1. What is a fault? ____________________________________________________________
ID: 160470 • Letter: 1
Question
1. What is a fault? _______________________________________________________________
For normal faults , regardless of the absolute age of the rocks involved, it is always true that rocks that are relatively ___________________ are displaced on top of rocks that are relatively _____________________________________.
2. What is a fold? ______________________________________________________________
Why are earthquakes typically NOT associated with folding? ___________________________ ___________________________________________________________________________________.
3. What principle is demonstrated by the fact that part of a cube of ice floating in water lies above the water? ________________________________.
Who first discovered this principle? ________________________.
How might this principle relate to belts of high topography (i.e. mountain chains?) _____________________________________________________________________________.
4. You are out in the field and stumble upon an aesthetically pleasing rock; your colleague tells you that it is part of a large mafic dike and it has been dated using U-Pb zircon methods as 450 +/-1.3 million years; what geologic EON does it belong to? _____________________________
What is the strike of the fault? ________________________
In a relative sense, when did motion along this fault occur? __________________________________________.
6. What is a strike-slip fault? __________________________________________________ ___________________________________.
7. What are seismic P and S waves? ___________________________________.
How do they differ? ______________________________________________________
Roughly, how fast does seismic energy pass through rocks in the earth’s crust? __________________________________ .
8. Most earthquake foci in continents are located at depths less than about 20 km. Why? ______________________________________________________________________________ ____________________________________________.
Earthquakes with foci at depths greater than about 20 km are typically referred to as “deep focus” earthquakes. Where do these occur, and why? _________________________________________________________________ ________________________________________________________________________________.
9. How was the boundary between the crust and mantle initially discovered? __________ _________________________________________________________________________________.
In the middle of a continent (e.g., Kansas), about how thick is continental crust? _____________________.
Have we ever drilled to the crust mantle boundary in any continent? _____________________.
10. Generalizing, what three general plate tectonic environments are responsible for most earthquakes? ______________________________________________________________ ____________________________________________________________________________.
13. Most people like mountains, especially the beings who really belong on Earth. How might mountains remain mountains (high topography) for long periods of geologic time?????_________________________________________________________ __________________________________________________________________________.
14. You pick up a sandstone, which, on the basis of fossils contained in it, you know was deposited in the Cenozoic era, at about 30 million years ago. It has a concentration of detrital zircon grains in it, and ALL of the zircon grains you subject to high precision U-Pb zircon age dating yield age estimates between 30 and 33 million years ago. How might you explain this observation? _____________________________________________________________________ ________________________________________________________________________________.
15. Your “weight” is a direct function of your mass and the mass of Earth, like it or not. If you measured your weight at sea level, above an area in the crust where there is a 10 km diameter buried mass of marshmallow, how would your weight compare to a different site, where there is normal crust below you ? _____________ ___________________________________________ _________________________________________________________
With this as a background, how can gravity be used to investigate the internal structure of our planet? ______________________________________________________________________________
16. How could you use gravity data to demonstrate that a part of a continent, with abundant mountain belts and also low relief and low elevation plains is in isostatic equilibrium? _________________________________________________________________________________.
18. How are earthquake locations determined? __________________________________ _____________________________________________________________.
What realistic assumptions are made in determining their location? ______________________________ _________________________________________________________ _____________________
What is the difference between the earthquake focus and the epicenter? _________________________________________________________________________________.
20. What is the geomagnetic polarity time scale? _______________________________________ ____________________________________________________________________________________.
21. In the context of plate tectonics, continents have different kinds of margins. What is a passive margin, and provide an example. _______________________________________ ________________________________________________________________________________.
Would you expect much seismicity in a passive margin setting? Why or why not? _____________________________________________________________________________
22. In what kind of plate tectonic setting did the March, 2011, Japan earthquake take place? ___________________________________________________________________________.
Explanation / Answer
1.
Answer: A fault is a rupture or a crack or a fracture at boundaries of the plates or within the subsurface due to high pressure and temperature.
For normal faults, regardless of the absolute age of the rocks involved, it is always true that rocks that are relatively horizontally deforms are displaced on top of rocks that are relatively increasing age from top to bottom.
2.
A zig zag structure of the rocks is called fold. Thus, the sedimentary strata bent or curved as a result of permanent deformation.
A hot magma come out on the Earth surface due to Earthquake, during this process hot magma exposed at all area and deposited one another. If lave comes slowly, and then the deposition pattern shows horizontally only. The magma is igneous rock, so there no chance to folding.
3.
Water gets expands during the time of freezing nearly 9%. In this process volume of the ice increases than normal volume of water, the low density ice easily floats on high density water. Density of ice is 0.91 gm/cc and density of water is 1gm/cc.
6.
The vertical fracture of layers, where the blocks has moved horizontally is called Strike-Slip fault.
7.
Seismic P-Wave also called Primary wave. It is an elastic wave and it arrives first at the receiving station. The motion of the particle in P-Wave is parallel to the propagation of the wave. S-wave also called secondary wave or shear wave. The particle motion of the S-wave is vertical to the propagation of the wave. It will not pass through liquids because the rigidity modulus of S-Wave is zero. It the second receiving wave at the receiver station.
These are differed by particle motion and speed of traveling with in the Earth’s subsurface.
The velocity of P-wave in crust is 6 to 8 km/s and the velocity of S-wave in crust is 2 to 4 km/s.
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