The 6.4–7.1 Mw Lisbon earthquake kills about thirty thousand people.

Seismic magnitude scales are used to describe the overall strength or "size" of an earthquake. These are distinguished from seismic intensity scales that categorize the intensity or severity of ground shaking (quaking) caused by an earthquake at a given location. Magnitudes are usually determined from measurements of an earthquake's seismic waves as recorded on a seismogram. Magnitude scales vary based on what aspect of the seismic waves are measured and how they are measured. Different magnitude scales are necessary because of differences in earthquakes, the information available, and the purposes for which the magnitudes are used.

The 1531 Lisbon earthquake occurred in the Kingdom of Portugal on the morning of 26 January 1531, between 4 and 5 o'clock. The earthquake and subsequent tsunami resulted in approximately 30,000 deaths. Despite its severity, the disaster was not widely documented until the rediscovery of contemporary records in the early 20th century.

January 26 is the 26th day of the year in the Gregorian calendar; 339 days remain until the end of the year.