Seismic waves

Question 1

structure of the earth

Answer 1

crust (solid)

mantle (solid, but flows slowly)

outer core (liquid nickel and iron)

inner core (solid nickel and iron)

Question 2

3 types of seismic waves

Answer 2

P waves

S waves

surface waves

Question 3

P waves

Answer 3

longitudinal

relative speed is faster

can travel through solids and liquids

Question 4

S waves

Answer 4

transverse

slower than P waves

only travel through solids

Question 5

surface waves

Answer 5

longitudinal

travel along surfaces

slowest

Question 6

epicentre (of an earthquake)

Answer 6

the point on the earth’ surface directly above the focus of an earthquake

Question 7

How can the epicentre be determined?

Answer 7

seismic records

time lag between the arrival of P and S waves at a seismometer station

information from three stations is needed

the distance of the earthquake from each station can be calculated using the time lag

this gives us a distance/radius for each station

where the circles overlap the earthquake started

Question 8

What happens to the speed of P and S waves as they travel deeper into the mantles?

Answer 8

increases

Question 9

Describe the path of P waves as they travel through Earth

Answer 9

• curved paths due to constant change in density/refraction as they travel through Earth
• travel on the same path through the mantle and inner core
• can pass through the solid innercore but refract towards the normal when they enter it
• refract away from the normal again when they leave the inner core

(the outer core and mantle are similar enough in density that not much refraction occurs)

Question 10

Describe the path of S waves as they travel through the Earth

Answer 10

• curved paths due to constant change in density/refraction as they travel through Earth
• cannot pass through the Earth’s core as it is liquid
• are stopped by the core unless they glance off the sides/don’t reach it

Question 11

Why are the paths of P and S waves through the Earth curved?

Answer 11

• Earth’s density changes gradually as the depth changes
• this change in density causes the waves to be refracted as they pass through Earth
• because it isn’t a sudden refraction, the paths are curved

Question 12

S wave shadow zone

Answer 12

the area of the Earth’s surface where S waves are not detected following an earthquake

Question 13

How does the S wave shadow zone help geologists understand the existance/size of the liquid core?

Answer 13

as S waves can’t pass through liquid it tells them that some part of the Earth must be liquid

they can calculate the size of the core from the measurements

Question 14

P wave shadow zone

Answer 14

the area of the Earth’s surface where P waves are not detected following an earthquake

it is split into two zones/areas

Question 15

How does the P wave shadow zone help geologists understand the existance of the inner core?

Answer 15

P waves are refracted as they travel through Earth

as S waves are not, this tells geologists that a significant change in density occurs after the waves pass through the outer core

this tells them that there is a solid inner core

the measurements can help to calculate its size