Yesterday, four minor earthquakes shook Terceira Island, Azores within a seven-minute span. The Azores Seismovolcanic Information and Surveillance Center (CIVISA) revealed that these earthquakes were part of an ongoing Seismo-Volcanic crisis
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These earthquakes were recorded between 12:59 local time (11:59 in Lisbon) and 13:06 and were felt in the municipality of Angra do Heroísmo.
Details of the Terceira Island Earthquakes
The first earthquake occurred at 12:59 p.m. having a magnitude of 2.4 on the Richter scale. Moreover, the epicenter was approximately four kilometers east of Serreta.
This was followed by another one with an epicenter approximately three kilometers east of Serreta. It had a magnitude of 2.3 and it happened at 1:00 p.m. A minute after the third earthquake was reported.
This was less severe and only had a magnitude of 1.7 with the origin three kilometers away from Serreta. Lastly, the fourth one happened at 1:06 pm. It was a kilometer farther from the previous one. It had a magnitude of 2.3.
CIVISA reported that several earthquakes were felt across Serreta, Doze Ribeiras, Santa Bárbara, and Raminho, all within the municipality of Angra do Heroísmo. The maximum intensities of III and IV (Modified Mercalli scale) were observed.
Additionally, another earthquake, with a magnitude of 2.1, occurred at 11:44 am local time. Its epicenter was approximately two kilometers to the southeast of Serreta. This earthquake was felt with maximum intensity III/IV (Modified Mercalli scale) in Doze Ribeiras (Angra do Heroísmo municipality).
Continued Monitoring by CIVISA
The CIVISA continues to monitor the evolution of the situation. The organization said that:
These events are part of the ongoing seismic-volcanic crisis on Terceira Island since June 2022.
Earlier this year, on June 27, CIVISA raised the alert level for the Santa Bárbara volcano to V3 due to increased seismic activity on Terceira Island. Moreover, it changes the fissure volcanic system of the Island to V1.
According to the information on the CIVISA website in volcanic alert levels, V0 means a state of rest and V6 means ongoing eruption. Level V3 confirms the reactivation of the volcanic system, with signs of high activity.
The Richter scale classifies earthquakes as the following
- Micro (less than 2.0)
- Very Small (2.0-2.9)
- Small (3.0-3.9)
- Slight (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)
- Extreme (when greater than 10)
The Modified Mercalli scale measures degrees of intensity and their description. The Portuguese Institute of the Sea and Atmosphere explains that a level IV intensity earthquake is considered moderate and causes noticeable effects.
For instance, suspended objects begin to sway, and vibrations feel similar to those caused by the passage of heavy vehicles.
The sensation can resemble that of a heavy object hitting walls, parked cars may sway, while windows, doors, and glassware rattle or shake. At the upper end of this intensity, walls and wooden structures may even creak.
However, an intensity III is considered weak. Its can is felt inside the house, and hanging objects sway, feeling a vibration similar to that caused by the passage of heavy vehicles.
