Attenuation in fine‐grained marine sediments: Extension of the Biot‐Stoll model by the “effective grain model” (EGM)

Abstract

It is postulated that the presence of swelling clay minerals in unconsolidated fine‐grained saturated marine sediments leads to deviations from the normally assumed ideal elasticity of the solid phase. In the proposed “effective grain model” (EGM), the elastic grain material is consequently replaced by an effective medium made up of a homogeneous elastic mineral phase that is isotropically interspersed with cylindrical, “penny‐shaped” inclusions of low aspect ratio representing the intracrystalline water layers in the swelling clay minerals. The two‐phase nature of the grain material thus specified results in a wave‐energy consuming squirt‐flow process from the inclusions into the pore space. Introducing the EGM into the Biot‐Stoll model (BSM) via the complex bulk modulus of the dissipative grain material leads to a better fit to literature data on the attenuation of compressional waves than does the original BSM alone. Since swelling clay minerals occur in nearly all clay‐bearing sediments, it is concluded that the attenuation mechanism of the EGM may represent a universal contribution to the overall intrinsic anelasticity of unconsolidated fine‐grained saturated marine sediments in the frequency range from a few kilohertz to about 1 MHz.

In situ acoustic and laboratory ultrasonic sound speed and attenuation measured in heterogeneous soft seabed sediments: Eel River shelf, California

“…We are not, however, convinced that dispersion, as predicted by Biot^Stoll models (e.g., Yamamoto and Turgut, 1988;Leurer, 1997) and concluded from data presented by others (Stoll, 1989;Kibblewhite, 1989;Bowles, 1997;Ba⁄, 1999) produces di¡erences of the observed magnitude in Eel margin sediments. While attenuation is much more di⁄cult to measure than sound speed because of its sensitivity to noise and transducer response, these limitations should not produce the distinct di¡erences that we see in our data.…”

“…3B,C), negating any suggestion of intrinsically more attenuating ¢ne-grained sands as proposed by Hamilton (1972). Leurer (1997) has theoretically asserted that ¢ne-grained cohesive, clay-rich marine sediments can exhibit high attenuation because of viscous absorption mechanisms that are related to squirt £ow. We, however, attributed the signi¢cant gradient of in situ attenuation with depth not to poroviscoelastic processes (Biot, 1956a,b), but to the presence of thin layers in the near surface that are associated with the £ood deposit (Wheatcroft et al, 1996(Wheatcroft et al, , 1997.…”

Investigation of ocean acoustics using autonomous instrumentation to quantify the water-sediment boundary properties

“…Hovem [34] gives a brief description of three of the major models including Hamilton and Biot. Other models that have been proposed to explain broad band data are the "effective grain model" [35], an effective density fluid model variant of Biot theory [36], a grain shearing model [37], and a Biot model variant with contact squirt flow and shear drag [38]. There are also a plethora of other papers discussing approximations to the full Biot theory, which typically has up to 13 independent parameters defining the properties of the sediment.…”

International Benchmark on Numerical Simulations for 1D, Nonlinear Site Response (PRENOLIN): Verification Phase Based on Canonical Cases

“…We only consider intrinsic material damping (Biot, 1956;Johnston et al, 1979;Leurer, 1997) without any additional component from scattering. Intrinsic attenuation can be quantified by the quality factor Q (more commonly used in seismology), or the damping ratio ξ (used in engineering seismology).…”