The Azores Seismovolcanic Information and Surveillance Centre (CIVISA) said that the earthquake was recorded at 03:27 (04:27 in Lisbon) and had an epicentre about three kilometres south of Raminho, in the municipality of Angra do Heroísmo.

In a statement, CIVISA added that the earthquake was felt in the western part of Terceira, with a maximum intensity of V on the Modified Mercalli scale. The event was also felt with an intensity of IV/V in the eastern half of the island.

The Modified Mercalli scale measures "degrees of intensity and their respective description".

With intensity V, considered strong, earthquakes are felt outside the home, people are woken up, liquids oscillate and some overflow, small objects in unstable equilibrium move or are knocked over, doors oscillate, close or open, while blinds and paintings move and clock pendulums stop or change their state of oscillation, according to the description of the Portuguese Institute of the Sea and Atmosphere (IPMA) on its website.

With intensity IV, considered moderate, “suspended objects sway, the vibration is similar to that caused by the passage of heavy vehicles or the sensation of a heavy ball hitting the walls, parked cars sway, windows, doors and crockery shake, glass and crockery rattle or tinkle and at the highest level of this degree, walls and wooden structures creak”, describes the IPMA.

The IPMA assessed the earthquake as having a magnitude of 3.9 (Richter) and estimated that the epicentre was located around four kilometres east-southeast of Serreta, in the municipality of Angra do Heroísmo.

Another tremor, with a magnitude of 2.6 on the Richter scale, was recorded at 01:26 (02:26 in Lisbon) and had an epicentre around four kilometres east of Serreta, said CIVISA.

In a statement, CIVISA said that "the earthquake was felt with a maximum intensity of IV (Modified Mercalli Scale) in Serreta, Raminho, Altares, S. Bartolomeu (municipality of Angra do Heroísmo) and Biscoitos (municipality of Praia da Vitória)".

The tremors this morning are part of "the ongoing seismovolcanic crisis on Terceira Island since June 2022", said CIVISA.

On 27 June, CIVISA raised the alert level for the Santa Bárbara volcano to V3 and for the fissure volcanic system on Terceira Island to V1.

In the volcanic alert levels, V0 means “state of rest” and V6 means “ongoing eruption”, according to the information available on the CIVISA website. Level V3 confirms the reactivation of the volcanic system, with signs of high activity.

A first tremor, measuring 2.6 on the Richter scale, was felt at 23:32 (00:32 today in Lisbon) on the island of Faial, which is also part of the central group of the Azores, the center reported.