Earthquakes and associated hazards Flashcards
Where do earthquakes occur most frequently?
At conservative plate boundaries where two plates slide past each other
What type of plate boundary is associated with the highest magnitude earthquakes?
Destructive plate boundaries where subduction takes place
What triggers an earthquake?
The fault suddenly releases stored stress
Define stress in the context of geology.
The force per unit area acting on a plane within a body
What are the three types of stress that can build up in faults?
- Tensional stress
- Compressional stress
- Shear stress
Compressional stresses cause a rock to shorten.
Tensional stresses cause a rock to elongate, or pull apart.
Shear stresses causes rocks to slip past each other.
What is the focus of an earthquake?
The point in the fault where stress was released
What does the epicenter of an earthquake represent?
The point directly above the focus where energy on the surface is greatest
List the three types of faults.
- Normal faults
- Reverse faults
- Strike-slip faults
How can rising magma in volcanoes cause earthquakes?
Increased frequency of earthquakes serves as warnings prior to eruption
What human activities can induce earthquakes?
- Mining activities
- Use of dynamite
- Heavy machinery
- Dam construction
- Fracking
What are the three distinct types of seismic waves?
- Primary waves (P-waves)
- Secondary waves (S-waves)
- Surface waves
What characterizes Primary waves (P-waves)?
Alternating compressions and dilations moving in the same direction as wave propagation
What is the speed range of P-waves in the Earth’s crust?
5-7 km/s
What is the characteristic motion of Secondary waves (S-waves)?
Alternating transverse motions perpendicular to the direction of propagation
Do S-waves travel through fluids?
No, S-waves do not exist in fluids
What type of motion do Love waves exhibit?
Transverse horizontal motion, perpendicular to the direction of propagation
What is unique about Rayleigh waves?
Motion is both in the direction of propagation and perpendicular, generally elliptical
What are primary hazards of earthquakes?
- Movement of the surface
- Rolling and shaking
- Fracturing of brittle surfaces
- Collapsing infrastructure
What are secondary hazards associated with earthquakes?
- Fires from broken gas lines
- Tsunamis
- Liquefaction
What is a tsunami classified as?
A shallow water wave
What causes tsunamis?
Fault movement in a subduction zone
How does a tsunami behave in deep ocean versus coastal areas?
- In deep ocean: long wavelengths, low amplitude
- Near shore: slows down, amplitude increases dramatically
What is soil liquefaction?
Ground failure causing solid soil to behave temporarily as a viscous liquid
What conditions lead to soil liquefaction?
Occurs in water-saturated unconsolidated soils affected by seismic S waves
What can earthquakes cause in terms of landslides?
They can lead to secondary hazards like landslides and avalanches
