Magnitude 4.6 earthquake felt across São Miguel, with no damage reported

The earthquake struck around 06:54 local time. The reviewed US Geological Survey record places its origin at 07:54:06 UTC, its depth at 10 kilometres and its epicentre 41 kilometres west of Mosteiros. This was an earthquake beside Portugal’s Atlantic islands, not off the mainland. Mosteiros is a coastal parish in the municipality of Ponta Delgada, on São Miguel in the autonomous Azores region.⁠1⁠12⁠15⁠16

The important development after the first Portuguese notice was confirmation that people had felt the tremor. IPMA initially had not received information establishing felt shaking. Its later assessment recorded maximum modified Mercalli intensity III/IV in Ginetes and weaker shaking in seven other parishes. The absence of felt reports in the first notice had been a gap in information, not proof that the earthquake had gone unnoticed.⁠3⁠6

Those lower-intensity reports came from Mosteiros and from São Sebastião, São José and São Pedro in Ponta Delgada, as well as Matriz, Ribeira Seca and Ribeirinha in the municipality of Ribeira Grande. Together, they establish that the offshore event was experienced across several communities on São Miguel; they do not, by themselves, establish damage.⁠3

The figures 4.6 and 4.7 describe the same earthquake through different measurements. The reviewed USGS value is a body-wave magnitude, abbreviated mb, which uses seismic waves travelling through the Earth. IPMA’s event map labels its estimate ML, or local magnitude. Neither figure should be confused with the III/IV intensity reported in Ginetes: magnitude measures the earthquake itself, while intensity describes its effects at a particular place.⁠1⁠3

There was also a revision within the Portuguese assessment. SAPO reported that IPMA first put the magnitude at 4.6, then raised it to 4.7 as more information arrived. That change does not withdraw or replace the separate USGS body-wave measurement of 4.6. Simply calling this an earthquake “upgraded from 4.6 to 4.7” would blur two different things: a revision by one agency and a distinct measurement maintained by another.⁠6⁠1⁠3

The agencies’ origin estimates differ slightly, too. IPMA places the epicentre about 40 kilometres west of Ginetes and gives an origin time of 07:54:07 UTC—one second later than the USGS record. IPMA explains that calculated locations depend on the available data, algorithms and models of how seismic waves travel. Different agencies can therefore reach slightly different results, and preliminary determinations can change when more information is integrated.⁠1⁠3

A second earthquake followed at 06:59 local time, five minutes after the first. IPMA’s later notice gives that event a local magnitude of 3.8 and maximum intensity II in Mosteiros, with no reported personal or material damage. SAPO’s earlier account had described it as magnitude 4.0 and said felt shaking had not yet been confirmed. The later official notice supersedes those early details; it is a separate tremor, not another estimate of the first earthquake.⁠3⁠6

The USGS record lists no PAGER earthquake-impact alert and a tsunami flag of “no.” Those entries have limits: neither demonstrates that a complete damage survey found nothing, and the tsunami field is not a formal, event-specific all-clear bulletin. The USGS event record itself supplied no casualty or damage assessment.⁠1

IPMA’s notice provides the more useful account of conditions on the island: confirmed felt shaking, without reported injuries or material damage at that point. The remaining practical question is whether later reports alter that early picture. IPMA says it will issue further notices if developments justify them, rather than announcing a scheduled update, and advises the public to follow civil-protection instructions. For now, the evidence supports a felt offshore earthquake—not a claim of destructive effects, and not an unconditional declaration that every consequence has been ruled out.⁠3