Coupling of Airborne Sound into the Earth.
Abstract
As an acoustic wave propagates above the surface of the earth, part of the energy is transferred from motion of air to motion of the earth's surface which can be detected by a geophone. The purpose of the study described here was to establish the physical mechanisms responsible for this acoustic to seismic transfer of energy, to develop a mathematical formulation for quantitative predictions of the acoustic/seismic transfer function, and to collect for comparison to the physical model. The physical model chosen to describe coupling of energy into the earth was developed by Biot and later extended by Stoll primarily for describing sound propagation in ocean sediments. The Biot-Stoll model describes sound propagation in a medium composed of fluid saturated pores and an elastic frame (matrix). The differential equations which arise from this formalism allow for a fast wave which propagates, primarily, in the frame and a slow wave which propagates, primarily in the fluid. For our application we assume that the fluid is air and that the porous material is a layer between the air (an upper semi-infinite half space) and homogenous clay (a lower semi-infinite half space). Calculations suggest that the predicted transfer functions are not strongly affected by the flow resistance of the porous layer, the elastic properties of the clay, and the thickness of the porous layer. These three quantities were independently measured.
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 01, 1984
- Accession Number
- ADA146231
Entities
People
- H. E. Bass
- L. N. Bolen
Organizations
- University of Mississippi