According to CIVISA, the tremors were recorded at 8:50 PM local time (9:50 PM in Lisbon), with the first having a magnitude of 2.1 and the second 2.2 on the Richter scale.
The earthquakes had epicenters approximately three kilometers south-southeast of Serreta and three kilometers northeast of Doze Ribeiras, respectively.
“Based on the available information, the earthquakes were felt with a maximum intensity of III/IV on the Modified Mercalli scale in Serreta (municipality of Angra do Heroísmo),” CIVISA stated.
The events are part of the ongoing seismo-volcanic crisis on Terceira Island since June 2022.
According to the Richter scale, earthquakes are classified by magnitude as micro (less than 2.0), very minor (2.0-2.9), minor (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 (over 10).
The Modified Mercalli scale measures “degrees of intensity and respective description.”
With an intensity of III, a tremor is considered weak, felt indoors with swaying of hanging objects, and is similar to the vibration caused by heavy vehicle traffic, as described by the Portuguese Institute for Sea and Atmosphere (IPMA) on its website.
With an intensity of IV, considered moderate, “suspended objects sway, the vibration is akin to the passage of heavy vehicles or the impact of a heavy ball on the walls, parked cars shake, windows, doors, and dishes rattle, glassware and dishes clash or tinkle, and at the higher end of this degree, walls and wooden structures creak.”
