Azores tectonic or vulco-tectonic in nature, but in general low to medium intensities, occasionally punctuated by events of level 5 or greater on the Richter magnitude scale. The most severe earthquake was registered in 1757, near Calheta on the island of São Jorge, which exceeded 7 on the Richter magnitude scale. In comparison, the 1522 earthquake that was mentioned by historian Gaspar Frutuoso measured 6.8, but its effects were judged to be X ("Extreme") on the Mercalli intensity scale, and was responsible for the destruction of Vila Franca do Campo and landslides that may have killed more than 5,000 of the
Apparent magnitude brightness of sources at ultraviolet, visible, and infrared wavelengths. An apparent magnitude is usually measured in a specific passband corresponding to some photometric system such as the UBV system. In standard astronomical notation, an apparent magnitude in the V ("visual") filter band would be denoted either as "m" or often simply as "V", as in ""m" = 15" or ""V" = 15" to describe a 15th-magnitude object. The scale used to indicate magnitude originates in the Hellenistic practice of dividing stars visible to the naked eye into six "magnitudes". The brightest stars in the night sky were said to be