Earthquakes

Question 1

Active fault

Answer 1

There are a variety of definitions, but one is displacement along a fault in the past 10,000 years; another definition is multiple displacements in the past 35,000 years.

Question 2

design basis ground motion

Answer 2

defined as the ground motion that has a 10 percent chance of being exceeded in a 50-year period

Question 3

dilatancy-diffusion model,

Answer 3

assumes that the first stage in earthquake development is an increase of elastic strain in rocks that causes them to dilate

Question 4

dilate

Answer 4

undergo an inelastic increase in volume

Question 5

Directivity

Answer 5

With respect to earthquake hazards, refers to the fact that during some moderate to large earthquakes the rupture of the fault is in a particular direction and the intensity of seismic shaking is greater in that direction.

Question 6

earthquake segment

Answer 6

parts of a fault zone that have ruptured as a unit during historic and prehistoric earthquakes

Question 7

earthquake cycle

Answer 7

The earthquake cycle hypothesis proposes that there is a drop in elastic strain after an earthquake and there is a reaccumulation of strain before the next event.

Question 8

epicenter

Answer 8

the location on the surface of Earth above the focus, which is the point at depth where the rocks ruptured to produce the earthquake

Question 9

Fault

Answer 9

A fracture or fracture system that has experienced movement along opposite sides of the fracture.

Question 10

Fault segmentation

Answer 10

A concept recognizing that faults may be divided into specific segments depending upon their geometry, structure, and earthquake history.

Question 11

fault zones

Answer 11

group of related faults roughly parallel to each other in map view

Question 12

fluid pressure

Answer 12

force per unit area exerted by a fluid

Question 13

Focus

Answer 13

The point or location in Earth where earthquake energy is first released; during an earthquake event, seismic energy radiates out from the focus.

Question 14

Liquefaction

Answer 14

Transformation of water-saturated granular material from the solid state to a liquid state.

Question 15

material amplification

Answer 15

how the amplitude of shaking, or the vertical movement, is greatly increased in unconsolidated sediments, such as silt and clay deposits.

Question 16

Modified Mercalli Scale

Answer 16

A scale with 12 divisions that subdivide the amount and severity of shaking and damage from an earthquake.

Question 17

Moment magnitude

Answer 17

The magnitude of an earthquake based on its seismic moment, which is the product of the average amount of slip on the fault that produced the earthquake, the area that actually ruptured, and the shear modulus of the rocks that failed.

Question 18

P waves

Answer 18

also called compressional waves, are faster than S waves and can travel through solid, liquid, and gaseous materials (see Figure 6.10a). The velocity of P waves through liquids is much slower.

Question 19

Recurrence interval

Answer 19

The time between events, such as floods or earthquakes or other natural processes. Often we are interested in the average recurrence interval, which is determined by finding the mean of a series of recurrence intervals between events.

Question 20

Shake map

Answer 20

Map showing pattern and extent of seismic shaking from an earthquake.

Question 21

Slip rate

Answer 21

Long-term rate of slip (displacement) along a fault; usually measured in millimeters or centimeters per year`

Question 22

Slow earthquake

Answer 22

Earthquake produced by fault rupture that can take days to months to complete.

Question 23

surface waves

Answer 23

travel more slowly than either P or S waves and cause much of the earthquake damage to buildings and other structures.

Question 24

S waves

Answer 24

can travel only through solid materials. Their speed through rocks, such as granite, is approximately one-half that of P waves

Question 25

tectonic creep

Answer 25

Slow, more or less continuous movement along a fault.

Question 26

tectonic framework

Answer 26

geometry and spatial pattern of faults or seismic sources