Seismic activity and inflation continue at lower levels
Weak inflation also continued to be registered, which is why the official alert level remains at the second highest level of V4.
São Jorge (Azores) seismic activity continues above normal levels. Although it has decreased in hourly frequency and magnitude, it is still ongoing. Since 19 March at least 226 events were felt by the population. For updates follow @PROCIVazores and CIVISA https://t.co/nTI0gn2FPH pic.twitter.com/VrujkrVfjF— Adriano Pimentel (@AdrianoAzoVolc) April 5, 2022
Earthquakes slow down
Including quakes too small to be localized, official data speak of more than 25,000 tremors in total having occurred since the start of the seismic crisis.
In the absence of other published data, it is impossible to interpret the situation well or make well-founded predictions, but the scenario of a volcanic eruption in a near future seems to become less likely if seismic activity ceases. However, the official alert level remains at V4 (on a scale of 1-6).
Magnitude 4 quake rattles São Jorge island
While the numbers of quakes has been lower in the past few days, it should be taken into account that last night's quake accounts for approximately the same seismic energy as all quakes during the past 7 days combined. This is because magnitude is a logarithmic scale: one magnitude 4 earthquake is approx. equivalent to 30 quakes of magnitude 3, or 1,000 magnitude 2 events.
Whether this marks a shift in the underlying processes, and whether it is tectonic in origin or caused by magmatic processes or a combination of both, remains unclear.
There were no damages reported by the magnitude 4 earthquake, but authorities and local population remain alarmed because the potential of stronger quakes and/or a volcanic eruption in the near future remains real.
São Jorge Island (Azores): likelihood of eruption increases as 20 million cubic meters of magma estimated intruded at depth
If the figures are correct, the likelihood of a volcanic eruption in the Azores is no longer a small one, and we therefore assign our color code "orange", as a warning of potential activity in the near future.
For comparison, the initial magma intrusion leading up to last year's eruption on La Palma Island in the Canary Islands was estimated to be only 11 million cubic meters only, while it erupted a total of approx. 300 cu m of magma in the course of the 3-month-long eruption from September-December 2021. The preceding seismic swarm lasted from 13-19 Sep 2021 and is in many ways quite similar to what is being observed now on São Jorge.
The estimates on magma intrusion volume are based on modeling the observed ground deformation, in particular its vertical inflation, from the analysis of synthetic aperture radar data acquired by the Sentinel-1 satellite of the European Space Agency. This method compares radar images of the same area but obtained on two different dates; small differences in phase variations of the reflected radio waves can be used to detect changes in the relief of the earth's surface on the scale of millimeters.
The areas with most uplift is near the northeastern coast approx. 10 km east of Velas, where ground uplift has amounted approx. 10 cm alone by now. It can be presumed that the center of the magma source is located under this area.
The seismic swarm under São Jorge itself so far contained more than 700 quakes of magnitudes above 2.0, with 26 quakes above magnitudes 3.0-3.6. In the past days, it has continued to decrease in intensity, although this does not necessarily mean that the danger is over. Earthquakes occur, when magma pressure opens new pathways, fracturing rock layers at depth. What if the rocks beneath the island are already fractured? This could be true as result of the quakes that already took place, the general setting of the island being in a tectonically active rift zone and the presence of older dikes from past eruptions. In that case, magma accumulation could take place without significant quake activity, and - as we had seen before and during La Cumbre Vieja's eruption on La Palma - an eruption could start any time with little immediate warning.
Possible scenarios for São Jorge volcano:
It is impossible to predict what will happen, whether an eruption will take place in the near future. All of the following scenarios are possible, but we do not know how likely each of them might be:
1) An eruption takes place within days or weeks from now, with little warning.
2) The seismic swarm and ground deformation end gradually or abruptly, only to be repeated in months or years from now. Eventually one of these will be leading up to an eruption then.
3) A stronger earthquake occurs and changes the configuration of the magma intrusion, either to stall or to break through to the surface in an eruption.
4) Activity dies down, and the magma intrusion at depth slowly cools over years and decades to come with no further activity directly related to it.
Authorities preparing for emergency
Soldiers have arrived on the Azorean island of São Jorge and are setting up military tents where people can sleep in case of evacuation pic.twitter.com/0BBkazhPVN— Catarina Demony (@CatarinaDemony) March 27, 2022