• the shaking of the Earth's crust caused by sudden releases of energy
• the result of motion in the lithospheric plates
• the most destructive of natural disasters

• theory- earthquakes occur when stress building up between two lithospheric plates overcomes force of friction between plates
• causes sudden movement, release of energy
• plates "snap back" to former shapes, but at new location

• point within Earth's crust at which earthquake originates
• this source of energy can occur at depths up to 7900km below Earth's surface

• the point on Earth's surface directly above the focus of an earthquake

• How many types of earthquake waves are there?
• List types (full name, not letter type)

• compression waves
• shear waves
• surface waves

• compression waves -particles back & forth
• alternately stretches/ compresses materials 
• body waves - travel through body of earth
• primary earthquake waves
• pass through anything: rock, water, air, magma
• fastest wave - 2X faster than secondary

• secondary, slower waves
• side-to-side wave, so particles move at right angle to wave direction
• travels through body of earth
• can travel through solids but not liquids or gasses

• slowest type of waves
• surface waves - circular, radiating out
• make ripples

Define seismograph

(seismo - graph)

• an instrument (machine)
• records seismic waves - pen lines
• each wave type recorded different way
• used to Triangulate - three seismograph readings will plot center of an earthquake

Define seismogram

(seismo - gram)

• the paper roll where the record of erathquakes is written by the siesmograph machine
• a record of the time, type and strength of an earthquake
• waves are recorded according to arrival speed

1. P waves

2. S waves

3. L waves

the graph shows:

• relationship between P & S wave travel times
• earthquake epicenter distance

• measurement scale for earthquake magnitude (strength)
• from 1 to 10 ('10' is strongest)
• '7' can easily knock down buildings
• exponential : '7' is 10X stronger than '6'

• more accurate measurement of earthquake magnitude than Richter Scale

How does earthquake damage occur?

Give a few examples.

How: up/down as well as side to side violent movement of Earth's plates

• buildings may crack or totally collapse
• water, electric, gas lines break
• trees, posts fall/ ground, streets break
• rivers change course at major shift areas

• most buildings survive minor up/down, but foundations damaged by side to side movements
• walls, foundations, roofs, ceilings crack/ power, water, gas lines can be ripped
• Delta: wood houses bolted to foundations- reduces damage
• extreme conditions -landslides, huge cracks shift entire building / secondary damage - tsunamis, fires, flooding

• liquifaction- violent shaking of earth causes
• ground water forced upwards by waves
• dirt and ground water mix, making soil like very soft bog mud

• unstable ground- no support for structures
• structures may tip, crack or partially sink
• if structure not supported- may colapse
• solid bedrock safer than landfill or soil
• Richmond likely to liquify during earthquake- so foundations reinforced floating slabs

• seismic gaps that have not moved in long time
• microquakes (very small tremors)
• increase in elevation of ground- swelling
• decrease in electrical resistance of ground
• increase in ammount of radon (natural, low level radioactivity in Earth)

• shaking
• earth tremors = small earthquakes

• "Moho"= boundary between crust & mantle
• found at an average depth of 32km under continents, 8km under oceans
• continents stand higher on crust, sink deeper into mantle, so thicker

• wide area around Earth on side opposite of focus of an earthquake
•  no "P" or "S" waves arrive here

• largest magnitude in 1900's
• movement along subduction zone
• 800 mile zone affected - huge
• ground rolled like huge ocean waves
• +5 minutes- most last seconds
• 260 000 sq. km land rose 2 m
• 65 000 sq. km moved sideways
• caused tsunami along coast, to Hawaii, Japan

• strongest earthquake in 40 years
• little damage to human infrastructure as it was in less populated area

• boundary : Pacific Plate & North America Plate
• 1100 km. of California moving north relative to rest of the continental United States