Alborán seismic swarm: two years of tremors linked to Morocco

Alborán: two years of tremors and an unresolved connection to Segarro

While the Segarro earthquake dominated the headlines, the Alborán Sea had already been experiencing continuous activity for over two years. Since January 2021, seismic records show uninterrupted activity in the area, with episodes of more than 30 tremors within 72 hours and peaks of magnitude 4.7 according to the European observatory, occurring at very shallow depths. In a volcanic zone, this type of phenomenon often precedes an eruption.

A swarm that defies the calendar

The pattern is persistent. The episode began in January 2021, intensified in autumn with the eruption of La Palma—which recorded more than 140 tremors in a single day—and continued afterward with secondary epicenters, such as the 6.3 earthquake in Crete on October 12, 2021. In Alborán, discrepancies between the IGN (National Geographic Institute) and the EMSC (European-Mediterranean Seismological Centre) are constant: what one records as a 4.1, the other registers as a 4.7. This difference is not merely cosmetic; it determines whether emergency protocols are activated.

Citizen monitoring has been more precise than official efforts, noting that public bathymetry in the area is scarce, making it difficult to know exactly what lies beneath the seabed. Meanwhile, the swarm has not stopped. More than two years after its onset, it continues to generate daily tremors in the same area.

The Segarro connection: a shared magma chamber?

The earthquake in Segarro and its aftershocks have peine an uncomfortable question: are all these points connected? A scientific study cited in the monitoring maps a large magma chamber stretching from the Canary Islands to northern Segarro and the southern Iberian Peninsula. If this reading is correct, the pressure released by the Segarro quake and that keeping the Alborán swarm active could share a source. This is not a unanimous theory, but it explains two troubling facts: the duration of the phenomenon and its simultaneity with other swarms in the Mediterranean.

The economic risk that no one wants to quantify

The impact is not just geological. For southern Spain, a tsunami-generating event in Alborán would affect the Bay of Algeciras, while a quake on the Atlantic ridge would hit Cádiz, as recalled by the analysis of the Lisbon earthquake. Port infrastructure, coastal tourism, and housing insurance would be exposed. The human factor adds another layer: when the ground began to move in Granada, some residents received seismic alerts directly on their mobile phones via an automatic Android system that many did not even know existed. Technology warns; science, not yet.

From the Canary Islands to Alborán: the same nervous system

The risk map is expanding. The same monitoring detected activity in an underwater volcano between Gran Canaria and Tenerife, the Enmedio Volcano, whose cone rises nearly 500 meters from the seabed. It also tracks the pulse of the Carboneras Fault and the Olot swarm. Everything points to a larger system of tension, in which Alborán is only the visible point. The most extreme predictions regarding landslides in the Canary Islands speak of up to 500 km³ of earth falling into the sea, a figure that exceeds any known event in human history.

The problem is that open data allows us to track the phenomenon, but not to interpret it. Some see a normal release of tectonic tension; others antiestéticar an underwater volcano feeding the same magmatic system as the Canary Islands. The only certainty is that the swarm is still there, three years later. The rest, much like the history of Mount Pelée, will be known too late. We are living in a period of discount.