HAZARDS - earthquakes Flashcards
where do earthquakes occur?
closely related to location of plate boundaries.
nature of earthquake at constructive boundaries
shallow focus
mid ocean ridge = low hazard
nature of earthquake at collision boundaries
shallow focus
fold mountain formation
nature of earthquake at destructive boundaries
deeper focus in the benioff zone due to compressional forces
nature of earthquake at conservative plate boundaries
shallow focus
what percentage of earthquakes are intraplate?
10%
focus
point at which the pressure was released within the crust
epicentre
point at the surface, directly above the focus. where the most intense shaking occurs.
seismic wave
shockwaves that radiate from the focus.
what are the two types of seismic waves?
body waves and surface waves
body waves
travel through the earth
there are primary and secondary body waves
primary waves
LONGITUDE waves
high frequency
FASTEST of the body waves
travels through SOLIDS and LIQUIDS
secondary waves
TRANSVERSE waves
high frequency
half the speed of p waves - SLOW
travels through SOLID only
what type of movement do P and S waves cause
P = back and forth = ground cracks S = shaking up and down
surface waves
travel along the earths surface = larger hazard
love waves
type of surface wave = shakes ground at 90* to the direction of movement
slower = more damage
damages infrastructure and buildings
Rayleigh waves
type of surface wave
rolling motion
radiates from epicentre in complex low frequency motion
breaks surface
liquefaction
secondary impact of earthquakes
unconsolidated sediment is saturated with water and acts like liquid due to the shaking
effect of liquefaction
subsidence of building foundation
destruction of utility pipes
landslides
unstable material on slopes fall due to ground shaking
effects of landslides
injuries, blocked path, emergency aid unable to pass
Tsunamis
effect of earthquakes
large waved formed due to subduction of plate offshore
over 10m high
coastal flooding and destruction
what are the three scales earthquakes can be measured in?
mercalli scale
Richter scale
moment magnitude scale
mercalli scale
I - XII
based on observations
I = not felt only detected by instruments
XII = total destruction
richter scale
1-8
logarithmic scale
amplitude of wave and distance from focus
use a seismometer
moment magnitude scale
logarithmic scale with no upper limit
more accurate than the richter scale
measure the total moment released- distance fault moved and forced require to move it (energy)
no upper limit
short term impacts
death injury destroyed infrastructure and buildings burst pipes fires
long term impacts
- infrastructure problems
- disruption to supply lines and economy
- 2/3 of Haiti’’s working in agriculture and industry were unemployed
- looting
nature of an earthquake is affected by 3 main factors
margin type, rate of movement, depth of focus.
compare deep focus and shallow focus earthquakes
shallow = lower magnitude deep = higher magnitude shallow = more damage deep = less damage
relationship between frequency and magnitude of earthquakes
high frequency earthquakes tend to have low mag.
high magnitude earthquakes happen less frequently.
regularity of earthquakes
don’t follow any pattern
frequency is not an indicator
predictability of earthquakes
scientist can monitor tectonic movement and and predict areas at risk
imposible to predict a time and magnitude
preparation and mitigation strategies
educate - drills
emergency response
earthquake proof buildings
how to make a house earthquake proof
strengthened corners
shock absorbance
