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/ www.sciencexpress.org / 29 July 2010 / Page 1 / 10.1126/science.1192094
We observed vertically displaced coastal and river
markers after the 27 February 2010 Chilean earthquake
[moment magnitude (Mw) 8.8]. Land-level changes range
between 2.5 and -1 meters, evident along an
approximately 500-kilometer-long segment identified here
as the maximum length of coseismic rupture. A hinge line
located 120 kilometers from the trench separates uplifted
areas, to the west, from subsided regions. A simple elastic
dislocation model fits these observations well; model
parameters give a similar seismic moment to seismological
estimates and suggest that most of the plate convergence
since the 1835 great earthquake was elastically-stored and
then released during this event.
The February 27, 2010 [moment magnitude (Mw) 8.8] south-
central Chilean earthquake was the fifth largest event
recorded by modern seismology. We present field
measurements of coseismic land-level changes from 24 sites
along the coast and 9 sites at estuarine valleys (Fig. 1). A
white fringe formed by a dead coralline crustose algae
(Lithothamnium), raised above the lower intertidal zone,
provides a direct measure of uplift (1); whereas submerged
anthropogenic markers and the lower limit of vegetation
indicates subsidence (fig. S1)(2). Estimated vertical
displacements agree with preliminary GPS results (3).
The largest uplift of up to 2.5 m occurred in the Arauco
Peninsula (37.1ºS-37.7ºS), where marine platforms emerged,
shifting the coastline up to 0.5 km toward the ocean (fig. S1).
Detectable displacements occurred between 34ºS and
38º30’S, in coincidence with the first hour of aftershocks
(Fig. 1A-B, fig. S2). During the following hours, seismicity
expanded to the north and south, covering an area between
33ºS and 39ºS. We propose that the maximum length of
coseismic rupture is confined between 34ºS and 38º30’S
(~500 km), in agreement with preliminary slip models (4-6).
Aftershocks outside this area would be associated with an
accommodation of stress changes induced by the mainshock
on adjacent segments of the megathrust fault.
The trench-perpendicular trend of vertical displacements
reveals a hinge line located 118±2 km inland from the trench
(Fig. 1C). The uplift-subsidence pattern is well-fitted by a
simple elastic dislocation model that considers uniform slip
on a rectangular fault (Fig. 1C, table S2). This is a first-order
approximation to fault source parameters and the scattering of
our data with respect to the model suggests that the slip was
spatially variable. However, parameters for the best-fitting
model give a moment magnitude Mw=8.81 (2), which is
equivalent to that reported by NEIC (7).
Considering the current plate convergence (6.8 cm/yr (8)),
our modeled slip (10 m) is slightly lower than the 11.9 m
expected from full plate coupling since the last earthquake in
this region (175 years ago). This, and the closely reverse
pattern of coseismic displacements with respect to a
geodetically-constrained interseismic model (8), suggests that
most of the strain accumulated during the seismic cycle was
elastically released by the February 27 earthquake.
References and Notes
1. L. Ortlieb et al., Quat. Sci. Rev. 15, 949-960 (1996).
2. Materials and methods are available as supporting material
on Science Online.
3. C. Vigny et al., paper presented at the AGU Chapman
Conference, Valparaíso, Chile, 16-24 May 2010.
4. http://www.geol.ucsb.edu/faculty/ji/big_earthquakes/2010/
02/27/chile_2_27.html
5. http://earthquake.usgs.gov/earthquakes/eqinthenews/2010/
us2010tfan/finite_fault.php
6. http://www.tectonics.caltech.edu/slip_history/2010_chile/p
relim-gps.html
7. National Earthquake Information Center,
http://neic.usgs.gov
8. J.C. Ruegg et al., Phys. Earth Planet. Inter. 175, 78-85
(2009).
Land-Level Changes Produced by the Mw 8.8 2010 Chilean Earthquake
Marcelo Farías,1* Gabriel Vargas,1 Andrés Tassara,2 Sébastien Carretier,3 Stéphane Baize,4 Daniel Melnick,5 Klaus Bataille2
1Departamento de Geología, Universidad de Chile, Plaza Ercilla 803, Santiago, Chile. 2Departamento de Ciencias de la Tierra,
Universidad de Concepción, Casilla 160-C, Concepción, Chile. 3IRD, LMTG, UPS (OMP), Université de Toulouse, 14, Av.
Belin, Toulouse 31400, France. 4Institut de Radioprotection et de Sûrete Nucléaire (IRSN), BP 17, 92262 Fontenay-aux-Roses,
France. 5Institut für Erd- und Umweltwissenschaften, Univesität Potsdam, Haus 27, Zi. 2.26, Karl-Liebknecht-Str. 24, 14476
Golm, Germany.
*To whom correspondence should be addressed. E-mail: mfarias@dgf.uchile.cl
/ www.sciencexpress.org / 29 July 2010 / Page 2 / 10.1126/science.1192094
9. Y. Okada, Bull. Seismol. Soc. Am. 82, 1018-1040 (1992).
10. Harvard Centroid Moment Catalog,
http://www.globalcmt.org/
11. This study was funded by FONDECYT grants 11085022,
1070279, 1101034, PBCT PDA-07, Millenium Nucleus on
Seismotectonics and Seismic Hazard (CIIT-MB, Grant
P06-064F), the French IRD, INSU, and IRSN, and Grant
ME 3157/2-1 of the Deutsche Forschungsgemeindschaft.
Supporting Online Material
www.sciencemag/org/cgi/content/full/science.1192094/DC1
Materials and Methods
Figs. S1 to S3
Tables S1 to S2
References
10 May 2010; accepted 30 June 2010
Published online 29 July 2010; 10.1126/science.1192094
Include this information when citing this paper.
Fig. 1. Land-level changes along- and across-strike and their
spatial correlation with aftershocks. (A) Aftershocks (M>4.5)
during the first three hours (8). (B) Vertical displacements
along latitude. Colors identify different latitudinal segments.
(C) Vertical displacements versus distance perpendicular to
the trench. The color scale is the same as in (B). The
correlation between (A) and (B) suggests that the maximum
length of rupture is confined between 34ºS and 38º30’S. In
(C) the smaller uplift at Mocha suggests a lower displacement
at the southern tip of the rupture region, or elastic
accommodation south of the rupture area. Thus, uncertainties
on the rupture length are emphasized in the width of the
yellow box in (B). The red line in (C) corresponds to vertical
displacements predicted by an elastic dislocation model based
on Okada (9) (details in (2) and Table S2). This model
considers a fault dip of 18º (10), the depth to the updip- and
downdip-limit of rupture as 0 and 43 km, respectively, and a
uniform coseismic slip of 10 m (2).
