The 1909 Benavente earthquake occurred on April 23 at 17:39:36 local in the

Santarém District The District of Santarém ( pt, Distrito de Santarém ) is a district of Portugal, located in Portugal's ''Centro Region''. The district capital is the city of Santarém. The district is the 3rd largest in Portugal, with an area of , and a pop ...

of the

Central Region, Portugal The Central Region ( pt, Região do Centro, ) or Central Portugal is one of the statistical regions of Portugal. The cities with major administrative status inside this region are Coimbra, Aveiro, Viseu, Caldas da Rainha, Leiria, Castelo Branco ...

. The earthquake had an estimated

moment magnitude The moment magnitude scale (MMS; denoted explicitly with or Mw, and generally implied with use of a single M for magnitude) is a measure of an earthquake's magnitude ("size" or strength) based on its seismic moment. It was defined in a 1979 pape ...

of 6.0 and a maximum intensity assigned at X (''Extreme'') on the

Mercalli 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 ...

. It nearly destroyed the town of Benavente, killing 60 and injuring 75 people as a result.

Earthquake

Reassessment of the earthquake magnitude suggest a magnitude of 6.0 on the

moment magnitude scale The moment magnitude scale (MMS; denoted explicitly with or Mw, and generally implied with use of a single M for magnitude) is a measure of an earthquake's magnitude ("size" or strength) based on its seismic moment. It was defined in a 1979 pape ...

. The reassessed magnitude is significantly smaller than the previous value of 6.6. The most consistent

focal mechanism The focal mechanism of an earthquake describes the deformation in the source region that generates the seismic waves. In the case of a fault-related event it refers to the orientation of the fault plane that slipped and the slip vector and is ...

solution is

reverse fault 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 ...

ing along a northeast–southwest striking fault plane at an estimated

depth of focus Depth of focus is a lens optics concept that measures the tolerance of placement of the image plane (the film plane in a camera) in relation to the lens. In a camera, depth of focus indicates the tolerance of the film's displacement within the ca ...

of 10 km. The location suggest it occurred in a

seismic zone In seismology, a seismic zone or seismic belt is an area of seismicity potentially sharing a common cause. It may also be a region on a map for which a common areal rate of seismicity is assumed for the purpose of calculating probabilistic ground ...

in the Lower Tagus Valley. There are no documented

surface rupture In seismology, surface rupture (or ground rupture, or ground displacement) is the visible offset of the ground surface when an earthquake rupture along a fault affects the Earth's surface. Surface rupture is opposed by buried rupture, where the ...

s associated with the earthquake. It is thought that the

earthquake rupture In seismology, an earthquake rupture is the extent of slip that occurs during an earthquake in the Earth's crust. Earthquakes occur for many reasons that include: landslides, movement of magma in a volcano, the formation of a new fault, or, most ...

along the seismogenic structure near the surface were distributed along branch faults or dips at very shallow angles. If surface ruptures were to occur, it is likely they were destroyed due to flooding in the valley. Surface

fissure A fissure is a long, narrow crack opening along the surface of Earth. The term is derived from the Latin word , which means 'cleft' or 'crack'. Fissures emerge in Earth's crust, on ice sheets and glaciers, and on volcanoes. Ground fissure A ...

s and sand volcanoes were observed in the ground.

Impact

The earthquake produced extreme shaking, peaking at X (''Extreme'') near 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 ...

, over an area of 450 km².

Liquefaction In materials science, liquefaction is a process that generates a liquid from a solid or a gas or that generates a non-liquid phase which behaves in accordance with fluid dynamics. It occurs both naturally and artificially. As an example of the ...

occurred in the

Tagus The Tagus ( ; es, Tajo ; pt, Tejo ; see #Name, below) is the longest river in the Iberian Peninsula. The river rises in the Montes Universales near Teruel, in mid-eastern Spain, flows , generally west with two main south-westward sections ...

and

Sorraia The Sorraia is a rare breed of horse indigenous to the portion of the Iberian peninsula, in the Sorraia River basin, in Portugal. The Sorraia is known for its primitive features, including a convex profile and dun coloring with primitive mark ...

river plains. At Lisbon, 30 km away, the quake was felt VI (''Strong''). Intensity VI was also felt in the cities of

Setúbal Setúbal (, , ; cel-x-proto, Caetobrix) is a city and a municipality in Portugal. The population in 2014 was 118,166, occupying an area of . The city itself had 89,303 inhabitants in 2001. It lies within the Lisbon metropolitan area. In the ti ...

and

Évora Évora ( , ) is a city and a municipality in Portugal. It has 53,591 inhabitants (2021), in an area of 1307.08 km2. It is the historic capital of the Alentejo and serves as the seat of the Évora District. Due to its well-preserved old to ...

, causing some damage. Moderate shaking (V) was felt in

Spain , image_flag = Bandera de España.svg , image_coat = Escudo de España (mazonado).svg , national_motto = ''Plus ultra'' (Latin)(English: "Further Beyond") , national_anthem = (English: "Royal March") , i ...

. Despite being known as the Benavente earthquake, named after the town, it was in the towns of Samora Correia and Muge were the heaviest damage occurred. Nearly 90% of the towns were destroyed. In Benavente, the foundation of a building detached from its structure and tumbled into the

river. Two churches were severely damaged and unsafe for use. A

seminary A seminary, school of theology, theological seminary, or divinity school is an educational institution for educating students (sometimes called ''seminarians'') in scripture, theology, generally to prepare them for ordination to serve as clergy, ...

sustained damage when plasters fell from the front facade.

Earthquake

Impact

See also

References

Further reading