Demasking Multiple Artifact in Crustal Seismic Images from Marine Reflection Data in the Southern California Borderland

Marine seismic reflection surveys are often masked by strong water-bottom multiples that limit the use of data beyond the first multiple waves.In this study,we have successfully suppressed much of the multiple artifacts in the depth images of two of the marine seismic reflection profiles from the Los Angeles regional seismic experiment(LARSE) by applying reverse time migration(RTM).In contrast to most seismic reflection methods that use only primary reflections and diffractions,the two-way RTM migrates both primaries and multiple reflections to their places of origination:seabed multiples to the sea bottom and primaries to the reflecting interfaces.Based on the RTM depth sections of LARSE lines 1 and 2,we recognize five stratigraphic units from the sea bottom to a depth of 6 km.These units are Pliocene and younger strata,probably Miocene syntectonic strata,two deeper sequences of unknown age and lithology as well as Miocene volcanic layers on Catalina ridge.Several inferred igneous intrusions in the upper crust comprise a sixth unit.The existence of a thick sedimentary section in the Catalina Basin,which might include Paleogene and Cretaceous fore-arc strata,has important geologic significance.If borne out by further studies,significant revisions of current structural and stratigraphic interpretations of the California borderland would be warranted.