Topic 4 - Waves and the Earth Flashcards
What is Ultrasound?
Any sound above a frequency of 20, 000 hertz (hZ)
How is Ultrasound used by animals, doctors and ships?
Animals:
- Dolphins - use to communicate between each other.
- Bats - use to see use relection to build a picture of what is around them.
Ships: Send out ultrasound signals to determine the depth of the water as the time tells us the distance travelled.
Distance = speed x time
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Doctors: they use Ultra sound to image the foetus. Each type of tissue reflects ultrasound by different amounts + time it takes for relected ultrasound tells us where it is with these peices of info combined the picture can be made without harming the baby
What is infrasound?
Infrasound are soundwaves below 20 hZ and they travel further than higher frequncies before they become to faint to detect.
How do animals, meteoroligists, and animal enthusiasts use infrasound?
Animals such as elephants and whales use infrasound to communicate over long distances.
Volcanic eruptions and meteors can be detected (and monitored) by infrasound detection centres.
Animal enthusiasts use infrasound to locate animals that they are studying and follow their movements throughout the year.
What causes Seismic Waves?
Earthquakes or any other movements inside the earth cause “compression and relaxation” waves within the rocks of the earth.
Seismic waves can be P & S type. What is the difference?
S can travel through solids cannot travel through liquids and are transverse and are slower than P waves.
P waves can travel through solids and liquids are longitudinal and are faster than S waves.
What do the terms focus and epicentremean in regards to an earthquake.
Focus is where the rocks move inside the Earth and the epicentre is the point on the Earth dirctly above it
How can seismic waves be used to study the composition of the Earth’s physical mass i.e crust and downwards
Oil, gas and mining companies use controlled explosions and seismometers to investigate the rocks beneath the surface.
Scientists can use (the much stronger) seismic waves generated by earthquakes to investigate the mantle and the core.
What do the oil, gas and mining companies and scientists look at with their seismometeres?
When a seismic wave meet a rock boundary some will be reflected and some refracted as it speeds up upon passing through a different type of rock.
It is the relected and refracted waves that scientists use.
Why is predicting earthquakes and tsunamis dificuilt?
The tectonic plates experience forces due to convection currents in the mantle. However, due to friction between plates their movement is very restricted. Earthquakes and tsunamis are caused by sudden movements between the tectonic plates that are due to a build up of pressure over a long period of time.
- Scientists can’t measure pressure between tectonic plates. However, statistical data can be used to make rough predictions.
How can P waves and S waves be used to locate the epicentre?
The time lag between P and S at a seismometer together with their known difgference in speed can be used to work out the distance to the earthquake. This is done at several diferent seismometer stations each of which then can be used to generate an arc where the arcs intercept is the epicentre.
