Other quakes may follow, authorities warn
The island of São Miguel in the Portuguese archipelago of the Azores experienced a series of small but noticeable earthquakes on Monday night (June 16), with magnitudes ranging from 3.0 to 3.7, according to the Azores Seismo-Volcanic Information and Surveillance Centre (CIVISA).
The three quakes were recorded within a span of just under 20 minutes – at 9.49pm, 9.55pm and 10.07pm local time (one hour later in Lisbon).
According to the Richter scale, the recent quakes fall in the “small” category (3.0–3.9). However, how a quake is felt varies depending on the Mercalli Modified Intensity Scale, which focuses on impact: Intensity III is considered “weak” but is felt indoors and can lead to swaying hanging objects and sounds similar to the rumble of a passing truck; Intensity IV is considered “light” and can involve moderate shaking, from windows rattling to parked vehicles rocking slightly; Intensity V is dubbed “moderate” and strong enough to wake people, be felt outdoors and cause objects to fall.
The first tremor, with a magnitude of 3.0, had its epicentre 12 km south of Faial da Terra and was felt with IV intensity in the municipality of Povoação.
The second, and strongest, measuring 3.7, had its epicentre 14 km south-southeast of Faial da Terra. This one was felt with V intensity in Povoação and with lighter effects (III) in Nordeste, Vila Franca do Campo, and even Ponta Delgada.
The third quake, at magnitude 3.2, occurred slightly southwest of the earlier epicentres and was again felt in Povoação with intensity IV.
These latest tremors are part of a seismic sequence that began on June 3 in waters 10 to 20 km south of Povoação, explains the Portuguese meteorological institute (IPMA). So far, the largest quake in this sequence has been Monday’s 3.7-magnitude tremor, with authorities warning that more could follow in the coming hours.
CIVISA has urged residents to follow civil protection guidelines, particularly avoiding unstable areas such as cliffs or steep slopes, and staying out of buildings that may be structurally vulnerable to seismic activity.
