Three seismic events occurred over a period of about two hours.
The first was recorded at 10:13 (11:13 in Lisbon) with a magnitude of 1.9 on the Richter scale and an epicenter approximately 4 km northwest of the parish of Santa Bárbara on Terceira Island.
The event was perceived with a maximum intensity of III on the Modified Mercalli scale in Santa Bárbara, within the municipality of Angra do Heroísmo.
At 10:35 (11:35 in Lisbon), a second earthquake was registered with a magnitude of 2.0 on the Richter scale and an epicenter about 5 km northeast of Santa Bárbara, felt with a maximum intensity of III/IV on the Modified Mercalli scale in the parish of Santa Bárbara.
The third event occurred at 12:26 (13:26 in Lisbon) with a magnitude of 2.6 on the Richter scale, also with an epicenter approximately 5 km northwest of Santa Bárbara.
This was perceived with a maximum intensity of IV on the Modified Mercalli scale in the parishes of Santa Bárbara, Cinco Ribeiras, Doze Ribeiras, Serreta, Raminho, and Altares in the municipality of Angra do Heroísmo, and in the parish of Biscoitos in the municipality of Praia da Vitória.
These three earthquakes form part of the ongoing seismic-volcanic crisis on Terceira Island, which began in June 2022.
On November 6, the Crisis Office of the CIVISA and the Institute of Volcanology of the University of the Azores (IVAR) raised the alert level of the Santa Bárbara volcano to V3, indicating “volcanic system in reactivation phase.”
The decision was based on “increased seismic activity” showing a “growing trend” compared to the earlier months of the year, and the continued albeit slight “crustal deformation in the area where the seismic-volcanic crisis is developing.”
The alert level for the Santa Bárbara volcano had previously been at V3 from June to December 2024 but had remained at V2 since then, signifying “volcanic system in an instability phase.”
Since June 2022, Santa Bárbara volcano’s seismic activity has been “above normal reference values,” with the most energetic event occurring on January 14, 2024, with a magnitude of 4.5 on the Richter scale.
The volcanic alert scale used by IVAR consists of eight levels, where V0 signifies a volcanic system in a resting phase and V7 represents an ongoing magmatic or hydromagmatic eruption with colossal to megacolossal explosivity.
According to the Portuguese Institute for the Sea and the Atmosphere (IPMA), an intensity IV earthquake on the Modified Mercalli scale causes vibrations similar to those produced by passing heavy vehicles or the sensation of a heavy ball hitting walls. Suspended objects sway, parked cars rock, windows, doors, and dishes tremble, and glassware and dishes clink.
