EARTHQUAKEEARTHQUAKE

REPORTERS:REPORTERS:Princess Danielle MatasPrincess Danielle Matas

Melvin MantillaMelvin MantillaCharles NomusCharles Nomus

What is an earthquake?What is an earthquake?

Earthquakes occur with the passage of Earthquakes occur with the passage of large seismic waves.large seismic waves.

Earthquakes are the effects of a large Earthquakes are the effects of a large seismic wave.seismic wave.

Seismic wavesSeismic waves result from slip and  result from slip and rupture (breakage) of rocks along faults.rupture (breakage) of rocks along faults.

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.

Where Do Earthquakes Where Do Earthquakes Happen?Happen?

1.Along Plate Edges

2.Along Faults 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 Earth quakes occur when a fault ruptures and stored energy is released as seismic waves. seismic waves.

Quakes Quakes focusfocus -> the point on the fault that first ruptures. -> the point on the fault that first ruptures.

Quakes Quakes epicenterepicenter -> the point on the Earth's surface directly above the focus. -> 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 wavesSurface waves:: Seismic waves traveling  Seismic waves traveling parallel to the Earth's surface. parallel to the Earth's surface. 

Love wavesLove waves: Shear waves parallel to Earth's : Shear waves parallel to Earth's surface.surface.

Rayleigh wavesRayleigh waves:: Rolling waves  Rolling waves perpendicular to the Earth's surface.perpendicular to the Earth's surface.

  

Earthquakes primarily cause damage throughEarthquakes primarily cause damage through::

1.Shaking1.Shaking

--Shaking: Shaking: Natural and man made factors can affect the amount Natural and man made factors can affect the amount of damage caused by ground shaking;of damage caused by ground shaking;

  Natural FactorsNatural Factors: The effects of an earthquake can be amplified : The effects of an earthquake can be amplified depending on the material upon which structures are built. This is depending on the material upon which structures are built. This is known as known as ground ground amplificationamplification. Different materials will also transmit . Different materials will also transmit and enhance seismic waves of different frequencies.and enhance seismic waves of different frequencies.

Locating Earthquakes

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 structuresHigh 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

• • SeichesSeiches The rhythmic sloshing of water in lakes,The rhythmic sloshing of water in lakes,

reservoirs, and enclosed basinsreservoirs, and enclosed basins Waves can weaken reservoir walls and causeWaves can weaken reservoir walls and cause

destructiondestruction

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 predictionsShort-range predictions

• Goal is to provide a warning of the location and Goal is to provide a warning of the location and magnitude of a large earthquake within a narrow magnitude of a large earthquake within a narrow time frame.time frame.

• Research has concentrated on monitoring Research has concentrated on monitoring possible precursors – phenomena that precede a possible precursors – phenomena that precede a forthcoming earthquake such as measuring uplift, forthcoming earthquake such as measuring uplift, subsidence, and strain in the rocks.subsidence, and strain in the rocks.

Long-range forecasts 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 Earthquakes are often accompanied by precursor events that may be able to provide short term warnings.events that may be able to provide short term warnings.

  

Fore shocksRelease of radon gas.Ground deformationDrop in water table.

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God bless!!God bless!!^__^^__^