Seismology

09/20/10:
  • Body Waves: P and S waves

    P and S waves are the two fundamental elastic waves that are generated during an earthquake. fit between Africa and South America (figure from Stein and Wysession, 2003).

  • Surface Waves: Love and Rayleigh waves


    Surface waves develop from trapped compressional and shear waves along the surface of the earth. For most earthquakes, it is these later phases that cause the most damage. (figure from Fowler, 2005).

  • Separation of Arrivals on Seismogram

    (figure from Stein and Wysession, 2003)

  • Seismic Wave Propagation through Earth

    (figure from Stein and Wysession, 2003).

  • Because different waves travel different paths and speeds, their arrivals change and direct waves become more spread out at greater distances (a.k.a. moveout).
    (figure from www.iris.edu).

  • Global Predicted Arrival Time Table

    Figure shows the predicted arrival of earthquake seismic phases at locations around the world.

09/27/10:
  • Seismic Wavefronts through the Earth

    Illustration of wavefronts (orthogonal to ray-path) of seismic share waves through the mantle.

  • Bulk Earth Structure through Seismic Velocities
    Laterally averaged compressional and shear wave velocities and derived density structure through the earth.

  • Whole Mantle Tomography (a refraction method): Slabs to the core

    Shown here are two global tomographic images that suggest a relative fast (cold) feature extending to the earth's core. It is widely believed that these are subducted slabs, and are highly suggestive of whole mantle convection (as apposed to multi-layer convection cells).

  • Inner Core Rotation

    Using repeated ray-paths from earthquakes and seismometers that travel through the inner core, we can now identify a differential rotation.

  • Seismic Reflection: Single flat layer

    (figure from Stein and Wysession, 2003).

  • Seismic Reflection: Single Syncline

    Non-regular subsurface layers can create highly irregular paths, and may be difficult to reconstruct. In the example of a syncline, ray-paths will become focused toward the axis of folding, while an anticline will have ray-paths focus away from the folding axis (figure from Stein and Wysession, 2003).

  • Seismic Reflection Profile

    Example seismic profile, showing deep crustal structure in the central North American continental crust. Features of deep crustal faults are barely visible to the naked eye. It takes reflection seismology experience, structural geology training, and sometimes a good imagination ability to interpolate and extrapolate to develop interpretations.

  • 3D: Reflection Seismology

    Schematic illustration of 3D illumination of a salt diapir (salt dome), which is a structure that is highly beneficial for trapping natural gas and oil.
10/06/10:
  • Gutenberg-Richter power-law Relationship of earthquake recurrence
    On average, for every unit magnitude increase, we see a factor of 10 less earthquakes. Since magnitude scales as 2/3 log10 moment, we will see a similar relationship for moment increase (figures from Stein and Wysession, 2003).

Intro. to Geophysics: Supp. | Intro. to Geophysics: Home | Updated: Wed Oct 6 08:37:17 EDT 2010