Body wave data recorded at a small network of broadband seismograph stations are analyzed to investigate local events with focal depths deeper than about 50 km. For these events the initial portion of P-wave displacement represents well the source time function with a scaler correction for the seismic moment. The magnitudes of the analyzed earthquakes range from MW = 3.1 to 6.5. It is shown that the seismic moment M0 and the pulse width τ are well correlated as M0/τ3 = constant, indicating that the stress drop is largely constant. This dynamic similarity seems to be valid for a vast range of earthquake sizes: MW = 1 ∼ 8. It is also shown that source complexity such as a multiple shock nature is not a characteristic of only large earthquakes but is often observed even for small earthquakes.