On 16 October 1983, at 19:40 (UTC), a magnitude 3.8 earthquake occurred near Lake Charles in southwestern Louisiana. The earthquake was felt over an area of 2600 km2 and had a maximum Modified Mercalli intensity of V. This was the first significant Louisiana Gulf Coast earthquake to be recorded and located by nearby microseismic networks. One possible foreshock and three aftershocks also were recorded and located using a velocity model developed for this study.
The focal mechanism of the earthquake was determined based on P-wave first motions from 22 local and regional stations. The solution indicates a predominantly east-west trending, southeast-dipping normal fault with a small strike-slip component. The depth of this event (14+ km) provides the first significant evidence that normal faulting within the crystalline basement may control shallower growth faults along the Gulf Coast.