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In search of the 31 March 1761 earthquake and tsunami source

M. A. Baptista, J. M. Miranda and J. F. Luis
In search of the 31 March 1761 earthquake and tsunami source
Bulletin of the Seismological Society of America (April 2006) 96 (2): 713-721


Earthquake catalogs for the Iberian Peninsula report three strong- magnitude events in the eighteenth century: 27 December 1722, 1 November 1755, and 31 March 1761. These events have magnitudes greater than 7 and generated tsunamis that damaged the Portuguese coasts. However, their source areas are controversial because of the lack of detailed and coherent historical descriptions. The 31 March 1761 earthquake was felt in Lisbon at noon, alarming the inhabitants and throwing down ruins of the past 1 November 1755 earthquake. According to several sources the earthquake was followed by a tsunami that was observed as far as Cornwall (United Kingdom), Cork (Ireland), and Barbados (Caribbean). The Portuguese catalogs locate this event on the Horseshoe Abyssal Plain, south of Gorringe Bank, and attribute a magnitude of 7.5. The Caribbean tsunami catalog (Lander et al., 2002) locates the event further north 37 degrees N 10 degrees W and estimates of its epicenter intensity as IX. In this study we present a reappraisal of the available historical reports concerning the 1761 event, a revision of the macroseismic intensities along Iberia, and the tsunami observations along the western Portuguese and Galicia coasts, England, Ireland, and the West Indies. With this dataset we use backward raytracing techniques to discuss the location of the event and its integration with one of the major tsunami generation areas in the western Portuguese margin. We conclude that the 31 March 1761 earthquake took place at 12:01 a.m. (Lisbon time). Its epicenter was located about 34.5 degrees N 13 degrees W and had a tsunami magnitude close to 8.5. Online material: Felt reports from the 31 March 1761 earthquake.

ISSN: 0037-1106
EISSN: 1943-3573
Serial Title: Bulletin of the Seismological Society of America
Serial Volume: 96
Serial Issue: 2
Title: In search of the 31 March 1761 earthquake and tsunami source
Affiliation: Universidade de Lisboa, Instituto Superior de Engenharia, Lisbon, Portugal
Pages: 713-721
Published: 200604
Text Language: English
Publisher: Seismological Society of America, Berkeley, CA, United States
References: 31
Accession Number: 2006-041193
Categories: Quaternary geologyEnvironmental geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables, sketch maps
N50°00'00" - N55°45'00", W06°30'00" - E01°30'00"
N41°47'60" - N43°47'60", W09°19'60" - W06°45'00"
N51°30'00" - N55°19'60", W10°30'00" - W06°30'00"
N37°00'00" - N42°10'00", W09°30'00" - W06°10'00"
N10°00'00" - N25°30'00", W85°00'00" - W59°00'00"
Secondary Affiliation: University of Algarve, PRT, Portugal
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, Seismological Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 200623
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