Two seismic events were recorded by the Azores Seismological Information Center (CIVISA), the first of which, measuring 1.9 on the Richter scale, occurred at 12:42 a.m. local time (1:42 a.m. in Lisbon), with an epicenter approximately four kilometers southeast of Raminho in Angra do Heroísmo.
The second earthquake, registering a magnitude of 2.2, happened at 12:43 a.m. local time, with its epicenter located roughly five kilometers south-southwest of Altares, also within Angra do Heroísmo.
“According to available information, both earthquakes were felt with a maximum intensity of III (Modified Mercalli Intensity Scale) in Serreta and Altares, located in the Angra do Heroísmo municipality,” stated CIVISA.
The incidents are part of an ongoing seismic-volcanic crisis on Terceira Island that began in June 2022.
The alert level for the Western Fissural Volcanic System of Terceira has been elevated to V3 (reactivation phase), matching the status for the Santa Bárbara volcano, as reported by the Azores Volcanology Institute (IVAR) on Wednesday.
According to an IVAR communique, its Crisis Office convened to assess the seismic-volcanic activity in the Azorean island, maintaining the V3 alert for Santa Bárbara volcano and similarly raising the alert to V3 for the Western Fissural Volcanic System of Terceira.
“Throughout November, the seismic activity on the island, though of low magnitude, has consistently exceeded reference levels, showing an upward trend, especially around the perimeters of Santa Bárbara Volcano and the Western Fissural Volcanic System of Terceira, particularly in the region known as Mistérios Negros,” it added.
IVAR notes that this situation “has led to several earthquakes felt by the population.”
Despite the rise in seismic activity, IVAR’s Crisis Office explained that it decided to maintain the V3 alert level for Santa Bárbara volcano and elevate to V3 for the Western Fissural Volcanic System due to “the Mistérios Negros area being an intersection zone where the two volcanic systems communicate.”
On the Richter Scale, earthquakes are categorized by magnitude from micro (less than 2.0) to extreme (greater than 10).
The Modified Mercalli Intensity Scale measures “degrees of intensity and their corresponding descriptions.”
An intensity of III is considered weak, felt indoors, with hanging objects swinging and a “vibration similar to that caused by passing heavy vehicles,” describes the Portuguese Institute for Sea and Atmosphere (IPMA) on its website.
