KTU

40. Earthquakes
• Parts of the Earth are always moving, usually so
slowly that we do not feel anything.
• Most earthquakes happen when
parts of the Earth move quickly:
rocks break and slip along a fault
(a crack in the Earth’s surface).
• Aftershocks are the shocks that
people feel for hours or even days
after an earthquake.
©McGill University 2010
San Andreas Fault, California
www.wikipedia.org. Public domain.

41. How does the Earth move?
• The crust is the Earth’s outermost layer.
• The crust is made up of huge rocks broken
into large sections called tectonic plates. It
lies on top of the mantle, which consists in
part of molten rock.
©McGill University 2010
www.studentcenters.wikispaces.com: licensed under a Creative Commons Attribution Share-Alike 3.0 License
Crust
Mantle
Outer core
Inner core

42. Tectonic plates (i)
©McGill University 2010
www.wikipedia.org. Public domain.
• The tectonic plates are always moving
slowly (2-12 cm/year).

43. Tectonic plates (ii)
• The plates can separate, collide, or slide
past one another.
©McGill University 2010
www.wikipedia.org. Public domain.

44. Tectonic plates (iii)
• When two plates meet and try to slide past
each other or push against each other,
pressure can build below the surface. This
pressure builds until it is too strong and
must be released.
• The plates shift suddenly, energy is
released, and shock waves are sent
out that produce an earthquake.
©McGill University 2010

45. Volcanoes and human activity
• Volcanoes and human activity also cause
earthquakes:
– Volcanic eruptions can release
huge amounts of energy that can
be felt as earthquakes.
– Human activities such as mining,
dam reservoirs, and nuclear
explosions can trigger minor
earthquakes. Earthquakes caused
by humans always occur close to
the site where an activity is being
carried out. They are not felt far away.
©McGill University 2010
www.wikipedia.org. Public domain.
Reinhard Jahn. www.wikipedia.org. License:
Creative Commons Attribution-Share Alike 2.0
Germany

46. What happens during an
earthquake?
• During an earthquake, energy is released:
– as movement along the fault
– as heat
– as seismic waves that radiate out in all
directions and cause the ground to shake
when they reach the surface. The word
“seismic” comes from the Greek work
“seismos”, which means “a shaking”.
©McGill University 2010

47. Source: GSHAP, Switzerland
Earthquake geography

60. Causes: accumulated strain
leads to fault rupture
- the elastic rebound model

61. Causes: fault movement releases energy as
seismic waves radiating from rupture
Seismic waves

62. Hypocentre vs. epicentre (i)
• The focus, or hypocentre, of the
earthquake is the place at which the
energy is released. The focus is
underground — in Canada it ranges from
1 to 100 km deep.
• The epicentre is the point
on the Earth's surface
directly above the focus
of the earthquake.
©McGill University 2010
www.wikipedia.org: licensed under a
Creative Commons Attribution Share-Alike 3.0 License

63. Hypocentre vs. epicentre (ii)
• Ground motions caused by seismic waves
reaching the surface will depend on:
– the depth of the focus
– the type of rock found locally
– the magnitude of the earthquake
©McGill University 2010

64. Faults
• Faults, or breaks in the Earth’s crust, form
where rocks have broken from the forces
created by the moving tectonic
plates.
• Some faults are large enough
that they split open the ground.
• Fault lines range in length from
a few centimeters to hundreds
of kilometers.
©McGill University 2010
San Andreas Fault, California
www.wikipedia.org. Public domain.

65. Types of faults
Thrust (Reverse) fault
Normal
fault
Strike-slip fault

66. Strike-Slip Faults
Left-lateral Right-lateral

79. MAGNITUDE CLASSIFICATION
M ≥ 8.0 Great Earthquake
7.0 ≥ M < 8.0 Major / Large Earthquake
5.0 ≥ M < 7.0 Moderate Earthquake
3.0 ≥ M < 5.0 Small Earthquake
1.0 ≥ M < 3.0 Microearthquake
M < 1.0 Ultra Microearthquake
Hagiwara, 1964

80. 1) Foreshocks
2) Main shock
3) Aftershocks
4) Earthquake Swarm
5) Normal Seismic activity

81. CLASSIFICATION DISTANCE
1) Teleseismic Earthquake > 1000 km
2) Regional Earthquake > 500 km
3) Local Earthquake < 500 km
1) Tectonic Earthquake
2) Volcanic Earthquake
3) Collapse Earthquake
4) Explosion Earthquake

82. EARTHQUAKE INTENSITY
Ø Rossi-Forel Intensity Scale (I – X)
Ø Modified Mercalli (MM) Intensity Scale
(1956 version), (I – XII)
Ø Medvedev-Sponheuer-Karnik (MSK) Intensity Scale
(1992 Version), (I – XII)
Isoseismals
Isoseismals are the curved lines joining the localities of same intensity.

83. log E = 12 + 1.8 ML
log E = 5.8 + 2.4 mb
log E = 11.4 + 1.5 Ms
1.0 10.0 times about 32 times
0.5 3.2 times about 5.5 times
0.3 2.0 times about 3 times
0.1 1.3 times about 1.4 times
Magnitude versus ground motion and energy
local magnitude
body wave magnitude
surface wave magnitude

88. • Shaking = accelerated ground motion
• Liquefaction = failure of waterlogged sandy substrates
• Landslides, dam failures, etc.
• Tsunamis = seismic sea waves
• Fire, etc.

109. SEISMIC SAFETY FACTORS

110. The earthquake induced inertia forces
are are represented bt the design
building codes as the seismic design
base shear.

112. SEISMOLOGY

117. THANK YOU