Determining accurate source parameters of small magnitude earthquakes is important to understand the seismic source physics and tectonic processes that activate a seismic source. The determination is also important to make more accurate estimates of the probabilities of the recurrences of large earthquakes based on the statistics of smaller earthquakes. Methods used to constrain the source parameters of earthquakes with Mw 4.0 and above are not applicable to earthquakes below Mw 4.0 due to the low signal-to-noise ratio available for these earthquakes. This talk presents a new method that can accurately determine focal depths and moment magnitudes of earthquakes with Mw 4.0-2.5 and focal mechanisms of earthquakes with Mw 4.0-3.0 using the broadband seismic waveforms recorded at the local and regional seismic stations within 60-424 km of the epicenters. The method is tested on the aftershocks of the Mw 5.7 2011 Mineral, Virginia earthquake and the aftershocks of the Mw 4.5 2013 Ladysmith, Quebec earthquake.