Paleoseismological evidence for historical surface faulting in São Miguel island (Azores)

• Main Authors: Rita Carmo, José Madeira, Ana Hipólito, Teresa Ferreira
• Format: Article
• Language: English
• Published: Istituto Nazionale di Geofisica e Vulcanologia (INGV) 2014-02-01
• Series: Annals of Geophysics
• Subjects: Azores; Neotectonics; Active faulting; Paleoseismology; Seismic hazard
• Online Access: http://www.annalsofgeophysics.eu/index.php/annals/article/view/6221

<p class="MsoNormal" style="margin: 0cm 0cm 0pt; text-align: justify; line-height: 150%;">The Azores archipelago is located at the triple junction between the Eurasian, Nubian and North American lithospheric plates, whose boundaries are the Mid-Atlantic Ridge and the Azores-Gibraltar Fault Zone. São Miguel is the largest island of the archipelago and is located on the eastern part of the western segment of the Azores-Gibraltar Fault Zone. The Achada das Furnas plateau, located in the central part of the island, between Fogo and Furnas central volcanoes, is dominated by several WNW-ESE and E-W trending alignments of basaltic cinder cones. Two E-W trending scarps were identified by aerial photo interpretation. Transect trenches exposed two active normal faults-the Altiprado Faults – confirming the tectonic nature of the scarps. Several paleoearthquakes were deduced, most of which in historical times, producing 1.38 m and 0.48 m of cumulative displacement. Maximum expected magnitudes (MW) determined from slip per event range from 5.7 to 6.7. One of the events probably corresponds to the historical earthquake of October 22nd, 1522, the deadliest in the archipelago. Radiocarbon ages are in agreement with this interpretation.</p>