Earthquakes triggered by slow slip at the plate interface in the Hikurangi subduction zone, New Zealand

Abstract

An earthquake swarm in the crust of the subducted plate in the southern Hikurangi subduction zone in April-May 2004 was most likely triggered by slow slip at the plate interface directly downdip during the previous year. Double-difference relocation indicates that the swarm represents incremental slip on adjacent patches of the same fault. A subsequent ML 5.5 earthquake in January 2005 occurred on a separate, deeper fault, sub-parallel to that of the 2004 swarm, but separated from it by about 1 km. This suggests a rapid decrease in mechanical damage in the slab with depth below the plate interface. The normal faulting observed in both earthquake sequences represents unbending of the subducted plate. Such unbending may be diagnostic of deformation on the deeper edge of a strongly coupled region of the plate interface resulting from adjacent slow slip. Copyright 2007 by the American Geophysical Union.