Any one in the Azores should read this article. There are concerns about a major earthquake or volcanic eruption.

[AntarcticPilot]

Yes, I got the impression that you have a professional interest, from here and some previous threads we have both been in. Unfortunately, I did not follow geological interests after completing my degree in '71, other than working as a surveyor with marine geophysicists.

Latest situation is that since midnight 700 minor tremors recorded, none strong enough to be felt by the population. However, "the estimated volume of a possible intrusion of magma on the island of São Jorge is around 20 million cubic meters, comparable to that recorded by the deformation of the soil before the eruption of Cumbre Vieja in La Palma in 2021." * so potentially very serious.

*google translate from Portuguese.

I got my degree in 1974, and I've been in allied trades throughout my academic career - glaciology and geographic information, mainly.

I just had another look at the seismic map, and it appears that the focus is now on the western cluster, right next to the town of Velas. All the events within the last 24 hours are there; the eastern cluster has no events within 24 hours. I also note that a much bigger event (3.8) took place just offshore.

 

[srm]

The 3.8 quake yesterday evening was also felt in Angra, and no doubt elsewhere on the south side of Terceira.

Below are the main points from this morning's briefing by CIVISA, run through Google translate:

"The most energetic earthquake of this crisis occurred on March 29, at 21:56 (local time = UTC-1), had an epicenter about 2 km SSW of Velas and a magnitude 3.8 (Richter). So far, around 215 earthquakes felt by the population have been identified. During yesterday, March 29, the preliminary analysis of the seismic records allowed to count about 1417 events. Between 00:00 and 10:00 today, approximately 893 events were recorded, with seismic activity being stationary in relation to the last few days, although with a slight increase.

"All earthquakes recorded so far are of low magnitude and show a tectonic origin. The campaign to measure gases and temperature in the soil that CIVISA has been carrying out since the beginning of this crisis in the epicentral area has not resulted, to date, in the identification of any anomaly, and field surveys will continue in the coming days.

"Within the scope of geodetic monitoring, CIVISA, in collaboration with other entities, is strengthening the observation network based on GNSS stations and processing satellite images. Existing data to date corroborate the seismological observations by indicating the existence of some deformation in the epicentral area. The integration of available information allows us to conclude that the tectonic structures where the historical eruptions of 1580 and 1808 developed, and the seismovolcanic crisis of 1964, in the Fissural Volcanic System of Manadas, were reactivated, and it is possible to admit the occurrence of a deep magmatic intrusion .

"CIVISA warns of the possibility of earthquakes that can reach magnitudes higher than those recorded so far, as well as the danger of landslides potentiated by seismic activity. There is a real possibility that a volcanic eruption could occur, but there is no evidence that this is imminent."

Ponto de Situação

 

[AntarcticPilot]

The 3.8 quake yesterday evening was also felt in Angra, and no doubt elsewhere on the south side of Terceira.

Below are the main points from this morning's briefing by CIVISA, run through Google translate:

"The most energetic earthquake of this crisis occurred on March 29, at 21:56 (local time = UTC-1), had an epicenter about 2 km SSW of Velas and a magnitude 3.8 (Richter). So far, around 215 earthquakes felt by the population have been identified. During yesterday, March 29, the preliminary analysis of the seismic records allowed to count about 1417 events. Between 00:00 and 10:00 today, approximately 893 events were recorded, with seismic activity being stationary in relation to the last few days, although with a slight increase.

"All earthquakes recorded so far are of low magnitude and show a tectonic origin. The campaign to measure gases and temperature in the soil that CIVISA has been carrying out since the beginning of this crisis in the epicentral area has not resulted, to date, in the identification of any anomaly, and field surveys will continue in the coming days.

"Within the scope of geodetic monitoring, CIVISA, in collaboration with other entities, is strengthening the observation network based on GNSS stations and processing satellite images. Existing data to date corroborate the seismological observations by indicating the existence of some deformation in the epicentral area. The integration of available information allows us to conclude that the tectonic structures where the historical eruptions of 1580 and 1808 developed, and the seismovolcanic crisis of 1964, in the Fissural Volcanic System of Manadas, were reactivated, and it is possible to admit the occurrence of a deep magmatic intrusion .

"CIVISA warns of the possibility of earthquakes that can reach magnitudes higher than those recorded so far, as well as the danger of landslides potentiated by seismic activity. There is a real possibility that a volcanic eruption could occur, but there is no evidence that this is imminent."

Ponto de Situação

That all sounds very convincing. Unfortunately, they don't show depth estimates on the earthquake map, which would corroborate their statement about magma emplacement at depth. Seismic activity confirmed by rises in surface elevation is a good indicator of magma being emplaced, though. It could still all die out without an eruption - it isn't inevitable at this stage.

Did you notice the discretization effects on the earthquake positions? They are nicely arranged on a lat/long grid, which presumably relates to the precision of the positional determination.

 

[srm]

Unfortunately, they don't show depth estimates on the earthquake map, which would corroborate their statement about magma emplacement at depth.

Yes, a bit surprising that its not included in the tables. However, the IPMA map and table does give depths. If anything they are slightly shallower in the last 24 hours. Now trending at a bit less than 10 km whereas earlier most were deeper than 10km. One outlier around the middle of the island showing zero km depth.

Had not zoomed in really close, but once you do the grid effect is obvious.

We are all hopeing that it will quietly die down. After the 1964 earthquake a significant part of the island's population gave up and migrated, many to the USA and Canada where there are Azorian communities.

 

[srm]

CIVISA Update 31 march: (via Goggle translate)

During yesterday, March 30, the preliminary analysis of the seismic records allowed to count about 1629 events. Between 00:00 and 10:00 today, approximately 273 events were recorded, with the seismic activity being stationary for the last few days. All earthquakes recorded so far are of low magnitude and show a tectonic origin.
The campaign to measure gases and temperature in the soil that CIVISA has been carrying out since the beginning of this crisis in the epicentral area has not resulted, to date, in the identification of any anomaly, and field surveys will continue in the coming days.
Within the scope of geodetic monitoring, CIVISA, in collaboration with other entities, is strengthening the observation network based on GNSS stations and processing satellite images. Existing data to date corroborate the seismological observations by indicating the existence of some deformation in the epicentral area.
The integration of available information allows us to conclude that the tectonic structures where the historical eruptions of 1580 and 1808 developed, and the seismovolcanic crisis of 1964, in the Fissural Volcanic System of Manadas, were reactivated, and it is possible to admit the occurrence of a deep magmatic intrusion .
CIVISA warns of the possibility of earthquakes that can reach magnitudes higher than those recorded so far, as well as the danger of landslides potentiated by seismic activity. There is a real possibility that a volcanic eruption could occur, but there is no evidence that this is imminent.
>>>
I noticed a headline on a cafe TV this morning that there has been a 3.3 tremor.
IPMA map puts it as 3.6, its near the west end of the island, depth 6km, so its away from the main clusters.

This article sumarises volcanic history and current monitoring in the Azores:
Geological Hazards and Monitoring at the Azores (Portugal) - Earthzine

 

[srm]

Velas is still gently rumbling on with a high number of low level tremors, but a smaller daily number above 2.0 on the richter scale, all at around 10 km depth. The twice daily briefing on the CIVISA website has not changed significantly since I posted above last thursday.

 

[Concerto]

Velas is still gently rumbling on with a high number of low level tremors, but a smaller daily number above 2.0 on the richter scale, all at around 10 km depth. The twice daily briefing on the CIVISA website has not changed significantly since I posted above last thursday.

Thank you for the updates, I do hope it just rumbles and nothing else.

 

[srm]

Another week of the same level of activity. Around 150 to 250 micro tremors per day plus a handful that were felt in the range 2.0 to 2.9 on Richter scale. Reported depths still +/- 10 Km. No significant surface deformation or surface gas measured but alert level remaining at V4. Newspaper reports suggest that the scientists are puzzled by this pattern of activity.

 

[AntarcticPilot]

Another week of the same level of activity. Around 150 to 250 micro tremors per day plus a handful that were felt in the range 2.0 to 2.9 on Richter scale. Reported depths still +/- 10 Km. No significant surface deformation or surface gas measured but alert level remaining at V4. Newspaper reports suggest that the scientists are puzzled by this pattern of activity.

It does seem strange. Declining activity would make sense, or shallowing activity would also make sense; in either case it's fairly easy to suggest models for what's going on. But continuing activity at constant depth is harder to explain, especially without any surface deformation. The lack of gas activity isn't so puzzling considering the depth.

 

[webcraft]

It does seem strange. Declining activity would make sense, or shallowing activity would also make sense; in either case it's fairly easy to suggest models for what's going on. But continuing activity at constant depth is harder to explain, especially without any surface deformation. The lack of gas activity isn't so puzzling considering the depth.

It's the Morlocks

- W

 

[jamie N]

More like Borlocks.

 

[AntarcticPilot]

It does seem strange. Declining activity would make sense, or shallowing activity would also make sense; in either case it's fairly easy to suggest models for what's going on. But continuing activity at constant depth is harder to explain, especially without any surface deformation. The lack of gas activity isn't so puzzling considering the depth.

On further thought, the emplacement of a body such as a laccolith or sill would probably have this signature.

 

[srm]

The seismic activity continued over another week. There was a slight decrease in recorded tremors at the beginning of the week, though some of the weaker ones may have been masked by wind and weather effects. However activity seems to be increasing again. 157 events recorded yesterday (15th) as opposed to 87, of which only one was felt, the day before.

Alert level remains a V4 and monitoring continues though no gas or significant surface deformation recorded.

Looking at the maps each day I get the impression that there are significantly fewer recorded tremors this week than during the first two weeks. Despite the local authorities discouraging visitors to Sao Jorge and a large nuber of locals having left Velas I have been told that the available accommodation is full with visitors who hope to see an eruption.

 

[AntarcticPilot]

The seismic activity continued over another week. There was a slight decrease in recorded tremors at the beginning of the week, though some of the weaker ones may have been masked by wind and weather effects. However activity seems to be increasing again. 157 events recorded yesterday (15th) as opposed to 87, of which only one was felt, the day before.

Alert level remains a V4 and monitoring continues though no gas or significant surface deformation recorded.

Looking at the maps each day I get the impression that there are significantly fewer recorded tremors this week than during the first two weeks. Despite the local authorities discouraging visitors to Sao Jorge and a large nuber of locals having left Velas I have been told that the available accommodation is full with visitors who hope to see an eruption.

There's nowt so queer as folk!

Well, I'd love to witness an eruption, but a) in a parallel universe I might have been a vulcanologist (I almost did a PhD on them) and b) I'm still a geologist! Rather rusty and out-of-date, but still a geologist at heart.

 

[Concerto]

The seismic activity continued over another week. There was a slight decrease in recorded tremors at the beginning of the week, though some of the weaker ones may have been masked by wind and weather effects. However activity seems to be increasing again. 157 events recorded yesterday (15th) as opposed to 87, of which only one was felt, the day before.

Alert level remains a V4 and monitoring continues though no gas or significant surface deformation recorded.

Looking at the maps each day I get the impression that there are significantly fewer recorded tremors this week than during the first two weeks. Despite the local authorities discouraging visitors to Sao Jorge and a large nuber of locals having left Velas I have been told that the available accommodation is full with visitors who hope to see an eruption.

Hoping the activity remains similar or settles down.

 

[robertj]

I presume if a catastrophic eruption there would cause a tsunami here in the Uk?

 

[AntarcticPilot]

I presume if a catastrophic eruption there would cause a tsunami here in the Uk?

A definite maybe. If it caused flank collapse, probably yes, otherwise no.

Later: a tsunami occurs as a result of a volcanic eruption if and only if there's a big movement of rock beneath the sea, displacing a large volume of water. So if the eruption causes part of the volcano to slide into the sea, or there's a submarine landslide, then that generates a tsunami. In an extreme case (unlikely in the Azores), caldera collapse could cause massive tsunamis. That's when the magma chamber under the volcano empties and the volcano basically falls into it! But most volcanic eruptions on islands cause slight or even no tsunamis.

 

[Stemar]

a tsunami occurs as a result of a volcanic eruption if and only if there's a big movement of rock beneath the sea, displacing a large volume of water. So if the eruption causes part of the volcano to slide into the sea, or there's a submarine landslide, then that generates a tsunami.

Am I right in thinking that that's a when rather than an if for one of the Canaries? I seem to remember lots of knickers getting twisted about it a few years back.

 

[AntarcticPilot]

Am I right in thinking that that's a when rather than an if for one of the Canaries? I seem to remember lots of knickers getting twisted about it a few years back.

Yes, there's a concern about a fault adjacent to one of the Canaries; I forget which. However, I gather that more recent studies have found the fault to be more stable than was first thought. But there's always the potential for tsunamis arising from volcanic edifices, or even from steep submarine slopes. The Storegga slide is a classic non-tectonic tsunami; it arose from a submarine landslide into the deep trench off the coast of Norway and caused widespread (prehistoric!) flooding on the East coast, especially in Scotland; there are widespread deposits from it. Volcanoes are very liable to landslides; the edifice is inevitably at or near the angle of repose, so an eruption or even just non-volcanic weathering can result in a landslide that then triggers a tsunami.

 

[srm]

Just in case anyone is still interested Sao Jorge has had another week of low level seismic activity plus one or two tremors on all but one day registering 2.0< on the Richter scale.

From today's briefing (via google translate):

"Over the course of yesterday, April 22, the preliminary analysis of the seismic records allowed to count about 91 events, with the seismic activity having decreased in relation to that observed the previous day. Between 00:00 and 10:00 today, approximately 35 events were recorded. Most of the earthquakes recorded so far are of low magnitude and show a tectonic origin. "

Alert level still at V4, since 23 March.

The President of the Republic visited Sao Jorge during the week, seemed to be a PR exercise to reassure the tourist industry that all is safe.