Core-log-seismic Integration at IODP Sites U1394, U1395, U1397, and U1399: An Approach to Velocity Modeling based on Synthetic Seismograms

DESCRIPTION: The project will use core-log-seismic integration, first reprocessing P-wave velocity waveforms, determining the best density curves where no density logs were recorded, and using these to generate synthetic seismograms. This analysis is critical for making seismic to borehole correlations to interpret seismic stratigraphy and ground-truth the interpretation of subsurface debris avalanche deposits and turbidites in the Lesser Antilles region.

OUTCOMES: For Sites U1394 and U1395, only the S-wave data required reprocessing; for Sites U1397 and U1399, both P-wave and S- wave data required reprocessing.

All waveforms were filtered with an upper and lower limit appropriate for the sources used to generate the P-wave and S-wave logs. The standard slowness-time coherence processing method (Kimball and Marzetta, 1984, “Semblance processing of borehole acoustic array data”, Geophys. 20, 516-538) was used to reprocess the monopole and lower dipole waveforms at Expedition 340 sites. The method was refined by constraining the processing with a slower slowness range and adjusting key parameters, such as the length of the integration time window and the search bandwidth. Through these methods, the quality of velocity data was significantly improved for the four sites (Figure 1). These post-cruise processed sonic data have played a critical role in a co-authored study on rock physics, led by Expedition 340 scientist Matthew Hornbach. The resulting manuscript, “High pore pressure in Lesser Antilles submarine slide deposits inferred from seismic velocities and rock physics models”, has been submitted to the Journal of Geophysical Research - Solid Earth.