Earthquakes - v6b

Q2-6: What information is gained about an earthquake from using a seismograph?

A2-6: Information gained from a seismograph: what kinds of waves occur, their strength, and the time they arrive at the instrument. Three seismographs can be used to "triangulate" the exact location of the epicenter of an earthquake.

Q2-7: How would a seismologist use seismographs to study a small part of a fault zone?

A2-7: By comparing reading from several seismographs in a small area, seismologists can determine the materials underneath the area, the location of epicenters of local earthquakes, and establish the location of faults by charting locations of several earthquakes.

Q2-8: What is measured to determine the location of an EPICENTER?

A2-8: To determine the location of an epicenter, you need to calculate the difference in time between the arrival of P and S waves, which indicates the distance of the seismic station to the epicenter. By comparing the distance from an epicenter to three different seismic stations, the location of an epicenter can be found.

Q2-9: How many data stations are needed to find the epicenter of an earthquake?

A2-9: 3

Q3-1: What two (2) measurements are taken during and after an earthquake?

A3-1: The energy released and the damage caused.

Q3-2: Compare and contrast the three (3) earthquake measuring scales discussed in this section: a. The Richter Scale: b. The Moment Magnitude Scale: c. The Mercalli Intensity Scale:

A3-2: Richter Scale: according to size of seismic waves recorded on a seismograph. Each number change = 10 times increase in wave energy; Moment Magnitude scale also rates the total energy released by an earthquake. Numbers on this scale combine energy ratings & descriptions of rock movement; The Mercalli Intensity scale has 12 categories which rate the damage suffered by buildings, the ground, and people. Because damage can be different from place to place, a single earthquake may have different Mercalli numbers in different locations.

Q3-3: On the Richter Scale how many times stronger is a 3.0 magnitude earthquake compared to a 2.0 magnitude earthquake?

A3-3: Ten times stronger

Q3-4: A friend tells you that he once experienced an earthquake and saw books and other objects falling off a bookcase. a. What was the magnitude on the Merdcalli Intensity Scale? b. What was the magnitude on the Richter Scale?

A3-4: a: Mercalli (VI Strong); b. Richter (5)

Q3-5: The largest earthquake ever recorded occurred in Chile. Why are earthquakes to be expected in Chile? Explain your answer.

A3-5: There is a large and active convergent boundary very close to Chile involving the Nazca plate and the South American plate. As the Nazca plate subducts underneath the South American plate, potential energy builds up along their convergent boundary. That energy build up can be released as an earthquake.

Q3-6: How can the same earthquake have different Mercalli Intensity scale ratings in different locations?

A3-6: The intensity and damage of an earthquake reduces as the distance from its epicenter increases. Two locations that are not the same distance from the epicenter of an earthquake will not feel the same intensity. They experience different effects from the same earthquake.

Q3-7: Why don't earthquakes follow plate boundary lines exactly?

A3-7: Because plate boundaries tend to be zones of seismic activity.

Q3-8: Future earthquakes will probably occur near the San Andreas Fault because the fault is "active." What does it mean to say that a fault is "active?"

A3-8: The plates involved are still moving and coming into contact with each other. This would build up energy over time that is periodically released in the form of earthquakes.

Q4-1: What is the translation for the Japanese word ... "tsunami?"

A4-1: Harbor wave

Q4-2: Why are tsunamis barely noticeable out in the ocean, but develop into huge waves when they reach the shore?

A4-2: In the ocean, tsunami waves have a long wave length, often hundred of kilometers between wave crests. Sea levels might change only 12 inches under a ship. When the waves reach shore, the wave length bunches up and rises -- sometimes over 100 meters in height.

Q4-3: Why is is NOT correct to refer to a tsunami as a "tidal wave?"

A4-3: High and low tides are created by the moon's gravity. Tunamis are not caused by the moon and are not related to gravitational pull. Tsunamis are not "TIDES."

Q4-4: How are tsunamis generated?

A4-4: When the sea floor abruptly deforms (moves) and displaces the overlying water -- a tsunami is created.

Q4-5: How fast can a tsunami wave travel? How far can tsunamis travel?

A4-5: A tsunami wave can travel up to 500 miles per hour. A tsunamic wave can travel thousands of miles across the open ocean.

Q4-6: Can a tsunami be generated by a landslide? -- either underwater or at the sea shore?

A4-6: Yes!

Q4-7: What is "drawback?"

A4-7: If the first part of the tsunami that reaches shore is a "trough," water along the coast will recede dramatically, exposing normally submerged areas. This "drawback" will fool people because soon the actual wave will come speeding into the harbor area.

Q4-8: Describe the Pacific Tsunami Warning System. What is a DART buoy?

A4-8: The Pacific Tsunami Warning System uses buoys to monitor seismic activity and passing tsunami waves. DART buoys relay seismic signals and wave height data to yield tsunami warnings.

Q4-9: If a Japanese city built a 4.5 meter high tsunami wall along their harbor, would this be sufficient protection against future tsunamis? (Why or why not?)

A4-9: NO. 4.5 meters is only 15 feet. A tsunami can reach heights of 100 feet or more.

Q5-10: (Definition)-- Scale which rates the total energy of an earthquake.

A5-10: Moment Magnitude Scale

Q5-11: Define the word "friction."

A5-11: The resistance that results from the relative motion of two objects that rub against each other.

Q5-12: What is a "slickenside?"

A5-12: A surface of exposed rock that resembles a polished finish. It is the result of two large masses of rock moving against each other with enough force to smooth out the rock surface.

Q5-13: When two plates slide past each other, what happens to the crusts of these plates? What happens to the upper mantle parts of these plates?

A5-13: They stick together until the potential energy exceeds the strength of the rock, at which point the crust breaks and an earthquake occurs. The upper mantle, which is plastic, continues to flow underneath.

Q5-14: Describe surface waves and how they affect an area that is experiencing an earthquake.

A5-14: They travel slower than body waves, but cause the most damage. They can move up and down, almost like an ocean wave and side to side, often causing buildings to collapse.

Q5-15: If each Richter value represents seismic waves 10 times greater than the one before, then how much larger are the waves of an earthquake with a magnitude of 6 versus a magnitude of 3?

A5-15: 1,000 times greater

Q5-16: If P-waves travel at 7 km/s and S waves travel at 3.6 km/s, how much faster are P-waves?

A5-16: About twice as fast

Q5-1: (Definition)-- The place on the Earth's surface above where rock breaks during an earthquake.

A5-1: epicenter

Q5-2: (Definition)-- Stick-slip motion between lithospheric plates.

A5-2: earthquake

Q5-3: (Definition)-- The point below the epicenter.

A5-3: focus

Q5-4: (Definition)-- Where rocks break and there is movement.

A5-4: fault

Q5-5: (Definition)-- Seismic waves that travel at the surface.

A5-5: surface waves

Q5-6: (Definition)-- Seismic waves that travel through the planet.

A5-6: body waves

Q5-7: (Definition)-- Name of instrument used to record seismic waves.

A5-7: seismograph

Q5-8: (Definition)-- Scale in which each number change means a10-fold increase in seismic wave energy.

A5-8: Richter Scale

Q5-9: (Definition)-- Scale in which eyewitness accounts of earthquake damage are incorporated into this earthquake measurement scale.

A5-9: Mercalli Intensity Scale

Q6-10: (Definition)-- Small tremors that follow an earthquake.

A6-10: aftershocks

Q6-11: (Definition)-- Seismic waves that travel through the interior of Earth.

A6-11: body waves

Q6-12: (Definition)-- Body waves that reach and travel along Earth's surface.

A6-12: surface waves

Q6-13: (Definition)-- A scientist who records and interprets seismic waves.

A6-13: seismologist

Q6-14: (Definition)-- An instrument that shows the kinds of waves that occur, their strength, and the time they arrive at the instrument.

A6-14: seismograph

Q6-15: (Definition)-- A scale that rates earthquakes according to the size of the seismic waves recorded on a seismograph.

A6-15: Richter Scale

Q6-16: (Definition)-- A scale that rates the total energy released by an earthquake. Numbers on the scale combine energy ratings and rock movement.

A6-16: Moment Magnitude Scale

Q6-17: (Definition)-- A scale that rates the damage suffered by buildings, the ground, and people during an earthquake.

A6-17: Mercalli Intensity Scale

Q6-18: (Definition)-- Faults at transform boundaries tend to have many branching faults. Thus is encompasses an entire area.

A6-18: earthquake zone

Q6-19: (Definition)-- Ocean waves that can travel thousands of miles from an underwater earthquake site.

A6-19: tsunami

Q6-1: (Definition)-- Movement of Earth's crust resulting from the building up of stored energy between 2 stuck lithospheric plates.

A6-1: earthquake

Q6-20: Chinese philosopher who created the first earthquake recording instrument in 132 AD.

A6-20: Chang Heng & his seismoscope

Q6-21: (Definition)-- Where water enters the spaces between dirt and sand particles in man-made land, and then the "soil" behaves like a liquid and will not support buildings.

A6-21: liquefaction

Q6-2: (Definition)-- The point below Earth's surface where a rock breaks and causes an earthquake.

A6-2: focus

Q6-3: (Definition)-- A region on Earth's surface that is split into two pieces.

A6-3: fault

Q6-4: (Definition)-- A point on Earth's surface right above the focus of an earthquake.

A6-4: epicenter

Q6-5: (Definition)-- Able to change shape without breaking.

A6-5: plastic

Q6-6: (Definition)-- Stored energy -- energy built up but not yet used or released.

A6-6: potential energy

Q6-7: (Definition)-- A motion which occurs when two surfaces are touching and stuck together and then suddenly release with a jolt.

A6-7: Stick-slip motion

Q6-8: (Definition)-- A surface of exposed rock that resembles a polished finish. It is the result of two large masses of rock moving against each other with enough force to smooth out the rock surface.

A6-8: slickensides

Q6-9: (Definition)-- Small bursts of shaking that may precede an earthquake.

A6-9: foreshocks

Q1-1: 1. What is the name of the kind of motion that causes an earthquake? a. Give an everyday example of this kind of motion. b. What three (3) conditions are needed for this motion?

A1-1: The motion is called stick-slip. a) Pulling a sock off of your foot -- or a door stuck in a door jam. b) 3 things needed: friction, two objects in contact, & forces that make the objects move.

Q1-2: Lithospheric plates: a. Name the two (2) parts: b. Describe how they are different from each other.

A1-2: Lithospheric plates are made of the crust which is brittle and the upper mantle which is plastic and flows.

Q1-3: What causes lithospheric plates to build up pressure and finally "give" along transform faults?

A1-3: Lithospheric plates are in motion. Therefore, as two plates move in the opposite direction, sometimes the plates get stuck at the crust. Because the upper mantle is flowing, pressure builds. Eventually, the stuck place at the crust "gives" and an earthquake occurs.

Q1-4: What is the difference between the FOCUS and the EPICENTER of an earthquake?

A1-4: The focus is the point below Earth's surface where a rock breaks and causes an earthquake. An epicenter is a point on the Earth's surface right above the focus of an earthquake.

Q1-5: How is a lithospheric plate like a long line of moving grocery carts?

A1-5: A lithospheric plate moves like a line of jostling grocery carts. However, parts of the plate are still able to move independently (like the individual carts).

Q1-6: (Definition)-- The polished surfaces of rock which are the result of rock moving against rock along a fault are known as ________________

A1-6: slickensides

Q1-7: Why do some earthquakes occur inside plate boundaries in the interior of a lithospheric plate?

A1-7: Sometimes lithospheric plates have ancient plate boundaries. At these old plate boundaries in the middle of the plates, earthquakes can occur. This is why the New Madrid Fault Zone in the middle of the United States has occasional earthquakes. The New Madrid Fault is an old plate boundary.

Q1-8: Explain why the movement of a plate can be UNEVEN along its boundary.

A1-8: The movement of the plate is uneven. Some parts can be stuck at the boundary and then when there is a break at the boundary, the plate moves.

Q1-9: How can one earthquake cause another?

A1-9: If it has been a long time since an earthquake has released built-up potential energy between two plates, then an earthquake occurring in one section of the plate may increase the stress and built-up potential energy in the second section of the same plate. The added stress can trigger another earthquake in the second section.

Q2-10: S-waves from a quake arrive at a seismic station 40 seconds after the arrival of P-waves. How far away is the EPICENTER?

A2-10: 340 km

Q2-11: The distance scale on a map is 1 cm = 10 km. The distance from a seismic station to the epicenter of an earthquake is 50 km. To locate the epicenter, what would be the radius of the circle that is drawn around this station on the map?

A2-11: 5 cm

Q2-1: What is the difference between "body waves" and "surface waves?"

A2-1: Body waves travel through Earth's interior. Surface waves travel on Earth's surface. Body waves can become surface waves when they reach the surface.

Q2-2: Which body wave is fastest & pushes / pulls rock in the direction the wave travels?

A2-2: P-waves (primary)

Q2-3: Which seismic wave moves rock in a motion that is perpendicular to the direction of the moving wave?

A2-3: S-waves (secondary)

Q2-4: Which type of seismic waves (body ... or ... surface) tend to cause the most damage during an earthquake?

A2-4: Surface waves

Q2-5: List what can happen to a seismic wave as it moves from one material to another as it travels through the Earth.

A2-5: Seismic waves can change speed by moving faster in cooler material and slower in hot material. They can also be bent, reflected, or even stopped, depending on what type of material they are moving through.

Q1-10: Put these events in order and then DESCRIBE each: aftershock, foreshock, and earthquake.

A1-10: The correct sequence is -- Foreshock, earthquake, aftershock. Foreshock--small earthquakes that occur before the main event; Earthquake -- the main event; Aftershocks-- tremors that occur after the main event.