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What do jerky starts and stops in plate motions directly cause?

Major earthquakes


What are some indirect benefits of earthquakes?

-give us uplift in landscape, which allows rivers to have principle sources of water

-if not, land would erode to tide level and diversity in flora and fauna wouldn't exist


Where do earthquakes occur?

At plate tectonics (ex: San Andreas)


When do rocks break?

When stress is greater than rock strength.


What does energy released during an earthquake cause?

Causes faults to form ("plane of slip") and can generate frictional heat


What do s the difference in time between the arrival of the P and S waves tell us?

Precise location of earthquake (epicenter)


What did Charles Richter call the total energy released during an earthquake?

Magnitude of the quake


How much more energy is released with each increase in one magnitude?

Logarithmically, by factor of just over 30 times more energy released.


What happens when the period of an earthquake save matches that of a building?

The seismic energy is added to the oscillation of the building, resulting in an increase in the swaying of the building (as long as it is at the natural period).


What does a creep meter measure?

Movement in a specific localized area.
Measures when faults slip (recording amount of motion).
Highly sensitive and covers about 10 meter zone


What changes in water wells in the days preceding an earthquake?

Sudden drop in water levels in wells.


What is the energy source for earthquakes?



What is an earthquake?

A sudden release of energy in earth's crust or upper mantle, usually caused by movement along fault plans or by volcanic activity and resulting in generation of seismic waves


What are seismic waves?

The waves of energy caused by sudden breaking of rock within the earth or an explosion. They are the energy that travels through the earth and is recorded on seismographs.


What is the earthquake rupture patch?

Starts at he focus (depth)

Distance between focus and epicenter?


How are earthquakes measured (and compared?

-magnitude: The amount of energy released (magnitude is stable, regardless of distance)

-intensity: the effects of ground motion on people and structures (intensity varies depending on closeness to epicenter)


Explain the modified Mercalli scale?


-Descriptive scale of earthquake effect intensity (at different locations)

-distinguished by use of Roman numerals

-how to find info? Descriptive; based off experiences

*check 2/9/17 packet


Explain the Richter magnitude scale.

A base-10 logarithmic scale, which defines magnitude as the logarithm of the ratio of the amplitude of the seismic waves to an arbitrary, minor amplitude

-based on movement of instrument
-deficient at high energies(big earthquakes)
-Now use the Moment Magnitude Scale


Explain the moment magnitude scale. Equation?

MMS or MvW

Used by seismologists to measure earthquakes in terms of energy released.
*think of volcanoes-looking image*

rock rigidity x fault area that slipped x slip distance


What is a foreshock? What is an aftershock?

Foreshock:Smaller earthquakes that occur shortly (usually up to days or weeks or months) before a major earthquake.

Aftershock: occur after major earthquake

(Foreshock)The fault movement that produces the large shock typically leaves areas of relieved stress or strain build up along the fault. (Aftershock) subsequent failures in these areas produce aftershocks

-many will lie along fault plane, but may occur on other nearby faults


Why is an aftershock especially dangerous?

Because the buildings and roads are already weakened.

Landslides and mudslides are also effects.

-ground failure


How is friction important in faulting?

Faulting = fault rupture

Friction along the fault slows, prevents, o from arrests motion

Even motion of lithospheric plates is slowed by friction along their boundary

Rough areas may break off and fault can move


What is stress?

Stress = force/unit area

Pressure or tension exerted on plates

When stress on a fault becomes greater than strength of rock, fault ruptures and moves


Define fault.

A fracture or system of fractures along which movement has occurred parallel to the fracture surface in association with a loss of cohesion

-i.e. Earth's crust on one side of fracture moved relative to rocks on opposite side


What is a footwall?

Block of rock that lies on the underside of an inclined fault

You would walk on the footwall.

Footwall motions downwards ↙️↘️


What is a hanging wall?

Block of rock that lies above an inclined fault

You would hang your lamp from the hanging wall

Motions upward ↗️↖️


What are the different types of faults?

Dip Slip - Normal & Reverse (or thrust) fault

Strike Slip - Left Lateral or Right Lateral Fault

Oblique Slip Fault


Dip Slips

Move Up & Down

Normal Faults: hanging wall block moves down relative to footwall

-stretched and thins crust
-common along divergent margins and extending intraplate areas

Reverse (or Thrust) Faults: hanging wall block moves up relative to footwall

-shortens and thickens crust
-common along convergent margins and relatively nearby areas


Strike Slips

Move horizontally

Left Lateral Strike-Slip Fault: rocks across the fault from you move to the left

Right Lateral Strike-Slip Fault: rocks across from you move to the right

-blocks of rock move past each other

-conservative (no to little extension or shortening)

-many are transform faults along plate boundaries like San Andreas fault


Oblique Slip

Move horizontally AND up and down

Oblique Slip Fault: hanging wall moved in both strike slip and dip slip directions relative to footwall