The 1998 Aiquile, Bolivia earthquake: A seismically active fault revealed with InSAR

Using SAR interferometry (InSAR), the deformation field of the Mw=6.6, 1998 Aiquile, Bolivia earthquake is mapped, and the epicentre accurately located for the first time. Elastic dislocation modelling is used to demonstrate that the measured displacements are best explained with a ∼N-S oriented fault, with a strike that is oblique to the principal topographic features in the region, and a location that agrees with a Modified Mercalli Intensity map constructed from observations of damage in the surrounding area. A variable-slip solution for a fault in this orientation is obtained which predicts peak slip of 1.42 m at depths of ∼4-5 km on the fault plane and has an estimated seismic moment, M0=8.44×1018 N m, which agrees with estimates from long-period seismology. This is the first time that a fault has been demonstrated unambiguously to be active in the Central Andes, and since there was no previous knowledge of an active fault with this location or orientation, a necessary conclusion is that our understanding of seismic hazard in this region is limited.