Hello there,
Introduction:
Seismic waves are a unique feature that Scientists get from Earthquakes.
Seismic waves are vibrations that essentially travel through Earth carrying the energy released during an earthquake. The three types of seismic waves are P waves, S waves and surface waves.
P waves, or primary waves, are a type of seismic wave that compresses and expands the ground. This type of wave moves the fastest and can go through both solids and liquids.
S waves, or secondary waves, are a type of seismic wave that moves the ground up an down or side to side. S-waves can NOT go through liquid and are slower than P waves.
Surface waves are when P waves and S waves reach the Earth's surface. Surface waves are by far the most dangerous.
Questions:
A How are seismic waves formed? (or produced)
Seismic waves are initially generated by the juddering of rock surfaces as they grind past each other when forces overcome friction. The fault interface is not smooth like many imagine. Its faces are dotted with protrusions of a range of sizes which before the quake mesh and grind together. These features are called asperities and can be as small as rock crystals on the size of a hillside.
The shearing and tearing of the asperities under unimaginable forces created a broad spectrum of frequencies within the event as a whole. If you rub two rocks together, you'll feel vibrations as the surface push past each other, and hear the vibrations as they're transferred to your ear through the air.
However this is just the beginning. The fault, or weakness in the rocks, may be many km long and if a lot of force is present over a wide area the fault failure will spread along it in a gigantic lurch. The crack, if you will, grows from initial failure outwards at a speed of many kilometers per second with each segment of the failing fault generating its own source of vibration. The changes in stress the quake creates may also be sufficient to make adjoining rock interfaces or fault break. The end result is a three dimensional network of vibrational sources which evolves over the seconds or minutes the complete event takes. And this sends a community of seismic waves radiating outwards.
Also, these waves are attenuated as they travel, some travelling deep others to the surface. But the net result is that when we experience a quake it's vibrations created by the grinding and tearing of rock.
B What are two characteristics of P waves?
- Fastest wave
- A longitudinal (compression) wave
C What are two characteristics of S waves?
- A transverse wave
- Cannot travel through a liquid
D How do absorption, reflection, and refraction change the movement of P waves?
Each have a separate effect on P waves.
- Absorption reduces the energy of P waves.
- Reflection will reflect or bounce P waves back and fourth.
- Refraction will change refract or change direction of the P-waves (based on what surface they are spiraling off of or bouncing off of).
Thank you,
Eddie