Geological Hazards Exam 2 Flashcards
Earthquakes
Physical response to the release of built up stresses in the lithosphere.
Strength of the rock is exceeded –> rapid release of elastically stored energy (seismic waves and heat)
Release of plate tension
Too much stress is released and an earthquake happens because the plates slip.
How is an earthquake located?
Seismologists use the difference in arrival time between the P and S waves to calculate the distance between the source and the seismograph. Data is used from multiple seismographs. Circles are drawn around each seismograph. The earthquake originated in the intersection between the circles.
Seismograph
Instrument that measures motions of the ground, including those of seismic waves generated by earthquakes, volcanic eruptions, and other seismic sources. Records of seismic waves allow seismologists to map the interior of the Earth, and locate and measure the size of these different sources.
Mercalli Scale
Measures shaking intensity
Uses California buildings as standards
Maps intensity by destruction of buildings
Richter Scale
Based on the amplitude of the largest seismic wave
Only useful for shallow earthquakes over short distances
Log based scale
Now walled Local Magnitude (M1)
Moment Magnitude
Measures the strain energy released
Uses total energy released
More difficult to calculate (can still be one with a seismograph)
Variables: strength of the rock, area of surface, average amount of slip.
Moment = XAD
X = 32 GPA (crust) or 75 Gpa (mantle)
A = Area (LW)
D = Average displacement along rupture surface
How is one earthquake different from another? What can very?
Different types of faults (strike-slip), zones (subduction zone), boundaries (convergent boundaries), and locations can create different types of earthquakes.
Dip-slip faults
3 categories: Normal Faults, Reverse Faults, Thrust Faults.
2 broad categories of faults
Dip-slip faults
Strike-slip faults
Extension (earthquakes)
Dip-slip faults
Same amount of rock takes up more space
Basin or range
Form along divergent boundaries
Compression (earthquakes)
Dip-slip faults
Rock smashed together so it takes up less space
Himalayan Mountains
Normal Fault
Dip-slip fault
Can result in extension or compression
Form along divergent and convergent boundaries
Reverse Fault
Dip-slip fault
Rocks squishing together
Angle up to 60 degrees
Form along convergent boundaries
Thrust Fault
Dip-slip fault
Between 10 and 30 degree angle
Created at convergent boundaries and subduction zones
Strike-slip Fault
Usually large earthquakes
Types: right lateral, left lateral
Form along transform boundaries
Divergent Boundaries
Plates moving away from each other or spreading
Shallow earthquakes usually happen at these boundaries.
Convergent Boundaries
Plates moving towards each other
Transform Boundaries
Plates sliding past each other
Main hazards associated with earthquakes (5)
Shaking Liquefaction Landslides Tsunami Damage to infrastructure
Hypocenter / focus
Means “below the center”
The position where the strain energy stored in the rock is first released, marking the point where the fault begins to rupture.
Occurs at the focal depth below the epicenter.
Epicenter
The point on the Earth’s surface that is directly above the hypocenter or focus and where the fault begins to rupture.
The point where an earthquake originates.
P-Wave
Pressure wave Primary wave Compression and Contraction Moves quickly Travels
S-Wave
Shear wave
Verticle motion
Moves slower
Travels –>
L-Wave
Love wave
Moves from side to side
Moves slower
Travels –>