Geology: chapter 13
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The weak, ductile layer of rock that constitutes the lower part of the upper mantle (below the lithosphere) and over which the lithosphere plates slide. (from Greek asthenes, meaning "weak")
Pertaining to a material that undergoes smooth and continuous deformation under increasing stress without fracturing and does not spring back to its original shape when the stress is released.
The strong, rigid outer shell of Earth that comprises the crust and uppermost part of the mantle down to an average depth of about 100 km. (From Greek lithos, meaning "stone")
A ground vibration produced by an earthquake.
The region that forms the main bulk of the Earth, between the crust and core, containing rocks of intermediate density.
The thin outer layer of Earth, averaging form about 8 km thick under the oceans to about 40 km thick under the continents.
The dense central part of the Earth below the core-mantle boundary.
Layers of the Earth (order)
- upper mantle (asthenoshpere)
- lower mantle
- outer core
- inner core
The sinking of oceanic lithosphere beneath overriding oceanic or continental lithosphere at a convergent plate boundary.
Convergent Plate Boundary
A boundary between lithospheric plates where the plates move toward each other and one plate is recycled into the mantle.
An earthquake that occurs as a consequence of a previous earthquake of a larger magnitude. (compare foreshock)
A small earthquake that occurs in the vicinity of, but before, a main shock. (compare aftershock)
The boundary between Earth's core and its mantle.
The violent motion of the ground that occurs when brittle rock under stress suddenly breaks along a fault.
Elastic Rebound Theory
A theory of faulting and earthquake generation holding that, as the crustal blocks on either side of a fault are deformed by tectonic forces, they remain locked in place by friction, accumulating elastic strain energy, until they fracture and rebound to their under formed state.
The geographic point on Earth's surface directly above the focus of an earthquake.
The point along a fault at which slipping initiates an earthquake
The orientation of the fault rupture and the slip direction of a fault that caused and earthquake
The distance of the displacement of the two blocks of rock on either side of a fault that occurs during an earthquake.
A scale for estimating the intensity of a destructive geologic event, such as an earthquake or hurricane, directly from the events destructive effects.
A scale for estimating the size of an earthquake using the logarithm of the largest ground motion registered by a seismograph (Richter magnitude) or the logarithm of the area of the fault rupture (moment magnitude).
A layer near the base of the lithosphere, where S-wave speed abruptly decreases, marking the top part of the asthenosphere.
The first type of seismic wave to arrive at a seismograph from the focus of an earthquake; a type of compressional wave. (They travel as a succession of compressions and expansions.)
The second type of seismic to arrive at a seismograph from the focus of an earthquake, a type of shear wave. S-Waves cannot travel through liquids or gases. (They displace material at right angles to their path of travel.)
A type of seismic wave that travels around Earth's surface for the focus of an earthquake and arrives at a seismograph later than S waves. (Confined to Earth's surface and outer layers, move more slowly than S waves)
An instrument that records the seismic waves generated by earthquakes.
- (1) A zone beyond 105 degrees from the focus of an earthquake where S-Waves are not recorded because they are not transmitted through Earth's liquid outer core.
- (2) A zone at angular distances of 105 degrees to 142 degrees from the focus of an earthquake where P and S waves are not recorded because they are refracted downward into the core and emerge at greater distances after the delay caused by their detour through the core.
The time interval between the arrival or the P and S waves can be used to determine the:
Distance to the earthquake
An earthquake with a magnitude of 7.5 on the Richter scale releases about ??? times more energy than one with a magnitude of 6.5.
If an area has shallow, intermediate, and deep earthquakes, then you can infer:
- - It is near a subduction zone
- - The shallow earthquakes will be closer to the trench than deeper ones.
- - The depth pattern of earthquakes can be used to determine which way the slab is inclined.
- -This area has the potential for large earthquakes
The characteristics of P-Waves include:
They compress and then expand the rock in the direction the waves travel.
Earth's crust is thicker than average in:
What is an earthquake?
The shaking of the ground that occurs when brittle rocks being stressed by tectonic forces break suddenly. When they break, the elastic energy built up over years of slow deformation is released rapidly, and some of it is radiated as seismic waves.
Where do earthquakes occur?
Most earthquakes originate at plate boundaries, where stresses are concentrated and straining of the crust is intense.
What are the 3 types of seismic waves?
- P- Waves
- S- Waves
- Surface Waves
The two types of waves that travel through the Earth's interior:
- P (primary) waves: transmitted by all forms of matter and move fastest
- S (secondary) waves: transmitted only by solids and move at a little more than half the velocity of P waves.
What is earthquake magnitude?
Earthquake magnitude is a measure of the size of and earthquake.
How frequently do earthquakes occur?
About 1,000,000 earthquakes with magnitudes greater than 2 take place each year. This number decreases by a factor of 10 for each magnitude unit. Hence, there are about 100,000 earthquakes with magnitudes greater than 3, about 1000 with magnitudes greater than 5, and about 10 with magnitudes greater than 7. The largest earthquakes, with magnitudes of 9 to 9.5, are rare and are confined to thrust faults and subduction zones.
What do seismic waves tell us about the Earth's core?
Seismic waves reflected from the core-mantle boundary locate this sharp boundary at a depth of 2890 km. The failure of S waves to penetrate below the core-mantle boundary indicates that the outer core is fluid. A jump in P wave velocity marks the boundary between the liquid outer core and the solid inner core at a depth of 5150 km. Several lines of evidence show that the core is composed mostly of iron and nickel, with minor amounts of some lighter element, such as oxygen or sulfer.
What governs the type of faulting that occurs in an earthquake?
- The fault mechanism of an earthquake is determined by the type of plate boundary at which it occurs.
- -Normal faulting, caused by tensional forces, occurs at divergent boundaries.
- -Strike-slip faulting, caused by shearing forces, occurs along transform -fault boundaries.
- -The largest earthquakes, caused by compressive forces, occur on megathrusts at convergent boundaries.
- -A small number of earthquakes occur far from plate boundaries, mostly within the continents.
What causes the hazards of an earthquake?
Faulting and ground shaking during an earthquake can damage or destroy buildings and other infrastructure. They can also trigger secondary hazards, such as landslides and fires. Earthquakes on the seafloor can trigger tsunamis, which may cause widespread destruction when they reach shallow coastal waters.
What can be done to reduce the risks of earthquakes?
- -Land-use regulation can restrict new building near active fault zones.
- -Construction in high- hazard areas can be regulated by building codes so that structures will be strong enough to withstand the expected intensity of seismic shaking.
Can scientists predict earthquakes?
Scientists can characterize the level of a seismic hazard in a region, but they cannot consistently predict earthquakes with the accuracy that would be needed to alert a population hours to weeks in advance. (no)
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