EARTHQUAKE
Seismic Waves
Seismic waves are waves of energy that travel
through the Earth's layers, and are a result of
an earthquake, explosion, or a volcano that imparts
low-frequency acoustic energy. An instrument called seismogram can detect these seismic waves.
Earthquake
is the sudden shaking of the Earth's surface caused by the rock masses that
suddenly shift in position.
Where Earthquakes Occur?
Plate Edges
Faults are cracks in the Earth where sections of a plate or two plates are moving in different directions.
Types Of Faults
Normal Fault Foot wall moves up, hanging wall down
Reverse Fault: Opposite of normal fault
Strike-Slip Fault: Most common, sides shift against each other.
Most Earthquakes occur along the edge of the oceanic and continental plates. The plates are moved around by the
motion of a deeper part of the Earth, the mantle, that lies underneath the crust.
Focus and Epicenter
Seismology
-the study of earthquakes and the waves they create
-travel out from the epicenter onto the surface of the Earth.
Surface Waves
-comparatively weaker than the body waves
-last to be recorded by a seismogram--Slowest
Body Waves
-waves that travel through the interior of the Earth
-they provide seismologist with information on the nature and composition of the Earth's interior
Primary Waves
are compressional waves that are longitudinal in nature. These waves can travel through any type of material, including
fluids, and can travel at nearly twice the speed of S waves.
Secondary Waves are shear waves that are transverse in nature. These waves arrive at seismograph stations after the
faster moving P waves during an earthquake and displace the ground perpendicular to the
direction of propagation.
Secondary Waves
> Travel only in solids
> Second to be recorded by a seismograph
> Cause the particles of a material to move up and down or left and right but always perpendicular to the direction the
wave travels
Primary Waves
> Travel in all types of media
> First to be recorded by a seismograph
> Cause the particles of a material to move forward and back like an accordion as it passes through
Comparison of the Primary and Secondary Seismic Waves
Focus and Epicenter
Focus is where slipping or releasing of energy along the fault occurs causing the earthquake.
Epicenter is where the earthquake is felt the strongest. The epicenter can be located above the focus but that can vary
depending on the density of the surrounding and nearby rock strata.
Damages Produced
by Earthquakes
Magnitude and Intensity
Magnitude measures the energy released at the source of the earthquake. Magnitude is determined from
measurements on seismographs.
Intensity measures the strength of shaking produced by the earthquake at a certain location. Intensity is determined
from effects on people, human structures, and the natural environment
Richter Scale -named after Dr. Charles F. Richter
-best-known logarithmic scale used in measuring magnitude of earthquakes.
Modified Mercalli Scale -expresses the intensity of an earthquake as felt in a given location or region in values ranging
from I to XII, with I as the most feeble and XII as the strongest and can cause total damage to property
PHYSICAL DAMAGES
Landslides
Tsunami
Mudslides
Fires
Buildings Collapse
STRUCTURAL DAMAGES
Roadway Collapse
Emotional Damage
EMOTIONAL DAMAGES
**Death