Science: Earthquakes

Terms in this set (2)

Earthquake Study Guide:

*Stress: Movement of the Earth's plates creates great forces that squeeze and pull the rock in the crust. A force that acts on an area of rock to change its shape or volume.

*Tension: Type of stress called tension pulls on the crust, stretching rock so that it becomes thinner in the middle (Landform result-Valley)

*Compression: Type of stress called compression squeezes rock until it folds or breaks (Landform result- Mountains)

*Shearing: Stress that pushes a mass of rock in two opposite directions
(Landform result- Faults & Earthquakes)

*Faults: A break or crack in Earth's lithosphere, along which the rock moves. Breaks in the Earth's crust where rocks have slipped past each other.

*Folding: bends in rock that form when compression shortens and thickens part of the Earth's crust.

*Anticline: A fold in rock that bends upward into an arch(picture#178)

*Syncline: A fold in rock that bends downward to form a valley (picture #178)

*Normal Fault: Tension in Earth's crust pulls rock apart. The fault is at an angle, so one block of rock lies above the other block of rock. (picture #176)

*Hanging Wall: The block that lies above is called the hanging wall.

*Footwall: The rock that lies below is called the footwall.

*Reverse Fault: In places where the rock of the crust is pushed together, compression causes reverse faults to form. It has the same structure as the normal fault, but the blocks of rocks move in the opposite direction (picture # 177)

*Strike-Slip Fault: In places where the plates move past each other, shearing creates strike slip faults. The rocks on either side of the fault slip past each other sideways, with little up or down motion.

*Plateau: Large area of flat land elevated high above sea level. Some form when forces in the Earth's crust push up a large, flat block of rock. It is wider then it is tall.

*Earthquake: Is the shaking that results from the sudden movement of rock along a fault. Most earthquakes begin in the lithosphere.

*Focus: Is the area beneath Earth's surface where rock that is under stress breaks, triggering an earthquake.

*Epicenter: The point on the surface directly above the focus.

*Seismic Wave: Vibrations that travel through Earth carrying the energy released during an earthquake. They carry energy from an earthquake away from the focus, through the Earth's interior and across the surface.

*P Wave: The first waves to arrive from the earthquake are "Primary Waves", They are seismic waves that compress and expand the ground like an accordion. Can move through solids & liquids.

*S Waves: After P Waves come the "Secondary Waves." They are seismic waves that vibrate from side to side as well as up and down. They shake the ground back and forth. They can't move through liquids, just solids.

* Surface Waves: When P and S waves reach the surface, some become surface waves. They move more slowly then P & S waves, but produce severe ground movements, Moves ground like ocean waves and shakes buildings side to side.

*Mercalli Scale: was developed to rate earthquakes according to their intensity or strength at a given place- 12 step scale- the same earthquake can have different Mercalli ratings because it's intensity varies depending on locations.
*Richer Scale: assigns a magnitude number to an earthquake based on the size of seismic waves.

*Moment Magnitude Scale: Rating system that estimates the total energy released by an earthquake. Can be used to rate earthquakes of all sizes, near or far away. The geologists use the data on how much movement occurred along the fault and the strength of the rocks that broke when the fault slipped. Used now by most geologists.

*Magnitude: a number that geologists assign to an earthquake based on the earthquake size. The geologists determine the magnitude by measuring the seismic waves and fault movement during earthquakes.

*Seismograph: The seismic waves are measured by the seismograph. An instrument that records and measures seismic waves.

*Seismogram: The record of an earthquakes seismic waves produced by a seismograph. Zigzag pattern of lines that represent the earthquake.

*Liquefaction: occurs when an earthquakes violent shaking suddenly turns loose, soft soil into liquid mud. Is likely where the soil is full of moisture. As the ground gives way, buildings sink and pull apart.

*Aftershock: Is an earthquake that occurs after a larger earthquake in the same area. May strike hours, days or months later.

*Tsunami: When an earthquake jolts the ocean floor, plate movement causes the ocean floor to rise slightly and push water out of its way. The water displaced by the earthquake may form a large wave called a tsunami. As it approaches shallow water, the wave grows into a mountain of water.

*Base isolator: designed to reduce the amount of energy that reaches the building during an earthquake. Base isolator buildings rest on shock absorbing rubber pods or springs.

*Mass Damper: Dampers work like the shock absorbers in a car to absorb some of the energy of seismic waves.

*Flexible pipes: Water and gas pipes have flexible joints that bend when energy passes through them, reducing damage.

*Active tendon system: Sensors notify a computer that the building is moving. Then, the computer activates devices to shift a large weight to counteract the movement.

*Steel cross braces: are placed between stories of a building to stiffen a buildings frame and absorb energy during an earthquake.


Where do earthquakes mainly occur? In the United States the highest risk is along the Pacific Coast in California, Washington & Alaska.

2. What causes earthquakes? The forces of plate movement cause earthquakes. Plate movements produce stress in Earth's crust, adding energy to rock and forming faults. Stress increases along a fault until the rock breaks. An earthquake begins. In seconds, the earthquake releases a large amount of stored energy.

3. List 3 types of plate motions and write what kind of fault and earthquake are associated with each?
Is diverge, collide and sliding.

4. Describe the different types of faults:
A. Normal Faults: The fault is at an angle, so one block of rock lies above the other. Occur where plates diverge or pull apart.
B. Reverse Faults: Same as Normal Faults but blocks of rock move in opposite directions. Helps produce mountains.
C. Strike-Slip Faults: Where plates move past each other and slip past each other sideways. Example is San Andreas Fault.

5. What are the effects of the different types of stress?
A. Tension: The effect of tension on rock is somewhat like pulling apart a piece of warm bubble gum.
B. Compression: The effect of compression can compress rock like a giant trash compactor.
C. Shearing: The effect of shearing can cause rock to break and slip apart and change shapes.

6. What is the difference between faulting and folding?
Folds (Example-rug) are bends in the rock when compression shortens and thickens part of the Earth's crust. Faults are breaks in the rock of the crust where rock surfaces slip past each other.

7. How are the focus and epicenter related?
The focus is the area beneath Earth's surface, where rock that is under stress breaks, triggering an earthquake. The point on the surface directly above the focus is called the epicenter.

8. How do geologists determine the epicenter of an earthquake?
Geologists use seismic waves to locate an earthquakes epicenter. They then draw at least 3 circles using data from different seismographs set up at stations all over the world. The point where all 3 circles intersect is the location of the epicenter.

9. Describe the movements and speeds of different types of
Seismic waves?
A. P-Waves: Compress and expand the ground like an accordion. Can move through solids, liquids, and gases. Fast Moving(1-5mph)
B. S-Waves: Vibrates side to side and up and down. Can only move through solids. Slower then P-Waves.
C. Surface Waves or L Waves: Rolls in like a wave. Can produce severe ground movements. Moves the slowest.

10. What are the different ways to measure earthquakes? How are the different?
A. Mercalli Scale: Based on amount of damage an earthquake
produces. Uses 12 steps.I-III is weak earthquake & VII-IX is strong
B. Richter Scale: based on the size of the seismic waves. The
Stronger the quake, the larger the seismic wave.
- Magnitude number 0-10 assigned to it.
- Measures wave size and fault movement
- Measured by a seismograph
- Accurate for small, nearby earthquakes
C. Moment Magnitude Scale: based on the amount of energy an
Earthquake releases.
-Can measure all sizes of earthquakes near and far away.
- Study seismographs data, fault movement and rocks strength
that broke from fault slippage.

11. What is the difference between an earthquake that measures
magnitude 2.0 and 3.0? For each one number increase in
magnitude- ground shaking increases by a factor of 10.

12. How do geologists monitor faults? They use tillimeters,
creepmeters, laser-ranging devices and GPS satelites to record
changes in elevation, tilting of the land surface and ground move-
ment along the faults.

13. What determines an area's earthquake risk? Geologists can
determine earthquake risk by locating where faults are active,
where past earthquakes have occurred and where the most
damage was caused.

14. How do earthquakes cause damage?
A. Shaking
B. Liquefaction
C. Aftershocks
D. Tsunamis

15. Describe the 5 things that are used to keep buildings safe
during an earthquake?
A. Secure brick chimneys with metal brackets and plywood
B. Bolt the house to its concrete foundation
C. Strap the water heater to the wall
D. Use metal connectors to strengthen the house frame
E. Use plywood panels to strengthen the walls

16. How do you prepare for an earthquake?
A. Store an earthquake kit containing food, water & first aid
B. Fasten bookshelves and cabinets to wall studs so they don't
fall during an earthquake
C.Move beds away from windows and heavy items away from
walls above beds

17. How do you stay safe in an earthquake?
A. Drop, cover and hold- to protect from flying glass & objects
B. Go beneath table or desk and hold on
C. If no table, use inner wall and cover head/neck with arms
D.Avoid windows, mirrors, wall hanging and furniture that may fall
E. If outside- move to open area like a playground
F. Avoid power lines, trees, vehicles and buildings- sit to avoid
Being thrown down