1985 Algarrobo earthquake explained

1985 Algarrobo earthquake
Timestamp:1985-03-03 22:47
Anss-Url:usp0002ccz
Isc-Event:529084
Local-Time:19:47 UTC-3
Magnitude:8.0 Mw[1]
Depth:33km (21miles)
Countries Affected:Chile
Landslide:Yes
Casualties:177 dead, 2,575 injured

An earthquake measuring 8.0 struck Santiago, Chile, on 3 March 1985, killing 177 people and injuring about 2,575 others.[2] This earthquake was being felt between the northern Antofagasta Region and the southern Los Lagos Region. It was felt with a maximum intensity of VIII on the Mercalli intensity scale.

Damage and effects

The quake left 177 people dead, 2,575 injured, 85,358 houses damaged or destroyed and about a million people homeless.[3] Many landslides were registered too, pavement breaks with the destruction of the Pan-American Highway in several points, broken-down bridges and considerable damage in affected town's infrastructure, with a long interruption on basic services. The damage was valued in more than 1 billion US dollars.[4]

RegionDeathsInjuriesHomelessHouses
RefugeesNon-refugeesTotalDestroyedMinor damage
Valparaíso689233849252 800256 64917 25728 242
O'Higgins28254322190 144190 466666112 374
Maule260743 41143 41820795549
Santiago8013387936488 075496 01159 36163 814
Total178257512 114974 430986 54485 358109 979

Reports by local residents in the coastal area from Matanzas to several kilometers north of Algarrobo indicated unusually low tides for a period of 3 to 5 days following the earthquake. After this, the tides reportedly returned to normal. This suggests that there was earthquake-related uplift along parts of the coast which was recovered in 3 to 5 days after the earthquake. Near Algarrobo, an estimate of the change is about 20 cm uplift.

Tectonic setting

Chile lies on the boundary between the Nazca Plate of the South Pacific continental plate. This results in Chile being one of the most seismically active regions in the world. On average, a magnitude 8 earthquake or greater occurs in the region about once every 25 years. Meaning that there is an expectation that a similar earthquake will happen in Chile in the future every 25 years. The main shock was actually made up of at least two shocks, with the initial motion beginning at approximately 11:00 PM followed by a greater event soon after. The magnitudes of the first and second shocks were calculated to be 5.2 and 6.9 respectively. The calculated proportion of energy released as aftershocks vs the main shock was relatively high, most likely due to the 7.2 aftershock on 9 April.

Scientific understanding

The earthquake was seen as particularly powerful, garnering the attention of the United States. They sent a team of geologists to study its effects because the overall information that could be gained from studying the earthquake could give better understandings overall of these powerful earthquakes. This earthquake in particular was considered extremely important in the understanding of earthquakes as "it was very significant as a geophysical event and that the scientific and engineering study of this major shock would be of great value in improving our understanding of plate margin earthquakes, the distribution of strong ground motion, resulting building damage and geologic effects such as soil liquefaction and landsliding". The 1985 Algarrobo earthquake shows a clear example of how these types of natural phenomenon can be studied and be used to better help humanity in the future in order to minimize the damages to both infrastructure and human lives. The precautions that Chile takes now in order to mitigate future risks is to educate its citizens in drills on how to react, having better building codes, and studying seismic data.[5]

See also

External links

-33.24°N -72.04°W

Notes and References

  1. Servicio Sismológico Universidad de Chile, Sismos importantes o destructivos desde 1570
  2. News: Associated Press. 4 March 1985. A quake in Chile kills at least 82 and injures 2000. en-US. The New York Times. 1 December 2021. 0362-4331.
  3. Web site: Mensaje Presidencial: 11 de septiembre de 1984-11 de septiembre de 1985 . Pinochet, Augusto . Memoria Chilena . 11 September 1985. Augusto Pinochet .
  4. El Mercurio, Grandes terremotos en Chile
  5. Web site: Deutsche Welle. Earthquake preparedness: What can we learn from Chile?. 16 November 2020. live. en-GB. https://web.archive.org/web/20201116102120/https://www.dw.com/en/earthquake-preparedness-what-can-we-learn-from-chile/a-55613842 . 16 November 2020 .