nature of seismicity, relation to plate tectonics

Question 1

what are earthquakes?

Answer 1

.a primary hazard that occur as a result of tectonic movement in the lithosphere
.they are essentially a series of tremors

Question 2

how do earthquakes occur?

Answer 2

.movement of tectonic plates causes pressure to build up in the lithosphere -when the pressure is released, a series of tremors occur

Question 3

what percentages of earthquakes occur at plate margins?

Answer 3

.90% of earthquakes occur at plate margins the rest are intraplate

Question 4

on average how many people die from seismic hazards each year?

Answer 4

.63,000

Question 5

what are the forms of seismic hazards?

Answer 5

.shockwaves
.tsunamis
.liquefaction
.landslides

Question 6

how do shockwaves occur?

Answer 6

.friction along plate margins builds up in the lithosphere and when the pressure is finally released, they fracture along cracks called faults, sending a series of seismic shockwaves to the surface

Question 7

what does the nature of a seismic hazard depend on?

Answer 7

.depth of focus
.width of seismic activity
.frequency of earthquakes
.magnitude of earthquakes

Question 8

what is the breaking point of the pressure called?

Answer 8

.the focus of the earthquake

Question 9

what is the epicentre of the earthquake?

Answer 9

.the point on the surface directly above the focus, it usually experiences the most intense ground shaking

Question 10

how many types of depths of focus are there?

Answer 10

3

Question 11

what are the 3 types of depths of focus?

Answer 11

.shallow focus earthquakes -0-70km deep and tend to cause the greatest damage -account for
75% of all earthquake energy released
.intermediate focus occur between 70-300km
.deep focus earthquakes occur at depths of 300-700km

Question 12

what are the factors that affect the nature of a seismic hazard at a constructive plate margin?

Answer 12

.shallow focus earthquakes <60km - as a result of tensional forces in the crust -often small in size and occur at mid-ocean ridges so pose little risk to people
.narrow zone width
.regular frequency
.low magnitude

Question 13

what type of focus depth is there at a conservative plate margin?

Answer 13

.shallow focus earthquakes up to 20km
.narrow zone width
.infrequent
.high magnitude

Question 14

what type of focus depth is there at a destructive collision plate margin?

Answer 14

.mainly shallow
.wide zone width
.infrequent
.high magnitude

Question 15

what type of focus depth is there at a destructive subduction plate margin?

Answer 15

.range from intermediate to deep 70-700km
.wide zone width
.infrequent
.high magnitude