Earthquakes Flashcards
Earthquake
- Vibration of earth produced by rapid release of energy
- result of movement between crustal blocks along fault surface
Focus
Place within earth where the earthquake waves originate
Epicenter
place on earths surface that lies directly above the focus of an earthquake
Earthquake causes
- volcanic eruption
- nuclear test
- collapses of an empty pool
- moments along faults
faults
large fractures in earth’s crust
mechanism
-(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
Foreshocks
aftershocks
small earthquakes
strong earthquakes
San Andreas
Most studied fault system
displacement occurs 100 to 200 km apart
motion between blocks is called strike slip
occur every 50 to 200 years
seismographs
record seismic waves
idea based on inertia -objects at rest stay in rest
two types - left, vertical. right, horizontal
body waves
P waves and S waves
Primary waves p waves
- 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
Secondary waves S waves
- shake motion at right angles to their direction of travel
- travel only through solids
- slower velocity than p waves
- greater amplitude then p waves
surface waves
L waves complex motion long waves greatest amplitude and slowest velocity waves have greatest periods
Method of triangulation
- 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
earthquake belts
-about 95 percent of the energy released by earthquakes originates in a few relatively narrow zone that wind around the globe
major earthquake zones
Circum pacific belt
Mediterranean Sea region
Himalayan complex
Oceanic ridge system
earthquake depths
-depths ranging from 5 to 700 km
foci classified as - shallow ( surface to 70 km depth)
- intermediate ( between 70km to 300km)
-deep ( over 300)
Shallow focus earthquakes
occur along the oceanic ridge system
deep focus earthquakes
occur at circum pacific belt
Two measurements that describe the size
- intensity is based on amount of damage
- magnitude estimates the amount of energy released
intensity scales
- 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
magnitude( richter scale)
- 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
Liquefaction of the ground
- materials saturated with water turn into a mobile fluid
- effects - buildings acting like quicksand, sand boils
seiches
- sloshing of water in lakes, reservoirs and enclosed basin
- waves can weaken reservoir walls and cause destruction
tsunamis
- tidal waves
- result from vertical displacement along a fault located on the ocean floor or a large undersea landslide triggered by an earthquake
open ocean
- height is usually less than 1 meter
- speed is about 800km per hour
shallow coastal waters
water slows down to ~ 300 -50 km per hour and piles up to heights that occasionally exceed 30 meters, becoming very destructive
earthquake predictions
short range -groundwater levels -electoral conductivity of rocks - animal behavior long range - paleoseismology -looking for the cycles - calculating probabilities
