Transcript EARTHQUAKE

EARTHQUAKE
REPORTERS:
Princess Danielle Matas
Melvin Mantilla
Charles Nomus
What is an earthquake?
An earthquake (also known as a quake, tremor or temblor) is the result of a
sudden release of energy in the Earth's crust that creates seismic waves.

 Earthquakes occur with the passage of
large seismic waves.
 Earthquakes are the effects of a large
seismic wave.
 Seismic waves result from slip and
rupture (breakage) of rocks along faults.
Where Do Earthquakes
Happen?
1.Along Plate Edges
2.Along Faults
Faults: Three types

Normal fault: Hanging wall moves down relative to the
foot wall. Normal faults develop where the crust is under
tension (is being pulled apart).

Reverse fault: Hanging wall moves up relative to the
foot wall. A thrust fault is a reverse fault where
movement occurs at a low angle. Reverse and thrust
faults develop where the crust is undergoing
compression.

Strike-slip (Transform faults): Block of crust on either
side of the fault slip horizontally past one another. Right
lateral: Right side of fault move towards you. Left lateral:
Left side of fault moves towards you.
Earth quakes occur when a fault ruptures and stored energy is released as
seismic waves.
Quakes focus -> the point on the fault that first ruptures.
Quakes epicenter -> the point on the Earth's surface directly above the focus.
Most earthquakes occur in the upper 10 Km of the crust. It is here that rocks
are cold enough to break in a brittle fashion and behave elasticly.
Elastic rebound theory:
•
Rocks on either side of a fault bend as stress builds up. This stores
energy in the rock.
•
At some point, the rock ruptures (breaks) and the rocks on the two
sides of the fault snap back to their original shale (elastic behavior).
•
Energy is released as seismic waves.
Seismology
 The study of earthquake waves,
seismology, dates back almost 2000 years
to the Chinese
 Seismographs, instruments that record
seismic waves
• Records the movement of Earth on a
rotating drum, magnetic tape, or digital
computer in relation to a stationary mass
Types of seismic waves:
Body waves; Seismic waves that pass
through the Earth.
Primary waves: Compressional waves. Velocity5-8 km/sec
- known as push-pull
-fastest kind of seismic waves. It can push and pull the materials
which can travel through solids and fluids when it moves through it.
Secondary waves: Shear waves, Velocity 3.5-4.5 km/sec.
- called as shear or secondary waves.
-The wave moving through up and down or side-to-side
-involves the rotation and shearing of the material. The
movement of the wave can be transverse with moving particles and
perpendicular to the ray.
Surface waves: Seismic waves traveling
parallel to the Earth's surface.
Love waves: Shear waves parallel to Earth's
surface.
Rayleigh waves: Rolling waves
perpendicular to the Earth's surface.
Locating Earthquakes
Earthquakes primarily cause damage through:
1.Shaking
-Shaking: Natural and man made factors can affect the amount of
damage caused by ground shaking;
Natural Factors: The effects of an earthquake can be amplified
depending on the material upon which structures are built. This is
known as ground amplification. Different materials will also transmit
and enhance seismic waves of different frequencies.
Material
Degree of Amplification
Seismic wave frequency
Rock
Little amplification
Higher frequencies
Sand and gravel
Moderate amplification
Intermediate frequencies
Mud
Moderate amplification
Low frequencies
Low frequency seismic waves will cause most damage to large, tall structures
High frequency seismic waves will cause most damage to smaller structures
2.Liquefaction
-A process where water saturated sand or silt loose their strength and
ability to support structures when affected by shaking. A normally stable
sediment or soil will behave like a liquid and structures will sink.
Liquefaction allowed this sewer to float upward
• Seiches
 The rhythmic sloshing of water in lakes,
reservoirs, and enclosed basins
 Waves can weaken reservoir walls and cause
destruction
Tsunamis, or seismic sea waves
• Destructive waves that are often
inappropriately called “tidal waves”
• Result from vertical displacement along a
fault located on the ocean floor or a large
undersea landslide triggered by an
earthquake
Can earthquakes be
predicted?
Short-range predictions
• Goal is to provide a warning of the location and
magnitude of a large earthquake within a narrow
time frame.
• Research has concentrated on monitoring
possible precursors – phenomena that precede a
forthcoming earthquake such as measuring uplift,
subsidence, and strain in the rocks.
Long-range forecasts
• Based on the premise that earthquakes
are repetitive or cyclical
• Give the probability of a certain magnitude earthquake
occurring on a time scale of 30 to 100 years, or more
• Give the probability of a certain magnitude earthquake
occurring on a time scale of 30 to 100 years, or more
• Using historical records or paleoseismology
• Are important because they provide information used to
 develop the Uniform Building Code
 Assist in land-use planning
Earthquakes are often accompanied by precursor
events that may be able to provide short term warnings.
Fore shocks
Release of radon gas.
Ground deformation
Drop in water table.
..END..
God bless!!
^__^