The Loading and Relaxation Processes In Northern Chile Seismic Gap Seen From GPS and Sar
Abstract
The North Chile region between 18S and 23S is one of the most important seismic gaps in the world with no rupture having occurred since 1877 in this area. The two ex- tremities of this gap have experienced major earthquakes in recent years (the Mw=8.1 Antofagasta earthquake in 1995 ; the Mw=8.4 South Peru earthquake in 2001). SAR interferometry and GPS measurements are powerfull tools to constrain the loading processes that take place on the subducting interface. We have mapped the present- day crustal deformation by processing interferograms of ERS satellites between 1995 and 1999 and determining the GPS vectors of 40 points measured between 1996 and 2000. The GPS signal observed in the central part of the gap is dominated by an elon- gated interseismic velocity gradient parallel to the arc with 20-30 mm/yr eastward dis- placement with respect to South America. This is consistent with 15-20 mm/yr range decrease determined by SAR interferometry. Both GPS and SAR measurements can be modelled with 100% coupling of the thrust interface of the subduction to a depth of 35km with a 40km wide transition zone beneath. The slip in this zone increases linearly from zero to plate convergence rate (79mm/yr from NUVEL-1). South of this gap, the interferometric map exhibits different pattern and the GPS vectors are sig- nificantely different in direction and amplitude. This change is located at the place where the M=8.1 Antofagasta earthquake occured in 1995. We interpret the signal to be post-seismic relaxation with after-slip located in the transition zone (35-55 km). Aseismic slip at 20-45km of the subduction interface is also required under the Mejil- lones peninsula that appears to be an intersegment between 1877 and 1995 rupture zone with no rupture during 1995 earthquake.
- Publication:
-
EGS General Assembly Conference Abstracts
- Pub Date:
- 2002
- Bibcode:
- 2002EGSGA..27.3245C