Upgrade to remove ads
Only $35.99/year

geo 101 - chapter 8

Terms in this set (58)

earthquake activity
seismicity
waves of energy emitted at the focus of an earthquake
seismic (earthquake) waves
the amount of movement or slip across a fault plane
displacement (offset)
a small step on the ground surface where one side of a fault has moved vertically with respect to the other
fault scarp
the rock mass above a sloping fault plane is the ___
hanging wall
the rock mass below the fault plane is the ___
footwall
when the hanging wall slips down the slope or ___ of the fault, it's a ___ fault
dip, normal
when the hanging wall slips up the slope, it's a ___ fault or ___ fault
reverse, thrust
a ___ fault is a near-vertical fracture on which slip occurs parallel to an imaginary horizontal line
strike-slip
___ faults form during extension of the crust; the hanging wall moves down
normal
___ faults form during shortening of the crust; the hanging wall moves up & the fault is steep
reverse
___ faults form during shortening of the crust; the fault's slope is gentle (less than 30°)
thrust
on a ___ fault, one block slides laterally past another, so no vertical displacement takes place
strike-slip
the location where a fault slips during an earthquake (hypocenter)
focus
the point on the surface of the Earth directly above the focus of an earthquake
epicenter
the ___ is the point within the Earth where slip begins, & the ___ is the point on the Earth's surface vertically above the focus
focus, epicenter
a representation of the energy released by an earthquake, as indicated by the amplitude of specific seismic waves as they would be recorded by a seismometer at a set distance from the epicenter
earthquake magnitude
a scale that defines earthquakes on the basis of the amplitude of the largest ground motion recorded on a seismogram
Richter scale
because of the distance limitation, a number given by the Richter scale is now called a ___
local magnitude
uses amplitude & S-P time
Richter scale
the relatively narrow strips of crust on the Earth under which most earthquakes occur
seismic belts (seismic zones)
a region in which earthquakes happen fairly frequently; a seismic belt is an elongate ___
seismic zone
most seismic belts correspond to plate boundaries, & earthquakes within these belts are called ___
plate-boundary earthquakes
earthquakes that occur away from plate boundaries are called ___
intraplate earthquakes
at ___ boundaries (mid-ocean ridges), two oceanic plates form & move apart
divergent
divergent boundaries consist of spreading segments linked by ___
transform faults
along spreading segments, stretching generates ___ faults; whereas along ___ faults, strike-slop displacement occurs
normal, transform
earthquakes along mid-ocean ridges take place at depths of less than 10 km, making them ___ earthquakes
shallow-focus
at ___ boundaries, where one plate slides relative past another without producing or consuming oceanic lithosphere, most faulting results in strike-slip motion
transform
all transform-fault earthquakes have a shallow ___, so the larger ones on land can cause disaster
focus
___ boundaries, where on plate subducts under another, tend to host several different kinds of earthquakes
convergent
convergent-boundary seismicity:

as the downgoing plate begins to subduct, it bends, causing ___ faults to develop in the downgoing plate, seaward of the trench

then, where it scrapes along the base of the overriding plate, large ___ faults form, defining the contact between the downgoing & overriding plate
normal, thrust
a sloping band of seismicity defined by intermediate- & deep-focus earthquakes that occur in the downgoing slab of a convergent plate boundary
Wadati-Benioff zone
the stretching of crust at continental rifts generates ___ faults
normal
two continents collide when the oceanic lithosphere that once separated them has been completely ___; such collisions produce great mountain ranges
subducted
mosts earthquakes in collision zones involve movement on ___ faults that accommodate crustal shortening
thrust
stress applied to the boundary of a plate can cause the interior of the plate to break suddenly at weak, pre-existing ___, which may have initially formed during the Precambrian
fault zones
the severity of the shaking at a given location depends on four factors:

1. the ____ of the earthquake, because larger events release more energy

2. the distance from the ___, because earthquake energy decreases as waves pass through the Earth

3. the nature of the ___ at the location, meaning the character & thickness of materials beneath the ground surface, because earthquake waves tend to be amplified in the weaker of these

4. the ___ of the waves, meaning the number of waves that reach a point in a specified interval of time, because this affects the way buildings sway
magnitude, focus, substrate, frequency
a sudden movement of rock & debris down a nonvertical slope
landslide
the shaking of an earthquake can cause ground on steep slopes or ground underlain by weak sediment to give way; this movement results in a ___
landslide
when pressure in the water in the pores push sediment grains apart so that they become surrounded by water & no longer rest against each other, & the sediment becomes able to flow like a liquid
sediment liquefaction
the settling of sedimentary layers down into a liquified layer can also disrupt ___, can lead to formation of open ___ of the land surface, & can trigger ___
bedding, fissures, slumping
a large wave along the sea surface triggered by an earthquake or large submarine slump
tsunami
geologist use the term ___ for a wave produced by the sudden displacement of the seafloor
tsunami
in the case of an earthquake-generated ___, the process begins due to the sudden vertical displacement of an area of seafloor
tsunami
___ tsunamis travel toward nearby shores, whereas ___ tsunamis head out across the ocean
near-field, far-field
which seismic waves produce the most damage
surface waves
seismic waves that pass through the interior of the Earth
body waves
seismic waves that travel along the Earth's surface
surface waves
waves in which particles of material move back & forth parallel to the direction in which the wave itself moves
compressional waves
seismic waves in which particles of material move back & forth perpendicular to the direction in which the wave itself moves
shear waves
the two types of body waves:
P-waves, S-waves
the two types of surface waves:
L-waves, R-waves
___ are compressional body waves
P-waves (stands for primary)
___ are shear body waves
S-waves (stands for secondary)
___ are surface waves that cause the ground to shimmy back & forth
L-waves (stands for Love)
the different types of seismic waves travel at different velocities:

___-waves travel the fastest
___-waves are the nest fastest
___ waves are the slowest
P, S, surface
___ are surface waves that cause the ground to undulate up & down
R-waves (stands for Rayleigh)
Sets found in the same folder