1995 Antofagasta earthquake explained

1995 Antofagasta earthquake
Timestamp:1995-07-30 05:11:23
Anss-Url:usp000714t
Isc-Event:96080
Local-Time:01:11
Magnitude:8.0
Depth:46km (29miles)
Location:-23.35°N -70.32°W
Affected:Chile
Damages:$1.791 million
Pga:0.29 g
Casualties:3 dead
58–59 injured
575–630 homeless

The 1995 Antofagasta earthquake occurred on July 30 at 05:11 UTC (01:11 local time) with a moment magnitude of 8.0 and a maximum Mercalli intensity of VII (Very strong). The Antofagasta Region in Chile was affected by a moderate tsunami, with three people killed, 58 or 59 injured, and around 600 homeless. Total damage from the earthquake and tsunami amounted to $1.791 million.

Tectonic setting

Chile lies along the oblique convergent boundary between the oceanic Nazca plate and the continental South American plate. Crustal deformation is primarily accommodated by two main types of faulting: strike slip and reverse faulting subduction zone earthquakes.[1] [2] [3] Reverse faulting deformation is taken up by the Peru-Chile Trench, on which this earthquake occurred.[1] Slip rate on the fault is NaNmm/yr, and as a result the subduction zone is responsible for many megathrust earthquakes in the region. Some of the largest recorded earthquakes ever recorded occurred in the area, such as the 1960 Valdivia earthquake, the 1730 Valparaíso earthquake, and the 1420 Caldera earthquake.[1] [4] Strike slip faulting is taken up the by the Liquiñe-Ofqui Fault.[2] [3] It is responsible for a 7.7 earthquake as part of the aftershock sequence of the 1960 Valdivia earthquake, and potentially was involved with the main rupture as well.[5] [6]

Earthquake

At 1:11 local time on July 30, 1995, a large earthquake struck northern Chile. The 8.0 earthquake struck at a depth of 46km (29miles) with an epicenter near Antofagasta. The focal mechanism of this earthquake indicates thrust faulting along the subduction zone, which is consistent with other large earthquakes along the plate boundary in this region.[7] [8] The maximum slip was 5.4m (17.7feet) along a NaNkm (-2,147,483,648miles) zone of rupture.[9] [7] [10] Foreshock activity was minimal, but large aftershocks lasted a while after the mainshock, with the largest being a shallower 6.4 event with a Modified Mercalli Intensity of VII three days later.[11] The event occurred at the edge of a known seismic gap that produced the 1877 Iquique earthquake, and research suggests that this earthquake may have put more stress on the region as well.[12] The event is not thought to have ruptured the shallow plate interface in the region, leaving it susceptible to future large megathrust earthquakes such as the 1877 event.[12]

Tsunami

The tsunami observed was smaller than expected, however this may be explained by the depth of the event. Maximum run-up height was measured at 2.8m (09.2feet) at Antofagasta.[8] Tide gauges at Antofagasta, Caldera, and Iqiuque recorded wave heights of 1.5m (04.9feet), 0.6m (02feet), 0.3m (01feet) respectively.[13] 10 hours after initial rupture, tsunami waves reached French Polynesia where anomalously large run-ups of 2.5m (08.2feet) and crest-to-trough wave heights of 3m (10feet) were recorded.[14] Tahiti itself recorded a small tsunami of 20cm (10inches), while Hilo, Hawaii registered heights of 80cm (30inches).

See also

Notes and References

  1. Dura . Tina . Cisternas . Marco . Horton . Benjamin P. . Ely . Lisa . Nelson . Alan . Wesson . Rob . Pilarczyk . Jessica . Coastal evidence for Holocene subduction-zone earthquakes and tsunamis in central Chile . Quaternary Science Reviews . April 2015 . 113 . 93–111 . 10.1016/j.quascirev.2014.10.015 . 17 August 2022.
  2. De Pascale . Gregory P. . Froude . Melanie . Penna . Ivanna . Hermanns . Reginald L. . Sepúlveda . Sergio A. . Moncada . Daniel . Persico . Mario . Easton . Gabriel . Villalobos . Angelo . Gutiérrez . Francisco . Liquiñe-Ofqui's fast slipping intra-volcanic arc crustal faulting above the subducted Chile Ridge . Scientific Reports . March 2021 . 11 . 1 . 7069 . 10.1038/s41598-021-86413-w . 33782456 . 8007613 . 2021NatSR..11.7069D . 17 August 2022.
  3. Cembrano . José . Hervé . Francisco . Lavenu . Alain . The Liquiñe Ofqui fault zone: a long-lived intra-arc fault system in southern Chile . Tectonophysics . 1996 . 259 . 1–3 . 55–66 . 10.1016/0040-1951(95)00066-6 . 1996Tectp.259...55C . 17 August 2022.
  4. Abad M.. Izquierdo T.. Cáceres M.. Bernárdez E.. Rodríguez-Vidal J.. 2018. Coastal boulder deposit as evidence of an ocean-wide prehistoric tsunami originated on the Atacama Desert coast (northern Chile). Sedimentology. 67 . 3 . 1505–1528 . 10.1111/sed.12570. 135386871 .
  5. Kanamori . Hiroo . Rivera . Luis . An M_w = 7.7 slow earthquake in 1960 near the Aysén Fjord region, Chile . Geophysical Journal International . 1 October 2017 . 211 . 1 . 10.1093/GJI/GGX292 . 17 August 2022.
  6. Kanamori . Hiroo . Evidence for a large strike-slip component during the 1960 Chilean earthquake . Geophysical Journal International . July 2019 . 218 . 1 . 1–32 . 10.1093/gji/ggz113 . free . 9 July 2022.
  7. Web site: Barrientos . Sergio . UPDATE ON NORTHERN CHILE EARTHQUAKE (August 1, 1995) . European Organisation for Astronomical Research in the Southern Hemisphere . 17 August 2022.
  8. Pritchard . M. E. . Simon . M. . Rosen . P. A. . Hensley . S. . Webb . F. H. . Co-seismic slip from the 1995 July 30 Mw= 8.1 Antofagasta, Chile, earthquake as constrained by InSAR and GPS observations . Geophysical Journal International . 2 August 2002 . 150 . 2 . 362–376 . 10.1046/j.1365-246X.2002.01661.x . 2002GeoJI.150..362P . 15894908 . free .
  9. Web site: USGS Finite Fault . United States Geological Survey . 17 August 2022.
  10. Ruegg . J. C. . Barrientos . S. . Campos . J. . Armijo . R. . Serrurier . L. . Lazo . D. . Ortlieb . L. . QUANTIFICATION OF THE 1995 ANTOFAGASTA EARTHQUAKE FROM GEODETIC MEASUREMENTS AND MODELLING . International Geological Correlation Program Project 367: Late Quaternary Coastal Records of Rapid Change: Application Ta Present and Future Conditions . November 1995 . 18 August 2022.
  11. Web site: USGS Nearby Seismicity . United States Geological Survey . 17 August 2022.
  12. Métois . M. . Socquet . A. . Vigny . C. . Carrizo . D. . Peyrat . S. . Delorme . A. . Maureire . E. . Valderas-Bermejo . M.-C. . Ortega . I. . Revisiting the North Chile seismic gap segmentation using GPS-derived interseismic coupling . Geophysical Journal International . 3 September 2013 . 194 . 3 . 1283–1294 . 10.1093/gji/ggt183 . free .
  13. Ihmlé . Pierre F. . Ruegg . Jean-Claude . Source tomography by simulated annealing using broad-band surface waves and geodetic data: application to the Mw=8.1 Chile 1995 event . Geophysical Journal International . October 1997 . 131 . 1 . 146–158 . 10.1111/j.1365-246X.1997.tb00601.x . 1997GeoJI.131..146I . free .
  14. Guibourg . Sandrine . Heinrich . Phillippe . Roche . Roger . Numerical modeling of the 1995 Chilean Tsunami. Impact on French Polynesia . Geophysical Research Letters . 1 April 1997 . 24 . 7 . 775–778 . 10.1029/97GL00317 . 1997GeoRL..24..775G . 129776108 . free .

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