My teacher and I argued about whether a seismic event causing a force in itself or being an inertial response of the system. As I read in Chopra and Paz, the effect of an earthquake can be interpreted either as a force or as an inerntial response, either way yielding in the same results. I think it can be seen as both and my teacher says its an inertial response and nothing else. So I told my teacher and the class that we both were correct, but my teacher argued (and threatened) that he's right and I'm wrong. I wanted to see other peoples opinion.