ANSWERS TO “TEST YOUR KNOWLEDGE” ON PAGE 28
Answers: 1. The answer is choice “b” or “sensitivity.”
The activity ratio of a soil or sediment is the ratio of its plasticity index over the percentage of its clay fraction (Ar = Ip / %clay).
The ultimate strength of a soil or rock is the maximum stress the material can withstand before eventually failing. It is the highest point reached on the stress-strain curve.
The ductility of a soil or rock is the total percent deformation it achieves before rupture occurs. Ductile behavior is equivalent to plastic deformation.
2. The answer is choice “c” or “Transforming seismic reflection data into quantitative rock properties.”
Choice “a” mainly relates to the process of “migration” which is critical in attenuating “diffractions.” When seismic energy hits a discontinuity (such as a subsurface fault plane), a burst of energy will be transmitted in all directions forming an arch-like (hyperbolic) pattern. These “diffractions” may look like geologic structures, but they are not real. “Migration” involves geometric repositioning. In “migration” events are corrected and mapped to their proper position in space.
In choice b”, the processing step of “demultiplex” allows the field recorded data to be separated into trace sequential order. Data is rearranged so that all samples for any given channel are in sequence from time zero to the end of the record. The output is a “trace” in sequential form. In the processing step known as “muting” traces are muted elimi- nating the shallow parts of longer traces (those further away from the source). The idea is to exclude that part of the trace that contains more “noise” than “signal”.
In choice “d”, attenuation or elimination of “multiples” is achieved in processing steps such as “deconvolution” and “stacking.” Seismic energy bouncing more than once from the same reflector has the same travel time as energy travel- ing to a much deeper reflector. This results in an apparent, phantom, deeper reflector that may be thought of as being a real horizon. These phantom reflectors are known as “multiples.” “Deconvolution” is a processing step performed to improve the vertical resolution of seismic data by compressing the basic wavelet. The process is used to minimize “multiples” and enhance the reflection events. Generally, it is applied before “stacking”, but it is also sometimes done after “stacking”. It is performed to obtain the idealized impulse response of the earth model. “Stacking” constitutes another crucial processing step, where individual traces are combined into one trace for each common depth point (CDP). “CDP” suppresses “multiples.”
3. The answer is choice “a” or “turritella.” Exogyra and gryphaea are extinct pelecypods of the oyster family. Exogyra lived in the Jurassic to Cretaceous time span. Gryphaea ranged from Triassic to mid Paleogene but was mostly restricted to the Triassic to Jurassic periods.
Orbitolina refers to a foraminifer with a conical siliceous test with agglutinated sandy particles that lived in Cretaceous times.
4. The answer is choice “d” or “Magnetite.” Please refer to the table shown below.
Mineral Magnatite Crystal Hardness Isometric Hematite Orthorhombic Goethite Pyrite Hexagonal Isometric 30 TPG •
Oct.Nov.Dec 2021 5.5-6.5 5.0-5.5 5.5-6.5 6.0-6.5
Specific Gravity
5.18 3.3-3.4 5.26 4.95-5.10 Streak black
yellow-yellow- ish-brown
red
greenish-black to brownish- black
Chemical Formula
Fe2+Fe3+2O4 Fe3o4
Fe3+O(OH) FeO(OH)
Fe2O3 FeS2 Gravity Iron Oxide Iron Hydroxide Iron oxide Iron sufide
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