Earthquakes

Question 1

Earthquakes

Answer 1

Shaking or vibration in the ground, which is the release of built-up stress (from friction) occurring when rocks being deformed suddenly breaks along a fault.

Question 2

Elastic Rebound

Answer 2

With the sudden displacement and release of stress during an earthquake, the rocks snap back elastically to their previous dimensions.

Question 3

Slip

Answer 3

The distance of the displacement during an earthquake.

Question 4

Types of Faults

Answer 4

Normal Faults (due to tensile stress), Thrust Faults (due to compressive stress), Strike-Slip (due to shearing stress).

Question 5

Focus

Answer 5

The point on a fault at which the first movement or break occurs during an earthquake.

Question 6

Epicenter

Answer 6

The point on the Earth’s surface is directly above the focus.

Question 7

When the blocks slip suddenly at the time of the earthquake, intense vibrations called _______ travel outwards from the focus.

Answer 7

Seismic Waves

Question 8

Richter magnitude

Answer 8

The damage an earthquake causes is typically measured as the amount of ground displacement or shaking it produces at the epicenter. This scale is logarithmic (magnitude 5 is 10 times as strong as magnitude 4).

Question 9

Types of Seismic Waves

Answer 9

P waves, S waves, surface

Question 10

P waves

Answer 10

compressional or primary waves that move parallel to the direction of movement. They move faster through solids than in liquids (6-8 km/s).

Question 11

S waves

Answer 11

shear or secondary waves. They move perpendicular to the direction of movement. They only travel through solids (4-5 km/hr)

Question 12

Surface waves

Answer 12

confined to Earth’s surface. They are the slowest moving but the most damaging. There are two types of surface waves (rolling/elliptical and sideways shaking)

Question 13

How can a seismologist determine the distance to an earthquake epicenter

Answer 13

Seismic waves from an earthquake move out concentrically from the focus point. Because P waves travel almost twice as fast as S waves, the interval between their arrival times increases with distance. By matching the observed interval to known travel-time curves, a seismologist can determine the distance to the epicenter.

Question 14

The radius of the Earth

Answer 14

6,371 km

Question 15

Surface Topography depth

Answer 15

20 km to deepest trench to highest mountain

Question 16

Depth of crust

Answer 16

0-40 km

Question 17

Density vs P/S wave relationship

Answer 17

Speed of waves increases with density

Question 18

Which waves do not make it through the liquid-outer core

Answer 18

S-waves

Question 19

Earthquakes originate both at ____ (at spreading ridges) and _____ (along subduction zones)

Answer 19

shallow depths, deep in the earth

Question 20

Shallow earthquakes

Answer 20

Assiciated with divergent boundaries and transform faults, as well as on continents due to crustal movements

Question 21

Deep Earthquakes

Answer 21

At subduction zones, they occur because the brittle lithosphere is forced deep into the asthenosphere

Question 22

Seismic hazard map

Answer 22

based on ground motion due to seismic activity

Question 23

Isostatic rebound

Answer 23

Earthquakes occur not due to plate margin, but, due to old faults that were once part of ancient plate boundaries.

Question 24

Examples to address issues from earthquakes

Answer 24

1. permit access to slack in power line and pipeline construction
2. design earthquake-resistant buildings
3. building only on solid rock

Question 25

Liquefaction

Answer 25

Occurs when water-saturated soil is shaken, thereby reducing the friction between soil particles that give the soil strength, causing the soil to start to become like quicksand.

Question 26

Tsunami

Answer 26

Seismic sea waves. When an undersea or near-shore earthquake occurs, the sudden movement of the seafloor creates waves that travel through the ocean as broad swells on the surface. However, when the tsunamis approach land, they develop into large breaking waves as the waves touch the shallow ocean floor. Tsunamis can travel quickly, with speeds in excess of 1000 km/hr.