Earthquakes Flashcards
Active fault
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.
design basis ground motion
defined as the ground motion that has a 10 percent chance of being exceeded in a 50-year period
dilatancy-diffusion model,
assumes that the first stage in earthquake development is an increase of elastic strain in rocks that causes them to dilate
dilate
undergo an inelastic increase in volume
Directivity
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.
earthquake segment
parts of a fault zone that have ruptured as a unit during historic and prehistoric earthquakes
earthquake cycle
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.
epicenter
the location on the surface of Earth above the focus, which is the point at depth where the rocks ruptured to produce the earthquake
Fault
A fracture or fracture system that has experienced movement along opposite sides of the fracture.
Fault segmentation
A concept recognizing that faults may be divided into specific segments depending upon their geometry, structure, and earthquake history.
fault zones
group of related faults roughly parallel to each other in map view
fluid pressure
force per unit area exerted by a fluid
Focus
The point or location in Earth where earthquake energy is first released; during an earthquake event, seismic energy radiates out from the focus.
Liquefaction
Transformation of water-saturated granular material from the solid state to a liquid state.
material amplification
how the amplitude of shaking, or the vertical movement, is greatly increased in unconsolidated sediments, such as silt and clay deposits.
Modified Mercalli Scale
A scale with 12 divisions that subdivide the amount and severity of shaking and damage from an earthquake.
Moment magnitude
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.
P waves
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.
Recurrence interval
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.
Shake map
Map showing pattern and extent of seismic shaking from an earthquake.
Slip rate
Long-term rate of slip (displacement) along a fault; usually measured in millimeters or centimeters per year`
Slow earthquake
Earthquake produced by fault rupture that can take days to months to complete.
surface waves
travel more slowly than either P or S waves and cause much of the earthquake damage to buildings and other structures.
S waves
can travel only through solid materials. Their speed through rocks, such as granite, is approximately one-half that of P waves
tectonic creep
Slow, more or less continuous movement along a fault.
tectonic framework
geometry and spatial pattern of faults or seismic sources
