.8 Mw | |
Tsunami 1.14 m (3 ft 9 in)3 runups Aftershocks 6.3 Mw Feb 28 at 04:25:35 UTC Similar 1755 Lisbon earthquake, 1968 Illinois earthquake, 2007 Peru earthquake, 1964 Alaska earthquake, 1989 Loma Prieta earthquake | ||
The 1969 Portugal earthquake struck western Portugal and Morocco on February 28 at 02:40 UTC. Originating west of the Strait of Gibraltar, the earthquake registered a magnitude of 7.8 and the maximum felt intensity was VII (Very strong) on the Mercalli intensity scale. In total, thirteen people died. Far more people sustained minor injuries.
Contents
Tectonic setting
The epicenter 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 and the Eurasian Plate. 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 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). Damage to local buildings was "moderate", according to the United States Geological Survey. 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.