The seismological background of the Northridge earthquake on a blind t
hrust fault is presented. The extensive data base of recorded ground m
otion provided the opportunity to review the effectiveness of some wid
ely used attenuation relations for peak horizontal acceleration and ps
eudo-spectral velocity. Large pulses of velocity and displacement were
noted in some records and the potential implications of these for tal
l buildings are noted. Some major damage centres coincided with alluvi
al basins. Generation of surface waves within the basins during the ma
in shock contributed to increased amplification and duration. Surface
waves were detected at the site of the collapse of the I-10 interchang
e and in the damaged area of Sherman Oaks using aftershock data. Cedar
Hill seismographic station in Tarzana recorded the highest accelerati
ons of the earthquake, much higher than motions at nearby stations. Th
ese are currently attributed to topographic effects of the hill on whi
ch the station is located. Aftershock data from two major arrays found
that the low amplitude motions were magnified significantly at the cr
est of the hill compared to motions at the base.