Synthetic Seismograms, Migrated Seismic Reflection Profiles, and Lithologic Correlations for Leg 135 Sites in the Lau Basin and Tonga Arc

Abstract

At Leg 135 sites where velocity and density logs were acquired, synthetic seismograms are constructed to match seismic reflection data available for the sites. These synthetic seismograms provide a way to correlate the seismic data with the borehole lithology, and to determine what lithologic contrasts are causing the seismic reflections. Single-channel seismic reflection profiles acquired on board the JOIDES Resolution were reprocessed and migrated, and the synthetic seismogram was spliced into the profile at the location of the borehole. For Sites 840 and 841, synthetics were also constructed to match migrated multichannel seismic reflection profiles obtained by the U.S. Geological Survey research vessel S.P. Lee. The match between synthetic and real data is variable; for lines crossing Sites 834, 835, 838, 839, and 840, some excellent correlations can be made; for Site 841, the match of synthetic to real data is poor. Observed reflections are associated with lithologic unit boundaries; with coarse beds such as conglomerate, vitric gravel, and vitric sand; with basalts either within the basement or, as at Site 841, within the sedimentary section; and with sedimentary interbeds in basement basalts. Poor correlations between synthetic and real data are caused by rapid lateral changes in lithology at Site 840, and probably by a combination of rapid lithologic changes and faulting at Site 841.Hawkins, J., Parson, L., Allan, J., et al., 1994. Proc. ODP, Sci. Results, 135: College Station, TX (Ocean Drilling Program).