Two earthquakes, magnitude 4.5 and 3.8, shake Azores' São Miguel five minutes apart

Two felt quakes five minutes apart

On Thursday, 29 October 2026, two earthquakes were felt on the Azores island of São Miguel, five minutes apart. The Portuguese agency IPMA reported that the first struck at 07:54 UTC (06:54 local time) with a local magnitude of 4.5 on the Richter scale. Its epicentre lay about 40 kilometres west of Ginetes, at an estimated depth of two kilometres. The tremor was felt at a maximum intensity of III/IV on the Modified Mercalli scale in the Ginetes parish, and more weakly in several other localities on the island. Five minutes later, at 07:59 UTC, a second quake of local magnitude 3.8 hit the same zone, felt at a maximum intensity of II in Ginetes.

A swarm building since 20 October

IPMA says seismic activity in the Fossa de Hirondelle area has risen sharply since 20 October. Up to the time of its note, 75 earthquakes had been located in that area, and four of them were felt. The event with the greatest macroseismic impact in the zone so far occurred on 20 October, with a local magnitude of 5.1 (moment magnitude 5.3 Mw). It was felt at a maximum intensity of IV/V in the western part of São Miguel, with weaker effects in other parishes of São Miguel and on Terceira.

The moment tensor for the 20 October event, as IPMA published it, points to a normal fault with a northwest-southeast alignment. The earlier figures are not final, since the agency's count runs only up to the time of its note.

How the tremors are classed

IPMA's scale sorts earthquakes by magnitude: 4.0 to 4.9 is light (ligeiro), 3.0 to 3.9 is small (pequeno), and 5.0 to 5.9 is moderate (moderado). On that scale the 4.5 quake of Thursday morning falls in the light class, the 3.8 event in the small class, and the 20 October event in the moderate class. The Modified Mercalli scale measures degrees of intensity and their description. According to the agency's explanation, intensity II is considered very weak.

Past crises and what comes next

IPMA places the activity in a zone where seismic crises have recurred before, and it names earlier episodes in the same area. In its statement the agency said the following.

“The observed seismic activity is located in a seismogenic zone where seismic crises periodically occur, such as those of 1997 and 1988”

The agency added that other events may occur in the coming days and that it is following the situation closely. It said it may issue new bulletins if the situation warrants them.