Active tectonics and first paleoseismological results in Faial, Picoand S. Jorge islands (Azores, Portugal)

Abstract

The neotectonics of the islands of Faial, Pico and S. Jorge (Azores) is presented. Preliminary paleoseismology
data from trench exposures across three active fault zones (Lomba do Meio, Lagoa do Capitão and Pico do
Carvão faults) complement the information. Radiocarbon age constraints of paleoearthquakes suggest clustering
of surface rupturing events. Slip rates deduced from paleoseismology analysis range from 0.10 to 0.40 cm/year
and validate long-term slip rates obtained by neotectonic studies (using Pleistocene markers). The studied faults
allowed a preliminary seismic hazard assessment: magnitudes of the largest paleoearthquakes, determined from
slip per event range from Mw = 6.9 to 7.1, and maximum expected magnitudes, estimated from rupture length or
rupture area, vary from Mw = 6.4 to 6.8. The former Mw estimates are in closer agreement with the magnitude of
the major historic and instrumental seismic events in the archipelago, even though the used empirical relations
between magnitude and rupture parameters may not be the most adequate due to the unique tectonic setting of
Azores.