An earthquake measuring 3.3 Richter was felt early Monday morning in Doze Ribeiras, Angra do Heroismo, on the Azorean island of Terceira, without causing any casualties or damage, IPMA reported.
According to the Portuguese Institute of the Sea and Atmosphere (IPMA), the earthquake was recorded at 04:10 local time (05:10 Lisbon time) at stations of the Azores archipelago seismic network, and the epicenter was located near Serreta on the Third Island.
IPMA also reported that the earthquake was felt at intensity III/IV on the modified Mercalli scale.
The earthquake came after three others measuring 2.1, 2.4 and 2.6 on the Richter scale were felt early Sunday morning on the island of Terceira in the Azores.
The first of the three earthquakes was recorded at 05:29 local time (06:29 in Lisbon) and had a magnitude of 2.4 on the Richter scale and an epicentre approximately six kilometres north-east (NE) of Santa Barbara, while the second, at 05:36 local time (06:36 in Lisbon), had a magnitude of 2.1 and an epicentre approximately five kilometres south-southwest (SSW) of Altares.
Subsequently, at 06:19 local time (07:19 Lisbon time), a new event was recorded, measuring 2.6 on the Richter scale and with an epicentre approximately five kilometres south-southwest (SSW) of Altares, Terceira Island.
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), weak (4.0-4.9), moderate (5.0-5.9), strong (6.0-6.9), large (7.0-7.9), important (8.0-8.9), exceptional (9.0-9.9) and extreme (when greater than 10).
The modified Mercalli scale measures “degrees of intensity and corresponding description.”
At intensity III, considered weak, the shaking is felt inside the house and hanging objects swing, feeling “a vibration similar to that caused by the passage of heavy vehicles,” the Portuguese Institute of the Sea and Atmosphere (IPMA) said on its website.
At intensity IV, considered moderate, parked cars shake, windows, doors and dishes shake, “glasses and dishes rattle or clank,” and walls or wood structures may creak.