Secondary drop breakup due to shock wave disturbances was studied for the multimode breakup regime, emphasizing the temporal evolution of breakup for shock wave disturbances. Measurements were carried out in a shock tube using pulsed shadowgraphy and holography to observe the mechanism and outcome of breakup. Test conditions involved water and ethanol drops, liquid/gas density ratios greater than 500, Ohnesorge numbers less than 0.1 and Weber numbers of 15-150. The evolution of properties in the multimode breakup regime with increasing Weber number begins at the end of the bag breakup regime with the appearance of a plume drop at the apex of the bag at a Weber number of roughly 15, continues in a bag/plume breakup regime which involves the presence of both bag-like structures and plume drops and transitions when bags are no longer present at a Weber number of roughly 40, and ends with a plume/shear breakup regime which involves development of plume-like structures that progressively evolve into a parent drop and ligament system as the shear breakup regime is approached at a Weber number of roughly 80. Measurements over the test range provide breakup times, drop deformation properties and drag coefficients before the onset of breakup, distributions of drop liquid and resulting drop sizes for various breakup structures, drop velocities after breakup, and liquid removal rates during breakup; all these properties are provided as a function of Weber number in the multimode breakup regime. (C) 2001 Elsevier Science Ltd. All rights reserved.