EarthquakesDone by:

Sun Yudong (1o2 27)Teo Jun Wei (1o2 30)

What is an earthquake?a shaking of the ground caused by the

sudden breaking and movement of large sections (tectonic plates) of the earth's rocky outermost crust

Earthquakes shake at different intensitiesThey can be measured and presented as data

using the Richter scale.

Shaking intensity of an earthquakeMeasured on Shaking intensity scales

developed to standardize the measurements and ease comparison of different earthquakes.

Shaking intensity varied from barely perceptible to completely destructive.

The lower numbers represent imperceptible shaking levels, XII represents total destruction.

Below is the table to measure the shaking intensity:

Devices to measure the earthquakeEarthquakes are measured using

seismometers. The moment magnitude is the most common scale on which earthquakes larger than approximately 5 are reported for the entire globe.

These earthquakes are measured as some number on the Ricther scale.

Earthquake fault typesThree main types of fault that may cause an

earthquake: Normalreverse (thrust)strike-slip as shown on the right

Earthquake fault typesNormal and reverse faulting are examples of

dip-slip, the displacement along the fault is in the direction

of dipmovement on them involves a vertical component.

Normal faults occur mainly in areas where the crust is being extended such as a divergent boundary.

Strike-slip faults are steep structures where the two sides of the fault slip horizontally past each other.

Why do earthquakes happen away from plate boundaries?Plate boundaries an obvious place for

earthquakes to occur. However, the stresses at plate boundaries can

manifest themselves some distance away from the surface evidence of the boundary.

Equally, boundaries have fault lines which radiate from them and are common causes of earthquakes.

Far from plate

boundaries complex strata

deep fault zones

earthquakes in

apparently stable

regions

Countries that commonly experience earthquakesJapanChinaChileAustralia continent

Countries around the Ring of fire

AlaskaPhilippinesIndonesiaHaiti

What is an aftershock?Is an earthquake that occurs after a previous

earthquake, the mainshock. Is in the same region of the main shock but

always of a smaller magnitude. If an aftershock is larger than the main

shock, the aftershock is redesignated as the main shock and the original main shock is redesignated as a foreshock.

Aftershocks are formed as the crust around the displaced fault plane adjusts to the effects of the main shock

The possible effects of earthquakesShaking and ground ruptureLandslides and avalanchesSoil liquefactionTsunami

The possible effects of earthquakesAn earthquake may cause

injury and loss of liferoad and bridge damagegeneral property damagecollapse or destabilization of buildings

potentially leading to future collapse

The possible effects of earthquakesThe aftermath may bring

Diseaselack of basic necessitieshigher insurance premiums

Earthquakes can also cause volcanic eruptions, bringing further problems.

Shaking and ground ruptureGround rupture is a visible breaking and

displacement of the Earth's surface along the trace of the fault

may be of the order of several metres in the case of major earthquakes.

Ground rupture is a major risk for large engineering structures such as dams, bridges and nuclear power stations

requires careful mapping of existing faults to identify any likely to break the ground surface within the life of the structure.

Shaking and ground ruptureShaking and ground rupture are the main effects

created by earthquakes, principally resulting in more or less severe damage to

buildings and other rigid structures. The severity of the local effects depends on the

complex combination of the earthquake’s magnitudethe distance from the epicenterand the local geological and geomorphological

conditions,

which may amplify or reduce wave propagation. The ground-shaking is measured by ground

acceleration.

Shaking and ground ruptureSpecific local geological, geomorphological,

and geostructural features can induce high levels of shaking on the ground surface even from low-intensity earthquakes.

This effect is called site or local amplification. It is principally due to the transfer of the

seismic motion from hard deep soils to soft superficial soils and

to effects of seismic energy focalization owing to typical geometrical setting of the deposits.

Landslides and avalanchesEarthquake

s severe storms

volcanic activity

coastal wave attackwildfire

s

Landslides and avalanches

Landslides and avalanches

Landslides and avalanches

can produce slope instability leading to landslides or avalanchesLandslide is a major geological hazardLandslide danger may persist while

emergency personnel are attempting rescue.

Soil liquefactionSoil liquefaction occurs when, because of the

shaking, water-saturated granular material (such as sand) temporarily loses its strength and transforms from a solid to a liquefied solid.

Soil liquefaction may cause rigid structures, like buildings and bridges, to tilt or sink into the liquefied deposits.

This can be a devastating effect of earthquakes. For example, in the 1964 Alaska earthquake, soil

liquefaction caused many buildings to sink into the ground, eventually collapsing upon themselves.

TsunamisTsunamis are long-wavelength, long-period

sea waves produced by the sudden or abrupt movement of large volumes of water.

In the open oceanthe distance between wave crests can surpass

100 kilometers (62 miles)the wave periods can vary from five minutes to

one hour.

TsunamisSuch tsunamis travel 600-800 kilometers per

hour (373–497 miles per hour), depending on water depth.

Large waves produced by an earthquake or a submarine landslide can overrun nearby coastal areas in a matter of minutes.

Tsunamis can also travel thousands of kilometers across open ocean and wreak destruction on far shores hours after the earthquake that generated them.

TsunamisOrdinarily, subduction earthquakes under

magnitude 7.5 on the Richter scale do not cause tsunamis, although some instances of this have been recorded.

Most destructive tsunamis are caused by earthquakes of magnitude 7.5 or more.

ReferencesSpecial thanks to:http://eqseis.geosc.psu.edu/~cammon/HTML/

Classes/IntroQuakes/Notes/intensity.htmlhttp://en.wikipedia.org/wiki/Earthquakehttp://earthquake.usgs.gov/