The sediment nuclei extracted from four lakes in Guatemala record the distinctive direction that the earthquake traveled during an earthquake of magnitude 7.5 of 1976 that devastated the country, according to the researchers of the annual meeting of the seismological society of America.
The earthquake, which killed more than 23,000 people and left around 1.5 million homeless people, took place along the Motagua failure, on the border between the limit of the tectonic plate of North America and the Caribbean.
The tremor of the severe earth of the 1976 earthquake caused landslides and turbidity currents loaded with sediments that can be clearly seen in nuclei taken from the beds of the lakes. Normally, researchers could expect this tremor to produce the thinnest sediment deposits in the lakes farther from an earthquake, since the seismic waves weaken as they travel away from an epicenter of earthquakes.
But in the Guatemalan lakes, the nuclei with the thickest sediment traces of the earthquake occur at the end of the breakdown of the fault, said Jonathan Obrist-Farner, a geologist at the University of Missouri Science and Technology. “What we see are the lakes that are actually the closest to the epicenter, but right next to the path of breakdown they have very thin deposits.”
Jeremy Maurer, geophysicist also at the University of Missouri, suggested that the unusual pattern had registered in this case the directivity of the 1976 tremor.
It is not unusual for scientists to find evidence of pastmotes past in the sediment nuclei of the lake, Maurer added, pointing out examples of New Zealand to Turkey that offer a vision of how far a particular earthquake could have.
“What has not been done so much is to see where these lakes are in relation to guilt,” Maurer said. “Are they outside the axis or on the axis? Does the direction of the break have an effect on sediment deposits?”
When the US Geological Service collected field data after the 1976 earthquake, “they found, for example, the adobe houses that were 10 kilometers south of the route of the main break that were still standing, but those that were really in the trail of the fault and towards the propagation direction collapsed,” Maurer said. “I think there is a lot of evidence that points to the directivity of the rupture and now we are only looking at it sedimentologically from the lakes.”
The researchers began to recover and analyze the centers of the lakes in 2022. “We think it would be a very interesting opportunity not only to look at the 1976 earthquake, but in reality learning a little more about the paleoseismic history of the plaque limit, of what we know very little,” said Obrist-Farner, who originates from Guatemala.
Although there was a brief avalanche of seismologists in the region after the 1976 earthquake, the impacts of a 36 -year civil war and a scarce instrumentation have left the limit of the badly monitored plaque. Paleoseismic data such as lake records are important to build a more complete image of the country’s seismic risk.
Last year, the Obrist-Farner team recovered its largest nuclei in the lakes, with sediment lengths that can represent up to four thousand years of lake history. Its initial analysis shows evidence of the 1816 earthquake of at least the magnitude 7.5 that is mainly known about historical documents.