Done by: Sun Yudong (1o2 27) Teo Jun Wei (1o2 30) Earthquakes Done 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 intensities They can be measured and presented as data using the Richter scale.

Shaking intensity of an earthquake Measured 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 earthquake Earthquakes 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 types Three main types of fault that may cause an earthquake: Normal reverse (thrust) strike-slip as shown on the right

Earthquake fault types Normal and reverse faulting are examples of dip-slip, the displacement along the fault is in the direction of dip movement 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 earthquakes Japan China Chile Australia continent Countries around the Ring of fire Alaska Philippines Indonesia Haiti

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 earthquakes Shaking and ground rupture Landslides and avalanches Soil liquefaction Tsunami

The possible effects of earthquakes An earthquake may cause injury and loss of life road and bridge damage general property damage collapse or destabilization of buildings potentially leading to future collapse

The possible effects of earthquakes The aftermath may bring Disease lack of basic necessities higher insurance premiums Earthquakes can also cause volcanic eruptions, bringing further problems.

Shaking and ground rupture Ground 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 rupture Shaking 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 magnitude the distance from the epicenter and the local geological and geomorphological conditions, which may amplify or reduce wave propagation. The ground-shaking is measured by ground acceleration.

Shaking and ground rupture Specific 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 avalanches Earthquakes severe storms volcanic activity coastal wave attack wildfires Landslides and avalanches

Landslides and avalanches can produce slope instability leading to landslides or avalanches Landslide is a major geological hazard Landslide danger may persist while emergency personnel are attempting rescue. Landslides and avalanches

Soil liquefaction Soil 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.

Tsunamis Tsunamis are long-wavelength, long-period sea waves produced by the sudden or abrupt movement of large volumes of water. In the open ocean the distance between wave crests can surpass 100 kilometers (62 miles) the wave periods can vary from five minutes to one hour.

Tsunamis Such 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.

Tsunamis Ordinarily, 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.

References Special thanks to: http://eqseis.geosc.psu.edu/~cammon/HTML/Classes/IntroQuakes/Notes/intensity.html http://en.wikipedia.org/wiki/Earthquake http://earthquake.usgs.gov/