The 2007 Tocopilla earthquake and its aftershock sequence - A subduction zone earthquake at the edge of the northern Chile seimic gap
Abstract
On 14 November 2007 a large Mw 7.7 earthquake occurred in the region of Tocopilla in Northern Chile. The earthquake took place in the southern end of the Northern Chile seismic gap which is supposed to be at the end of its seismic cycle. Studying the event and its aftershock sequence will provide closer insight into the behavior of a subduction zone earthquake at the edge of a subduction zone segment. We present a comprehensive study of the rupture area combining seismic and geodetic data. The aftershock sequence following the earthquake was very well recorded by a local seismic network of 34 short period and broad band stations. The spatial distribution of the aftershock sequence shows a concentration of aftershocks around the north-western part of the Mejillones Peninsula and along the coast up to the Río Loa. The distribution into depth shows that the majority of the hypocenters are located along the subduction interface, reaching down to ~ 50 km depth. In the western part, the aftershock sequence splits into two branches, one heading towards the trench, the other bending into the crust in front of the Mejillones Peninsula. These seismic observations lead to the conclusion that the fault rupture propagated towards the south-west with a fault plane of about 150 km length leaving the shallow part in the north west probably unbroken. To better understand the behavior of the aftershock distribution we model the Coulomb stress transfer along the fault plane. The results show that stresses are increased in the southern part of the rupture area where we find a high concentration of aftershocks. This is consistent with the calculated energy release that shows two main patches along the plate interface rupturing from north to south. The 2007 Tocopilla earthquake is the first large event that occurred inside the Northern Chile seismic gap since the 1877 Iquique event. The rupture process stopped underneath the Mejillones Peninsula, a proposed segment boundary along the north Chilean subduction zone. This complex pattern of seismicity beneath the Mejillones Peninsula, indicates that structures under the peninsula play a significant role in the subduction process. To better understand the complex structure in this area it is important not only to analyse the seismic behavior in depth but also to correlate these results with observations at the surface. Therefore, we generate an InSAR time series of the deformation field spanning periods of 2003 to 2010 using ENVISAT radar acquisition. The result is a space-time surface deformation of the rupture area at different stages before and after the earthquake giving further insight into the behavior of the subduction zone’s segment at the end of a seismic cycle.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.T11D2134E
- Keywords:
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- 1240 GEODESY AND GRAVITY / Satellite geodesy: results;
- 7240 SEISMOLOGY / Subduction zones;
- 7240 SEISMOLOGY / Subduction zones;
- 8170 TECTONOPHYSICS / Subduction zone processes