Comment: 17:35 - 18:25 (00:50) Source: Annenberg/CPB Resources -
Earth Revealed - 9. Earthquakes Keywords: Parkfield, "Tom
Daley", "San Andreas Fault", "fault structure", "Vibra-seis
truck", wave, energy, velocity, "subsurface structure",
earthquake Our transcription: One of the most fundamental
aspects of the Parkfield Experiment focuses on the structure of
the San Andreas Fault itself. To learn more about this
structure, geophysicists have set up the Vibra-seis Project. At
the heart of this effort is a specially equipped truck that
shakes the ground, triggering waves of seismic energy. Radiating
into the earth, the seismic waves moves at different velocities
through different rock types. Analysis of the velocity changes
makes it possible to unravel the intricacies of the subsurface
geologic structure. As the waves penetrate the Earth, they are
reflected and refracted off the various rock layers, and by
measuring first the direct wave, which travels directly from the
source to receivers, we can get the veloc