Interseismic strain accumulation measured by GPS in the seismic gap

I

Interseismic strain accumulation measured by GPS in the seismic gap

between Constitución and Concepción in Chile

J.C. Ruegga,∗, A. Rudloff b, C. Vignyb, R. Madariagab, J.B. de Chabaliera, J. Camposc,

E. Kauselc, S. Barrientosc, D. Dimitrovd

 

nterseismic strain accumulation measured by GPS in the seismic gap

between Constitución and Concepción in Chile

J.C. Ruegga,∗, A. Rudloff b, C. Vignyb, R. Madariagab, J.B. de Chabaliera, J. Camposc,

E. Kauselc, S. Barrientosc, D. Dimitrovd

 

 

The Concepción–Constitución area [35–37◦S] in South Central Chile is very likely a mature seismic gap,

since no large subduction earthquake has occurred there since 1835. Three campaigns of global positioning

system (GPS) measurements were carried out in this area in 1996, 1999 and 2002. We observed

a network of about 40 sites, including two east–west transects ranging from the coastal area to the

Argentina border and one north–south profile along the coast. Our measurements are consistent with

the Nazca/South America relative angular velocity (55.9◦N, 95.2◦W, 0.610◦/Ma) discussed by Vigny et al.

(2008, this issue) which predicts a convergence of 68mm/year oriented 79◦N at the Chilean trench near

36◦S. With respect to stable South America, horizontal velocities decrease from 45mm/year on the coast

to 10mm/year in the Cordillera. Vertical velocities exhibit a coherent pattern with negative values of

about 10mm/year on the coast and slightly positive or near zero in the Central Valley or the Cordillera.

Horizontal velocities have formal uncertainties in the range of 1–3mm/year and vertical velocities around

3–6mm/year. Surface deformation in this area of South Central Chile is consistent with a fully coupled

elastic loading on the subduction interface at depth. The best fit to our data is obtained with a dip of 16±3◦,

a locking depth of 55±5 km and a dislocation corresponding to 67mm/year oriented 78◦N. However in

the northern area of our network the fit is improved locally by using a lower dip around 13◦. Finally a

convergence motion of about 68mm/year represents more than 10mof displacement accumulated since

the last big interplate subduction event in this area over 170 years ago (1835 earthquake described by Darwin).

Therefore, in a worst case scenario, the area already has a potential for an earthquake of magnitude

as large as 8–8.5, should it happen in the near future.

© 2009 Elsevier B.V. All rights reserved.

FUENTE:
Saludos,

 

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