Chapter 1 : Seismic (Elastic) Wave Theory Flashcards
Elastic Solid
Deforms under external force but returns to original size and shape when force removed
Stress
Force/unit area
Normal Stress
Force normal to surface (pressure)
Shear stress
Force tangential to surface (traction)
Static equilibrium
No motion; normal and shear forces balance
Strain
Relative deformation of body under stress (fractional change in size and shape)
Normal strain
Volume change
Cubic Dilatation
Fractional change in volume due to deformation
Shear Strain
Deformation
Hooke’s Law
Strain directly proportional to the stress that produced it
Isotropic materials
No directional variation
Body Waves
Waves that propagate through the body of the earth
Compressional (Primary) Waves
Volume change, no rotation
Shear (Secondary) Waves
Rotational disturbance
Vertically Polarized S wave
Particle motion in vertical plane perpendicular to surface
Horizontally polarized S wave
Particle motion in horizontal plane parallel to surface
What are the body wave conversions?
Sh=no conversion, SvP
What is the critical angle?
Incident angle when the wave experiences no transmission
Angle of intromission
Incident angle when the wave experiences no reflection, complete transmission
Surface waves
Waves that propagate at the surface of a medium, have both P and S components
Retrograde motion
Motion at the top of the ellipse is opposite in direction to wave propagation
Prograde motion
Motion at the top of the ellipse is the same direction as wave propagation
Rayleigh Wave
Surface wave that travels near the surface of solids (P and S components)
Group Velocity
Velocity at which energy (or envelope) at a particular frequency propagates
Phase velocity
Velocity at which a particular phase propagates
Love wave
An Sh wave trapped near the surface by reflection/refraction
What order do love waves arrive at a distant station?
Low frequencies first, then mix of high and low frequencies, finally a single frequency corresponding to min cg arrives (Airy phase)
