Seismic hazards reassessed in the Andes

Sep 02, 2014
Gulf of Guayaquil and Andes. Credit: IRD / L. Audin

Although being able to predict the date on which the next big earthquake will occur is still some way off becoming a reality, it is now possible to identify the areas where they will occur. IRD researchers and their French, Ecuadorian and Peruvian partners have just measured the current deformation in the northern part of the Andes for the first time using GPS, where the tectonics of the Pacific and South American plates govern the high seismic activity in the region. The scientists then identified the areas where the fault, located at the interface of these two plates, is capable of generating large earthquakes or not.

This work, which was published in Nature Geoscience, also shed light on the formation of large tectonic structures such as the Bolivian highlands and the Gulf of Guayaquil in Ecuador, with the discovery of a continental microplate in Peru and southern Ecuador.

First measurement of the deformation in the northern Andes

The Andes have had three of the largest earthquakes ever recorded: on the border between Colombia and Ecuador in 1906, as well as in Chile, in 1960 and again in 2010. When will one of these happen there again? It is impossible to say... But scientists can now identify the areas where it will occur. Researchers from the Géoazur, ISTerre and ISTEP laboratories and their partners from geophysical and geographical institutes in Ecuador and Peru, have just measured the deformation in the northern Andes caused by the subduction of the Pacific Oceanic plate under the South American continental plate. Using a vast GPS network which has been deployed since 2008 and observational data collected since the 1990s, they have quantified the movements of 100 measurement points from central Peru to southern Colombia, with an accuracy of about one millimetre per year.

Clearly determined seismic areas

The researchers were able to locate the areas at risk. Only two fault segments can produce mega-earthquakes (greater than 8.5 on the Richter scale), potentially accompanied by tsunamis: the first is located in central Peru and the second is further north, extending from northern Ecuador to southern Colombia. In between these two active segments, the research team identified a third subduction segment. Somewhat surprisingly, this is characterised by sliding that is mainly "aseismic". So in this area spanning more than 1,000 km from the north of Peru to the south of Ecuador, or 20% of the length of the Andean subduction, the accumulated energy seems insufficient to produce a mega-earthquake. Across the region, earthquakes remain more superficial and more modest in magnitude, as shown in recent history.

Andean structures explained

These studies have also enabled the researchers to discover a large continental block, wedged between the Pacific and South American plates. This piece of continent was called the "sliver Inca" by the authors of the study and is more than 1,500 km long and 300 to 400 km wide. It is separated from the continental plate and moves 5 to 6 mm per year towards the south-east in relation to it. This finding suggests that the current deformation of the Andes from Venezuela to southern Chile, and the seismic activity in the region are dominated by the movements of several microplates of that type.

The discovery of the "sliver Inca" also explains the location of major tectonic structures. For example, the Bolivian highlands, the second highest plateau in the world, was created by the "sliver Inca" and the central Andes microplate coming together. In contrast, the opening of the Gulf of Guayaquil in Ecuador is a result of the divergence of the Inca block and the northern Andes microplate.

These studies allow a better understanding of recent developments in the Andes and their continental margins. They therefore make better estimates of seismic hazards in the region possible.

Explore further: Foreshock series controls earthquake rupture: New insights into this year's April great earthquake in Chile

More information: "Motion of continental slivers and creeping subduction in the northern Andes." Nature Geoscience, 2014, 7 (4), p. 287-291. ISSN 1752-0894

add to favorites email to friend print save as pdf

Related Stories

Geologists warn of mega quake for north Chile

Aug 14, 2014

North Chile is at risk of a mega earthquake after a tremor in April released only some of the tension building along a high-risk fault zone since 1877, researchers said Wednesday.

Is there an ocean beneath our feet?

Jan 27, 2014

(Phys.org) —Scientists at the University of Liverpool have shown that deep sea fault zones could transport much larger amounts of water from the Earth's oceans to the upper mantle than previously thought.

GPS data reveals more on mega-thrust earthquakes

Apr 29, 2011

(PhysOrg.com) -- New GPS data of the 2010 earthquake that devastated parts of Chile and killed over 500 people is revealing new clues about large earthquakes such as the quake in Chile and the magnitude 9.0 ...

Deep Alpine Fault sensitive to nearby earthquakes

Aug 25, 2014

(Phys.org) —Victoria University of Wellington researchers have discovered that seismic waves produced by earthquakes happening several hundred kilometres away trigger activity deep beneath the Alpine Fault.

Double quake highlights Italy's seismic perils

May 29, 2012

Two killer earthquakes that struck northeastern Italy in nine days have shed light on the brutal but complex seismic forces that grip the Italian peninsula, scientists say.

Recommended for you

Improving forecasts for rain-on-snow flooding

8 hours ago

Many of the worst West Coast winter floods pack a double punch. Heavy rains and melting snow wash down the mountains together to breach riverbanks, wash out roads and flood buildings.

The Greenland Ice Sheet: Now in HD

8 hours ago

The Greenland Ice Sheet is ready for its close-up. The highest-resolution satellite images ever taken of that region are making their debut. And while each individual pixel represents only one moment in time, ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.