288 felt by the population
Açoriano Oriental reports that the island of São Jorge has, as of yesterday, registered 37,810 earthquake tremors since March 19, of which 288 were felt by the population, revealed the Azores Seismovolcanic Information and Surveillance Centre (CIVISA).
In a situation report made today about the seismolvolcanic crisis on that Azorean island, published on its official website, CIVISA states that, “so far, approximately 37,810 events of low magnitude and of tectonic origin have been recorded”.
CIVISA “maintains monitoring levels” on the island, while “is providing the reinforcement of the permanent seismovolcanic observation network, in order to detect precursor signs of a new pre-eruptive situation”.
“The integration of available information allows us to conclude that the tectonic structures where the historic eruptions of 1580 and 1808 and the 1964 seismovolcanic crisis, in the Herds Fissural Volcanic System, were reactivated”, describes CIVISA.
On the other hand, it is “to be admitted that, at the beginning of the phenomenon, there was a deep magmatic intrusion”.
On Thursday, CIVISA lowered the alert level on the island of São Jorge from V4 (threat of eruption) to V3 (active system with no imminent eruption).
“The decrease in seismic activity, albeit slowly, and the observation of such a pattern over the last few weeks, as well as the absence of other anomalous signs in terms of deformation, gases and waters, led to the descent of the scientific alert level”, he justifies.
The island had been since March 23, at 15:30 (another hour in Lisbon), with the volcanic alert level V4 out of a total of seven, where V0 means “state of rest” and V6 “eruption in progress”, following the seismovolcanic crisis recorded since 19 March.
Prior to that, alert V2 had been activated on March 20 at 00:40 and V3 on the same day at 02:40.
Despite the lowering of the alert, “seismic activity remains well above the reference values for the region, so there is still the possibility of registering felt events”.
In addition, “the possible occurrence of earthquakes of higher magnitude cannot be excluded”.
“Globally, the seismic activity of the last few weeks shows a slightly decreasing trend, sometimes interrupted by short periods of higher frequency and/or energy released, with the hypocenters currently being located, in general, at depths greater than five kilometres”, describes the report. CIVIL.
The earthquake of greater magnitude (3.8 on the Richter scale) of this crisis occurred on March 29, at 21:56.
CIVISA states that “within the scope of geodetic monitoring, the existing data since the beginning of April do not show significant deformation in the epicentral zone”.
“The campaigns to measure gases and temperature in the soil that have been developed since the beginning of this crisis in the epicentral area have not resulted, to date, in the identification of anomalies resulting from seismovolcanic activity, maintaining the field surveys”, he adds.
On the other hand, “the hydrogeochemical campaigns in the groundwater of the two monitored wells have not revealed significant variations that could be associated with the ongoing seismovolcanic crisis”.