EARTHQUAKEM5.1

M5.1 earthquake near Mosteiros, Portugal

Map: the earthquake near Mosteiros, Portugal, with plate boundaries

A magnitude 5.1 earthquake struck 39 km (24 mi) west of Mosteiros, Portugal on Tuesday, October 20, 2026 at 18:07 UTC, at a depth of 10 km (6 mi), according to the U.S. Geological Survey. Shallow quakes like this one shake the surface hardest. The nearest city of a million or more people is Lisbon, Portugal, about 1,493 km (928 mi) away.

14 people reported feeling it to USGS “Did You Feel It?”.

MagnitudeM5.1
Depth10 km (6 mi)
Time (UTC)Oct 20 18:07
Location37.96°N 26.26°W
Nearest townMosteiros · 39 km
Energy674 tons TNT
Aftershocks M2.5+0
Tsunami flagNo
Felt reports14
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Why here?

This earthquake struck right along the boundary between the Eurasian and African plates. Most earthquakes happen along plate boundaries like this one, where the pieces of Earth’s outer shell collide, pull apart or grind past each other. Stress builds up over years until the rock suddenly slips.

The red lines on the map are plate boundaries.

What kind of fault?

USGS’s analysis of the seismic waves shows it was a normal-fault earthquake: the crust was being stretched, and one block dropped down relative to the other.

How strong was it?

Magnitude is logarithmic: each whole step releases about 32 times more energy. This magnitude 5.1 released roughly the energy of 674 tons of TNT. That is about 45 times the energy of a magnitude 4.0, a quake people nearby feel but that rarely causes damage. The strongest earthquake ever recorded, magnitude 9.5 in Chile in 1960, released about 4,000,000 times more than this one.

Aftershocks

In the first 5 days after it, USGS recorded no smaller earthquakes of magnitude 2.5 or more within 100 km (62 mi).

Outside the United States, USGS mainly lists quakes of about magnitude 4 and up, so smaller aftershocks there are undercounted.

Earthquake history here

Before this earthquake, USGS had recorded 5 earthquakes of magnitude 6 or larger within 300 km (186 mi) since 1900. The strongest:

Official details, updates and the shaking map: USGS event page.

See every earthquake on October 20, 2026 or earthquakes by day.

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