Earthquakes

Question 1

Earthquake

Answer 1

• Vibration of earth produced by rapid release of energy

- result of movement between crustal blocks along fault surface

Question 2

Focus

Answer 2

Place within earth where the earthquake waves originate

Question 3

Epicenter

Answer 3

place on earths surface that lies directly above the focus of an earthquake

Question 4

Earthquake causes

Answer 4

• volcanic eruption
• nuclear test
• collapses of an empty pool
• moments along faults

Question 5

faults

Answer 5

large fractures in earth’s crust

Question 6

mechanism

Answer 6

-(elastic rebound) first explained by h.F. Reid following 1906 san fransisco earthquake
-movement of blocks on both sides may become locked
-tectonic stresses push blocks of rocks into opposite directions
-stresses slowly deform the crustal rocks
-rocks store and bend elastic energy
slippage happens at the weakest point(focus)
-Reid termed the “springing back” -elastic rebound because the rock behaves elastically

Question 7

Foreshocks

aftershocks

Answer 7

small earthquakes

strong earthquakes

Question 8

San Andreas

Answer 8

Most studied fault system
displacement occurs 100 to 200 km apart
motion between blocks is called strike slip
occur every 50 to 200 years

Question 9

seismographs

Answer 9

record seismic waves
idea based on inertia -objects at rest stay in rest
two types - left, vertical. right, horizontal

Question 10

body waves

Answer 10

P waves and S waves

Question 11

Primary waves p waves

Answer 11

• push pull( compress and expand) motion chasing the volume of the intervening material
• travel through solid liquids and gases
• travel 1.7 times faster then S waves

Question 12

Secondary waves S waves

Answer 12

• shake motion at right angles to their direction of travel
• travel only through solids
• slower velocity than p waves
• greater amplitude then p waves

Question 13

surface waves

Answer 13

L waves 
complex motion 
long waves 
greatest amplitude and slowest velocity 
waves have greatest periods

Question 14

Method of triangulation

Answer 14

• three station recordings are needed in order to locate epicenter of an earthquake
• travel-time graph is used to determine the distance to the epicenter
• s-minus p wave time interval( vertical)
• distance (horizontal) from the station to the center through calculated curve

Question 15

earthquake belts

Answer 15

-about 95 percent of the energy released by earthquakes originates in a few relatively narrow zone that wind around the globe

Question 16

major earthquake zones

Answer 16

Circum pacific belt
Mediterranean Sea region
Himalayan complex
Oceanic ridge system

Question 17

earthquake depths

Answer 17

-depths ranging from 5 to 700 km
foci classified as - shallow ( surface to 70 km depth)
- intermediate ( between 70km to 300km)
-deep ( over 300)

Question 18

Shallow focus earthquakes

Answer 18

occur along the oceanic ridge system

Question 19

deep focus earthquakes

Answer 19

occur at circum pacific belt

Question 20

Two measurements that describe the size

Answer 20

• intensity is based on amount of damage

- magnitude estimates the amount of energy released

Question 21

intensity scales

Answer 21

• mercalli intensity scale was developed using California buildings as its standard
• the drawback is that the destruction may not be a true measure of the actual severity

Question 22

magnitude( richter scale)

Answer 22

• based on the amplitude of the largest seismic wave recorded
• 10 fold increase in wave amplitude and a 32 fold energy increase
• largest recorded was 9.5- may 22 1960 Valdivia Chile
• magnitudes less than 2.0 are not felt by humans

Question 23

Liquefaction of the ground

Answer 23

• materials saturated with water turn into a mobile fluid

- effects - buildings acting like quicksand, sand boils

Question 24

seiches

Answer 24

• sloshing of water in lakes, reservoirs and enclosed basin

- waves can weaken reservoir walls and cause destruction

Question 25

tsunamis

Answer 25

• tidal waves
• result from vertical displacement along a fault located on the ocean floor or a large undersea landslide triggered by an earthquake

Question 26

open ocean

Answer 26

• height is usually less than 1 meter

- speed is about 800km per hour

Question 27

shallow coastal waters

Answer 27

water slows down to ~ 300 -50 km per hour and piles up to heights that occasionally exceed 30 meters, becoming very destructive

Question 28

earthquake predictions

Answer 28

short range 
-groundwater levels 
-electoral conductivity of rocks 
- animal behavior 
long range 
- paleoseismology 
-looking for the cycles 
- calculating probabilities