Marine sediment shear velocity structure from the ratio of displacement to pressure of Rayleigh waves at seafloor. Issue 8 (5th August 2014)

• Record Type: Journal Article
• Authors: Ruan, Youyi; Forsyth, Donald W.; Bell, Samuel W.
• Is Part Of: Journal of geophysical research. Volume 119:Issue 8(2014:Aug.)
• Page Start: 6357
• Page End: 6371
• Publication Date: 2014-08-05
• Subjects: marine sediment -- shear wave speed -- D/P ratio method -- microseism noise -- Rayleigh waves -- admittance; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1002/2014JB011162
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: The complex ratio of vertical displacement to pressure (D/P) at seafloor is a function of frequency. It is sensitive to the subsurface elastic properties, particularly the shear modulus, and therefore can be used to determine the shear velocity and thickness of marine sediments. Instead of using compliance in response to loading of long‐period infragravity waves as in previous studies, we investigate the transfer function from pressure to displacement using Rayleigh waves generated by microseisms and earthquakes. We find that at frequencies between 0.1 and 0.2 Hz, the Rayleigh wave transfer function is very sensitive to marine sediments and can be reliably obtained from microseism noise. Using a surface wave mode method, we calculate synthetic D/P ratios and examine their sensitivity to water depth, shear wave speed, and thickness of sediments. We develop a method to invert the Rayleigh wave D/P ratio for a regional 1‐D profile of sediment shear wave speed and associated sediment thickness beneath each ocean bottom seismograph (OBS). We apply our method to a group of deep water OBSs deployed in the Cascadia Initiative and obtain a well‐resolved depth‐dependent shear wave speed for sediments on the Juan de Fuca plate and shear wave traveltime delays caused by sediments at each station. Key Points: Rayleigh wave D/P ratio method Shear wave speed and thickness of marine sediment Shear wave traveltime delays caused by sediments