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Unformatted text preview: SUBDUCTION ZONE Seismic Gap along Himalayas USGS web page on October 8 2005 magnitude 7.6 in Pakistan Can earthquakes be predicted?
Can earthquakes be predicted?
Short Term, Not very well Short-range predictions Goal: provide warning location & magnitude
within a narrow time frame
within Research on precursors due breaking prior
slip. Breaking of rock lets the fault slip
Breaking Breaks called fracture zones. T α L
Breaks Breaking causes volume increase (dilation)
and uplift in the rocks.
uplift Dilatancy causes many measurable changes Short-Term Earthquake Prediction Dilatancy of Highly Stressed Rocks 56 Investigating Earth’s Interior Earthquakes help us understand Earth’s Interior Structure. We use: Speed changes in different materials due changes rigidity, density, elasticity Reflections from layers with different properties Attenuation of Shear Waves in fluids Direction changes (Refraction) Result: 3 Major Layers of Earth 58 Shallow Components of Earth ! Seismicwave velocities are faster in the upper mantle Velocity increases w depth, waves bend back to surface. Waves that travel via mantle arrive sooner at far destinations Wave Velocities
Mohorovičić discontinuity Upper Mantle Fast Asthenosphere
Slow Lower Mantle Fast Mineralogy of Earth’s Layers http://pubs.usgs.gov/gip/interior/ The PWave Shadow Zone
Pwaves through the liquid outer core bend, leaving a low intensity shadow zone 103 to 143 degrees away from the source, here shown as the north pole
HOWEVER, Pwaves traveling straight through the center continue, and because speeds in the solid inner core are faster, they arrive sooner than expected if the core was all liquid.
Inge Lehmann Behavior of waves through center reveal Earth’s Interior The SWave Shadow Zone
Since Shear (S) waves cannot travel through liquids, the liquid outer core casts a larger shadow for S waves covering everything past 103 degrees away from the source. End of Earthquakes
End of Earthquakes...
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- Winter '14