Worldwide doublets of large shallow earthquakes

Abstract We investigated all the pairs of Mw ≥ 7.5 shallow earthquakes in the Harvard catalog that occurred at a centroid distance of less than 100 km. We showed that most of these pairs have similar focal mechanisms. Because these earthquakes generally should have focal regions in excess of 100 km diameter, their rupture zones apparently intersect. For all these pairs, the time interval is significantly less than the time span needed 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 these earthquake observations much better.