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					week 01, 08/23/04   ESCI461: Introduction           Slide 1   week 01, 08/23/04        ESCI461: Introduction                         Slide 2

              ESCI 461: Seismology I
 Instructor:
       Colin Zelt, room 311
                                                                Scheduled Office Hours: (other times possible by appointment)
       phone 713-348-4757, email: czelt@rice.edu
                                                                Instructor:
       Fenglin Niu, room 316
                                                                      Colin Zelt:
       phone 348-4122, email: niu@rice.edu
                                                                            MWF 11:00 – 12:00 AM                              room 311
 Time:
          LECTURES                                                      Fenglin Niu:
               MWF, 10:00 – 10:50 am                                              TTH 10:00 – 12:00 AM                        room 316
          Location:
               Room 105.
 WEB:
          http://terra.rice.edu/department/niu/ESCI461




week 01, 08/23/04   ESCI461: Introduction           Slide 3   week 01, 08/23/04        ESCI461: Introduction                         Slide 4


 Required Text Book:
                                                                                        Homework
     An Introduction to Seismology, Earthquakes, and            Homework is due 2 weeks after it is assigned
     Earth Structure by Stein and Wysession                      • Late homework will not be accepted one week after
                                                                   the deadline.
 Recommended Text Books:                                         • Late homework will be penalized: 80% (1 day late),
      Quantitative Seismology by Aki & Richards                    60% (2 day late), 40% (3 day late), 20 % (4 day late)
      Modern Global Seismology by Lay & Wallace                    and 10% (5-7 day late).
      Introduction to Seismology by Shearer

 Grading: is weighted as follows:
     Assignments (75%); Participation (25%),
     Lack of attendance (-10%).




week 01, 08/23/04   ESCI461: Introduction           Slide 5   week 01, 08/23/04        ESCI461: Introduction                         Slide 6

         What’s seismology about?                             “I cannot help feeling that seismology will stay in
                                                              the place at the center of solid earth science for
                                                              many, many years to come…

                                                              The joy of being a seismologist comes to you,
                                                              when you find something new about the earth’s
                                                              interior from the observation of seismic waves
To study the generation, propagation and                      obtained on the surface, and realize that you did it
                                                              without penetrating the earth or touching or
recording of elastic waves in the earth (and                  examining it directly.”
other celestial bodies) and of the sources
                                                                Keiiti Aki, presidential address to the Seismological Society of America, 1980
that produce them.
week 01, 08/23/04   ESCI461: Introduction              Slide 7   week 01, 08/23/04   ESCI461: Introduction                    Slide 8

                                                                              History of Seismology
    Contributions from Seismology
                                                                       Seismology - study of seismic waves, earthquakes,
                                                                       and earth structure derived from them
    Scientific Contributions
                                                                       Passive seismology uses EQ source for crustal to
     • Understanding the Earth’s deep interior                         whole earth scale studies
     • Helping the establishment of plate tectonics                    Active seismology uses artificial sources for
    Social and Political Applications                                  environmental, engineering, exploration studies, to
                                                                       crust and upper mantle scale studies
     • Disaster mitigations
                                                                       Most theoretical seismology texts slanted towards
     • Monitor WMD                                                     EQ seismology
                                                                       A large part of this course concerned with study of
                                                                       seismic waves ⇒ common to both passive and
                                                                       active methods




week 01, 08/23/04   ESCI461: Introduction              Slide 9   week 01, 08/23/04   ESCI461: Introduction                   Slide 10


   Quantitative seismology is ~100 years old
                                                                        What can we learn on earth’s
   In early 1800s, theory of elastic waves (body                        structure from seismology?
   and surface waves) developed by Poisson,
   Rayleigh, etc.
                                                                        Velocities
   First electromagnetic seismometers (basis for
   all modern seismometers) developed in early                          Density
                                                                                                             Inner
   1900s                                                                Attenuation                           core
                                                                                                                     Outer
    • The first seismoscope was built in 132 AD                         Anisotropy                                   core

    • The first mechanical seismometer was invented in                                                                   Mantle
                                                                        Boundaries
      1870’s




week 01, 08/23/04   ESCI461: Introduction             Slide 11   week 01, 08/23/04   ESCI461: Introduction                   Slide 12



                Interior of the Earth                                                    FACTS
                                                                        In 1909 Mohorovicic inferred velocity
   Crust:
   Crust: variable thickness with an average value of 35                discontinuity separating crust and mantle
                             7-
   km in the continents and 7-8 km in the oceanic regions.              (now referred to as Moho)
   Volume ~1019 m3 Mass 2.8 x 1022 kg.
                                                                        Presence of Earth’s core was inferred in 1906
   Mantle:                                    (crust-
   Mantle: between the Moho discontinuity (crust-
                                                                        based on absence of direct body waves at
                    core-
   mantle) and the core-mantle boundary (R = 3480 km).
   Volume 9 x 1020 m3 Mass 4 x 1024 kg.
                                                                        source-                              100°
                                                                        source-receiver offsets beyond about 100°
                                                                        (R.D. Oldham of Indian Geological Survey )
   Core:                                     core-
   Core: from the center of the Earth to the core-mantle
   boundary. Volume 1.77 x 1020 m3 Mass 1.94 x 1024 kg.
                                                                        Solid inner core discovered in 1936 by
                                                                        Lehmann
  week 01, 08/23/04    ESCI461: Introduction              Slide 13   week 01, 08/23/04    ESCI461: Introduction                  Slide 14



                                         Traveltimes of waves
                                         versus offset (traveltime                                                Standard reference
                                         tables) published by                                                     model established in
                                         Zoeppritz, Guttenberg                                                    1981 by Dziewonski
                                         and Jeffreys and Bullen                                                  and Anderson called
                                         in 1907, 1914 and 1940                                                   PREM (Preliminary
                                                                                                                  Reference Earth
                                         Traveltimes used to
                                                                                                                  Model)
                                         derive earth’s average
                                         velocity versus depth                                                    Current standard is
                                         structure over 50 years                                                  IASPEI91, AK135
                                         ago




  week 01, 08/23/04    ESCI461: Introduction              Slide 15   week 01, 08/23/04    ESCI461: Introduction                  Slide 16


     Earth divided into crust, mantle,                                       core-
                                                                          At core-mantle boundary
     inner and outer core                                                          P-     S-
                                                                          (CMB), P- and S-wave velocity
                                                                          drops from 14 to 8 km/s and
     Crust typically 6 km thick under
                                                                          from 7 to 0 km/s, larger than
             30-
     oceans, 30-50 km under
                                                                          velocity contrast at earth’s
     continents
                                                                          surface!
     Mantle shows rapid velocity
                                                                          CMB is sharp interface between
                        300-
     increase between 300-700km,
                                                                          solid mantle and fluid outer core
     termed “transition zone” due to
     several mineralogical phase                                          Within outer core velocity
     changes, e.g., at 410 and 660km                                      increases gradually consistent
                                                                          with well mixed fluid
     Beneath this, velocity increases
     gradually with depth as predicted                                    At inner core boundary (ICB),
     by pressure/temperature effects                                      core becomes solid as a result of
     on rocks of uniform composition                                      phase change in iron




  week 01, 08/23/04    ESCI461: Introduction              Slide 17   week 01, 08/23/04    ESCI461: Introduction                  Slide 18

                                                                                                              Percent deviation from
 Earth’s density structure                                                                                    reference models generally
 not constrained by                                                                                           decreases with depth, so that
                                                                                                              relative inhomogeneity is
 traveltimes, but can be                                                                                      large in the shallow near
 inferred from knowing                                                                                        surface (up to an order of
 earth’s mass and moment                                                                                      magnitude over meters both
                                                                                                              horizontally and vertically),
 of inertia, from lab studies,                                                                                but only a few percent in the
 normal modes, and from                                                                                       mantle and core
 seismic amplitude analysis
Adam-
Adam-Williamson equation
  d ρ (r )    g (r )ρ (r)
           =−
    dr           Φ(r)
week 01, 08/23/04   ESCI461: Introduction         Slide 19     week 01, 08/23/04             ESCI461: Introduction                     Slide 20


                                                                      Elastic Rebound Theory (H. Reid)
    Explosions and other active sources used in 1920s for
                                                                 Undeformed Rocks
    petroleum exploration in U.S. and Mexico                                                                         First the ground is
    Initially just refraction method and traveltimes                                                                 normal. Then the plates
                                                                                                                     start to move and stress
    Reflection method quickly took over as number of
                                                                                                                     is formed in the ground.
    receivers increased                                          Stressed to Elastic Limit
                                                                                                                     After it passed the limit
    CMP/stacking method for better SNR patented in                                                                   the ground snaps back in
    1956                                                                                                             place and an earthquake
    Vibroseis developed in 1950s                                                                                     occurs.
                                                                                                       Earthquake
    3D land and marine surveys now common,                       Rebound to Relieve Stress
    processing methods very advanced




week 01, 08/23/04   ESCI461: Introduction         Slide 21     week 01, 08/23/04             ESCI461: Introduction                     Slide 22

            Basic Types of Faulting                                    Seismicity – Geographic Distribution




week 01, 08/23/04   ESCI461: Introduction         Slide 23     week 01, 08/23/04             ESCI461: Introduction                     Slide 24

        Seismicity – Depth Distribution
                                                                Earthquake Faults & Plate Boundaries
                                                             Normal            Compression   Reverse                     Strike-Slip
                                                                               Tension
                                                             Fault                           Fault                       Fault
week 01, 08/23/04        ESCI461: Introduction                 Slide 25   week 01, 08/23/04   ESCI461: Introduction         Slide 26

         Seismic Velocity Structure                                          The Early History of Seismometry (132 A.D. )




                                                                          Chang Heng's seismoscope. It does not measure the
                                                                          ground motion, it only tells you the direction where the
                                                                          earthquake occurred.




week 01, 08/23/04        ESCI461: Introduction                 Slide 27   week 01, 08/23/04   ESCI461: Introduction         Slide 28

       The First Seismometer and
     the First Seismograph (1870s)                                                      Modern Seismometer




              Ewing's horizontal-pendulum seismometer (1880)

				
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