Seismic hazards

Question 1

what is the focus?

Answer 1

The point where pressure release occurs in the crust after the gradual building of pressure.

Question 2

what is the epicentre?

Answer 2

the point immediately above the focus on the earth’s surface

Question 3

what are the depth levels of the focus?

Answer 3

shallow=0-70km (most damaging)
intermediate=70-300km
deep focus=300-700km

Question 4

where to earhquakes occur?

Answer 4

destructive, conservative, and constructive plate boundaries. here the process of plates moving past eachother sends out shockwaves. these spread outfrom the focus.

Question 5

Primary effect of earthquake?

Answer 5

Ground shaking and ground rupturing (visible displacement of earth’s surface)-major risk to large engineered structures such as nuclear power stations and dams.

Question 6

What are the secondary effects of an earthquake?

Answer 6

tsunami
landslide
liquefaction

Question 7

tsunami?

Answer 7

generated by shallow focus underwater earquakes (most common cause), or volacnic eruption.

travel at speeds over 700km an hour

first warning is drawdown

can reach heights of excess 25m

Question 8

soil liquefaction?

Answer 8

when violently shaken ,soil with high water content loses mechanical strength and behaves like a fluid

Question 9

landslides?

Answer 9

slope failure as a result of ground shaking as shaking dislodges rocks.
loosened material can allow water to infiltrate. so even after earthquake the extra water weight can cause a landslide.

Question 10

what scales measure the magnitude of an earthquake?

Answer 10

Richter scale (1-10)its a logarithmic scale = measures the magnitude

Moment magnitude scale (MMS) which measures the total energy released by quake.

Mercilli scale - measures the intensity of an event and its impact. 12 point scale. level 12 equivalent to 8.5 on richter scale. Based on observaations of impact on people and place.

Question 11

predictability?

Answer 11

difficult, regions at risk can be identified using plate tectonics. some methods to predict are based on monitoring groundwater levels, release of radon gas, unusual animal behaviour, areas can be mapped to produce a hazard zone map. fault lines like the san andreas and magnetic fields can be monitored and measured

Question 12

tell me about magnitude and frequency