Cultural: See the comments following Mosiah 27:18 for more information on the cultural context of trembling. This would have been seen as yet another sign of the presence of the divine in Mesoamerica.
Geological: There are two aspects of this event that are important. The first is the very clear reference to an earthquake, a quake of sufficient power that the walls of the jail shook violently. The next reference is to an overshadowing cloud of darkness. The combination of these two features suggests that what occurred was the eruption of a volcano. As we will see in the events leading to the arrival of the atoning Messiah in the New World, this is an area of significant volcanic activity. The trembling of the earth is part of the eruption, as is the thick, dark, vapor cloud.