Researchers discover evidence of earthquakes that affected Chilean coast in the past 9,000 years


Share post:

A scientific team has discovered the geological footprint of earthquakes and tsunamis that affected the Aysen region (southern Chile) up to 9,000 years ago. This new study improves the assessment of seismic hazard in a wide area of the American continent prone to large earthquakes.

Researchers discover evidence of earthquakes that affected Chilean coast in the past 9,000 years
The new study is a first step forward to improve the evaluation of the seismic hazard in Andean regions
[Credit: Universidad de Barcelona]

The study, published in Journal of Geophysical Research: Solid Earth, enabled the researchers to establish the first paleoseismological record of the Liquine-Ofqui Fault Zone (LOFZ), a large geological structure that crosses southern Chile and is partially responsible for the seismic activity of the Andean country.

The LOFZ fracture area, which stretches over more than 1,000 kilometres north-south in Chile, is a geological structure associated with volcanism and that has an impact on the relief of the Andean country. This seismically hazardous area has some active volcanoes –such as Maca, Hudson and Mentolat- and steep reliefs that can enlarge the effects of the most violent geological phenomena.

In this area, Aysen fjord is a model to study geological processes –earthquakes, tsunamis, etc.— that can be a threat to the local population. According to Galderic Lastras, “the Aysen fjord is cross-cut by the strike-slip fault system (LOFZ) that causes local earthquakes, such as the crisis in 2007. The main earthquake of this crisis —magnitude 6.2— caused dozens of landslides and a local tsunami, with some casualties and important damage to fish farms.”

“Moreover, this fjord is quite close to the plate boundary between the South American and the Nazca Plates, an active subduction zone that causes large magnitude earthquakes,” says Lastras, expert on submarine cartography and head of the oceanographic survey DETSUFA that worked on the cartography of the geological footprint of submarine landslides in Aysen.

Aysen fjord: earthquakes and tsunamis in a natural laboratory

When an earthquake occurs –moderate or strong-, it can destabilize the mountain slopes that surround the fjord. Rock masses can slide and fall until reaching the fjord bottom, causing local tsunamis. This forms an increased risk for the population since there is an extremely short warning time. The geological footprint of these landslides -piled up at the bottom of the fjord and separated by sediments- is then visible in the sedimentary record.

Researchers discover evidence of earthquakes that affected Chilean coast in the past 9,000 years
The geological footprints of the last seismic crisis – April 21, 2007 – are still visible in the Aysén fjord
[Credit: G. Lastras]

According to Maarten Van Daele, postdoctoral researcher and expert on sedimentary deposits created by earthquakes, “strong seismic shaking triggers both onshore and subaquatic landslides. These are buried in the fjord and we can image and map them using geophysical methods. In this study, we also retrieved sediment cores, which allowed us to determine ages for the landslide events using radiocarbon dating of organic material in the sediment.”

Combining different geophysical techniques —reflection seismics, geochemistry of volcanic ashes, etc.— the scientific team constructed the first paleoseismic record of the Liquine-Ofqui Fault Zone. “For the first time —adds Van Daele— we have a rough idea of earthquake recurrence rates along this fault. Other similar studies are needed along the fault trace, but this is an important first step to improve the assessment of the seismic hazard in the region.”

Looking for the most violent seismic episodes

Earthquakes can destabilize fjord slopes and cause landslides, but other factors such as heavy rainfall can also be involved and enhance slope instability. As a result, the experts could identify evidence of ten earthquakes in Aysen fjord –including the most recent one in 2007— but the amount of such earthquake events is probably even higher since not every earthquake will cause a significant landslide.

Researchers discover evidence of earthquakes that affected Chilean coast in the past 9,000 years
The study presents the first paleoseismological record of the Liquiñe-Ofqui Fault Zone (LOFZ), a geological structure
that crosses southern Chile [Credit: University of Barcelona]

According to Katleen Wils, predoctoral researcher at Ghent University and first author of the study, “we know these landslides occurred due to a common trigger: an earthquake. In the Aysen region, the main source of seismic hazard comes from the LOFZ fault rather than the subduction zone. Those earthquakes had intensities similar to those occurring during the 2007 main episode, which was up to IX, corresponding to violent shaking and considerable damage.”

“According to the data, six of the analysed earthquake events took place in the fjord during the last 9,000 years, while the other four occurred before that. This shows that there is an important seismic hazard in the region, mainly originating from the LOFZ, but also from the subduction zone,” notes Wils, expert on geophysics and the study of earthquakes and seismic hazard.

The number of earthquakes recorded in Aysen fjord may be clear, but “it is more difficult to have a clear idea of their magnitude,” warns Galderic Lastras. “One of the identified events has a similar age (about 2,000 years before present) to a tsunami deposit described in the coastal Lake Huelde, in Chiloe Island, and with a turbidite in Lake Rinihue. Identifying signs of an earthquake in different locations far away from each other is a sign of a large magnitude earthquake, which has likely originated in the subduction zone.”

According to the authors, their study reveals that LOFZ is an active fault system that should be characterized in more detail in future studies in order to have more knowledge on the complete seismic system.

Paleoseismology: the unwritten history of great earthquakes

The paleoseismological record of Aysen fjord is an important part of the geological history of the region as a written record of past earthquakes in the area is non-existent. Understanding the rate at which earthquakes took place in the past is essential to infer the occurrence of future earthquakes.

Because of this uncertainty, “geological research is an essential tool to explain the unwritten history of the most violent earthquake events that affected a certain area. It is important to know as much as possible about past seismic activity of a region. This means that technology and scientific knowledge are the key to improve the assessment of seismic hazard, mitigate the effects of natural disasters and help society directly,” the authors write.

Source: University of Barcelona [March 07, 2018]



Related articles

Biodiversity loss in the oceans can be reversed through habitat restoration

Activities such as laying gas pipelines, trawling for fish, drilling for oil, and even burying internet cables in...

Adapt, move or die: How biodiversity reacted to past climate change

A new paper reviews current knowledge on climate change and biodiversity. In the past, plants and animals reacted...

Scientific expedition to Antarctica will search for dinosaurs and more

An international team of researchers supported by the National Science Foundation will journey to Antarctica this month to...

The Arctic Ocean was covered by a shelf ice and filled with freshwater

The Arctic Ocean was covered by up to 900 m thick shelf ice and was filled entirely with...

Researchers explore gigantic volcanic eruptions that led to mass extinctions

A paper published in Nature Communications by Virginia Tech researchers confirms a major feature in the formation of...

Ponds in High Arctic could be significant source of carbon emissions

A new Canadian study has found that carbon released by some ponds in the High Arctic could potentially...

Rising temperature difference between hemispheres could dramatically shift rainfall patterns in tropics

One often ignored consequence of global climate change is that the Northern Hemisphere is becoming warmer than the...

Glaciers cracking in the presence of carbon dioxide

The well-documented presence of excessive levels of carbon dioxide (CO2) in our atmosphere is causing global temperatures to...