1985 Algarrobo earthquake

Severe earthquake centered in Valparaíso Region, Chile March 2025 Citation bot 1985 Algarrobo earthquake Calle destruida por el terremoto de 1985.jpg South America 1985-03-03 22:47 529084 usp0002ccz yes 1985 03 03 19:47 UTC−03:00 69 seconds 8.0 Mw 35.0 km on -33.257 -71.858 inline, title Atacama Trench Megathrust Central Chile $1.5–1.8 billionComte Eisenberg Lorca Pardo Ponce Saragoni Singh Suárez 1986 452 Note 4 IX (Llolleo) .86 g (Llolleo)Booth Taylor 1988 8 Yes Yes 177–200 dead 2,483–2,575 injured 372,532–500,000 homelessFor the number of people made homeless, seismologist Bruce Bolt provides the minimum figure of 372,532, and EM-DAT (in the PAGER-CAT data set) provides the maximum figure of 500,000 1985 Algarrobo earthquake.jpg USGS ShakeMap A megathrust earthquake measuring 8.0 w struck just offshore the Greater Valparaíso area of Central Chile on 3 March 1985. The event followed a ten-day period of moderate and non-destructive foreshocks and left at least 177 people dead and about 2,500 injured. According to several reports, a small sector of damage in Llolleo corresponded to a maximum Mercalli intensity of IX (Violent), though the vast majority of damage was considered to align with intensity VIII (Severe) effects or less. The damage was significant and widespread, and was similar to numerous previous events that had severely impacted the Valparaíso and Santiago metropolitan areas. Great earthquakes related to the subduction zone have occurred directly under populated areas or very close offshore since records began with the arrival of Europeans in the sixteenth century. Because of its heavy impact (financial losses of $1.5–1.8 billion) in the Valparaíso, Santiago, O'Higgins, and Maule Regions, the event has been thoroughly studied across various disciplines. Numerous scientific and academic papers published beginning in the late 20th-century and continuing into the 21st-century have explored its features, including the geological, seismological, and epidemiological aspects of the event, and have improved the understanding of the complex plate boundary and how this specific event relates to the many that came before it. Most have been primarily of the megathrust type, but Central Chile is also subject to other types of earthquakes that are related to the relatively deep subduction zone as well as shallow and onshore crustal faults. A significant aftershock sequence followed that included many large (M6+) and very large (M7+) shocks. Only a small portion of these had destructive characteristics, including the twin 6.7 w shocks on 17 and 19 March and the 7.2 w Rapel Lake earthquake on 9 April. Multiple international scientific groups convened in the area to assist local universities with seismological, engineering, and geological surveys, including the study of a moderately-destructive and basin-wide tsunami that caused several million dollars' worth of damage along the Central Chilean coast. History Timeline of Santiago de Chile List of megathrust earthquakes Regions of Chile Types of earthquake Central Chile (roughly between 32° and 35° south latitude) has been repeatedly affected by great earthquakes. Since the arrival of Europeans in the sixteenth-century, onshore and offshore events have been documented in this region from the coastal cities of Valparaíso in the north and Concepción in the south. The majority of these events have been of the megathrust/interplate type; a limited number of them have been identified as normal/intraplate. It was one of these normal (dip-slip) events that was Chile's deadliest; the 1939 Chillán event resulted in 28,000–30,000 deaths (without the influence of a tsunami). The inland city of Santiago was heavily damaged in the 1730, 1822, and 1906 megathrust events. With a recurrence interval of a little more than 80 years, the 1985 event was not unexpected.Preliminary Report of Investigations of the Central Chile earthquake of March 3, 1985 The earthquakes of March 3, 1985, and the seismicity of Chile https://pubs.usgs.gov/of/1985/0542/report.pdf 1985 S. T. Algermissen E. Kausel United States Geological Survey 4 10.3133/ofr85542 1985usgs.rept...29AWood Wight Moehle 1987 6, 7, 55Comte Eisenberg Lorca Pardo Ponce Saragoni Singh Suárez 1986 449–452 Tectonic setting Chile triple junction Convergent boundary List of tectonic plate interactions Geology of Chile The Peru–Chile Trench, also known as the Atacama Trench, is the primary tectonic feature off the west coast of South America and has contributed to Chile being one of the most seismically active countries in the world. The Nazca plate is subducting to the east under the South American plate, with high-speed convergenceThe rate of convergence varies along the trench and sources also present different figures. For example, Yeats 2012 190 gives a rate of 84 mm on in Central Chile and 60 mm on per year in Colombia. Hayes Smoczyk Benz Villaseñor 2015 presents similar figures of 80 mm on in the south and 65 mm on in the north. Plafker 1985 14 and Mendoza Hartzell Monfret 1994 281 give Central Chilean slip rates of 92 mm on and 90 mm on respectively and finally, Wood Wight Moehle 1987 6, 7 gives a full 100 mm on per year for Chile and Peru. and sustained stick-slip action resulting in two types of earthquakes along the trench. There are the typical interplate events that occur at the subduction interface and the less common intraplate events that occur within the downgoing Nazca slab. An additional earthquake hazard comes in the form of shallow crustal faults. The San Ramón Fault, for example, is a thrust fault that is positioned along the easternmost districts of Santiago. Despite estimated slip rates of .5 mm us per year, paleoseismologists have uncovered evidence of several very large events (5 m us of slip). They acknowledged that a more typical event on this fault may only produce a large shock in the range of 6.2–6.7 as the fault is segmented.Hussain E. Elliott J. R. Silva V. Vilar-Vega M. Kane D. Contrasting seismic risk for Santiago, Chile, from near-field and distant earthquake sources Natural Hazards and Earth System Sciences 20 5 2020 1684-9981 10.5194/nhess-20-1533-2020 free 1533, 1534 2020NHESS..20.1533HActive Faults of the World Yeats R. 2012 Cambridge University Press 978-0521190855 Foreshocks Moment magnitude scale Seismic magnitude scales Foreshock activity occurred for eleven days prior to the mainshock, beginning on 21 February with a 5.7 w event. This magnitude was supplied by the National Earthquake Hazards Reduction Program (NHRP)/National Earthquake Information Center (NEIC) and a 2017 United States Geological Survey (USGS) study and data release. The NHRP/NEIC placed the intensity of this initial foreshock at VI (Strong). Over the course of the eleven days, 360 events over 3.0 c y occurred, but none with a higher intensity than the initial event. This included more than 50 events on 21 February and more than 100 the following day. The frequency of the activity caused great alarm in Valparaíso, to the extent that funds were immediately sought by Mexican and Chilean scientists for travel expenses and to bring additional equipment to set up portable seismograph stations. Prior to their arrival on 5 March, the final foreshock in the sequence arrived just seconds prior to the mainshock.Valparaíso 1985 https://earthquake.usgs.gov/earthquakes/eventpage/usp0002c3g/impact M 5.7 – 22 km SW of Valparaíso, ChileThe origin of the aftershock's intensity details, as detailed on the NHRP/NEIC website, are with the monthly listing of the Preliminary Determination of EpicentersNational Earthquake Information Center, National Earthquake Information Service Preliminary Determination of Epicenters https://babel.hathitrust.org/cgi/pt?id=uc1.31822031458763&seq=55 February 1985 U.S. Dept. of the Interior, Geological Survey, National Earthquake Information Service Golden, Colorado 8 HathiTrust Earthquake Characteristics Strike and dip Rake (geology) Wadati–Benioff zone The Centro Sismológico Nacional de la Universidad de Chile, the USGS, and the International Seismological Centre all place the magnitude at 8.0 w. Other figures exist, like the initial 1985 observation from the Preliminary Determination of Epicenters, which placed it at 7.8 s and the Harvard–Adam Dziewonski Observatory, which places it at 7.9 w. Harvard's slip parameters for the strike, dip, and rake are 11°, 26°, and 110°. A 1986 study, with only a one-degree change in the dip angle, placed the figures at 11°, 25°, and 110°. A 1994 study compared their own figures regarding rupture length, depth, and duration, with those of nine previous studies. Of the six studies that contributed duration information that was gathered using different seismic networks, a range was given from 40 to 80 seconds, with a mode of 69 seconds. The focal depth was equally diverse, with five kilometers on the low end to 60 km on the high end. The fault's rupture length had a range of 75 to 250 kilometers, with the highest figure derived from geodetic information alone.Mendoza Hartzell Monfret 1994 270Comte Eisenberg Lorca Pardo Ponce Saragoni Singh Suárez 1986 450 Figure 1 The authors of the same 1994 study presented more details from earlier workers, as well as their own analysis of the mainshock characteristics, which included data from both the Global Digital Seismograph Network and the GEOSCOPE Observatory. Their results showed a 200 km on bi-lateral rupture on the Nazca–South American plate boundary, though only three of the ten previous studies shared similar information regarding rupture directivity. They revealed that it primarily ruptured to the south of the epicenter, with just 50 km us of the rupture to the north, over a total duration of 70 seconds.Mendoza Hartzell Monfret 1994 270 Intensity Modified Mercalli intensity scale Seismic intensity scales Compared with on-the-ground observations of damage and ground effects, isoseismal maps provide a rudimentary overview of the intensity that was experienced. Professor Rodolfo Saragoni from the University of Chile provided one of these maps that shows zones of mixed intensities within roughly 150 km us of the epicenter,Professor Saragoni's map is not available as it was first published in printed form in Saragoni González Fresard 1985 but it appears on page 72 of Wood Wight Moehle 1987 and a slightly modified version appears in figure 4.1 of Booth Taylor 1988 where mixed groups include V–VI, VI–VII, or VII–VIII. These areas are relatively small and isolated areas of higher intensities embedded in much larger areas of lower intensity. For example, Rengo is in a very small intensity VIII (Severe) zone, but is itself surround by a slightly larger zone of VII (Very strong) intensity that includes Curicó, San Fernando, and Rancagua. Both of these areas are embedded within a VI–VII zone that stretches roughly 200 mi flip on from Talca to La Ligua. Another example is that the city of Algarrobo is in an area of VI–VII shaking, while embedded in a zone of VII–VIII shaking that includes nearby communities of Valparaíso, San Antonio, Llolleo, and Viña del Mar. Santiago was marked as intensity VII. Cities designated as having experienced intensity VI shaking included Linares and Illapel. The map shows a more linear pattern of attenuation farther from the epicentral area.Wood Wight Moehle 1987 72Booth Taylor 1988 Figure 4.1 On the ground, the shock's area of perceptibility was from Copiapó in the north to Valdivia in the south, a distance of more than 1400 km us.The distance from Copiapó to Valdivia (1407 km on), is comparable to that of Seattle to Las Vegas (1406 km on), Dublin to Milan (1418 km on), or Baghdad to Dubai (1381 km on) Some people in high rises felt their buildings sway on the east coast of South America, both at Buenos Aires, Argentina (1200 km on distant) and São Paulo in Brazil (2700 km on distant). Several other reconnaissance and damage surveys provided more specific details when describing the observed intensity than the isoseismal maps. The Earthquake Engineering Research Institute's report agreed with the University of Illinois study that the intensity was generally VII in Santiago. An intensity of VII is stated as the most appropriate intensity of shaking for Valparaíso and Viña del Mar, but an accommodation for intensity VIII effects was made, based on several instances of considerable damage or partial collapse of buildings. With areas of liquefaction, considerable damage and rock slides, San Antonio was placed at intensity VIII. The same could be said for Llolleo, but an exception was made for small areas of intensity IX (Violent) effects. A separate strong ground motion study also published a figure of IX for a heavily damaged school at Llolleo.Earthquake Engineering Research Institute The Chile Earthquake of March 3, 1985—Seismological Features Earthquake Spectra 1986 2 2 258, 259 10.1193/1.1585313 1986EarSp...2..253.Valparaíso 1985 https://earthquake.usgs.gov/earthquakes/eventpage/usp0002ccz/impact M 8.0 – 25 km WSW of Valparaíso, Chile Casualties Earthquake casualty estimation Deaths The USGS's Preliminary Determination of Epicenters and Utsu 2002 list 177 fatalities and 2,575 injuries, while the Belgian Centre for Research on the Epidemiology of Disasters' EM-DAT database lists slightly higher losses, with 180 dead and a slightly lower number of injured at 2,483. The National Geophysical Data Center again lists a slightly higher death toll of 200 and repeats the Utsu figure of 2,575 injured. President Augusto Pinochet said in a speech regarding the state of the nation that "Esta tragedia provocó en la zona central del país la pérdida de numerosas vidas humanas, más de dos mil quinientos heridos" (This tragedy caused the loss of numerous human lives in the central part of the country, more than two thousand five hundred injured).PAGER-CAT is a compilation of parametric earthquake catalogs. Included are the Preliminary Determination of Epicenters, PAGER, EM-DAT (from the Centre for Research on the Epidemiology of Disasters), and the National Geophysical Data Center Significant Earthquake Database, and othersAllen T. I. Marano K. D. Earle P. S. Wald D. J. David J. Wald PAGER-CAT: A Composite Earthquake Catalog for Calibrating Global Fatality Models Seismological Research Letters 80 1 2009 0895-0695 10.1785/gssrl.80.1.57 57–62 2009SeiRL..80...57AMensaje Presidencial 11 Septiembre 1984 al 11 de Septiembre 1985 http://bibliotecadigital.dipres.gob.cl/handle/11626/22254?show=full Ministerio de Hacienda 11 September 1985 XX Injuries A study on the epidemiology of the injured, authored by staff from Chile's Ministry of Health and Department of Planning, acknowledged the profound difficulties in establishing a complete understanding of the situation. Contributing to the problems were sometimes as simple as medical personnel failing to provide complete records or as complex as the complete loss of hospital or clinical facilities. Rengo Hospital, for example, collapsed entirely and 12 other hospitals required replacing due to structural damage, though no fatalities occurred at these facilities. The reduction in the number of beds available, misplaced files, and incomplete records all contributed to inconsistent numerical data. Despite these challenges, the authors presented an overview of the injured, and acknowledged a total figure of 2,575. Their work comprised a subset of those, which represented 811 women and 784 men for a total of 1,623.Ortíz M. R. Roman M. R. Latorre A. V. Soto J. Z. Brief description of the effects on health of the earthquake of 3rd March 1985 – Chile Disasters 10 2 1986 0361-3666 10.1111/j.1467-7717.1986.tb00578.x 125–140 1986Disas..10..125O Damage Basílica del Salvador Hospital del Salvador St. Joseph's Cathedral, Melipilla Parroquia Nuestra Señora de Andacollo, Santiago March 2025 Aftershocks 1985 Rapel Lake earthquake A number of large (M6+) and very large (M7+) aftershocks occurred in the following month, although the majority of them were moderate in intensity and did not cause any additional damage. Also, any casualties that occurred were not directly related and instead were attributed to sudden death from cardiac causes. On the day of the mainshock, two events of at least 6.4 s occurred and the following day, at least thirteen shocks took place, including a 7.4 w event. Six aftershocks took place on 5 March, then activity continued, but at a decreasing frequency, including the 6.7 w shocks on 17 and 19 March, and the 7.2 w Rapel Lake event on 9 April. These last three events had intensities of VII (Very strong), VI (Strong), and VI in Valparaíso. One heart attack and damage in Valparaíso was attributed to the 17 March event, and two deaths, several injuries, and additional damage occurred as result of the Rapel Lake shock on 9 April.Wood Wight Moehle 1987 61Nealy J. L. 2017 Valparaiso, Chile earthquake data 2017 10.5066/F71Z439C U.S. Geological Survey data release 1985_Valparaiso_catalog.csv Data set United States Geological SurveyUnited States earthquakes, 1985 C. W. Stover L. R. Brewer USGS Report 1991 10.3133/b1954 free Bulletin 1954 1991usgs.rept....7S Table 7Magnitudes for these aftershocks are taken from Nealy 2017; intensity details are from Wood Wight Moehle 1987; damage and effects are from Stover Brewer 1991 Tsunami List of tsunamis Subsidence Tectonic uplift A destructive local tsunami was observed.Lander, J. & Whiteside, L. & Lockridge, P. (2003). Two decades of global tsunamis 1982–2002. Science of Tsunami Hazards. 21. pp. 30, 31Preliminary Report of Investigations of the Central Chile earthquake of March 3, 1985 Geologic Reconnaissance of the March 3, 1985 Chile earthquake https://pubs.usgs.gov/of/1985/0542/report.pdf 1985 S. T. Algermissen G. Plafker United States Geological Survey 13–17 10.3133/ofr85542 1985usgs.rept...29A Aftermath Scientific response Strong ground motion Multiple seismological agencies from around the world were sent to assist professor Nicolas Velasco Saragoni from the University of Chile and professor Patricio Bonelli from Federico Santa María Technical University, as well as staff from Universidad Católica de Chile. The foreign teams assisted with damage, engineering, geological, and intensity surveys. Seismologists Mehmet Çelebi and George Plafker arrived on 21 March from the United States Geological Survey. Brought with them were additional seismometers and accelerographs, which were delivered to (and operated by) the National Autonomous University of Mexico and the University of Chile. These instruments were deployed at temporary locations to augment the existing Chilean seismograph network to improve its ability to locate aftershocks and gather strong motion data. Other foreign teams included the Earthquake Engineering Research Institute, the British Institution of Structural Engineers, the New Zealand National Society for Earthquake Engineering, and a trio from University of California, Berkeley, University of Michigan, and the University of Illinois.Preliminary Report of Investigations of the Central Chile earthquake of March 3, 1985 Introduction https://pubs.usgs.gov/of/1985/0542/report.pdf 1985 S. T. Algermissen United States Geological Survey 2 10.3133/ofr85542 1985usgs.rept...29ABooth Taylor 1988 1 Mental health effects March 2025 See also List of earthquakes in 1985 List of earthquakes in Chile Notes References 23em Earthquakes: 2006 Centennial Update – The 1906 Big One Bolt B. 2005 978-0-7167-7548-5 Fifth W. H. Freeman and Company 156 ISC-GEM Earthquake Catalogue Data set International Seismological Centre 2024 Version 11.0 10.31905/D808B825 free Preliminary Report of Investigations of the Central Chile earthquake of March 3, 1985 Site Selection and Field Experiments https://pubs.usgs.gov/of/1985/0542/report.pdf 1985 S. T. Algermissen S. T. Algermissen E. Kausel E. Sembera P. C. Thenhaus United States Geological Survey 27 10.3133/ofr85542 1985usgs.rept...29A PAGER-CAT Earthquake Catalog https://earthquake.usgs.gov/static/lfs/data/pager/catalogs/ 4 September 2009 United States Geological Survey Version 2008_06.1 Data set Sources The Chilean Earthquake of 3 March 1985 – A Field Report By EEFIT https://www.istructe.org/IStructE/media/Public/Resources/report-eefit-mission-algarrobo-chile-20190808.pdf E. D. Booth C. A. Taylor Earthquake Engineering Field Investigation Team 1988 Comte D. Eisenberg A. Lorca E. Pardo M. Ponce L. Saragoni R. Singh S. K. Suárez G. The 1985 Central Chile Earthquake: A Repeat of Previous Great Earthquakes in the Region? Science 233 4762 1986 0036-8075 10.1126/science.233.4762.449 449–453 17794569 1986Sci...233..449C Seismicity of the Earth 1900–2013: Seismotectonics of South America (Nazca Plate Region) Open-File Report 2015 10.3133/ofr20151031e free G. P. Hayes G. M. Smoczyk H. M. Benz A. Villaseñor K. P. Furlong USGS Report 25 2015usgs.rept...25H C. Mendoza S. Hartzell T. Monfret Wide-band analysis of the 3 March 1985 central Chile earthquake: Overall source process and rupture history Bulletin of the Seismological Society of America 1994 84 2 269–283 10.1785/BSSA0840020269 11 July 2025 1994BuSSA..84..269M Lee W. H. K. Jennings P. Kisslinger C. Kanamori H. International Handbook of Earthquake & Engineering Seismology, Part A Elsevier 2002-09-27 978-0-08-048922-3 Macroseismology R. M. W. Musson I. Cecić 807–822 H. R. Saragoni P. González M. Fresard Análisis de los Acelerogramas del Terremoto del 3 de Marzo de 1985 Universidad de Chile, Facultad de Ciencias Físicas y Matemáticas, Departamento de Ingeniería Civil, Sección Ingeniería Estructural 1985 es 81873703 Santiago International Handbook of Earthquake & Engineering Seismology Part A, Volume 81A A List of Deadly Earthquakes in the World: 1500–2000 T. R. Utsu 2002 Academic Press First 978-0-12-440652-0 The 1985 Chile earthquake—Observations on earthquake-resistant construction in Viña del Mar https://nehrpsearch.nist.gov/static/files/NSF/PB88107248.pdf 1987 S. L. Wood J. K. Wight J. P. Moehle University of Illinois at Urbana–Champaign 0069-4274 6156187 Civil Engineering Studies: Structural Research Series Structural Research Series No. 532 Further reading Çelebi M. Topographical and geological amplifications determined from strong-motion and aftershock records of the 3 March 1985 Chile earthquake Bulletin of the Seismological Society of America 77 4 1987 1943-3573 10.1785/BSSA0770041147 1147–1167 1987BuSSA..77.1147C Dowrick D. J. Preliminary field observations of the Chilean earthquake of 3 March 1985 Bulletin of the New Zealand Society for Earthquake Engineering 18 2 1985 2324-1543 10.5459/bnzsee.18.2.119-127 free 119–127 1985BNZSE..18..119D https://www.bulletin.nzsee.org.nz/index.php/bnzsee/article/download/873/847 Nakamura S. An analysis of the 1985 Chilean tsunami Marine Geodesy 15 4 1992 0149-0419 10.1080/01490419209388064 277–281 1992MarGe..15..277N External links 529084 A quake in Chile kills at least 82 and injures 2000 – The New York Times (4 March 1985) 1985 Algarrobo earthquake Category:1980s tsunamis Category:1985 earthquakes Category:1985 in Chile Category:March 1985 in South America Category:Tsunamis in Chile