26 March 1999
Vol 283, Issue 5410

About The Cover

Cover image expansion

COVER Six time-depth snapshots show amplitude variations as an initially uniform-amplitude earthquake shear wave propagates through a model of southern California crust from a depth of 8 km (bottom) toward the surface (yellow and blue are maxima). Material property variations in the crustal model modify the wave as it propagates, strongly affecting peak ground motions and explaining apparently nonlinear sediment responses during the Northridge earthquake. See page 2045 [Image: D. O'Connell]