Geophysics and Seismology Flashcards
7 cards from real ASBOG practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Geophysics and Seismology flashcards as text
The seismic moment M₀ is defined as the product of the shear modulus, the fault rupture area, and which third quantity?
Answer: Average slip on the fault
M₀ = μ × A × D, where μ is the shear modulus, A is rupture area, and D is the average displacement (slip) on the fault.
Telluric current surveys measure naturally occurring electric currents in the Earth. These currents are primarily induced by:
Answer: Variations in the geomagnetic field driven by solar activity
Telluric currents are induced in conductive Earth materials by time-varying external geomagnetic fields caused by ionospheric and magnetospheric disturbances.
In well-log analysis, the neutron porosity tool primarily responds to which subsurface property?
Answer: Hydrogen content (porosity/fluid)
The neutron log measures hydrogen index; because hydrogen is concentrated in pore fluids, it is a direct indicator of porosity.
Isostasy can be modeled using either the Airy or Pratt hypothesis. Which statement correctly distinguishes the two?
Answer: Airy assumes uniform crustal density with variable crustal thickness; Pratt assumes constant crustal thickness with variable density
Airy isostasy compensates topography with variable crustal roots at uniform density; Pratt compensates with lateral density variations at a fixed compensation depth.
During seismic data processing, NMO (Normal Moveout) correction is applied to convert:
Answer: Offset travel times to zero-offset travel times
NMO correction flattens reflection hyperbolas on common midpoint gathers by removing the offset-dependent travel time increase, producing approximate zero-offset traces.
Which geophysical method is most appropriate for mapping lateral variations in near-surface soil conductivity for agricultural or environmental applications?
Answer: Frequency-domain EM terrain conductivity (e.g., EM38)
Instruments like the Geonics EM38 use frequency-domain EM to measure apparent conductivity of the upper 1–2 m of soil rapidly across fields.
The focal mechanism (beach ball) of a pure thrust fault is characterized by which pattern?
Answer: Two dark quadrants at the top and bottom, two white quadrants on the sides
Thrust faults show compressional (dark) P-axis quadrants at the top and bottom of the focal sphere and tensional (white) T-axis quadrants on the sides.