1. WELCOME TO S E I M O L G Y

2. History of seismology
Simple elastic theory
Seismic waves

3. What’s seismology about?
Seismology is the study of the generation, propagation and recording of elastic waves in the Earth (and other celestial bodies) and of the sources that produce them.

4. Seismology is science dealing with all aspects of earthquakes:
What is seismology?
Seismology is science dealing with all aspects of earthquakes:
OBSERVATIONAL SEISMOLOGY
Recording earthquakes (microseismology)
Cataloguing earthquakes
Observing earthquake effects (macroseismology)
ENGINEERING SEISMOLOGY
Estimation of seismic hazard and risk
Aseismic building
‘PHYSICAL’ SEISMOLOGY
Study of the properties of the Earth’s interior
Study of physical characteristics of seismic sources
EXPLORATIONAL SEISMOLOGY (Applied seismic methods)...

5. Seismologists “read” seismograms to learn about the earth.

6. Get
Ready
To be
Blown by
HISTORY!

7. Earthquake mythology – ancient beliefs
India: The earth is held up by 4 elephants that stand on the back of a turtle. The turtle is balanced on top of a cobra. When the animals move, the earth trembles and shakes

8. Earthquake mythology – ancient beliefs
Mexico: El Diablo, an Indian devil god, made a giant rip in the ground so that he and his cohorts did not have to take the long way around, whenever they wanted to stir up mischief on the earth.
Siberia: The Earth rests on a sled driven by the god named Tuli. The dogs have fleas, When they stop to scratch, the Earth shakes
From:

9. Earthquake mythology – ancient beliefs
Japan: A great catfish, or namazu, lies curled up under the sea, with the islands of Japan resting on its back. A demigod, or daimyojin, holds a heavy stone over his head to keep him from moving. Once in a while, though, the daimyojin is distracted, the namzu moves and the earth trembles
Earthquake mythology – ancient beliefs

10. The first seismic instrument
The Chinese Seismoscope Invented 132 AD
The instrument is reported to have detected a four-hundred-mile distant earthquake which was not felt at the location of the seismoscope.
The instrument was said to resemble a wine jar of diameter six feet . On the outside of the vessel there were eight dragon-heads, facing the eight principal directions of the compass. Below each of the dragon-heads was a toad, with its mouth opened toward the dragon. The mouth of each dragon held a ball. At the occurrence of an earthquake, one of the eight dragon-mouths would release a ball into the open mouth of the toad situated below. The direction of the shaking determined which of the dragons released its ball. The instrument is reported to have detected a four-hundred-mile distant earthquake which was not felt at the location of the seismoscope. (From neic.usgs.gov/neis/seismology)‏

11. The first scientifically studied earthquake
The Lisbon Earthquake (Nov 1, 1755)‏
Probably magnitude 9 with a 3 large tsunamis, thousands killed
epicentre 200 km off SW corner of Portugal
destroyed the city of Lisbon, Portugal
tsunami's struck England and were detected across the Atlantic Ocean in North America
Its widespread physical effects aroused a wave of scientific interest and research into earthquakes.
The first scientifically studied earthquake
(From geology.about.com/library/
bl/bllisbon1755eq.htm)‏

12. ELASTIC
THEORY

14. E is the strain
Sigma is stress
Is it dimensionless

15. Elastic, anelastic and plastic behavior of materials
Hooke’s law.
Hooke‘s Law essentially states that stress is proportional to strain.
 At low to moderate strains: Hooke‘s Law applies and a solid body is said to behave elastically, i.e. will return to original form when stress removed.
elastic limit,
At high strains: the elastic limit is exceeded and a body deforms in a plastic or ductile manner: it is unable to return to its original shape, being permanently strained, or damaged.
 At very high strains: a solid will fracture, e.g. in earthquake faulting
brittle behavior.

16. m = shear stress = (DF /A) shear strain = (Dl /L) A shear stress
shear modulus
shear stress = (DF /A)
shear strain = (Dl /L)
shear stress
shear strain
m =

17. Seismic waves

19. Other Characteristics
Seismic Body Waves
Wave Type
(and names)
Particle Motion
Other Characteristics
P, 
Compressional, Primary, Longitudinal
Alternating compressions (“pushes”) and dilations (“pulls”) which are directed in the same direction as the wave is propagating (along the raypath); and therefore, perpendicular to the wavefront.
P motion travels fastest in materials, so the P-wave is the first-arriving energy on a seismogram.  Generally smaller and higher frequency than the S and Surface-waves.  P waves in a liquid or gas are pressure waves, including sound waves.
S, 
Shear, Secondary, Transverse
Alternating transverse motions (perpendicular to the direction of propagation, and the raypath); commonly approximately polarized such that particle motion is in vertical or horizontal planes.
S-waves do not travel through fluids, so do not exist in Earth’s outer core (inferred to be primarily liquid iron) or in air or water or molten rock (magma).  S waves travel slower than P waves in a solid and, therefore, arrive after the P wave.

20. Other Characteristics
Seismic Surface Waves
Wave Type
(and names)
Particle Motion
Other Characteristics
L,                 
Love, Surface waves, Long waves
Transverse horizontal motion, perpendicular to the direction of propagation and generally parallel to the Earth’s surface.
Love waves exist because of the Earth’s surface.  They are largest at the surface and decrease in amplitude with depth.  Love waves are dispersive, that is, the wave velocity is dependent on frequency, generally with low frequencies propagating at higher velocity.  Depth of penetration of the Love waves is also dependent on frequency, with lower frequencies penetrating to greater depth.
R,           
Rayleigh, Surface waves, Long waves, Ground roll
Motion is both in the direction of propagation and perpendicular (in a vertical plane), and  “phased” so that the motion is generally elliptical – either prograde or retrograde.
Rayleigh waves are also dispersive and the amplitudes generally decrease with depth in the Earth.  Appearance and particle motion are similar to water waves. Depth of penetration of the Rayleigh waves is also dependent on frequency, with lower frequencies penetrating to greater depth. Generally, Rayleigh waves travel slightly slower than Love waves.

21. 3-D Grid for Seismic Wave Animations
No attenuation (decrease in amplitude with distance due to spreading out of the waves or absorption of energy by the material) dispersion (variation in velocity with frequency), or anisotropy (velocity depends on direction of propagation) is included.

22. Compressional Wave (P-Wave) Animation
Deformation propagates. Particle motion consists of alternating
compression and dilation. Particle motion is parallel to the
direction of propagation (longitudinal). Material returns to its
original shape after wave passes.

23. Shear Wave (S-Wave) Animation
Deformation propagates. Particle motion consists of alternating transverse motion. Particle motion is perpendicular to the direction of propagation (transverse). Transverse particle motion shown here is vertical but can be in any direction. However, Earth’s layers tend to cause mostly vertical (SV; in the vertical plane) or horizontal (SH) shear motions. Material returns to its original shape after wave passes.

24. Rayleigh Wave (R-Wave) Animation
Deformation propagates. Particle motion consists of elliptical motions (generally retrograde elliptical) in the vertical plane and parallel to the direction of propagation. Amplitude decreases with depth. Material returns to its original shape after wave passes.

25. Love Wave (L-Wave) Animation
Deformation propagates. Particle motion consists of alternating transverse motions. Particle motion is horizontal and perpendicular to the direction of propagation (transverse). To aid in seeing that the particle motion is purely horizontal, focus on the Y axis (red line) as the wave propagates through it. Amplitude decreases with depth. Material returns to its original shape after wave passes.