All About Earthquakes

Question 1

What caused an earthquake?

Answer 1

• mobile crust - slow build up of stress within rocks

- pressure released suddenly - parts of the earth’s surface experience intense shaking = earthquake

Question 2

What is the focus point and epicenter of an earthquake?

Answer 2

• point were pressure releases = focus point

- directly above focus point on earth’s surface = the epicenter

Question 3

What methods of monitoring earthquakes are there?

Answer 3

• 1) modified mercali scale
• 2) magnitude scale (Mw)
• 3) Movement magnitude scale

Question 4

What are P (Primary) waves?

Answer 4

• travel through Earth’s interior
• move faster through denser rocks
• deflected by Earth’s core
• fastest waves 5-7km/s through Earth’s crust
• 8km/s+ Earth’s mantle and core
• can travel through air (heard as a low rumble)
• high frequency and low amplitude than S-waves

Question 5

What are S (Secondary) waves?

Answer 5

• slowest waves - 3-4km/s through Earth’d crust
• 4.5km/s Earth’s mantle and 2.5km/s inner core
• do not penetrate through core
• elastic - move material sideways
• cannot travel through fluid
• cannot penetrate magma in Earth’s liquid water core
• shadow zone = direct S-wave from a particular earthquake will not be deflected

Question 6

What are surface waves?

Answer 6

• do not penetrate Earth’s surface
• deform material vertically
• travel much more slowly than P/S waves 2-4km/s
• 2 types: Love waves slightly faster than Rayleigh waves
• speed and depth depends on the frequency

Question 7

How do we measure the intensity of an earthquake?

Answer 7

• we use the modified mercali scale to measures intensity & impact /relates ground movement to impacts
• 12 point scale (richer)
• qualitative measure based on observation & description

Question 8

How do we measure the energy released from an earthquake?

Answer 8

• we use a magnitude scale (Mw) to measured the energy released more accurately than the richer scale
• related to geographical properties e.g. rocks rigidity
• it is an accurate measure of movement on a fault of large earthquakes by the amount of physical movement = direct function of energy
• however, cannot be used for small earthquakes
• Mw2. Quarry blast -> mw5. Atomic Bomb