The 1790 Oran earthquake occurred on 10 October, striking near the coastal city of

Oran Oran () is a major coastal city located in the northwest of Algeria. It is considered the second most important city of Algeria, after the capital, Algiers, because of its population and commercial, industrial and cultural importance. It is w ...

Algeria Algeria, officially the People's Democratic Republic of Algeria, is a country in the Maghreb region of North Africa. It is bordered to Algeria–Tunisia border, the northeast by Tunisia; to Algeria–Libya border, the east by Libya; to Alger ...

. The

earthquake An earthquakealso called a quake, tremor, or tembloris the shaking of the Earth's surface resulting from a sudden release of energy in the lithosphere that creates seismic waves. Earthquakes can range in intensity, from those so weak they ...

had an evaluated maximum seismic intensity of VIII–X on the

European macroseismic scale The European Macroseismic Scale (EMS) is the basis for evaluation of seismic intensity in European countries and is also used in a number of countries outside Europe. Issued in 1998 as an update of the test version from 1992, the scale is referred ...

(EMS-98). An estimated 3,000 people died during the earthquake and accompanying

tsunami A tsunami ( ; from , ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and underwater explosions (including detonations, ...

. The

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 this earthquake has been disputed among members of the

paleoseismology Paleoseismology is the study of ancient earthquakes using geologic evidence, such as geologic sediments and rocks. It is used to supplement seismic monitoring to calculate seismic hazard. Paleoseismology is usually restricted to geologic reg ...

field, with estimates ranging from 7.5 to even as small as 5.5.

Impact

Beginning on 8 October, the Spanish-conquered city was rocked by a series of strong earthquakes which were felt as far as Spain and

Malta Malta, officially the Republic of Malta, is an island country in Southern Europe located in the Mediterranean Sea, between Sicily and North Africa. It consists of an archipelago south of Italy, east of Tunisia, and north of Libya. The two ...

. The earthquakes were felt by residents in

Granada Granada ( ; ) is the capital city of the province of Granada, in the autonomous communities of Spain, autonomous community of Andalusia, Spain. Granada is located at the foot of the Sierra Nevada (Spain), Sierra Nevada mountains, at the confluence ...

, Cartagena,

Málaga Málaga (; ) is a Municipalities in Spain, municipality of Spain, capital of the Province of Málaga, in the Autonomous communities of Spain, autonomous community of Andalusia. With a population of 591,637 in 2024, it is the second-most populo ...

, and Santa Fe. Violent shaking was felt at Oran until 25 October. Major damage occurred in Oran, with much of the historic city destroyed. Reports of damage also came from

Carthage Carthage was an ancient city in Northern Africa, on the eastern side of the Lake of Tunis in what is now Tunisia. Carthage was one of the most important trading hubs of the Ancient Mediterranean and one of the most affluent cities of the classic ...

Tunisia Tunisia, officially the Republic of Tunisia, is a country in the Maghreb region of North Africa. It is bordered by Algeria to the west and southwest, Libya to the southeast, and the Mediterranean Sea to the north and east. Tunisia also shares m ...

, and Spain across the

Mediterranean Sea The Mediterranean Sea ( ) is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean basin and almost completely enclosed by land: on the east by the Levant in West Asia, on the north by Anatolia in West Asia and Southern Eur ...

. On the morning of 10 October, at 01:15 local time, the most violent shock razed many homes in Oran to the ground, trapping 1,000 people. Multiple shocks occurred in the aftermath, causing destruction and killing many.

Landslide Landslides, also known as landslips, rockslips or rockslides, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, mudflows, shallow or deep-seated slope failures and debris flows. Landslides ...

s were triggered, spilling debris into the city. Modern construction, and a fortress in the city remained intact after the shocks, and no damage was reported outside Oran. According to the '' Gazeta de Madrid'', over 250 soldiers were among the 3,000 killed, while some sources suggest up to 600 died. An alcazaba sustained severely, killing a commander general and his daughter. A number of high-ranking military officials were killed by collapsing structures. At least 86 prisoners, and 23 prison officials died when a jail collapsed. Half of the inmate population managed to escape. Because the city streets were narrow, many survivors gathered at an open space right after the quake. Looting of personal belongings took place in the ruined city. In response, the colonial announced capital punishment for anyone caught. Aid was provided to the survivors one week later, which included tents, food, and medical assistance. The governor of Oran was appointed by

Charles IV of Spain Charles IV (; 11 November 1748 – 20 January 1819) was King of Spain and ruler of the Spanish Empire from 1788 to 1808. The Spain inherited by Charles IV gave few indications of instability, but during his reign, Spain entered a series of disa ...

to write a report on the earthquake a few days later. Damage to Oran and neighboring Mazalquivir were so severe that the

Spanish Empire The Spanish Empire, sometimes referred to as the Hispanic Monarchy (political entity), Hispanic Monarchy or the Catholic Monarchy, was a colonial empire that existed between 1492 and 1976. In conjunction with the Portuguese Empire, it ushered ...

eventually left the cities in 1792 because repair works were not viable. Many of the Spanish residents in Algeria resettled in

Ceuta Ceuta (, , ; ) is an Autonomous communities of Spain#Autonomous cities, autonomous city of Spain on the North African coast. Bordered by Morocco, it lies along the boundary between the Mediterranean Sea and the Atlantic Ocean. Ceuta is one of th ...

Tsunami

A notable

was triggered during the quake, and witnessed by many at the coast. Sailors on ships were thrown overboard when the strong waves struck. Many residents ran from the coast as the tsunami approached. The waves inundated the coasts of

North Africa North Africa (sometimes Northern Africa) is a region encompassing the northern portion of the African continent. There is no singularly accepted scope for the region. However, it is sometimes defined as stretching from the Atlantic shores of t ...

, but no disturbance of the sea was reported in

Morocco Morocco, officially the Kingdom of Morocco, is a country in the Maghreb region of North Africa. It has coastlines on the Mediterranean Sea to the north and the Atlantic Ocean to the west, and has land borders with Algeria to Algeria–Morocc ...

. Boats were taken from ports and drifted away. Small waves also struck the

Iberian Peninsula The Iberian Peninsula ( ), also known as Iberia, is a peninsula in south-western Europe. Mostly separated from the rest of the European landmass by the Pyrenees, it includes the territories of peninsular Spain and Continental Portugal, comprisin ...

in Almeria and Cartagena, wherein the latter location, the sea level rose by up to 6 feet.

Tectonic setting

The nation of

lies near a complex and poorly defined

convergent plate boundary A convergent boundary (also known as a destructive boundary) is an area on Earth where two or more lithospheric plates collide. One plate eventually slides beneath the other, a process known as subduction. The subduction zone can be defined by a ...

separating the African plate from the Eurasian plate. The converging plates create a zone of compression in northern Algeria, which are accommodated by mainly thrust and reverse faults onshore and inland. Thrusting of

strata In geology and related fields, a stratum (: strata) is a layer of Rock (geology), rock or sediment characterized by certain Lithology, lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by v ...

due to compression formed the

Atlas Mountains The Atlas Mountains are a mountain range in the Maghreb in North Africa. They separate the Sahara Desert from the Mediterranean Sea and the Atlantic Ocean; the name "Atlantic" is derived from the mountain range, which stretches around through M ...

in Algeria and

. The tectonic situation of Algeria also makes the country vulnerable to large and deadly seismic events with magnitudes greater than 6.0. The offshore thrust faults also pose a

threat to the Algerian coast during large earthquakes.

Earthquake

Previous studies of earthquakes in Algeria and on this particular event have assigned the maximum seismic intensity at IX–X on the MSK-64,

EMS-98 The European Macroseismic Scale (EMS) is the basis for evaluation of seismic intensity in European countries and is also used in a number of countries outside Europe. Issued in 1998 as an update of the test version from 1992, the scale is referred ...

and Mercalli scales. Based on inferring the historical descriptions of the event, Oran was assigned IX–X, while intensities IV–V was felt in Almeria and Cartagena (IV). At Mers-El-Kébir, the felt intensity was IV–V based on literature reviews. A re-evaluation of more recent literature describing the earthquake suggests the intensity was only VIII. The severe damage which occurred was due to poor construction practices. The intensity most likely did not achieve IX level because at Mers-El-Kébir, a mere 8 km from Oran did not report any damage suggesting the intensity was weaker than previously thought. In a 2019 journal, the authors assigned the coastal areas of Oran, where the greatest damage was reported, intensity IX–X. Intensity IX–X was inferred from original Spanish documents describing the effects of the earthquake. The high intensity shaking and tsunami generation is due to the shallow

hypocenter A hypocenter or hypocentre (), also called ground zero or surface zero, is the point on the Earth's surface directly below a nuclear explosion, meteor air burst, or other mid-air explosion. In seismology, the hypocenter of an earthquake is its ...

depth and offshore

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. Determination The primary purpose of a ...

location. According to Pedro María Legallois Grimarest, a military officer, the tremors began with the vertical movement of the ground and was followed by shaking in the southwest–northeast direction. This would suggest 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, mos ...

consisted of two sub-events on a

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 f ...

. The northwest coast of Oran hosts a reverse fault offshore which may be the source of the quake and tsunami. The source fault may be one that stretches from the sea to onshore. Based on considering the damage and tsunami, a seismic magnitude of 6.0–6.5 has been proposed for the event.

Other events

On 6 June 2008, a 5.5 earthquake struck off the coast of Oran with a maximum felt intensity of VII on the EMS-98 scale or VI on the Mercalli. The earthquake killed one person and caused dozens of injuries. The moment tensor solution indicated reverse faulting at a shallow depth with an epicenter offshore. The faults offshore are activated by northwest–southeast compression as a result of the Africa-Eurasia convergence in the Mediterranean.

References