Chapter 4 Earthquakes

Plateau

A large area of flat land elevated high above sea level. The Colorado Plateau in the "Four Corners" region of Arizona, Utah, Colorado and New Mexico.

Tsunami

A series of sea waves spreading rapidly in all directions from the sea bottom where a large earthquake, volcanic eruption or coastal landslide has occurred.

Magnitude

A single number that geologists assign to an earthquake based on the earthquake's size.

Transform Boundary

A strike-slip fault that forms the boundary between two plates. The San Andreas fault is an example of a transform boundary.

Effects of Earthquakes

1) avalanches(landslides) 2)shaking 3)recue work to remove trapped victims 4) fires 5)tsunamis

4 factors that can affect how much damage an earthquake doses

1) population of the area 2) the time it occurs 3) the kind of rock & soil in the area 4) the kind of buildings in the area(are they earthquake resistant?)

Besides plate boundaries, earthquakes can occur at...

1. Divergent Plate Boundaries 2. Convergent Plate Boundaries 3. Transform Plate Boundaries

3 types of seismic waves

1. Primary Waves (P-Waves) 2. Secondary Waves (S-Waves) 3. Surface Waves

Fault

A break in the Earth's crust along which rocks move.

Seismograph

An instrument that records and measures and earthquake's seismic waves. They are used to calculate the size of quakes and determine their locations.

Where do most earthquakes happen?

At plate boundaries in the earth's crust

Worst Tsunamis

Dec 2004 triggered by a 9.0 quake in Indonesia

Reverse Fault

Has the same structure as a normal fault, but the blocks move in the reverse direction. Hanging wall moves up and the footwall moves down.

Stress

Is a force that acts on rock to change its shape or volume.

3 ways to measure an earthquake

Modified Mercalli Scale, Richter Scale and Moment Scale

Modified Mercalli Scale

Rates the amount of shaking from an earthquake.

Biggest fault in California

San Andreas Fault

Moment Magnitude Scale

Scale to rate the total energy an earthquake releases. What most seismologist use today. Very consistent measurements.

Seismologist

Scientists who studies earthquakes and seismic waves

Secondary Waves (S-Waves)

Seismic waves that can vibrate from side to side or up and down. They are slower than P Waves and only travel through solids.

Primary Waves (P-Waves)

Seismic waves that compress and expand the ground like an accordion. They are the first waves to arrive. They are compression waves. P-Waves move through rock, they move back and forth parallel to the same direction that the wave travels. They travel through both solids and fluids. Can damage buildings.

Earthquake

Shaking and trembling that results from movement of rock beneath of the Earth's surface.

Shearing

Stress that pushes a mass of rock in two opposite directions.

Surface Waves

Surface waves move more slowly than P and S waves, but they can produce severe ground movement. Similar to waves in the ocean. They are the SLOWEST of the waves. They usually cause the MOST damage.

Two examples of mountain ranges in the World that have been caused by folding.

The Himalayas and the Alps

Aftershocks

smaller quakes produced after a major quake caused by rock shifting to new positons

Seismic waves

waves of energy that are released during an earthquake

Divergent Plate Boundary

Where rocks break under tension stress, forming normal faults. Most of these earthquakes occur in the crust at low depths and are small in size.

San Andreas fault

a huge crack that runs through most of California that separates the North American and Pacific plates

Most injury from quakes come from

falling of buildings, bridges, roads (then, fires, landslides, tsunamis)

Focus

The area beneath Earth's surface where rock that was under stress begins to break or move.

Footwall

The bloc of rock that lies under the fault.

Hanging Wall

The block of rock that sits over the fault.

Richter Scale

The earliest scale used to measure the strength or magnitude of an earthquake (uses numbers from 1-10)

Epicenter

The point on the earth's surface directly above the focus.

Strike-Slip Fault

The rocks on wither side of the fault slip past each other sideways, with little up or down motion.

Tension

The stress force that pulls on the crust and thins rock in the middle.

Compression

The stress force that squeezes rock until it folds or breaks.

How do seismic waves travel?

They move outward from the focus in all directions

Where do earthquakes start?

They start at the Focus (Foci) which is the location on a fault where rupture and movement begins.

Normal Fault

Where rock is pulled apart by tension in Earth's crust. The fault cuts through a rock at an angle, so one block of rock sits over the fault while the other block lies under the fault. Hanging wall moves down and footwall moves up.

Convergent Plate Boundary

Where rocks break under compression stress, forming strike slip faults.