1985 Algarrobo earthquake
| UTC time | 1985-03-03 22:47 |
|---|---|
| ISC event | 529084 |
| USGS-ANSS | ComCat |
| Local date | 3 March 1985 |
| Local time | 19:47 UTC−03:00 |
| Duration | 69 seconds |
| Magnitude | 8.0 Mw |
| Depth | 35.0 km (21.7 mi) |
| Epicenter | 33°15′25″S 71°51′29″W / 33.257°S 71.858°W |
| Fault | Atacama Trench |
| Type | Megathrust |
| Areas affected | Central Chile |
| Total damage | $1.5–1.8 billion |
| Max. intensity | MMI IX (Violent) (Llolleo) |
| Peak acceleration | .86 g (Llolleo) |
| Tsunami | Yes |
| Landslides | Yes |
| Casualties | 177–200 dead 2,483–2,575 injured 372,532–500,000 homeless |
A megathrust earthquake measuring 8.0 Mw 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 beginning 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 Mw shocks on 17 and 19 March and the 7.2 Mw 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.