The aftershock relocations and moment tensor inversion results indicate that both the 1999 and 2001 Kodiak Island earthquakes were located within the subducting Pacific plate. The former is down-dip of the locked portion of the megathrust and the latter one beneath the locked zone (Savage et al., 1999). The fault planes are parallel to the strike direction and cut across the plate through its significant portion. These earthquakes are the first well documented large intraplate events in the Alaska-Aleutian subduction zone. The tensional mechanism of the 1999 Kodiak Island earthquake and its location close to the down-dip end of the rupture zone of the 1964 earthquake (Christensen and Beck, 1994) is consistent with the slab-pull concentrating stress at the edge of a coupled interplate contact.

The 1999 Mw7, 2000 Mw6.5, and 2001 Mw6.9 events and their aftershocks recorded by the regional seismic network were relocated using the Joint Hypocenter Determination (JHD) method. Regional broadband data were used to calculate moment tensors for the mainshocks and their larger aftershocks. The relocated hypocenter of the 1999 Mw7 earthquake is positioned at 57.32N and 154.29W at 36.1 km depth. The majority of the relocated aftershocks are distributed between 27 and 85 km depth along a steeply dipping plane with a SW-NE orientation. The moment tensor inversion results for the mainshock indicate a fault plane trending at 29° azimuth and dipping at 67°. The moment tensor inversion for the Mw6.4 aftershock shows a nearly pure dip-slip mechanism with the fault plane striking at 233° azimuth.

The JHD location of the July, 2000 Mw6.5 earthquake is 41.6km deep and positioned at the northern end of the December aftershock zone (namely, at 57.41N and 154.21W). All of its 25 relocated aftershocks are concentrated to the north of the main shock location and the December aftershock sequence. The aftershocks in the subducting plate are located between 29 and 65km depth and delineate a roughly SSW-NNE striking surface. The regional moment tensor solution indicates the fault plane striking at 223° and dipping at 89°. The JHD location for the 2001 Mw 6.9 event is at 56.66N and 153.27W at 30km depth. The relocated aftershocks are distributed between 20 and 50km depth. Regional moment tensor solution for the mainshock is consistent with the Harvard CMT solution which has one focal plane striking at 58° and dipping at 84° and another plane striking at 227° and dippping at 6°. Regional moment tensor solutions for the three M4+ aftershocks have similar solutions with nearly vertical focal plane oriented in a SW-NE direction and the shallow dipping focal plane with a SE-NW orientation.