GEOL 1010 Lecture Notes - Lecture 13: Seismic Wave, Seismic Source, Pumice
28 Oct 2016
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Document Summary
Terminology: caldera - large circular depression formed after an eruption as the center of the volcano collapses, tuff - volcanic rock made of ash and pumice. How do we know about earth"s interior: direct information. Volcanic rocks - xenoliths - pieces of host rock brought up in volcanoes - these are pieces of the upper mantle. Seismic waves travel at different velocities in different materials. Passive source - use natural seismicity from earthquakes. Active source - use man-made seismic waves. Vibroseis trucks - shake ground for seismic experiments. Seismic wave reflections: bounce back at layer boundaries separating rocks of different densities and elastic properties. Seismic wave refraction: bending when crossing rock layer boundaries, wave velocity changes. Measuring seismic waves: x-axis: distance, y-axis: time (s, different slopes in graph = different rock layers. Seismic structure of the mantle: p-wave velocity increases with depth. Huge velocity jump at the lithosphere (it"s seismically fast).
