1998 Azores Islands earthquake

Earthquake in the Azores Islands, Portugal April 2024 1998 Azores Islands earthquake Portugal Azores A map of the Azores Islands distributed along a northwest–southeast trend with a bullseye marking the offshore epicenter in the central cluster of large islands 1998-07-09 05:19:07 1165443 usp0008r70 1998 07 09 yes 05:19:07 w 6.1 y 10 km mi 0 12 km north of Horta Azores, Portugal 38.650 N 28.626 W 10,600 recorded Strike-slip 8 10 dead, 100 injured, 1,000 homeless The 1998 Azores Islands earthquake (also known as the Faial earthquake) struck with an epicenter in the Atlantic Ocean, off the Azores Islands of Portugal at 05:19 local time. The 10 km deep mainshock, which measured 6.1 on the moment magnitude scale, was preceded by a strong foreshock 18 minutes prior. The mainshock was caused by movement on a strike-slip fault. A highly productive aftershock sequence followed with more than 10,600 recorded within four months. These aftershocks were mainly distributed across two west-southwest and south-southeast striking faults that intersect orthogonally off the coast of Faial while some occurred on faults associated with the Pedro Miguel graben on the island. The regional tectonics and kinematics suggests the shock occurred on the west-southwest trending plane. Elastic dislocation modelling further suggested that interaction between the primary rupture and faults of the Pedro Miguel graben could explain the GPS and geodetic ground deformation. The shock also caused some surface ruptures on the graben faults. The earthquake caused significant damage on Faial Island with the villages of Ribeirinha and Espalhafatos almost completely destroyed. At least 10 people died, 100 were injured, and 1,000 people were left without homes. More than 3,900 homes, most on Faial and some on Pico Island, were damaged. The severity of damage was due to the dominance of non-seismic resistant construction on the island. After the earthquake, the Azores Islands regional government began reconstruction works at a cost of 255 EUR million. Background The Portuguese founded the first settlements on the islands in the 15th century. Since its founding, there has been at least 30 damaging and deadly earthquakes. The first recorded damaging earthquake occurred in 1522—it destroyed Vila Franca do Campo and caused over 5,000 deaths. Deadly earthquakes were also reported in 1787 and 1980.Gaspar J. L. Queiroz G. T. Ferreira P. Amaral F. Viveiros R. Marques C. Silva N. Wallenstein Geological Hazards and Monitoring at the Azores (Portugal) https://earthzine.org/geological-hazards-and-monitoring-at-the-azores-portugal/ Earthzine 26 August 2021 12 April 2011 The largest recorded earthquake in the vicinity of the Azores was the 1941 magnitude 8.3 event which was associated with strike-slip faulting on the Eurasian–Nubian plate boundary.Maria Ana Baptista Maria Ana Baptista Jorge Miguel Miranda Josep Batlló Filipe Lisboa Joaquim Luis Ramon Maciá New study on the 1941 Gloria Fault earthquake and tsunami Natural Hazards and Earth System Sciences 22 August 2016 16 8 1967–1977 10.5194/nhess-16-1967-2016 2016NHESS..16.1967B 10400.21/7140 free free Earthquake Tectonic setting The Azores Islands are at a triple junction between the North American, Eurasian and African (Nubian) plates. The islands are atop a region of thickened crust called the Azores Plateau, where the crust is about 14–17 km thick. The well-defined Mid-Atlantic Ridge represents the North American–Eurasian and North American–Nubian boundaries representing two arms of the junction. Regionally, the third arm, the Eurasian–Nubian boundary, is represented by the Terceira Rift. This rift is a northwest–southeast to west-northwest–east-southeast trending zone of alternating basin and volcanic ridges. The southeastern Terceira Rift joins the Gloria Fault,D’Araújo J. Sigmundsson F. Ferreira T. Okada J. Lorenzo M. Silva R. Plate Boundary Deformation and Volcano Unrest at the Azores Triple Junction Determined From Continuous GPS Measurements, 2002–2017 Journal of Geophysical Research: Solid Earth 10.1029/2021JB023007 127 1 2022 which represents a significant portion of the Azores–Gibraltar Transform Fault.Batista L. Hübscher C. Terrinha P. Matias L. Afilhado A. Lüdmann T. Crustal structure of the Eurasia–Africa plate boundary across the Gloria Fault, North Atlantic Ocean Geophysical Journal International 10.1093/gji/ggx050 free 209 2 713–729 2017 With the exception of Flores and Corvo, situated on the North American Plate, all of the Azores Islands lie west of the Mid-Atlantic Ridge. There is no agreed plate boundary type for the Azores–Gibraltar Transform Fault, which bounds the Eurasian and African plates. Scholars have suggested it is a transform fault, leaky transform fault, oblique spreading center or rift zone.Matias L. Dias N. A. Morais I. Vales D. Carrilho F. Madeira J. Gaspar J. L. Senos L. Silveira A. B. The 9th of July 1998 Faial Island (Azores, North Atlantic) seismic sequence Journal of Seismology 2007 11 275–298 10.1007/s10950-007-9052-4 The two primary fault styles around the 1998 earthquake epicenter are west-northwest–east-southeast and north-northwest–south-southeast trending systems with steep dip angles. The west-northwest–east-southeast striking faults exhibit oblique-slip faulting with sinistral and normal components. Active faults are also present on Faial Island, concentrated in the Pedro Miguel graben. Within the graben, there are seven east-southeast striking faults with normal and dextral slip components. Similar-trending faults have been reported south of Caldeira Volcano and on the western part of Faial. Geology Strike-slip fault A strong foreshock was recorded at 05:01, which alerted residents near the epicenter. The mainshock occurred at 05:18 with an epicenter near that of the foreshock. The earthquake, measuring a moment magnitude of 6.1, struck at a depth of 10 km. OB 1165443 cs2 On-line Bulletin http://www.isc.ac.uk/cgi-bin/FormatBibprint.pl?evid=1165443 It was caused by sinistral strike-slip faulting along a north-northwest–south-southeast trending fault. Most earthquakes on the islands are associated with volcanism, making the 1998 a rare and large one of tectonic origin.J.F. Borges M. Bezzeghoud E. Buforn C. Pro A. Fitas The 1980, 1997 and 1998 Azores earthquakes and some seismo-tectonic implications Tectonophysics 2007 435 1–4 37–54 10.1016/j.tecto.2007.01.008 https://dspace.uevora.pt/rdpc/bitstream/10174/6383/1/Tectonophysics-2007-2.pdf Elsevier 2007Tectp.435...37B 10174/6383 free The strike-slip faulting mechanism was also unusual as most earthquakes in the area occur because of normal faulting. Using GPS and geodetic data, two nearly vertical rupture planes were identified as possible sources. One was a west–southwest trending dextral fault with a dimension of 9.5 by 4.6 km. The other was a south–southeast trending sinistral fault with a dimension of 9.6 by 4.2 km. These dimensions were consistent with the expected size of a w 6.1 earthquake derived from the geodetic data. In both slip planes, coseismic slip occurred at 2 to 6 km depth within the crust and peaked at about 1 m.Fernandes R. M. S. Miranda J. M. Catalão J. Luis J. F. Bastos L. Ambrosius B. A. C. Coseismic displacements of the MW = 6.1, July 9, 1998, Faial earthquake (Azores, North Atlantic) Geophysical Research Letters 2002 29 16 21-1-21-4 10.1029/2001GL014415 An estimated 10,600 aftershocks recorded were recorded in the first four months.Carlos Sousa Oliveira Mónica Amaral Ferreira Francisco Mota de Sá The concept of a disruption index: application of the overall impact of the July 9, 1998 Faial earthquake (Azores Islands) Bulletin of Earthquake Engineering 2012 10 1 7–25 10.1007/s10518-011-9333-8 2012BuEE...10....7O 109897250 http://www.civil.ist.utl.pt/~monicaf/DI_fulltext.pdf https://web.archive.org/web/20240608102634/http://www.civil.ist.utl.pt/~monicaf/DI_fulltext.pdf 8 June 2024 These aftershocks delineated the two orthogonal fault planes; one trending west-southwest and the other south-southeast. Some also occurred on the Ribeirinha and Lomba Grande faults of the Pedro Miguel graben. These aftershocks were located at depths of 3–13 km with the shallow ones occurring on the graben. The regional kinematics and damage distribution of the mainshock suggest the west-southwest plane was the source of the mainshock. Elastic dislocation modelling showed that a dextral fault with a dimension of 12 by 5.5 km slipping up to 1.17 m, and slip on two graben faults (Ribeirinha and Lomba Grande faults) could reproduce the observed geodetic deformation, aftershock distribution, and damage. In the model, the rupture parameters of the graben faults were 2 by 1 km with 15 cm of normal slip and 2.2 by 1 km with 34 cm and 14 cm of normal and sinistral displacement, respectively. Coulomb stress changes caused by the mainshock triggered aftershocks on the south-southeast trending fault.F.O. Marques J. Catalão A. Hildenbrand A.C.G. Costa N.A. Dias The 1998 Faial earthquake, Azores: Evidence for a transform fault associated with the Nubia–Eurasia plate boundary? Tectonophysics 21 October 2014 633 115–125 10.1016/j.tecto.2014.06.024 Elsevier Surface ruptures The earthquake caused surface ruptures that were mainly reported in the uplifted fault blocks of the Ribeirinha, Chã da Cruz and Lomba Grande faults. Dextral fractures and south-facing vertical scarps on the order of several centimeters occurred near the Chã da Cruz Fault. There was also a 10–20 cm scarp where the Lomba Grande Fault cuts beneath a road. These ruptures were discontinuous with some reaching 10 m long. Some of the deformation were open cracks while others contained strike-slip, normal or oblique-normal offsets. In areas where the fault's geometry inhibited the strike-slip component to produce zones of compression, ridges formed. Pull-apart basins formed in areas where bends in the fault caused localised extension. The location of surface ruptures were consistent with the linearment of previously mapped faults in northeastern Faial and had a slip vector consistent with them. Ground motion thumb|right|Strong ground motion map|alt= Color-gradient map illustrating the modelled ground motion intensity across the central Azores Islands indicating severe to very strong shaking on Faial in yellow and orange while the rest of the islands experienced strong to light shaking in green and blue. The Modified Mercalli intensity on Faial ranged from V to VIII. Damage to the towns of Ribeirinha and Espalhafatos in northeastern Faial were consistent with intensity VIII effects. The earthquake's intensity does not follow a simple seismic attenuation relationship with its distance from the epicenter; although Lombega, a village on southwest Faial, had intensity VII effects, the surrounding area was assigned intensity V. On Pico, areas closest to the epicenter were assigned intensity VI while Piedade at the eastern part experienced intensity III. Some areas of Pico experienced localised intensity VII, including Almagreira, whereas intensity IV was reported in the surrounding area. On São Jorge, areas closest to the epicenter was assigned intensity V while Topo at the eastern end experienced intensity III. The earthquake was also felt in Graciosa (IV), Terceira (III–IV), and São Miguel (III). Impact thumb|235px|The Ribeirinha lighthouse after the earthquake|alt= Heavily weathered ruins of a lighthouse with collapsed walls, severe cracks, and spalled walls and tiles exposing the interior masonry. Cracks and spalled walls extend along the height of the tower. The earthquake killed 10 people, injured 100, and left 1,000 others homeless on Faial.Quake in Azores kills 10 https://www.nytimes.com/1998/07/10/world/quake-in-azores-kills-10.html 22 August 2026 Reuters The New York Times 10 July 1998UPI Focus: Strong earthquake kills 10 in Azores https://www.upi.com/Archives/1998/07/09/UPI-Focus-Strong-earthquake-kills-10-in-Azores/4980899956800/ 26 August 2021 United Press International 9 July 1998 Lisbon, Portugal More than 3,900 buildings were damaged; many of them were on Faial, while some damage also occurred on Pico. About 70 percent of homes on Faial were destroyed while 20 percent of them were damaged on Pico.Sismo de 1998 mudou a ilha do Faial para sempre https://observador.pt/2016/08/08/sismo-de-1998-mudou-a-ilha-do-faial-para-sempre/ 22 August 2026 Lusa News Agency Observador 8 August 2016 pt The 1998 earthquake changed Faial Island forever The villages of Espalhafatos and Ribeirinha were almost completely destroyed while significant damage was reported in Pedro Miguel, Salão and Cedros. In these settlements, some 1,500 homes were heavily damaged and half had to be torn down. Some buildings fared better; newer constructions were undamaged even in areas of extreme damage. The traditional construction methods and materials used in many homes were not designed for earthquakes, resulting in the heavy damage. Many homes were made from stone and clay or mortar with wooden partition acting as walls.Madeira José Brum da Silveira António Tectónica e sismicidade na ilha do Faial e o sismo de 9 de Julho de 1998 Boletim do Núcleo Cultural da Horta 2007 pt 16 61–79 https://www.researchgate.net/publication/257428933_Tectonica_e_sismicidade_na_ilha_do_Faial_e_o_sismo_de_9_de_Julho_de_1998 Furthermore, most of the buildings damaged had two or three floors; in some instances, their masonry walls completely toppled or had large cracks.G. Zonno C. S. Oliveira M. A. Ferreira G. Musacchio F. Meroni F. Mota-de-Sá F. Neves Assessing Seismic Damage Through Stochastic Simulation of Ground Shaking: The Case of the 1998 Faial Earthquake (Azores Islands) Surveys in Geophysics 5 December 2009 31 3 361–381 10.1007/s10712-009-9091-1 54605828 Closest to the epicenter, the Ribeirinha lighthouse sustained large cracks in its tower to mid-height and rotated 15–20 cm clockwise. As most schools were reinforced-concrete construction, they sustained little to no damage. However, a kindergarten in Salão had to be demolished because its external masonry walls collapsed. At another school in Espalhafatos, the concrete and reinforced masonry components separated.Jorge Miguel Proença Damage in schools in the 1998 Faial earthquake in the Azores Islands, Portugal https://web-archive.oecd.org/pdfViewer?path=%2F2012-06-15%2F156309-33629167.pdf Institute of Structures, Territory and Construction Engineering, Higher Technical Institute, Portugal Churches that suffered severe damage were primarily masonry construction. Shear failure of the walls was a common damage pattern observed in churches. In the Ribeirinha Church, the arch between the nave and apse completely collapsed.Guerreiro L. Azevedo J. Proença J. Bento R. Lopes M. Damage in Ancient Churches During the 9th of July 1998 Azores earthquake Proceedings of the 12th World Conference on Earthquake Engineering 2000 https://www.iitk.ac.in/nicee/wcee/article/0780.pdf Auckland, New Zealand Aftermath The initial rescue effort in northern Faial was hampered by toppled trees and landslides that blocked roads. In response to the road conditions, the national radio station said four aircraft from the air force were planned to support evacuation and aid deliveries.Survivors describe Azores earthquake http://news.bbc.co.uk/2/hi/world/monitoring/129740.stm 8 September 2026 BBC 9 July 1998 Rescuers spent the night looking for survivors and retrieving bodies among the rubble. Concerned about aftershocks, the residents of Faial and Pico slept inside tents provided by the government.A thousand homeless after quake https://eresources.nlb.gov.sg/newspapers/digitised/page/straitstimes19980711-1.1.17 17 October 2024 Reuters The Straits Times 10 July 1998 The Portuguese Air Force deployed a Lockheed C-130 Hercules plane carrying tents and several thousand blankets from Lisbon; medical teams and supplies also arrived. Prime minister António Guterres visited Faial Island to survey the devastation.Brough David 10 die, 90 injured in Azores earthquake https://www.irishtimes.com/news/10-die-90-injured-in-azores-earthquake-1.171637 26 August 2021 The Irish Times 10 July 1991 The United States ambassador to Portugal, Gerald S. McGowan, declared the earthquake a disaster on 17 July. The Office of Foreign Disaster Assistance later allocated 22 USD thousand to the embassy for the Portuguese government to purchase lavatory essentials.USAID OFDA Annual Report for Fiscal Year 1998 https://reliefweb.int/report/world/ofda-annual-report-fiscal-year-1998 ReliefWeb 26 August 2021 1 Jan 1999 The Portuguese government dispatched medical doctors and nurses to treat the injured while sniffer dogs were mobilised for rescue missions.10 killed, 100 injured by earthquake in Azores https://www.tampabay.com/archive/1998/07/10/10-killed-100-injured-by-earthquake-in-azores/ 26 August 2021 Tampa Bay Times 13 September 2005 The regional government was tasked with reconstruction, resettlement and recovery, estimated at 255 EUR million.In 1998 monetary value One of the largest recovery efforts in the island's history, it involved constructing 670 prefabricated homes. About 72 percent of the reconstruction project was funded by the regional government while the remaining was from nationwide public funds. The reconstruction projects drastically changed the architecture of buildings on Faial as traditional stone and mud homes were replaced with ones built with blocks, iron and cement. See also List of earthquakes in 1998 List of earthquakes in the Azores List of earthquakes in Portugal Notes References Category:1998 earthquakes Category:Earthquakes in Portugal Category:1998 in Portugal Category:January 1998 in Europe Category:Azores Category:History of the Azores Category:Faial Island