Seismology
the study of earthquakes.
Fault
-a break in the Earth's crust along which blocks of the crust slide relative to one another.
-earthquakes occur along faults due to this sliding.
Deformation
The change in the shape of rock in response to stress.
Plastic Deformation
-rock of the crust bend and change shape without breaking.
-does not lead to earthquakes.
Elastic Deformation
-occurs when rock is stretched beyond its breaking point.
-leads to earthquakes.
Elastic Rebond
-the sudden return of elastically deformed rock to its original shape.
-occurs when more stress is applied to rock than the rock can withstand.
-during elastic rebond, rock releases energy that causes an earthquake.
Earthquake
-differ in strength and in depth at which they begin.
-depends on type of plate boundary.
Seismic Waves
Energy released by earthquakes that travel in waves.
Body Waves
Seismic waves that travel through the earth's interior - P waves and S waves.
Surface Waves
Seismic waves that travel along the earth's surface.
P-Waves
Primary waves;"pressure waves". Are the fastest seismic waves. Travel through solids liquids and gases. Similar to the squeezing of a tennis ball. As the ball is squeezed, pressure inside the ball increases. When the ball is released, pressure within in d
S-Waves
Secondary waves; "shear waves". Second fastest seismic waves. Shear (stretches sideways) rock back and forth. S waves are created when rock is deformed from side to side and springs back to its original form. Do not travel through the liquid parts of the
Surface waves
Move the ground up and down in circles as the waves travel along the surface. Travel slower than body waves (P and S waves) but are much more destructive. Can literally shake the ground from under a building.
Seismograph
A device used to detect seismic waves.
Seismograms
A tracing of earthquake motion created by a seismograph. Used to calculate when an earthquake started by comparing the arrival times of P and S waves. Used to determine epicenter of earthquake.
Epicenter
The point on the earth's surface directly above the earthquake's starting point.
Focus
The point inside the earth where the earthquake begins.
S-P-Time method
Seismologists collect and compare seismograms from 3 separate seismographs. Seismograms are placed on a time vs. distance graph. P waves are placed to line up with a P wave curve (known data). S waves are placed to line up with a P wave curve (known data)
Charles Richter
American Seismologist who in the 1930s developed a scale used to measure earthquake intensity. Richter Scale is listed between 1 and 10. Each increase of 1 unit represents an increase of 31.7 times the energy. Magnitude 3 has the equivalent of 31.7 times
Earthquake hazard
Measures how prone an area is to experience earthquakes in the future. Level is determined by past and present activity.
Gap hypothesis
States that sections of active faults that have had relatively few earthquakes are likely to be sites of strong earthquakes in the future. Helps seismologists predict approximate time, strength and location of earthquakes.
Seismic gap
The areas along a fault where relatively few earthquakes have occurred.
Earthquake Resistant Buildings
Technology is used to design and construct buildings and bridges capable of withstanding earthquakes.
Mass damper
A weight placed in the roof of the building. Computer sensor "senses" building movement due to earthquakes. The mass damper shifts position to counteract building movement.
Steel cross-braces
Placed between floors to counteract pressures that push and pull the side of a building during earthquakes.
Active tendon systems
Found in the basement and works similar to a mass damper. Computer sensors detect building movement and shift the active tendon to compensate.
Flexible pipes
Help prevent water and gas lines from breaking. Flexible joints better withstand twisting and bending.
Base isolators
Found in the foundation and act as shock absorbers. Made of layers of rubber and steel wrapped around a lead core. Absorb seismic waves, preventing them from traveling up the building.
Moho
The boundary between the earth's crust and mantle speed of seismic waves increase sharply at the Moho. Discovered by Andrija Mohorovicic. Also called the Mohorovicic discontinuity. Between 25 and 65 km deep on continents and between 5 and 8 km deep in oce
Solid inner core
Discovered in 1936. Prior to this seismologists believed the entire earth's core was liquid.
Shadow zone
The area on the earth's surface where no direct seismic waves from a particular earthquake can be detected. Suggests that the earth has a liquid core.
Moon
Seismograph placed there in 1969. Detects "moon quakes" that are shallow, but give off long lasting seismic waves. Detects meteoroid impacts.
Mars
Viking 1 brought a seismogram to Mars in 1976. Controlled remotely from earth. Inefficient because the seismograph is located on the surface of Viking 1 and is affected by the wind. Only detected 1 possible "Marsquake".
The sun
The information satellite SOHO seismic activity following solar flares. "Sunquakes" are much more powerful than earthquakes.