Few seismometers were operating in the region, but a group of temporary units that were set up following the mainshock recorded a number of aftershocks that were east of the Opak River Fault and were aligned along a 20 kilometers zone striking N°50E. Due to the ambiguous nature of the available information on the source of the Yogyakarta earthquake, a separate group of Japanese and Indonesian scientists applied one of the first uses of interferometric synthetic aperture radar to determine the source fault.