Two moderate size (mb=5.8, 6.0) earthquakes occurred within a local network of short-period seismograph stations in the Shumagin Islands, Alaska, on April 6, 1974. The network recorded about 70 aftershocks over the next 2 weeks. Both main shocks triggered a strong motion accelerograph (SMA) at Sand Point, 50 km NNW of their epicenters. High-quality relative locations obtained from local network arrivals for the main shocks and 25 aftershocks yield depths between 37 and 43 km and define a plane dipping about 30¿ to the NW. A nearly pure thrust focal mechanism for the larger (mb=6.0) earthquake was obtained from long-period data. The fault plane inferred from this mechanism dips 30¿ in the direction N16¿W. The sequence was located in the upper portion of the dipping seismic zone beneath the eastern Aleutians and was presumably related to underthrusting of the Pacific plate beneath the North America plate. Estimates of the source parameters of these earthquakes were obtained from analysis of the SMA data and World-Wide Standard Seismorgraphic Network (WWSSN) short-period data. The WWSSN data indicate that the earthquakes had approximately circular rupture areas. Modeling the SMA records with a quasi-dynamic source model provides the following estimates of the source parameters for the mb=5.8 and 6.0 earthquakes, respectively: moments, M0=3.6 and 6.6¿1024 dyne cm and static stress drops, Δ&sgr;=890 and 650 bars. A high frequency spectral falloff of ω-3 suggests that the ruptures stopped gradually. The b value of the sequence, 0.34, is quite low. Since the sequence occurred within an area that is likely to have a high potential for a future large earthquake, it is suggested that the low b value and the high stress drops of the main shocks represent precursory phenomena.