Seismic Anisotropy

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Transcript of Seismic Anisotropy

  1. 1. Solid Earth Geophysics-Geop503Ali Oncel [email_address] Department of Earth Sciences, KFUPM Seismic Anisotropy Reading: Fowler Chapter 8- Section 8.1
  2. 2. Summary: Lecture6
      • Seismic Tomography
        • What does tomography reveal?
      • Types of tomography
        • Local Earthquake Tomography
        • Teleseismic Tomography
      • Data
        • Global Seismographic Network
      • Application
        • Global Seismic Tomography
  3. 3. Seismic tomography is a very active and popular research field Then,Seismic Imaging the Earths interior
    • What is seismic/earthquake tomography ?
    • What information can it provide? 5-Minutes
  4. 4. Progress in Knowledge of Earth KRAEMER (1902) 1903s view of Earth BOLT (Inside the Earth, 1973) 1973s view of Earth DZIEWONSKI (~1990, from www) 1999s view of Earth 1800s view of Earth
  5. 5. Lateral mantle structure
  6. 7. Global network for past 40 years
  7. 8. Data: Arrival Time Travel time tomography uses first-arrivals of body waves (P- and/or S-waves) Observation: Arrival time of first arrival Modified after from Dr. Stephan Husens lecture notes M4 earthquake close to Brugg, Station DAVOX
  8. 9.
    • Broadband Seismometer
  9. 10. South American Earthquake on Oct. 28, 1997,at 06 H 15 M, epicenter located at 4.3 S, 76.6 W, depth = 124 km, magnitude = 6.5 This map shows the location of the first of the three earthquakes considered in the lab. The lines connecting the earthquake to the stations are great circles on a global Mercator projection. Source: EAS 388 Earthquake located here
  10. 11. Improvement in Seismic Stations
    • What is the nature of upwellings within the deep mantle?
    • Are there truly gaps in subducted slab within the lower mantle, as appears to be the case beneath East Asia?
    • Do slabs continue to the core-mantle boundary, if so, how?
    • What is the cause for the apparent difference in P and S velocity structure in the deepest mantle?
    Better models are within reach, given the large amount of high quality seismic data becoming available. Such models can reduce uncertainty in plate reconstructions and can helpresolve questionssuch as: From:
  11. 12. P-wave S-wave Global Seismic Tomography: A Snapshot
  12. 13. Map of Subduction Zones Present Past
  13. 14. Lower Mantle Both models showstriking high wave-speedstructuresin the mid-mantle beneath theAmericasandsouthern Eurasia. The two modelsagree in detail for the anomalybeneath the Americas. The fast anomaly stretchesfrom 30S to about 50Nbeneath thecentral part of North America.