A large (Mw=7.1) deep earthquake (606 km) occurred beneath Sakhalin Island, about 200 km away from the nearest well-defined Wadati-Benioff zone in southwestern Kurile. Moment tensors obtained in various frequency bands using the teleseismic data show that the Sakhalin event produced double-couple radiation over a very broadband frequency range, and the P waveforms appear simple at most teleseismic stations (Δ=30--90¿). On the other hand, many broadband seismometers successfully recorded the seismic waves at regional distances (Δ=3--25¿) in Japan, showing two significant arrivals in the P wave seismograms whose time interval is about 3 s. The two P wave arrivals have the same polarity, the same apparent velocity, and similar amplitudes, which suggests that the two arrivals are the result of two subevents in the source process of the Sakhalin event. Analysis of the regional and teleseismic waveform data suggests an anomalously rapid slip propagation in the source process of the Sakhalin deep event. The difference in P waveform between the regional and teleseismic stations can be explained by having a long distance (>14--15 km) and short time interval (<1.5--2 s) between the two subevents, which implies that the apparent rupture velocity is larger than the S wave velocity unless the two subevents occurred simultaneously. The observation that the source duration of the Sakhalin event is shorter than those of other deep events of the same size supports the notion of rapid slip-propagation for the Sakhalin event.