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Handouts on basic concepts on earthquakes
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In July 1990
In October 2013
How ready are we when
the next strong earthquake
jolts our land?
EARTHQUAKES
Shaking Grounds
Essential Questions
▪ What is an earthquake?
▪ What is a fault?
▪ What are the different types of faults?
▪ How are earthquakes formed?
Earthquake
▪ A natural geological phenomena caused by sudden and rapid movement of a large volume of rock
▪ A trembling or shaking of the earth’s crust
▪ The shaking is due to the release of energy from cracks between rocks called faults
Fault
▪ A fracture in a rock formation along which there has been movement of the blocks of rock on either side of the plane of fracture
Anatomy of a Fault
San Andreas Fault (most
famous in the world)
West Valley Fault
(The Big One)
Digdig Fault, Imugan,
Nueva Vizcaya
Kinds of Fault
Normal Fault
Reverse Fault
Strike-Slip Fault
How earthquakes
are formed?
Harry Fielding Reid
▪ An American geophysicist notable for his studies of the famous 1906 San Francisco Earthquake
▪ His most important contribution in the field of seismology was the explanation for the mechanism of an earthquake.
Elastic Rebound Theory
Elastic Rebound Theory
Elastic Rebound Theory
▪ Rocks undergo stress due to the forces from the Earth’s interior.
▪ Stress is built among rocks and stores it as elastic potential energy.
▪ However, there is a limit to which rocks can store this stress.
▪ Once the stress limit is reached, energy is released in the form of vibrations resulting to an earthquake.
Anatomy of an Earthquake
Seismology
The Science of Earthquakes
Seismology
▪ Dates back to attempts made by Chinese almost 2000 years ago to determine the direction from which these waves originated
Seismology
Seismograms
▪ Records obtained from seismographs
▪ Provide useful information about the nature of seismic waves
Seismic Waves
▪ A form of elastic energy that causes vibrations in the material that transmits them
▪ Mechanical in nature (needs medium for propagation)
Classes of Seismic Waves
Seismic Waves
Body Waves Surface Waves
P-wave S-wave
Body Waves
▪ Seismic waves that travel through the Earth’s interior
▪ Classified as p and s waves
P-waves
Characteristics of p-
waves
▪ Longitudinal
▪ Fastest in terms of speed
▪ Can travel through solid, liquid and gas
▪ Can temporarily change the volume of intervening material
S-waves
Characteristics of s-
waves
▪ Transverse
▪ Can change the shape of the material that transmits them
▪ Travel only in solids
Surface waves or L-waves
Characteristics of l-waves
▪ Motion is restricted to near the Earth’s surface
▪ Combination of longitudinal and transverse motion
Comparison among the
three seismic waves
▪ P-waves travel 1.7 times faster than s-waves.
▪ L-waves are roughly 10 percent slower than s-waves.
▪ L-waves have the longest amplitude, hence carries the most destructive energy.
Let’s wrap it up…
▪ What is an earthquake?
▪ What is a fault?
▪ What are the different types of faults?
▪ How are earthquakes formed?
