A study of large intraplate earthquakes with well-determined source parameters shows that these earthquakes obey a scaling law similar to large interplate earthquakes, in which M0 ∝ L2 or u = αL, where L is rupture length and u is slip. In contrast to interplate earthquakes, for which α ≈ 1 × 10−5, for for the intraplate events α ≈ 6 × 10−5, which implies that these earthquakes have stress drops about 6 times higher than interplate events. This result is independent of focal mechanism type. This implies that intraplate faults have a higher frictional strength than do plate boundaries, and hence that faults are velocity or slip weakening in their behavior. This factor may be important in producing the concentrated deformation that creates and maintains plate boundaries.