Chapter 6 Volcano-tectonic structures of São Miguel Island, Azores

Abstract

The Azores archipelago is located at the triple junction between the Eurasia, Nubia and North America lithospheric plates. São Miguel Island, situated at the southeastern part of the western segment of the Azores-Gibraltar Fracture Zone, presents an east-west elongated shape, comprising three quiescent central volcanoes with summit calderas linked by zones of fissure volcanism. The eastern part of the island is older and inactive. Active faulting is represented by prominent fault scarps that constitute important extensional structures, or by linear volcanic structures in fissural volcanic zones, with a dominant NW-SE to WNW-ESE trend. Although less frequent, there are also NNW-SSE to north-south, NE-SW and east-west faults, reflected by some volcanic alignments and linear segments of the drainage system and sea cliffs. The geometric and kinematic data are in agreement with that observed in the rest of the archipelago. However, at eastern São Miguel Island data indicate two distinct groups of conjugated faults characterized by three-dimensional strain: NW-SE to WNW-ESE normal dextral structures are conjugated with NNW-SSE normal left-lateral faults and NW-SE to WNW-ESE normal left-lateral faults are conjugated with NE-SW normal dextral structures, showing the presence of two different stress fields separated in time.

Chapter 7 Eruptive history and evolution of Sete Cidades Volcano, São Miguel Island, Azores

“…7.5) and is related to the regional tectonic regime of the Terceira Rift (e.g. Machado 1959;Queiroz 1997;Carmo et al 2015;Madeira et al 2015;Miranda et al 2015). In this context, the Mosteiros Graben on the NW sector of the volcano is a prominent structure with a dominant extensive component, forming scarps with displacements of up to 70 m. It cuts the caldera and extends towards the SE, controlling the alignment of numerous scoria cones (Queiroz 1997).…”

“…A more comprehensive analysis of tectonic features in Sete Cidades region is presented by Carmo et al (2015).…”

Chapter 4 Earthquakes and volcanic eruptions in the Azores region: geodynamic implications from major historical events and instrumental seismicity

“…About 15 major earthquakes and 16 seismic crises, of which 10 were related to observed or probable volcanic eruptions, have been responsible for numerous deaths and significant damage (Table 4.1). Lourenço et al (1997) and world topography and bathymetry from GEBCO_08 database 2010 (adapted from Carmo et al 2015). 4.3).…”

Chapter 8 Eruptive history of Fogo Volcano, São Miguel, Azores

“…For a more comprehensive analysis of tectonic features on Fogo reference should be made to Carmo et al (2015). For a more comprehensive analysis of tectonic features on Fogo reference should be made to Carmo et al (2015).…”