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The answer is B) It measures large earthquakes far from the seismograph.
Here are some notes that will help you with the whole lesson!
Earthquake: Sudden or violent shaking of the ground.
Epicenter: The point of the Earth's surface vertically above the focus of an Earthquake.
Focus: The focus is the place inside the Earth's crust where an earthquake originates.
Magnitude: The great size or extent of something.
Seismic wave: An elastic wave in the Earth.
Seismograph: An instrument that measures and records details of the Earthquake.
The Seismograph is used to find the Focus
Plate movement ⇒ Causes stress.
Stress ⇒ Increasing along faults.
Excess stress ⇒ Leads to rock breaking and an earthquake begins.
Earthquakes begin in the Lithosphere, usually 100km below the surface.
• Earthquakes have two centers
• The focus is the area beneath the surface where rocks beneath break under stress. It is the starting point of an Earthquake
• The Epicenter is the point on the surface directly above the focus
Earthquakes are caused by plate movement. And they begin at the focus.
• Waves carry energy as they travel
• The waves produced by an Earthquake are called Seismic waves
Seismic waves are classified into three categories
« P waves (primary) »
• Arrive first, travel fastest
• Compressed and expand the ground like an accordion
• Travel threw solids and liquids
« S waves (secondary) »
• Arrive after P waves
• Vibrate from side to side and up and down
• Shake structures violently when they reach the surface
• Travel ONLY threw solids
« Surface waves »
• Travel ONLY on the surface
• Were P and S waves move
• Move slowly
• Can produce dramatic ground movement
• May make the ground roll
The Mercalli scale rates an earthquake according to how much damage it causes. And has 12 levels of intensity.
The Mercalli scale rates earthquakes based on the amount of damage they cause.
The Richter scale measures magnitude based on the size of seismic waves.
• Magnitude is determined by measures based on the size of seismic waves.
• Seismic waves are measured by a seismograph
• This scale is good for measuring small, nearby earthquakes
The moment magnitude scale estimates the total energy released by an earthquake.
• Useful for earthquakes of all sizes and distances
• Data collected with seismographs
• Shows what kind of waves were produced and their strength
The Moment of magnitude scale takes into account the movement of rocks along fault lines.
The Sumatra earthquake of 2004 is the third strongest earthquake ever recorded.
• Measured 9.1-9.3 on the Moment magnitude scale
• Measured at the maximum intensity on the Mercalli scale
• Lasted approximately 9 minutes, the longest duration ever measured
• Triggers a massive tsunami and killed approximately 250,000 people
Geologists use Sisemic waves to locate an earthquake's Epicenter.
• Use Siesmograph to measure the difference between the arrival of P and S waves
• Compare data to seismographs from around the world
Earthquakes are caused by stress along faults due to plate movement.
«Traveling Of Energy»
• Seismic waves travel in all directions
• Three types of waves:
• P waves (primary)
• S waves (secondary)
• Surface waves
«Measuring Earthquake Energy»
• Mercalli scale
• Richter scale
• Moment magnitude scale
«Locating The Epicenter»
• Distance of epicenter measured from at least three seismographs
• Location of the epicenter is where three measurements overlap
Have a great day!