| On account of its
tectonic setting, both seismic and volcanic events are frequent in the
Azores archipelago. During the historical period earthquakes and seismic
swarms of tectonic and/or volcanic origin have struck S. Miguel Island
causing a significant number of casualties and severe damages. The
information present in historical records made possible a new macroseismic
analysis of these major events using the European Macroseismic Scale-1998
(EMS-98).
Among the strongest earthquakes of tectonic origin that
affected S. Miguel Island, six events were selected for this study. The
isoseismal maps drawn for these events enabled the identification of areas
characterized by anomalous values of seismic intensity, either positive or
negative, to constrain epicentre locations and to identify some new
seismogenic areas.
Regarding seismic activity associated with volcanic
phenomena six cases were also selected. For each of the studied cases
cumulative intensity values were assessed for each locality. The
distribution of local intensity values shows that the effects are not
homogeneous within a certain distance from the eruptive centre, the area
of major impacts relates with the eruptive style and damages equivalent to
high intensities may occur in Furnas and Sete Cidades calderas. Combining
all the historical macroseismic data, a maximum intensity map was produced
for S. Miguel Island. |