The depth (76 miles) and location of this earthquake indicate that it occurred inside the subducting Pacific Plate as an intraplate event. The rupture was caused by extension of the plate as it is pulled into the mantle by its own weight.

This is a common type of event for this region and depth. However, at magnitude 7.1 it is the largest intermediate-depth earthquake recorded beneath Cook Inlet since the regional seismic network was established in the late 1960s.

This cross section shows the location of the M7.1 earthquake deep below the surface, well within the subducting Pacific plate.

This animation visualizes the subduction process and stresses that produce intraplate earthquakes.

Moment tensor solutions produced internally (see graphic below) and by the USGS and GCMT demonstrate a pattern consistent with a fault rupture caused by down-dip pull on the subducting plate.