Scientific bulletin n° 355 - September 2010
On 27 February 2010, a
huge earthquake, with
magnitude 8.8, shook
Chile. It left 500 dead and
13 million Chileans were
affected, amounting to
nearly 80 % of the
country’s population. The
event was one of the six
most powerful earthquakes
since the beginning of the
20th Century. Coast uplift
has been proved by
research scientists from
Chile, France, and
Germany1. This rise
reached as high as 2.5 m
and resulted in an advance
of the shoreline of as much
as 500 m towards the sea
in places. Conversely, in
the hinterland, the ground
subsided by nearly 1 metre.
Since 1835, date of the
previous strong
earthquake in this zone,
the equivalent to 12 m of
deformation of the earth’s
crust, resulting from
tectonic block
convergence, had been
stored at the contact zone
between the Nazca Plate
and the South-American
Plate. On 27 February 2010,
rupture of the lithosphere3,
along a 500 km long fault
segment, released most of
this mechanical energy in a
single abrupt shock.
This study helps better
understand the seismic
cycle, with the long-term
objective of finding ways of
predicting and preventing
the seismic risk.
© IRD / Rose-Marie Ojeda
Chile: the earth shook
and the coast rose up
PEROU
BOLIVIE
BRESIL PARAGUAY
CHILI Océan Pacifique SANTIAGO
URUGUAY
ARGENTINE
Séisme de magnitude 8,8 Océan Atlantique The earthquake of 27 February 2010, whose epicentre is located about 6
km off the Chilean coasts, caused extensive damage (collapsed buildings,
electricity and telephone networks cut). Losses amounted to between 15
and 30 billion dollars.
At 3 a.m. in the morning on 27 February
2010, the centre of Chile shook for nearly 3
minutes. This enormous earthquake, of
magnitude 8.8, is one of the six most
powerful ever registered. The earthquake
and the tsunami which followed it left about
500 dead. Thirteen million Chileans, nearly
80 % of the population, were directly
affected. The quake caused substantial
damage. Buildings and bridges collapsed
and electricity and telephone networks
were cut off. Total losses were evaluated at
between 15 and 30 billion dollars. Its
epicentre was situated in the Pacific Ocean
about 6 km off the Chilean coast, 115 km
North of the town of Concepción and 325
km South-West of the capital, Santiago, the
furthest point where the shock was strongly
felt.
The earth rose up in some places…
The coastline lifted up. This uplift reached
2.5 m and was manifest by a coastline
advance towards the sea of as much as
500 m in places (see photos on verso side).
During the month following the disaster, the
Chilean, French and German1 researchers
studied the vertical ground displacements
generated by the earthquake. They used
white fringe marks, left by desiccated Lithothamnium algae that encrust the rocks2 of
the littoral zone, to make direct measurements of this uplift at 24 observation points
located along the coast.
… and subsided in others
However, 120 km from there, pushing
eastwards towards the country’s interior,
the team observed the opposite: the ground
had dropped down owing to subsidence.
Nine measuring points in the river valleys
­t aken at immersed landing stages, tree
trunks and river bank vegetation­ revealed
ground subsidence of as much as 1 m.
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on www.ird.fr/indigo
Excess energy
How can these opposing effects of the
CONTACTS:
earthquake on the topography be
Sébastien CARRETIER,
explained? The geophysicists established
researcher at the IRD
a scenario for the catastrophe. Most of the
country of Chile is located above the
Tel: 33 (0)5 61 34 26 39
sebastien.carretier@ird.fr
contact zone between the Nazca oceanic
Plate, which forms the South-East Pacific,
Laboratoire des mécanismes de
and the South American continental Plate.
transfert en géologie – LMTG
The Nazca plunges under the South
(UMR IRD / Université Paul
American plate, by a movement known as
Sabatier - Toulouse 3 / CNRS)
subduction. It drives down towards the
Earth’s mantle at a rate of 7 cm per year.
Address:
This rapid convergence of the two plates
LMTG
14 av. Édouard Belin
generates friction between them, which
31400 Toulouse, France
produces intense seismic activity at
regional scale, with at least one magnitude
8 earthquake every ten years and one of
REFERENCES:
over 8.7 magnitude once every century.
M. Farías, G. Vargas, A. Tassara,
The previous strong earthquake, with
K. Bataille, S. Carretier, S. Baize, magnitude 8.5, which had ruptured the
D. Melnick. Land-Level Changes
same segment of the Chilean subduction
Produced by the Mw 8.8 2010
zone, dates back to 20 February 1835, just
Chilean Earthquake. Science,
175 years earlier. Like a ruler with pressure
2010, 329(5994), p. 916.
exerted on to each end, the ground was
DOI: 10.1126/science.1192094
subjected to the thrust of each tectonic
block, gradually rising up in the hinterland
Ortlieb Luc, Barrientos S.,
and sinking towards the West while moving
Guzman N. Coseismic coastal
nearer towards the fault zone at the coast.
uplift and coralline algae record
in Northern Chile : the 1995
The equivalent of around 12 m of elastic
Antofagasta earthquake case.
deformation4 of the earth’s crust was
Quaternary Science Reviews,
gradually stored up by this fault, at the rate
1996, 15 (8-9), p. 949-960.
of 7 cm per year over more than a century
doi:10.1016/S0277-3791(96)00056-X
and a half.
On 27 February 2010, the lithosphere3
broke under the pressure along a 500 km
KEY WORDS:
long segment of the fault. The abrupt
release of the stress in a single shock libeEarthquake, Chile, ground
rated a large proportion of the enormous
accumulated energy. Hence the earthquake’s violence. The rocks, which had
been under strong compression until that
moment, suddenly distended and started
vibrating. The ground surface equilibrium
was then regained thanks to elastic
rebound4. The coastline therefore uplifted
in one sudden jolt while the hinterland
subsided.
These investigations show that this disastrous earthquake caused the release of an
enormous proportion of the 175 years’
energy stored in this segment of the Chilean
subduction zone. This could explain why to
date there has been no substantial aftershock, quite rare for earthquakes of such a
magnitude. These results help better
understand the mechanisms behind huge
earthquakes and seismic cycles, with the
long-term objective of predicting and
preventing the associated risk.
Gaëlle Courcoux – DIC
Translation: Nicholas Flay
1. These investigations were conducted by researchers
from Chile (University of Chile at Santiago and
University of Concepción), France (IRD, University
of Toulouse, Institut de Radioprotection et de Sûreté
Nucléaire) and Germany (University of Potsdam).
2. F
ollowing a sudden death phenomenon, evidenced
at the time of the 1985 earthquake in northern
Chile (Quaternary Science Reviews, 1996, 15
(8-9), p. 949-960).
3. L
iterally the “sphere of stone”, the earth’s envelope
nearest the surface.
4. An elastic deformation, as opposed to a plastic one,
is reversible: when the stress is removed, the
earth’s crust takes on its initial form.
© Université de Concepción / Simon Muñoz et Andres Tassara
Scientific bulletin n° 355 - September 2010
For further information
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The coastal uplift, as much as 2.5 m in places.
* Did you know?
The redistribution of masses associated with the earthquake on 27 February 2010 in Chile slightly
decreased the Earth’s moment of inertia, in other words its spin resistance, and thus shortened day
length by 1.26 millionth of a second.
Gaëlle Courcoux, coordinatrice
Délégation à l’information et à la communication
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