Accurate earthquake source parameters such as fault mechanism, depth, and moment magnitude are not only important in seismic‐hazard assessment, but also are crucial to studies of earthquake rupture processes and seismotectonics. Although large earthquakes (M_w 7+) may cause substantial damage, they occur less frequently. In contrast, moderate earthquakes (M_w 5.0–6.5) occur with much higher frequency and may occur on faults not geologically identified. Some of the moderate earthquakes cause damage in densely populated communities, especially in developing countries (Baumbach et al., 1994; Hamzehloo, 2005). For example, the 2011 M_w 5 earthquake in Lorca, Spain (Pro et al., 2014), the 2012 M_w 5.9 Ferrara earthquake sequence in northern Italy (Malagnini et al., 2012), the 2010 M_w 5 Suining earthquake in Sichuang Province of China (Luo et al., 2011), and the 1998 M_w 5.7 Zhangbei earthquake in Hebei Province of China (Li et al., 2008) all caused substantial economic loss and casualty. Compared with events larger than M_w 7, rupture processes of these moderate events can be approximated as point sources, which are usually described with a centroid moment tensor (CMT) because the rupture duration is usually shorter than the period used in the waveform inversion.