Post on 29-Jan-2016
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A. Gardi, ENS (IPGP)R. Madariaga ENSCh. Vigny ENSA. Rudloff ENSA. Lemoine DGF (BRGM)J. Campos DGF
PICS CNRS-CONICYTACI Catnat CNRS
ANR Chile
Sismicidad y deformación recientes del Centro-Norte de Chile:
¿Estamos asistiendo a la preparación de
un terremoto?
Grandes sismos deChile
1868-2005
Nuestra zona de
estudio
2005
Seismicity of central Chile 1995-2004
Source: DGF
1730
1943
1730
1971-85
1928
1906
1997
La sismicidad no seleccionada de Chile Central 1973-2004
There are three catalogs to study
NEIC this catalog is complete only for M>5.5 from 1970
and from M>4 in the last few years
Centennial catalog complete for M>7 since 1900
and for M>6 since
ISC not yet fully analysed
Sismicidad entre 1900 y 2006
b=0.8
Sismicidad del Catálogo Centennial
M>8
M>7
M>6
Recent events
Mecanismos de foco
desde 1997
Harvard CMT
Punitaqui 97
WWSSN
19851997
Diferentes tipos de
sismicidad de
Chile Central
-72° -70°
-32°
-30°
AB
070697
072197
072597
072797
110397
011298092999
052302
061802
062003
101597
Main events in the Coquimbo sequence
Punitaqui, 15/10/97
Sismos principales de la secuencia de Coquimbo (1997-2006)
July 97
10 sismos de subduccion con
M>6.
1 sismo de compresion
Desacuerdo
fundamental
entre la velocidad
de la placa y el
movimiento
en Ovalle
La velocidad de subducción desde 1993es 2 veces menor que la convergencia, porqué?
Coulomb stress applied by the July 97 sequence on the October 15 slab push event
15/10/97
July 97
Possible models of intermediate depth seismicity
Tension before thrust event
Compression after thrust
Fracture model
Coulomb stress applied by continuous slip at depthon the Fault of the Punitaqui earthquake
Chilean seismicity is driven by continuous slip of the Nazca plate with respect to the South American Continent.
The stresses due to continuous slip at depth load the Nazca plate producing earthquakes like that of Punitaqui of 15 October 1997 and all the others in fact..
July 97
15/10/97
23/06/03
1997
Relocated seismicity 1992-2004
15 Oct 97
0
50
100
0 50 100 150 200 250
0
50
100
0 50 100 150 200 250
Vertical cross-section at 30.5 S
15 october 1997 Punitaqui slab push earthquake
July 97Nov 97-Jan 04
Punitaqui earthquake (15/10/1997)
07/97 1997-2003
Seismicity from local network Jan 1999
From Pardo et al, 2003
Un sismo ‘extraño’, 10 de Enero de 2004
Sismo de falla normal
A 50 km de profundidad
¿Previsible?
10 Ene 04
8 Dic 04
220597 200498
230594
210699 291299
101294
110197
Conclusions
• 5 or 6 interplate thrust events of M~ 6.5 in July 97 were followed by a large slab push event in october 1997.• Did they trigger it?• The slab push event is clearly favored by aseismic slip at depth• The slab push event triggered abundant plate interface events
that are still in progress• Intermediate depth events are more likely due to aseismic slip
rather than long range stress transfer during the seismic cycle
• Continuous aseismic slip is an essential element of stress transfer in subduction zones.• Coulomb stress changes explain well the current seismicity in
the Coquimbo region in central Chile