The geometric and mechanical properties of fault zones are expected to have an important effect on the earthquake rupture process and seismic energy budget, but the details of these relationships are poorly understood. To investigate possible connections, I examine three active earthquake sequences that occurred in geometrically complex fault zones in southern California and Japan (2016 Mw 5.2 Borrego Springs, 2016 Mw 6.2 Tottori, and 2010 Mw 7.2 El Mayor-Cucapah). For each sequence, high-resolution relocated seismicity catalogs are produced with template matching to resolve details of the fault structure at depth. These observations are assimilated together with slip models for the mainshocks, estimates of radiated energy and efficiency, geodetic observations of postseismic deformation, and the spatiotemporal evolution of aftershocks to illuminate additional details of the mainshock rupture process and seismic energy budget. The results provide potential links between the properties of fault zone structures, earthquake source processes, and driving mechanisms behind aftershock production.