The epicentre of Spain's earthquake history is in the south

Encarni Hinojosa

Malaga

16/10/2023 a las 21:55h.

On 8 September, an earthquake measuring 6.8 magnitude triggered the disaster in Morocco. The proximity of the epicentre of this major earthquake to southern Spain is no coincidence.

Tectonic plates

Plate boundary

Convergent or destructive boundary

North American

Eurasian

African

Antarctic

South American

Australian

Source: USGS

E. H.

Tectonic plates

Plate boundary

Convergent or destructive boundary

North American

Eurasian

African

Indian

South American

Australian

Antarctic

Source: USGS

E. H.

Tectonic plates

Convergent or destructive boundary

Plate boundary

Eurasian

Arabian

Philippine

North American

African

Indian

Pacific

Pacific

South American

Australian

Nazca

Antarctic

Scotia

Source: USGS

E. H.

Tectonic plates

Convergent or destructive boundary

Plate boundary

Eurasian

North American

Juan de Fuca

African

Arabian

Philippine

Caribbean

Indian

Cocos

Pacific

Pacific

South American

Nazca

Australian

Antarctic

Scotia

Source: USGS

E. H.

Friction between the African (Nubian) and Eurasian tectonic plates, just north of the neighbouring continent, is responsible for most of the earthquakes documented in Spain since the 14th century by Spain's National Geographic Institute. This means that most of the epicentres of these earthquakes are located in southern Spain, specifically in Andalucía, Murcia and Alicante - on land - and in the Gulf of Cadiz and the Alboran Sea - on water.

Records over the years of these earthquakes and their parameters, together with other scientific analyses related to the geological characteristics of the terrain, allows the National Geographic Institute to produce the seismic hazard map of Spain. It was last updated in 2015 and represents the probability of earthquakes with a hazard magnitude in a return period of 475 years.

Seismic risk in Spain

Return period: 475 years,

ground acceleration data

Low risk

High risk

Source: Instituto Geográfico Nacional

E. H.

Seismic risk in Spain

Return period: 475 years,

ground acceleration data

Low risk

High risk

Source: Instituto Geográfico Nacional

E. H.

Seismic risk in Spain

Return period: 475 years, ground acceleration data

Low risk

High risk

Source: Instituto Geográfico Nacional

E. H.

Seismic risk in Spain

Return period: 475 years, ground acceleration data

Low risk

High risk

Source: Instituto Geográfico Nacional

E. H.

The map makes it clear where the most dangerous areas of the country are located. Next to the Pyrenees, Murcia - with influence in neighbouring Alicante - and Granada - with effects in Malaga, especially in the regions of Axarquía in the east and Nororma in the north.

An earthquake in detail

What are the main characteristics and how are they measured?

Hypocentre

Also known as the focus, it is the point within the Earth where an earthquake rupture starts.

Depth

The distance between the hypocentre and the Earth's surface.

Deep-focus

When the focus is at a depth of 300 kilometres or more.

Intermediate

When the focus is at a depth of between 300km and 70km.

Shallow

The most dangerous as the hypocentre is 70 kilometres or less from the Earth's surface.

Epicentre

The point on the Earth surface directly above the hypocentre and where the earthquake is felt the most.

Area

The zone around the epicentre where the earthquake is felt.

Intensity (Mercalli scale)

Subjective scale (based on past records documentary references, etc.) measured in Roman numerals. It focuses on earthquake damage.

Magnitude (Moment Magnitude Scale)

Objective scale (based on seismograph data). It focuses on the energy released and is used for modern-day earthquakes, replacing the similar Richter scale.

AUX STEP FOR JS

The National Geographic Institute compiles a list of the biggest earthquakes in the history of Spain based on their intensity, or Mercalli scale, which is determined by historical records, journalistic references, etc.

The list enumerates as many as 27 major earthquakes, from the year 1048 to the most recent one in Lorca (Murcia) in 2011. Of these 27, 17 - 6 out of every 10 - had their epicentre in or particularly affected Andalusian locations, such as the first one documented in Malaga, in 1494, or the one in 1680, which had its epicentre in Alhaurín el Grande.

But technology, specifically a seismograph, provides a more accurate record. The National Geographic Institute has stored objective data on all earthquakes with an epicentre in Spain or adjacent areas for the last 100 years. Seismographs, in addition to the magnitude on the Richter or Moment scale, also record the exact date and time of the earthquake, the location of the epicentre and the depth of the hypocentre.

The following interactive map shows all earthquakes with a magnitude greater than 3 with an epicentre in the south of Spain. The colour code represents the depth of the earthquake, with the earthquakes painted in red being the most dangerous, as their hypocentre is closer to the land or sea surface.

The area of Granada is not only one of the areas with the highest concentration of earthquakes, but also the majority of these earthquakes have a shallow depth (hypocentre at a depth of less than 70 kilometres). The area of Malaga with the highest concentration of epicentres is on the west coast (around the maritime-terrestrial limit of Fuengirola, Benalmádena and Torremolinos), although they are earthquakes of intermediate depth (70-300 kilometres).