Review Sheet Chapter 16 Earthquakes
Define earthquake (Hint: vibrations, energy and waves)
An Earthquake is a movement of ENERGY in the form of WAVES called seismic Waves caused by vibrations through the different medium of the Earth’s interior.
What causes an earthquake? (Hint: plates, friction, elastic/rebound theory, internal engine)
Earthquakes are causes by the huge amount of energy released from the sliding of plates as they build up friction. When that energy is released from the build up of friction along the plates it is called the elastic rebound theory. Like a rubber band being snapped.
What is a fault?
A fault is a fracture along which the blocks of crust on either side have moved relative to one another parallel to the fracture. Strike-slip, normal, and reverse faults. A reverse fault with a small dip angle is called a thrust fault.
What is the focus/ epicenter of an earthquake?
The Focus is the point where movement occurred which triggered the earthquake. The epicenter is the point at the surface directly above the focus. Make sure you know the difference. The focus is where the slip of the plate or fault initiated the earthquake.
What occurs when the ground dips vs. when it slips? What is the scarp?
The surface where the ground slips is where it is displaced and moves vertically. The dipping is when the grounds is displaced at an angle. A fault scarp is a small step or offset on the ground surface where one side of a fault has moved vertically with respect to the other.
What kinds of damage/dangers can occur as a result of an earthquake?
Tsunami, Intense ground shaking that can cause buildings to crumble, liquefaction, and landslides.
How are Tsunamis related to earthquakes?
Tsunamis can be triggeredby: undersea, earthquakes, landslides caused by earthquakes, and earthquakes generated by volcanic eruptions. Earthquakes can displace huge amounts of earth and water causing a tsunami.
How large does an earthquake have to be on the Richter scale to cause significant damage to Los Angles?
Anything above a 8 on the Richter scale would cause significant to Los Angeles this would correlate with a 10-12 on the modified Mercalli scale
How often do magnitude 8 earthquakes and above occur? How often do magnitude 3 and below occur? What types of plate boundaries to the largest earthquakes occur near?
Magnitude 8 and above happen only about once a year. Magnitude 3 and below can occur in the hundreds of thousands of times per year. Convergent plate boundaries are where the largest earthquakes ever have occurred such as those found along the ring of fire in the pacific rim.
What is the scale called that is used that measures destruction? Energy?
The Modified Mercalli scale measures the amount of destruction. This is very subjective to the observer and is from a 1to 12. The Richter scale was developed by Charles Richter and is used to measure the amount of energy released in an earthquake.
How do P and S waves travel through different mediums such as liquid and solid (Faster/slower)?
P waves slow down when traveling from a liquid to a solid. S waves stop when the state of matter changes from a solid to a liquid. Both speed up the more soild/rigid the state of matter/medium being travelled through. This slowing down and stopping of S and P waves occurs where the Mantle and Outer Core Meet.
Describe how accurately scientists can currently predict earthquakes? What signs can be seen before an Earthquake?
Scientists can characterize the seismic risk of an area, but can not yet accurately predict most earthquakes. An increase in the frequency of smaller earthquakes in the region, rapid tilting of the ground, rapid changes in water levels in wells.
What boundary do P and S waves stop or slow down in the interior of the earth? Why?
P waves are fastest so they arrive first on a seismogram. S Waves are the second fastest and arrive second on a seismogram Surface waves (Love and Rayleigh) arrive last because they are the slowest. P and S waves are considered body waves.
How can you tell the distance to the epicenter from a seismometer? (Talk about seismograms and how the waves are interpreted, time between the different types of waves, time travel curves list the steps)
The movement of the earth causes ground vibrations that seismographs use to create seismograms because the shaking of the Earth causes the pen to shake in place because of inertia of a heavy weight. The time between the arrival of the P and S waves at a seismograph station can be directly related to the distance of the epicenter of the Earthquake from the seismograph station. This is found using a time travel curve. The further away the earthquake occurred the longer the travel time and the greater time difference between P and S waves.
1. If you are given the time of the p wave and the time of the s wave you can find the time difference.
2. The time difference corresponds to a point on the time travel curve that you find using the small slip of white paper.
3. Directly below this point is the distance to the epicenter
How do you use seismograph readings from different seismometers to determine the location of the epicenter? ( How many do you need? Talk about time travel curves, distance from the epicenter to the multiple seismograph stations, radius etc. list the steps).
You need at least 3 seismograph stations and 3 accurate seismograms to determine the location of the epicenter.
1. Using the distance as the radius from each seismograph station you will use a compass to trace a circle.
2. Where all the circles combine you will have an exact location of the epicenter or a region.
3. Generally you will want to look at what city is nearest the point that all three circles cross.