According to CIVISA, the initial tremor, measuring 2.1 on the Richter scale, occurred at 8:24 PM local time (9:24 PM in Lisbon), followed by a second tremor of magnitude 2.6 at 8:25 PM (9:25 PM in Lisbon), with both epicenters located approximately four kilometers northeast of Santa Bárbara.
“Based on the available information, the first earthquake was felt with a maximum intensity of III (Modified Mercalli scale) in Santa Bárbara (municipality of Angra do Heroísmo),” reported CIVISA.
The second tremor registered an intensity of IV in Santa Bárbara, Doze Ribeiras, Serreta, and Cinco Ribeiras (municipality of Angra do Heroísmo) and reached a maximum intensity of III in Terra Chã, São Bartolomeu de Regatos, São Mateus da Calheta (Angra do Heroísmo), and Biscoitos (Praia da Vitória).
These events are part of the ongoing seismovolcanic crisis on Terceira Island since June 2022.
The Portuguese Institute for Sea and Atmosphere (IPMA) also issued a statement regarding the earthquake recorded at 8:25 PM local time, attributing it a magnitude of 3.1 on the Richter scale with an epicenter near Doze Ribeiras.
On the Richter scale, earthquakes are classified by magnitude as micro (less than 2.0), very small (2.0-2.9), small (3.0-3.9), light (4.0-4.9), moderate (5.0-5.9), strong (6.0-6.9), major (7.0-7.9), great (8.0-8.9), exceptional (9.0-9.9), and extreme (exceeding 10).
The Modified Mercalli Intensity scale measures “degrees of intensity and their descriptions.”
With an intensity level of III, an earthquake is considered weak, felt indoors, and causes hanging objects to sway, with a “vibration similar to the passing of heavy vehicles,” as described by IPMA on its website.
With an intensity of IV, considered moderate, “suspended objects sway, vibrations resemble the passage of heavy vehicles or the impact of a heavy ball against walls, parked cars rock, windows, doors, and dishes rattle, glassware and crockery clash or jingle, and at the higher end of this level, walls and wooden structures creak.”
