P12 - Seismic waves Flashcards
order of Earth’s composition
inner core - liquid outer core - mantle - crust
earthquake
-when forces inside earth increase and become strong enough to move pieces of rock(crust)
seismic waves
-energy transferred makes shock waves
-travel through/across earth
Earth’s crust
-earthquakes generate here
-outermost layer
crust beneath oceans
thinner/younger that crust beneath continents
focus
-point where earthquakes originate from
epicentre
-nearest point to focus on surface
seismometers
-detectors that record earthquakes on Earth’s surface
Primary waves (P -waves )
-causes initial tremors lasting 1 min
P waves are ..
-longitudinal
-push/pull on material as they move through Earth
Secondary waves (S waves)
-cause more tremors a few mins later
S waves are…
-transverse
-travel slower than P waves
-shake material that they pass through inside earth side to side
L waves
-arrive last
-cause violent movements on surface
-travel the slowest
-only happen in crust layer
P waves and S waves as they travel through mantle
P waves at boundary between mantle/outer core
refraction
-speed changes here
S waves boundary between mantle/outer core
cannot travel through liquid (outer core)
shadow zone
area of Earth from 150. to 142. where no p waves or s waves are recorded
prove existence of liquid outer core beneath mantle
-p waves are refracted at boundary (moves slower in liquid)
-second refraction cannot reach shadow zone
-s waves are transverse = cannot pass through outer core
weak p waves in shadow zone
prove inner core is solid
-refracts p waves at boundary of inner/outer core
prove boundary between crust/mantle
speed of seismic waves change 50km below surface - diff densities
