Why 14 million Spaniards are at risk from earthquakes

The constant nudging of the African continent toward Europe in a sort of geological “kiss” is the driving force behind earthquakes in the south of the Iberian peninsula. But fuelling the recent telluric movement in Granada – which has seen a number of tremors since January 23 – as well as other shocks registered in Spain’s southern province are the multiple faults that exacerbate tremors that are geologically considered to be low intensity. Together, these factors put more than 14 million Spaniards at risk, something that history confirms; earthquake records over the last 1,000 years show a map of high-risk levels around the edges of the continental plates, the east coast and the Pyrenees.

The Iberian peninsula is located at the point where the Eurasian tectonic plate, the African tectonic plate and the Mid-Atlantic Ridge – a volcanic mountain range that divides the ocean into north and south – converge. The two tectonic plates draw closer to each other by four and five millimeters each year, according to Jesús Galindo Zaldívar, a professor at the University of Granada.

1,000 years of earthquakes

in the Iberian Peninsula

Earthquakes of a magnitude of more than 3,

measured and documented since 1048 to 2015

Magnitude

8

6

4

3

Pyrenees

2011 earthquake

in Lorca (magnitude: 5)

Eurasian

Plate

African

Plate

Algeria

200 km

Morocco

Source: National Geographic Institute

1,000 years of earthquakes

in the Iberian Peninsula

Earthquakes of a magnitude of more than 3,

measured and documented since 1048 to 2015

Magnitude

8

6

4

3

Pyrenees

2011 earthquake

in Lorca (magnitude: 5)

Eurasian

Plate

African

Plate

Algeria

200 km

Morocco

Source: National Geographic Institute

1,000 years of earthquakes in the Iberian Peninsula

Earthquakes of a magnitude of more than 3, measured and documented since 1048 to 2015

Magnitude

8

6

4

3

ee

France

AST

Pyrenees

BIZ

CAN

ACO

GIP

LUG

ÁLA

PON

NAV

LE

BUR

PAL

RIO

OUR

GIR

HUES

LLE

ZAM

BAR

ZAR

VALL

SOR

SEG

TAR

GUA

SAL

TER

ÁVI

Portugal

MAD

CAS

CUE

BAL

TOL

CÁC

VAL

CR

ALB

BAD

ALI

MUR

2011 earthquake

in Lorca (magnitude: 5)

CÓR

JA

Eurasian Plate

HUE

SEV

GRA

ALM

MÁL

CÁD

CEU

African Plate

MEL

Algeria

200 km

Morocco

Source: National Geographic Institute

1,000 years of earthquakes

in the Iberian Peninsula

France

AST

Pyrenees

BIZ

CAN

ACO

GIP

LUG

Earthquakes of a magnitude

of more than 3, measured and

documented since 1048 to 2015

ÁLA

PON

NAV

LE

BUR

PAL

RIO

OUR

GIR

HUES

LLE

Magnitude

ZAM

BAR

ZAR

VALL

SOR

8

6

SEG

TAR

4

GUA

SAL

TER

3

ÁVI

Portugal

MAD

CAS

CUE

BAL

TOL

CÁC

VAL

CR

ALB

Eurasian Plate

BAD

ALI

MUR

2011 earthquake

in Lorca (magnitude: 5)

CÓR

JA

HUE

SEV

GRA

ALM

MÁL

CÁD

African Plate

CEU

MEL

Algeria

Morocco

200 km

Source: National Geographic Institute

But this geological “kiss” is only the foundation for the peninsula’s tremors. From December 2, 2020, to January 27 of this year, the National Seismic Network recorded more than 430 earthquakes of magnitudes between 3 and 4.5 on the Richter scale in Atarfe, a city close to the capital of Granada, according to a report by researchers Julián García-Mayordomo and Raúl Pérez López, for the Spanish Geological and Mining Institute (IGME). The movement of the plates (which are relatively rigid) and the deformation of the lithosphere (the rocky outer part of the Earth) produce a field of tectonic stress that impacts the faults – the fractured seams in the Earth’s floor that can be found throughout the peninsula, particularly from Lisbon in Portugal to Ourense in Galicia, throughout the Mediterranean arc and along the border with France.

According to Pérez López, “faults are the catalysts for earthquakes, such as the one recorded in Lorca [Murcia] in 2011 with a magnitude of over 5. In Granada, the two different faults – Santa Fe and Pinos Puente – provoke one other.”

Ana Ruiz Constán, geologist and IGME researcher, agrees. She says that while the approximation of the tectonic plates has been the driving force behind the seismic activity, the existence of associated faults in Granada has also been key.

These circumstances have been compounded further by the peculiar characteristics of the land. “The area is a three-kilometer deep basin with lake and river deposits from five million years ago,” says Pérez López. “These layers of sedimentary material are prone to amplifying the effects of earthquakes, as happens in Mexico City.”

Seismic sequences from December 1,

2020 to January 27, 2021

Greater than 4

3-4

2-3

Fault lines

Jaén

Sevilla

Granada

Almería

Málaga

Cádiz

Eurasian plate

Ceuta

African plate

Melilla

100km

Pinos Puente fault line

Granada

Santa Fe fault line

2km

Source: The Geological and Mining Institute of Spain (IGME)

Seismic sequences from December 1,

2020 to January 27, 2021

Greater than 4

3-4

2-3

Fault lines

Jaén

Sevilla

Granada

Almería

Málaga

Cádiz

Eurasian plate

Ceuta

African plate

Melilla

100km

Pinos Puente fault line

Granada

Santa Fe fault line

2km

Source: The Geological and Mining Institute of Spain (IGME)

Seismic sequences from December 1, 2020 to January 27, 2021

Greater than 4

3-4

2-3

Fault lines

Murcia

Jaén

Sevilla

Huelva

Granada

Almería

Málaga

Cádiz

Eurasian plate

Mediterranean Sea

Ceuta

African plate

Melilla

100km

Pinos Puente fault line

Granada

2km

Santa Fe fault line

Source: The Geological and Mining Institute of Spain (IGME)

Seismic sequences from December 1, 2020 to January 27, 2021

Greater than 4

3-4

2-3

Fault lines

Murcia

Jaén

Sevilla

Huelva

Granada

Mediterranean Sea

Almería

Málaga

Cádiz

Eurasian plate

Ceuta

African plate

Melilla

100km

Pinos Puente fault line

Granada

2km

Santa Fe fault line

Source: The Geological and Mining Institute of Spain (IGME)

On account of these geological peculiarities, Spain has what Pérez López terms an extensive “hot zone,” which stretches from Huelva to Alicante and includes the Pyrenees and part of Galicia. In these areas that are home to more than 14 million inhabitants, the risk of an earthquake is high, although there are not often large earthquakes. “The rate of deformation is slow and the shocks are few and far between,” says Pérez López. Ruiz Constán adds: “Andalusia and the east of the Iberian peninsula are at the plate boundary, but seismicity is diffused.”

Ruiz Constán points out that the risk area extends throughout North Africa, which has the same geological characteristics, pointing to seismological data recorded in areas such as Al Hoceima, in the north of Morocco. “The relief areas of the Baetic mountain range stretch into North Africa,” she says, referring to the Gibraltar Arc – the geological region that covers the Baetic System, one of the main mountain ranges in Spain, the Alborán Sea, the Strait of Gibraltar and the mountainous area of the Rif region of Morocco. Taking into account areas in both the Iberian peninsula and northern Morocco, more than 19 million people are living in an area at risk of seismic activity.

According to Ruiz Constán, “due to the magnitude of the tremors recorded, the associated faults, recurrence and other geodetic data, we can expect earthquakes of up to a magnitude of 6.”

The magnitude of an earthquake may not be important in geological terms, but it is important in social terms

Researcher Raúl Pérez López

But while prediction and prevention mechanisms are urgently needed, seismologists agree that it has not yet been possible to define the precursors of seismic movement. “The stress field, acceleration and cracks allow us to get closer, but we do not know when there will be an earthquake and while cracks allow us to make estimates, we neither know when an earthquake is going to happen or if it will be a big one,” says Pérez López.

Pérez López stresses that plans must take into account the risk of human exposure, arguing that the most important issue with respect to the earthquakes in Granada, and those that may happen in the future, is “the presence of vulnerable people who require a response.” He explains: “The magnitude of an earthquake may not be important in geological terms, but it is important in social terms.

“You don’t need a magnitude-8 earthquake like the one in Japan,” Pérez López continues. “Even if the seismic movement is of a lower magnitude and intensity, if it leads to 20,000 people sleeping in cars and forces the mobilization of civil protection resources, it is important. It is not only about earthquake-resistant construction regulations, which already existed in the times of Al Ándalus [711 to 1492 AC] and which were updated after the Lorca earthquake [in 2011]; the key is preparation, knowing what infrastructure can be damaged or being aware that aftershocks can cause landslides that harm people; or that, if temporary accommodation is needed, it should be located outside areas of aftershocks so as not to increase the anxiety of the population.”

As Ruiz Constán points out, earthquakes generate fear and uncertainty, which affect day-to-day life on top of the damage they incur. “We have to be aware that they happen every so often,” she says. “Sometimes, they are forgotten for a generation. There is a part of the population that does not remember, for example, that Albolote [Granada] suffered a catastrophic one in 1956. We have to be aware that they will continue to occur and be prepared, and make sure the politicians don’t forget.”

English version by Heather Galloway.