Hazards ( seismic hazards)

Question 1

describe how earthquakes are formed

Answer 1

the earth of the crust is comprised of seven major plates as well as several minor plates. at plate margins, when plates are travelling in different directions the plates get stuck and contribute to a build up of friction. when the pressure is released a series of tremors or earthquakes is felt. although 85 percent of earthquakes occur near plate boundaries some occur in intraplate locations.
at destructive plate margins earthquakes tend to occur at more depth as they are associated with the subduction of one crust under another in a narrow areas called the benioff zone. at constructive and conservative plate margins, the earthquakes tend to be shallow focused meaning the seismic waves have a shorter distance to travel to the surface and release greater energy

Question 2

describe how earthquakes are measured

Answer 2

-the richter scale is a logarithmic scale of 1-10, meaning a magnitude 5 earthquake is 10 times more powerful than a magnitude 4 earthquake. it is useful for measuring small scale earthquakes but decreases in accuracy the higher the magnitude
-moment magnitude scale is a 1-10 scale which measures the total distance a fault has moved and the force required to generate it known as the moment release of the earthquake. it is the only scale which can reliably measure the magnitude of the largest earthquakes
-the modified mercalli scale quantifies the power of the earthquake by evaluating its impact on the earth’s surface. the 12 point scale classifies the impact and severity of the earthquake on humans rather than using objective measures of the earthquake force. it is only helpful in evaluating in populated regions as it compares the damage produced.

Question 3

describe P waves and S waves

Answer 3

-p waves and s waves are body waves that travel through the rock. P waves are the fastest waves meaning they reach the surface first. they are compressional waves which can travel through the mantle and core. S waves are transverse waves which travel at a 90 degree angle to the direction of vibration. they travel at slower speeds

Question 4

describe rayleigh waves and love waves

Answer 4

-rayleigh waves cause the surface of the ground to move up and down as the ground shakes in an elliptical pattern
-love waves cause the surface of the ground to move side to side due to the horizontal motion of the ground shakes. they contribute to the most damage.

Question 5

describe the secondary seismic hazard of tsunamis

Answer 5

tsunamis are long wave length oceanic waves generated by the sudden displacement of water due to a shallow-focus underwater earthquake, volcanic eruption or submarine landslides.
the boxing day tsunami of 2004 was generated by an earthquake attributed to the subduction of the Indo-Australian Plate under the Eurasian plate. this caused the sea floor to be pushed upwards by 15 metres thus displacing a huge volume of water. this caused the death of over 200,000 individuals and economies dependent on fishing industries experienced a loss of income earners

Question 6

outline what liquefaction means

Answer 6

liquefaction occurs when vibrations within a mass of primarily waterlogged, unconsolidated soil cause the soil particles to lose contact with one another for example due to a seismic event. subsequently the soil behaves like a liquid with an inability to support its own weight contributing to the downward movement of the soil. this causes the collapsing of anything resting atop of it