Elastic moduli Young’s modulus, E –Shortening || stress Bulk modulus, k –Volume change / pressure Shear modulus,  –Rotation plane stress Poisson’s ratio,  –Ratio perp/parallel strains  11 =E(  L/L) LL

Young’s modulus, E –Shortening || stress Bulk modulus, k –Volume change / pressure Shear modulus,  –Rotation plane stress Poisson’s ratio,  –Ratio perp/parallel strains Elastic moduli K=-V dP/dV =  dP/d 

Young’s modulus, E –Shortening || stress Bulk modulus, k –Volume change / pressure Shear modulus,  –Rotation plane stress Poisson’s ratio,  –Ratio perp/parallel strains Elastic moduli  =  xy /  xy /2

Young’s modulus, E –Shortening || stress Bulk modulus, k –Volume change / pressure Shear modulus,  –Rotation plane stress Poisson’s ratio,  –Ratio perp/parallel strains  =-  22 /  11 Elastic moduli

Young’s modulus, E –Shortening || stress Bulk modulus, k –Volume change / pressure Shear modulus,  –Rotation plane stress Poisson’s ratio,  –Ratio perp/parallel strains Elastic moduli Auxetic material  =-  22 /  11

Richard Oldham Discovery of the Earth’s (outer) core (1906)

Richard Oldham Discovery of the Earth’s (outer) core (1906)

Andrija Mohorovicic Discovery of the MOHO discontinuity (1909 or 1910?)

Beno Gutenberg Accurate measure of the core-mantle boundary--or “Gutenberg discontinuity”--radius (1912)

Harold Jeffreys The core is fluid (1926)

Inge Lehmann Discovery of the Earth’s inner core (1936)

Inge Lehmann Discovery of the Earth’s inner core (1936) P-wave pathsS-waves

“Travel time” of seismic phases vs. epicentral distance (Jeffreys-Bullen)

Don Anderson Adam Dziewonski Preliminary Reference Earth Model (1981)

PREM radially symmetric earth model Best fit to following data: P and S wave travel times versus  Body wave evidence for boundaries crust-mantle transition zone (410 km, 660 km jumps) core-mantle boundary outer-inner core boundary Surface wave phase velocities as a function of wave period Rayleigh waves (SV and P) Love waves (SH) Periods of free oscillations Spheroidal (Standing Rayleigh waves + gravity) Torsional (Standing Love waves)

Fowler, page 106 Phases: freq dec. as distance inc. Groups: constant frequency/period

# great circles = l -1 Zero crossings

Varies w/ depth, too! Diff. modes sense different depths. “Sensitivity kernel”