Worldwide doublets of large shallow earthquakes

We investigated all the pairs of M-w greater than or equal to 7.5 shallow e arthquakes in the Harvard catalog that occurred at a centroid distance of l ess than 100 km. We showed that most of these pairs have similar focal mech anisms. Because these earthquakes generally should have focal regions in ex cess of 100 km diameter, their rupture zones apparently intersect. For all these pairs, the time interval is significantly less than the time span nee ded for plate motion to accumulate the strain released by the first event. These observations conflict strongly with quasi-periodic recurrence models on which the seismic gap hypothesis is based. Power-law recurrence fits the se earthquake observations much better.