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Q71. Which option represents porosity of a rock?
Porosity = Pore Volume / Bulk Volume. Since Pore Vol = Bulk Vol - Solid Vol, the formula is (V_bulk - V_solid) / V_bulk.
Q72. A phase-diagram with a specified bulk-composition is known as:
Pseudosections show stable mineral assemblages for a specific bulk composition over a P-T range. AFM/ACF are compatibility diagrams (projections).
Q73. The type of wave that arrives first at a station from an earthquake hypocenter is:
P-waves (Primary waves) are compressional waves and travel faster than S-waves or surface waves.
Q74. In which one of the following regions of the electromagnetic spectrum does the maximum atmospheric scattering occur?
Rayleigh scattering is inversely proportional to the fourth power of the wavelength (1/lambda^4). UV has the shortest wavelength among the options, thus undergoing maximum scattering.
Q75. For earthquakes of magnitudes 6 and 7, the seismic wave amplitudes are A6 and A7. Which is true?
Richter magnitude is logarithmic base-10 for amplitude. A magnitude increase of 1 corresponds to 10x amplitude. (Note: Energy increases by ~32x).
Q76. Which one of the following geophysical methods can provide information on deep Earth structures (of the order of 1000 km) with highest resolution?
Seismic tomography uses earthquake waves to image deep Earth structures with much higher resolution than potential field methods (gravity/magnetic).
Q77. Which logging technique is most suitable to detect a shale layer sandwiched between two sandstone layers?
Shale contains naturally radioactive elements (K, U, Th), resulting in a high Gamma Ray count compared to clean sandstone.
Q78. Which one of the following parent-daughter systems has the longest half life?
Sm-147 has a half-life of approx 106 billion years. Rb-87 is ~49 billion years. K-40 is ~1.25 billion years.
Q79. Select the option that lists oxide minerals only.
Spinel (MgAl2O4), Corundum (Al2O3), and Rutile (TiO2) are all oxides. Olivine is a silicate; Galena is a sulfide; Fluorite is a halide.
Q80. Which one of the following is a dinosaur?
Stegosaurus is a dinosaur. Stegodon is an extinct proboscidean (elephant relative). Equus is a horse. Otoceras is an ammonoid.