Transcript Slide 1

Types of seismic data used in
Earth models
• Body wave travel times
• Surface wave dispersion
• Normal modes (free oscillations or
standing waves on the earth)
Triplications and seismic discontinuities
Surface Wave
Dispersion
Surface wave sensitivity kernels
Normal modes (Free Oscillations)
Standing waves on the Earth
Radially symmetric (1-D) Reference Earth Models
• Jeffreys-Bullen Earth Model (JB) 1936-1958
• Preliminary Reference Earth Model (PREM)
Dziewonski & Anderson 1981
• IASPEI-91 Kennett & Engdahl (1991)
• AK135 Kennett et al (1995)
3-D Seismic models
Usually the strongest velocity variations are with depth
So 3-D models usually require a good 1-D model first
Methods:
•Size of area: local, regional, or global?
•Parameterization – blocks, nodes or spherical harmonics?
•Data: P & S wave travel times
•Surface waves – Love or Rayleigh - phase or group velocity
•Attenuation
Travel-time tomography
-- Uses observed travel time for many source-receiver
combinations to reconstruct seismic velocity image
-- Solves for the slowness sj = 1/vj of each block (node)
-- Travel time for each observation is the sum of travel times
in each block t = Lj sj
-- The matrix equation for all the travel times is: ti = Lij sj
-- Least Squares Solution: s = [LTL]-1 LTt
Regional Body Wave
Tomography – Tonga
Subduction Zone
Raypaths
Velocity
Conder & Wiens [2006]
Surface waves
group vs phase
velocity
Differential Attenuation
• Determine attenuation of a region by comparing two similar phases
• Advantage is eliminating source, receiver effects
Flanagan & Wiens [1998]
Difficulties with seismic tomography
Sources and Receivers
Ray path density
Rayleigh wave (70 s) tomography