São Miguel Feels a Magnitude 5.2 Earthquake Offshore, Then a Night of Smaller Tremors: No Damage Reported, and What to Do When the Ground Shakes

A magnitude 5.2 earthquake centred under the sea off the west coast of São Miguel was felt across the island at 18:07 local time on Tuesday 20 October (19:07 in Lisbon), and a second tremor of magnitude 3.4 followed at 18:30. According to the communiqué from IPMA (the Portuguese Institute for Sea and Atmosphere) the larger quake caused no injuries or damage on the information available so far.

Where it was felt

IPMA placed the epicentre about 40 km west of Ginetes, in the municipality of Ponta Delgada. It said the shaking reached a maximum intensity of IV/V on the Modified Mercalli scale in 15 parishes of São Miguel, among them Mosteiros, Relva, Santa Clara, the central Ponta Delgada parishes, Rabo de Peixe and Vila Franca do Campo. It was felt more weakly in dozens of other parishes on São Miguel and on Terceira.

The Azores seismic and volcanic monitoring centre, CIVISA, whose bulletins are reproduced by the Azores Regional Civil Protection and Fire Service (SRPCBA), gave slightly different preliminary figures: magnitude 5.1, an epicentre about 39 km west of Ginetes, and a maximum intensity of V/VI in Ponta Delgada. It reported intensity V in Ribeira Grande, Lagoa, Vila Franca do Campo and Povoação, and lighter shaking on Terceira and Santa Maria. IPMA notes that agencies' preliminary figures often differ and are usually revised.

The 18:30 tremor, about 37 km west of Ginetes, was felt with a maximum intensity of IV, according to CIVISA. Lusa, reported by Observador, also said no damage was recorded.

A night of smaller tremors

IPMA's open seismic data for the Azores lists 16 events in the same offshore area, the Hirondelle trough west of São Miguel, between 18:00 on Tuesday and 03:51 on Wednesday, all but two of them between magnitude 2.0 and 3.2. One of those, at 00:12, was felt in Santo António (Ponta Delgada) with an intensity of III/IV, CIVISA reported, giving its magnitude as 3.2. CIVISA says it is continuing to follow the situation.

What to do if the ground shakes

With every bulletin, the SRPCBA repeats the same self-protection advice: stay calm and expect aftershocks; do not light matches or lighters in case of gas leaks; leave your home at once if you suspect it is no longer safe; switch off gas, electricity and water if you doubt the circuits; never use lifts; and stay away from beaches, because a large undersea quake can cause a tsunami. Its earthquake leaflet (in Portuguese) adds:

• Before: fix furniture to the walls, keep heavy objects on low shelves, agree a family meeting point, and keep a kit with a torch, a battery radio, spare batteries, a first aid kit and two to three days of bottled water and tinned food.
• During: indoors, take shelter under a sturdy table or bed, away from windows, mirrors and furniture that could fall. Outdoors, move to an open space away from buildings, power lines, walls and the sea, and do not run through the streets.
• After: do not rush for exits, keep the roads clear for emergency vehicles, use the phone only for real emergencies, and call 112 if you need help.

IPMA's own guidance, with separate pages for before, during and after a quake, also advises protecting your head, avoiding stairs while the shaking lasts, and sending text messages rather than calling once it stops, to keep the network free.

Travelling to the islands this week? Check the ground handling strike timetable; the Azores run one hour behind Lisbon, and clocks go back on Sunday.