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Chapter 4 Seismology Measuring the interior School of Earth and Environmental Sciences Junkee Rhie 4.1 Waves through the Earth The importance of Seismology Seismology is the most powerful technique for sampling and constraining the physical structure of the Earth’s interior • By studying the propagation of elastic waves through the Earth we can learn about the physical properties of the Earth’s interior • Seismic waves sample narrow swaths of the Earth’s interior • We can produce a CAT-scan of the Earth • Seismology was central to the discovery of plate tectonics 1 4.1 Waves through the Earth Seismological techniques 4.1 Waves through the Earth Body waves and surface waves 2 4.1 Waves through the Earth Body waves 4.1 Waves through the Earth Energy sources and receivers 3 4.1 Waves through the Earth P-waves 4.1 Waves through the Earth S-waves 4 4.1 Waves through the Earth Waves 4.1 Waves through the Earth Seismic waveform 5 4.1 Waves through the Earth Seismometer 4.1 Waves through the Earth Velocity and density – Birch’s Law 6 4.1 Waves through the Earth Nafe-Drake curve 4.1 Waves through the Earth Vp vs. Depth 7 4.1 Waves through the Earth Surface waves 4.1 Waves through the Earth Surface waves - amplitude 8 4.1 Waves through the Earth Surface wave propagation ShakeMovie by Caltech (www.shakemovie.caltech.edu) 4.1 Waves through the Earth Love and Rayleigh waves 9 4.1 Waves through the Earth Love and Rayleigh waves 4.1 Waves through the Earth Seismic waveforms 10 4.1 Waves through the Earth Seismic waveforms 4.1 Waves through the Earth Surface waves – velocity sensitivity 11 4.1 Waves through the Earth Group and phase velocity 4.1 Waves through the Earth Dispersion 12 4.1 Waves through the Earth Dispersion curves and seismic velocity 4.1 Waves through the Earth Free oscillations 13 4.1 Waves through the Earth Free oscillations 4.1 Waves through the Earth Free oscillations – excited by 2004 Sumatra (Mw = 9.0) earthquake 14 4.2 Earthquake seismology Locating earthquakes 4.2 Earthquake seismology Locating earthquakes 15 4.2 Earthquake seismology Locating earthquakes 4.2 Earthquake seismology Locating earthquakes 16 4.2 Earthquake seismology Locating earthquakes 4.2 Earthquake seismology Earthquake depth 17 4.2 Earthquake seismology Earthquake distribution 4.2 Earthquake seismology Earthquake depth distribution 18 4.2 Earthquake seismology Earthquake size 4.2 Earthquake seismology Intensity : ShakeMap 19 4.2 Earthquake seismology Intensity and magnitude 4.2 Earthquake seismology Richter magnitude – Wood-Anderson seismometer 20 4.2 Earthquake seismology Richter magnitude – Wood-Anderson seismometer 4.2 Earthquake seismology Richter magnitude – Wood-Anderson seismometer 21 4.2 Earthquake seismology Richter magnitude – Today 4.2 Earthquake seismology Body wave magnitude (mb) 22 4.2 Earthquake seismology Surface wave magnitude (Ms) 4.2 Earthquake seismology Magnitude as a discriminator 23 4.2 Earthquake seismology Magnitude-frequency relation 4.2 Earthquake seismology Magnitude and frequency 24 4.2 Earthquake seismology Earthquake energy 4.2 Earthquake seismology Seismic moment – Best measure of earthquake size 25 4.2 Earthquake seismology Focal mechanism 4.2 Earthquake seismology First motion 26 4.2 Earthquake seismology Indicative fault type 4.2 Earthquake seismology Plate boundaries 27 4.2 Earthquake seismology Nomenclature 4.2 Earthquake seismology Waves through the Earth 28 4.2 Earthquake seismology Arrival times 4.2 Earthquake seismology Short period arrival times 29 4.2 Earthquake seismology Arrival times 4.2 Earthquake seismology 1D velocity model for the Earth 30 4.2 Earthquake seismology Velocity and Mineralogy 4.2 Earthquake seismology 3D velocity variations 31 4.2 Earthquake seismology Mantle convection 4.2 Earthquake seismology Tomography 32 4.2 Earthquake seismology Borehole tomography 4.2 Earthquake seismology Subduction 33 4.2 Earthquake seismology Subduction 4.2 Earthquake seismology Subduction 34 4.2 Earthquake seismology Mid-ocean ridge 4.2 Earthquake seismology Mid-ocean ridge 35 4.2 Earthquake seismology Hotspots and mantle plumes 4.2 Earthquake seismology Iceland 36 4.2 Earthquake seismology Iceland and Azores Canary Cape Verde 4.2 Earthquake seismology Hawaii plume 37 4.2 Earthquake seismology African cratons 38
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