Test 1: Earthquakes/Tsunamis Flashcards
What is a Fault?
Movement, fracture, or discontinuity in a rock.
What are the results from a rupture of rocks along a fault?
Energy is released in the form of seismic waves.
What is an Epicentre?
The point on the surface above the focus.
What is the Focus?
Directly below the epicentre
What are Seismographs?
Instruments used to record the motion of the ground during an earthquake.
Ground motion for a magnitude 3 is ____ than a magnitude 2
10 times more
The amount of energy released from an M3 is ____ than an M2
32 times more
M5= 32x32 of an M3
The scale is qualitative and based on damage to structures and people’s perceptions.
Modified Mercalli Intensity Scale
How are earthquakes measured?
Shaking, the energy released, and peoples perception
How to measure faults?
Extract rocks and date it
Strike-slip faults
Displacements are horizontal
Dip Slip faults
Displacements are verticle
Block below the fault plane
A miner would stand here
Footwall
Block above the fault plane
Hang a lantern here
Hanging wall
A hanging wall goes up relative to the footwall
Due to crustal shortening
The slope of fault is not steep
Thrust or reverse fault
The hanging wall goes down relative to the footwall
Due to crustal stretching
Normal Fault
Blind Faults:
Mountain building processes
Blind faults do not reach the surface
Active faults:
Movement in the past 11,600 years
Potentially active faults:
Movement during the past 2.6 million years
Inactive faults:
No movement during the past 2.6 million years
Tectonic creep:
Occurs when movement along a fault is so gradual that earthquakes are not felt
- Can slowly damage infrastructure
Seismic Wave:
A wave is produced by a sudden displacement of rocks along a fault; seismic waves move through or along the surface of the earth.
What are the two types of body waves?
P waves and S waves
P waves, primary, or compressional waves
P-Waves reach seismic graph first (Travel through solid, liquid, and gas) Compressional (Faster of the two waves, travel at 6km per second
S-Waves, secondary, or shear waves
Reach seismic graph second (Only travels through solids; whipping motion)
Surface Waves:
Travel along the earth surface horizontally and vertically
Moves slower than body waves
Damage near the epicentre
What are two types of surface waves?
Love waves and Rayleigh Waves
What are Love waves?
Cause horizontal shaking
What are Rayleigh Waves?
Rolling waves, elliptical motion
Which waves turn into Love and Rayleigh waves once they reach the surface?
P and S waves
How many stations are needed to find the exact epicentre?
3 stations
Distance to epicentre can be found by comparing travel times of waves using ___
triangulation
Which period causes stress builds in a fault?
The inactive period causes stress builds in a fault
Primary effects of earthquakes?
Shaking and Surface rupture.
Secondary effects of earthquakes:
liquefaction, changes in land level, landslides, fire, tsunami and disease.
Displacement along the fault causes cracks in the surface.
Ground Rupture
Causes damages to buildings, pipes, bridges, tunnels, dams
Measured as ground acceleration
Shaking
Occurs when energy is transferred from P and S waves to surface waves.
Amplification
A near-surface layer of water-saturated sand changes rapidly from solid to liquid (causes buildings to float)
Liquefaction
How are fires caused during earthquakes?
Shaking and surface displacements cause power and gas lines to break and ignite.
Earthquakes on the seafloor can generate deathly waves.
Tsunami
What is a tsunami?
A series of waves caused by the displacement of a large volume of water.
What are tsunamis triggered by?
Large earthquakes cause uplift or subsidence of the seafloor.
What happens when a tsunami approaches land?
Loses speed and gains height
Tsunami warning system?
Seismographs to detect earthquakes, tidal gauges to determine sea-level changes, buoy sensors to detected tsunamis in open oceans.
Can result in building and road collapse.
Changes in land level
Disease:
Ruptured sewer and water lines
Polluted water
Loss of sanitation
Earthquake preparations?
Secure large objects, do not panic, leave the building once shaking stops
Tsunami Primary effects:
Shortened coastline, damaged structures, debris everywhere, death from drowning and water impact.
Tsumani secondary effects:
Fires, contaminated water supplies, diseases.
