earthquakes and volcanoes

Seismic waves

Energy released during an earthquake

Focus

The point in the earth’s crust where seismic waves are released

Epicenter

The point at which earths surface directly above the focus

Seismometer

Instrument used to determine the magnitude of of earthquakes

Details on earthquakes

And how tectonic processes result in an earthquake

• it refers to the shaking of earth’s ground due to the sudden release of energy in the earth’s lithosphere

• Earthquakes generally occur along plate boundaries, which contain systems of the fractures called faults.

• Earthquakes occur when

• Rock mass on either side of a fault, a push by tectonic forces

• Friction causes them to get locked, and stress builds up

• When the stress exceeds the strength of the fault(or rocks) the rock, snap, or suddenly move to a new position

• Sudden movement causes seismic waves to be released resulting in ground shaking

• Point in the earth cross where seismic waves are released is known as focus

  • The focus is the origin of the earthquake

• The point on earth surface directly above the focus is called epicentre

  • shaking is generally felt most strongly near the epicentre

1. How are earthquakes measured?

• Earthquakes are measured using seismometers

  • These are sensitive instruments that detect ground vibration and determine the magnitude of an earthquake

• The greater the seismic energy release during the earthquake, the greater the magnitude

• Scientist use the following skills to read the magnitude of earthquakes

  1. Richter Scale(ML)

  2. moment magnitude scale(Mw)

Richter scale(ML)

• The richter scale, calculates earthquake magnitude using the height of the largest wave recorded on seismometers

• Thus,earthquake magnitude is measured based on the maximum seismic intensity reached,rather than the total seismic energy released throughout the earthquake

• The scale is numbered from one to 10,with 10 being the greatest magnitude

• Scale is logarithmic- for example, an earthquake of magnitude six release releases about 32 times more energy than a magnitude 5

• However, the richter scale has a limitation

  • The director scale would rate an earthquake with a single drastic spike and wave energy as having a higher magnitude than a long earthquake with many large,intense waves

Moment magnitude scale

• The Mw scale rates earthquake magnitude, based on the total energy release during the earthquake

• Estimates the total energy release during our earthquake, instead of just the largest wave like the Richter scale

• Hence, it is generally more accurate, especially and measuring earthquakes of magnitude eight and above

• Scientist have adjusted the magnitude of past earthquakes we were initially measured using Richter scale

• The MW scale is also logarithmic-and a quake of magnitude six releases about 32 times more energy than a magnitude five