The great wave absent in the records could have been caused by a great earthquake on the high seas
A major earthquake off the coast of south-central Chile in 1737 may have caused a massive tsunami absent from historical records, according to new research published Thursday in the journal Nature, Communications Earth & Environment. The discovery suggests that these records by themselves may not be enough to predict future tsunami risk, while also showing that these phenomena may occur more often than previously thought on the Chilean coast.
Historical records are used to predict how often tsunamis are likely to occur in a region in the future. Until now, tsunami-causing earthquakes were believed to have occurred in this area of Chile three times since the 1570s, including after the magnitude 9.5 earthquake of 1960.
However, this discovery of an unrecorded tsunami means that tsunamis may have hit the Chilean coast more frequently than previously believed. This means that the average time between historical tsunami events could be significantly reduced, to an average of 130 years.
Researchers from the universities of Northumbria and York in the United Kingdom analyzed 130 sediment cores within the salt marshes at Chaihuín, near Valdivia, near the area where the 1737 earthquake occurred. The analysis revealed the existence of extended sand layers, which date from the same time as the earthquake, closely resembling deposits made by tsunami waves in other areas.
The researchers also found a mix of freshwater and marine algae species and evidence of land subsidence, meaning they were able to rule out storms, river flooding or a remotely generated tsunami as the cause of the sand deposits.
Their findings show that the 1737 earthquake began primarily offshore, at much shallower fault depths than previously indicated in historical records.
Therefore, the researchers suggest that geological and historical records should be considered together when predicting future tsunami risk, as historical records alone may not provide complete documentation.
against the settlers
“Assessment of tsunami hazard is often based on historical records of flooding along particular coastlines, and the frequency of past tsunami occurrence is used to predict potential future hazard,” says Emma Hocking from the Department of Geography. and Environmental Sciences at Northumbria University. “However, these records are sometimes incomplete because tsunami reporting can be greatly affected by social unrest or other crises. In this case, it is believed that the unreported tsunami could be attributed to uprisings that had driven settlers out of most of the settlements in the area,” she adds.
“The implication of this is that tsunamis have occurred more frequently than previously believed, and therefore we suggest that the use of historical records alone may lead to miscalculations. Geological evidence is essential to verify and complement the historical record in order to obtain solid long-term patterns that serve as a basis for the evaluation of seismic and tsunami hazards.”
