The effect of sediment rigidity on bottom reflection loss in a typical deep sea sediment

The effect of sediment rigidity on bottom reflection loss, RL=−20 log10‖R‖, where R is the plane-wave reflection coefficient, is studied using a computational model. A single inhomogeneous turbidite layer overlying a homogeneous substrate is treated with an emphasis on low frequencies (10 to 200 Hz) and low grazing angles (0 ° to 45 °). We find that sediment rigidity can be neglected for thick layers (∠500 m) while it can produce significant increases in RL for thin layers (∠36 m). The frequency dependence of RL for thin layers has a low-frequency regime characterized by large peaks (∠25 dB) recurring at short (∠2 Hz) intervals. At high frequencies there remains a persistent increase in RL (∠4 dB). The most important mechanism for sediment S-wave excitation is found to be compressional wave conversion at the sediment–substrate interface.