search this site for "seismic" and im certain you will find a lot of into. ive posted links to fema451 along with several others. fema451 has a lot of presentation style material explaining the process, theory, calcs, etc. also check nehrp documents. like i said ive posted links to most of these documents several times here. if you have trouble stumbling on to them let me know and i'll repost. good luck.