A joint hypocentre location and velocity inversion technique applied to the Central Aleutians

Summary. Travel times of seismic waves from teleseismically recorded events that occurred within the Adak Island region of the Central Aleutian Islands are used to constrain both the velocity structure of the region and the locations of events. It is found that the P-wave velocity within the descending lithosphere is approximately 7–8 per cent faster than that in the surrounding mantle for a slab length of 300–400 km.
The velocity structure so determined is then used as a model for the relocation of events recorded only locally. It is found that features of the Benioff zone seen in locations made with a spherically symmetric model can be seriously in error. In particular, an apparent increase in dip of the zone with depth disappears when the locations are made with the inhomogeneous model. The new locally determined hypocentres are now also more consistent with the locations based on teleseismic data.