The April 28, 1968 (mb=5.5, Ms=5.2), earthquake in the Emperor Trough, a long linear deep east of the Emperor Seamounts in the North Pacific, is the only recorded seismic event in this region. The focal mechanism, determined using body and surface waves, shows faulting striking along the trough with the east side thrust upward. This mechanism is consistent with bathymetry showing the east flank 500 m higher than the west and suggests that the earthquake represents part of continuing deformation at the trough. This earthquake is one of a large number of intraoceanic plate events that occur on major bathymetric features. The focal mechanisms of earthquakes on such features probably represent the reactivation of already present faults or weak zones. The orientations of intraplate stresses inferred from the focal mechanisms may differ significantly from the true stress directions.