1. Earthquakes Kobe, Japan 1995 – 5000 deaths
It is estimated that there are
500,000 detectable earthquakes
in the world each year.
100,000 of those can be felt,
and 100 of them cause damage.
The world's deadliest recorded
earthquake occurred in 1557 in
central China. It struck a region
where most people lived in caves
carved from soft rock. These
dwellings collapsed during the
earthquake, killing an estimated
830,000 people.
In 1976 another deadly earthquake
struck in Tangshan, China, where
more than 250,000 people were
killed.

4. Earthquake
epicenters
in the U.S.

5. Seismic risk map for the U.S.
Colors on this map show the level of horizontal shaking that have a 1-in-10 chance of being exceeded in a 50-year period. Shaking is expressed as a percentage of g (g is the acceleration of a falling object due to gravity).

6. Turkey, August 17, 1999…in 40 seconds
$20 billion in losses – 10% of Gross National Product

7. Listening Team – Turkey, 1999
63,000 damaged buildings, 18,000 deaths, 50,000 injuries,
120,000 families without housing

8. Earthquakes happen
every day, every hour
somewhere in the world.

9. 95% of seismicity
in Hawaii is due to
volcanism –
magma movement.
Other 5% is due to
tectonic forces
on the
seafloor

10. Hawaii Island seismicity, 2000

12. Plate Tectonic framework for earthquakes
Convergent, Divergent and Transform Boundaries

13. Convergent Boundary
Divergent Boundary

16. Earthquakes and Plate Margins
Circum-Pacific seismic belt – 81% of worlds largest quakes
Alpide Belt – 17% of largest quakes
Mid-Atlantic Ridge

17. Elastic rebound as a cause of earthquakes
Slow storage of elastic energy
over time (deformation)
2. Forces holding rocks together are
overcome (displacement by elastic
rebound)
Foreshocks – build up of strain
Aftershocks – Continued strain release
Landforms – scarps, linear features
diverted

18. Locating an earthquake
Energy is first released at focus, as slippage.
This exerts strain along the fault, producing more
slippage elsewhere – this propagates as energy

19. Benioff Zone beneath the Tonga Trench
Earthquake foci
define the subducting
slab.

20. Surface waves (Long Waves)
Two types of wave groups generated –
Surface waves (Long Waves)
Travel along outer layer of crust at the surface causing ground roll
like a water wave and lateral shifting…travel slowly and generate
the most damage
Body waves (two types)
Primary waves (P) – compress and pull (dilate) rocks in the
direction of movement, involves changing the volume and shape of
material….solids, liquids and gases resist compression and will spring back.
Thus they propagate the waves forward. P waves travel through all types of matter
Fastest wave
Secondary waves (S) – motion is 90 degrees to direction of
propagation (up and down), involves only changing the shape of transmitting
media…fluid and gas do not resist shape change hence they will not spring back
and will not transmit the wave forward. S waves travel only through solids.
Second fastest wave

21. S Wave – solids only, second fastest
Seismic body waves
P Wave - all types of matter, fastest
S Wave – solids only, second fastest

22. Recording earthquakes

23. Typical Seismograph record Average travel-time curves
Delay between arrival of S and
P waves is proportional to the
distance traveled by the waves

24. Three seismographs each plot a circle
of the travel distance calculated
by the S-P delay…where three
circles intersect is the epicenter

26. Refraction and reflection of seismic body waves
Increased density allows wave to travel faster…causing slow refraction (bending)
Refraction also happens suddenly when wave crosses density front.
Waves also reflect off density interfaces.
Wave front
Wave ray

27. Seismic shadow zones - Measuring Earths Interior
P-wave refraction creates
a shadow zone
S-wave propagation
creates a shadow zone
P wave
shadow zone
S wave
shadow zone
Network of epicenters around
Earth’s surface defines the
interior zones

29. Changes in the seismic velocity of P and S waves mark discontinuities at 100 km (the low velocity zone – LVZ), 400 km (base of the upper mantle), 670 km (top of the lower mantle), 2900 km (top of the core), and 4800 km (inner core boundary).

31. 400 discontinuity - broad depression of the surface (green and blue) under most parts of the Pacific and Indian Oceans. Large elevations in the surface (red and yellow) under continental regions such as Eurasia, North America, Australia, Antarctica and parts of Africa. In general 400 km discontinuity correlates well continents and ocean basins.
670 km discontinuity - very different structure from 400 km surface. Notable features: deep depression in western Pacific, Tonga, and South America. Basin depths 25 km from average position of the surface; consistent with effect of subduction in these regions.
2900 discontinuity - at core-mantle boundary reveals broad basin under Indian Ocean and eastern Eurasia; western Africa, southern Indian Ocean, Australia, and western and central Pacific have a high topography related to thermally buoyant regions on core surface

33. Richter Magnitude – M = log X/T + Y (correction factor)
Energy of seismic wave is a function of both amplitude (X) and duration (T).
M = log X/T + Y (correction factor)

34. Table 13.3 – Frequency of Occurrence of Earthquakes since 1900
Descriptor
Richter Magnitude
Average Annually
Great
8 and higher 1
Major 18
Strong
120
Moderate
800
Light
6,200 (estimated)
Minor
49,000 (estimated)
Very Minor
< 3.0
Magnitude 2 - 3: about 1,000 per day Magnitude 1 - 2: about 8,000 per day

36. Modified Mercalli Intensity Scale
Table 13.2
Modified Mercalli Intensity Scale
I. Not felt except by a very few under especially favorable conditions.
II. Felt only by a few persons at rest, especially on upper floors of buildings.
III. Felt quite noticeably by persons indoors, especially on upper floors of buildings. Many people do not recognize it as an earthquake. Standing motor cars may rock slightly. Vibrations similar to the passing of a truck. Duration estimated.
IV. Felt indoors by many, outdoors by few during the day. At night, some awakened. Dishes, windows, doors disturbed; walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars rocked noticeably.
V. Felt by nearly everyone; many awakened. Some dishes, windows broken. Unstable objects overturned. Pendulum clocks may stop.
VI. Felt by all, many frightened. Some heavy furniture moved; a few instances of fallen plaster. Damage slight.
VII. Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys broken.
VIII. Damage slight in specially designed structures; considerable damage in ordinary substantial buildings with partial collapse. Damage great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture overturned.
IX. Damage considerable in specially designed structures; well-designed frame structures thrown out of plumb. Damage great in substantial buildings, with partial collapse. Buildings shifted off foundations.
X. Some well-built wooden structures destroyed; most masonry and frame structures destroyed with foundations. Rails bent.
XI. Few, if any (masonry) structures remain standing. Bridges destroyed. Rails bent greatly.
XII. Damage total. Lines of sight and level are distorted. Objects thrown into the air.