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