On 6 February 2016, an ML 6.6 earthquake occurred in the Meinong area of southern Taiwan, causing anomalously large ground shaking. In this study, a joint source inversion was performed to understand the rupture process of this event and to identify how the anomalous strong motion was produced. The results show that the rupture process of this event was complex; at least two asperities were identified on the fault plane. The rupture mainly developed in the down‐dip direction and propagated toward the northwest. Results from a 3D wave propagation simulation further indicate that the strong ground shaking observed in southwest Taiwan was caused by a combination of three effects: (1) rupture directivity, (2) source radiation pattern, and (3) sedimentary amplification. The results demonstrate that constructive source rupture and wave propagation effects due to a moderate earthquake can cause anomalously strong ground motion and serious seismic hazards in nearby densely populated areas.