Quiz answers 1: Compositional descriptions b)Mantle c)Crust 2: The mantle is made up primarily of: c)Olivine and Silicate minerals 3: The thickness of the continental crust is: c)10-70 km 4: Which one (1) of the following is a liquid? d)Outer Core 5: What is the temperature at the base of the crust? b)1000C 6: Name this ray path: pPPS

2001 Kunlun EQ (M s 8.1) rupture Observations at surface -> Whole-earth model?

Lecture 2: Intro to Seismic Waves Review from last time –Blackboard site! (Quiz Monday) Today –Overview of structure - target properties –Types of seismic waves Why are there different types? Broad-brush wave equation –Springs!

lithospheric boundary layer slowly convecting mantle: plate tectonic engine rapidly convecting outer core: geomagnetic dynamo solid inner core km ,000 subduction seafloor spreading Core-mantle boundary layer

Goals: –Composition of Earth –Temperature –Depth/horizontal variations  Interpretations of the above Observables: –Rocks brought to surface from depth (~100 km) –Gravity/magnetic fields –Earthquakes and their seismic waves How fast? What types? Rock types, temperature

USGS figure

Courtesy Fritz Keller

* Earthquake Wavefront Ray Path Ray Path is perpendicular to wavefront Seismograph Cross Section Through Earth Stations for Seismograms The Seismic Waves program From Alan Jones, SUNY, Binghamton

Compressional Wave (P-Wave) Animation Particle motion: alternating compression/dilation in propagation direction. No shear Vp = speed of sound. ~5.5 km/s in crust, 8+ km/s in mantle Animations: Larry Braille

Shear Wave (S-Wave) Animation Particle motion: alternating transverse motion perpendicular to propagation. Shear, no volume change or compression Can be in any direction, often divided into (SV; in the vertical plane) or horizontal (SH) shear motions. Velocity ~ 60% P-wave, 0 in fluids

Wave Type (and names) Particle MotionOther Characteristics P, Compressional, Primary, Longitudinal Alternating compressions ( “ pushes ” ) and dilations ( “ pulls ” ) which are directed in the same direction as the wave is propagating (along the raypath); and therefore, perpendicular to the wavefront. P motion travels fastest in materials, so the P-wave is the first-arriving energy on a seismogram. Generally smaller and higher frequency than the S and Surface-waves. P waves in a liquid or gas are pressure waves, including sound waves. S, Shear, Secondary, Transverse Alternating transverse motions (perpendicular to the direction of propagation, and the raypath); commonly approximately polarized such that particle motion is in vertical or horizontal planes. S-waves do not travel through fluids, so do not exist in Earth ’ s outer core (inferred to be primarily liquid iron) or in air or water or molten rock (magma). S waves travel slower than P waves in a solid and, therefore, arrive after the P wave. Seismic Body Waves

Rayleigh Wave (R-Wave) Animation Particle motion: Elliptical motions (generally retrograde elliptical) in the vertical plane and parallel to the direction of propagation. Amplitude decreases with depth. Vr ~ 3-4 km/s

Vertical section Vertical particle motion vrs time horizontal particle motion vrs time

Love Wave (L-Wave) Animation Particle motion: Alternating transverse motions, perpendicular to propagation Amplitude decreases with depth. No vertical motion VL ~ km/s

Wave Type (and names) Particle MotionOther Characteristics L, Love, Surface waves, Long waves Transverse horizontal motion, perpendicular to the direction of propagation and generally parallel to the Earth ’ s surface. Love waves exist because of the Earth ’ s surface. They are largest at the surface and decrease in amplitude with depth. Love waves are dispersive, that is, the wave velocity is dependent on frequency, generally with low frequencies propagating at higher velocity. Depth of penetration of the Love waves is also dependent on frequency, with lower frequencies penetrating to greater depth. R, Rayleigh, Surface waves, Long waves, Ground roll Motion is both in the direction of propagation and perpendicular (in a vertical plane), and “ phased ” so that the motion is generally elliptical – either prograde or retrograde. Rayleigh waves are also dispersive and the amplitudes generally decrease with depth in the Earth. Appearance and particle motion are similar to water waves. Depth of penetration of the Rayleigh waves is also dependent on frequency, with lower frequencies penetrating to greater depth. Generally, Rayleigh waves travel slightly slower than Love waves. Seismic Surface Waves