Test 3 Flashcards
Explain what causes an earthquake.
- Fault motion causes an earthquake
- Time 1 - Friction causes most faults to “stick”
- Time 2 - Build up of stress causes the rock to deform
- Time 3 - After some time (can vary), stress overcomes friction and causes fault movement (slip). i.e. earthquake
Where do earthquakes occur?
Earthquakes occur on faults, which are commonplace along plate boundaries.
Are there lots of earthquakes worldwide, or only a few throughout the year?
Yes there are lots of earthquakes world wide, around about 55 per day.
Define Strike
Horizontal line on an inclined surface
Define Dip
Inclination or slope of surface (measured from horizontal)
Define hanging wall
Above fault
Define foot wall
Below fault
What is a strike slip?
One block slides horizontally past another (and therefore parallel to the strike line), so there is no relative vertical motion.
What is a dip slip?
Sliding occurs up or down the slope (dip) of the fault
Explain the fault movement for a normal fault
Hanging wall moves down (tension)
Explain the fault movement for a Reverse fault
Hanging wall moves up (compression)
What type of stress leads to a reverse fault?
Compression
What type of stress leads to a normal fault?
Tension
What type of stress leads to a Strike-Slip fault?
Shear (side by side motion)
What controls the magnitude of an earthquake?
- The amount of slip along a fault
- the length of the fault that slips
Define epicenter
The point on the surface of the Earth directly above the focus of an earthquake.
Explain multiple reasons why earthquake prediction is so difficult.
- No reliable precursor
- No reliable way to measure stress or know how much stress a fault can handle
- For most faults, there is no clearly definable periodic earthquake behavior.
What are the 3 types of seismic waves and their relative velocities?
- P waves - Travel fastest arrive 1st
- S waves - arrive 2nd
- Surface waves - are the slowest, arrive last
What are the two types of surface waves?
L-waves and R-waves
What waves travel along Earth’s surface?
All surface waves
What waves travel through Earth’s surface?
P and S-waves
How seismograms vary as a stations distance from an earthquake increase.
If it is further away from an earthquake P-waves would arriver later and the gap between the arrival of P and S waves would be larger.
What type of seismic wave typically causes the most damage and why?
Surface waves because these waves physically move the ground/surface.
Describe the process of determining earthquake location using seismographs.
- Need at least 3 seismometer recordings of the event
- Distance from each station determined by time gap between P and S waves.
- Triangulation marks the epicenter.
Define magnitude and what scale is used to measure it.
A standard measure of the shaking and/or energy released (objective). Logarithmic scale
Define Intensity and what scale is used to measure it.
A measure of the effects on people and buildings (subjective) Measured by I-XII scale.
True or false: Earthquake magnitude and intensity are always correlated?
False
What plate boundaries can shallow earthquakes be found on?
-Convergent, Divergent, and Transform boundaries
What plate boundaries can deep earthquakes be found on?
Convergent boundaries
What is the common type of fault at a convergent boundary? What type of stress produces them?
Reverse faults which is caused by compression
What is the common type of fault at a divergent boundary? What type of stress produces them?
-Normal faults cased by tension
What is the common type of fault at a Transform boundary? What type of stress produces them?
Strike-slip faults caused by shear.
Where are shallow earthquakes like to occur
Divergent and transform boundaries
Where are deep earthquakes likely to occur?
Convergent Boundary
List common earthquake hazards
- Ground Shaking
- Aftershocks
- Landslides
- Elevation Changes
- Liquefaction
- Tsunami
Explain how liquefaction occurs.
Friction causes grain to settle together and water fills the pores between the sediment and shaking makes it weaker.
What kind of fault most commonly produces tsunamis?
Revers Fault
What is the principle of uniformitarianism?
What’s happening now happened in the past.