Maximum Observed Intensity Map for the Azores Archipelago (Portugal) from 1522 to 2012 Seismic Catalog

Abstract

The Azores archipelago is a seismically active region composed of nine islands and located at the triple junction of the American, Nubian, and Eurasian plates. Since its settlement in the fifteenth century, 33 earthquakes with intensity higher than VII have been reported. This article shows areas that experienced strong ground shaking using maximum observed intensity (MOI) mapping. For this purpose, 323 records from 167 earthquakes in the period 1522–2012 have been compiled, and MOI values are interpolated on a regular grid of points using the kriging method. The comparison of observed and calculated MOI for four damaging and deadly earthquakes indicates a good calibration of the procedure relative to the available dataset. For the islands of the central group, which comprises Terceira, Graciosa, Sao Jorge, Pico, and Faial, the highest calculated intensities (XI) are located in the eastern part of Sao Jorge Island. Intensities (X) are observed on Faial along a northwest–southeast stripe. For Graciosa, Terceira, and Pico, the estimated maximum intensities are IX, VIII, and VII, respectively. For the eastern group of islands, the highest intensities (X) are located in the southeastern part of Sao Miguel Island, and on Santa Maria Island the maximum intensity of VI is observed in its eastern part. Finally, Flores and Corvo Islands, located on the American plate, have a very low seismicity.