Geophysics final (multiple choice questions)

What are the units for frequency?

1) Hertz (Hz) 2) 1/s

What additional correction(s) must be made to gravity data collected on moving airplanes or ships?

1) The Eotvos correction for additional centrifugal accelerations using vehicle location, speed, and bearing. 2) Removal of 3-D acceleration effects from the data before processing.

The result of the Fourier Transform is ______

1) amplitude information vs. frequency or wavenumber 2) phase information vs. frequency or wavenumber

Vertical resolution on a seismic section is dependent on what factors?

1) the bandwidth of the wavelet or signal 2) the main frequency present in the wavelet or signal 3)the thickness of the beds that are being imaged *all of the above*

The _______ method uses a long insulated wire or grounded loop and a transmitter to generate EM waves, and one or more receiver coils to measure the response of conductive bodies in the subsurface.

Large-loop method

Which of the following magnitude scales gives us the best information about the actual size of an earthquake?

Moment magnitude (Mw)

Mafic dikes strike roughly NW-SE in an area. To visualize the dikes, magnetic data are collected on a grid. After reduction, the anomalies are made more obvious by the use of false illumination. Which would by the best orientation for the illumination to highlight the dikes?

North East

The illustration below shows the gravity profile over the buried object shown. What would happen if the object were moved deeper in the subsurface?

The anomaly would decrease in amplitude and the shape of the peak would be flatter.

The illustration below shows the gravity profile over buried object shown. What would happen if the object were moved deeper?

The anomaly would decrease in magnitude and the shape of the anomaly would flatten.

The illustration below shows the magnetic field over a buried object collected along a N-S line. What would happen if the object were moved deeper?

The anomaly would decrease in magnitude and the shape of the peak would be flatter.

The illustration below shows the gravity profile over the buried object shown. What would happen if the object were moved closer to the surface?

The anomaly would increase in amplitude and the shape of the break would be narrower.

The illustration below shows the gravity profile over buried object shown. What would happen if the object were moved closer to the surface?

The anomaly would increase in magnitude and the shape of the peak would be narrower.

The illustration below shows the magnetic field over a buried object collected along a N-S line. What would happen if the object were moved shallower?

The anomaly would increase in magnitude and the shape of the peak would be narrower.

In order for critically refracted waves to occur at a boundary in the subsurface, which of the following must be true?

the velocity of the lower layer must be greater.

If seismic reflections from a deeper reflector travel through a low velocity zone, what happens to the arrival times of those waves?

the waves arrive alter than waves not traveling through the low velocity zone.

________ is a relationship between resistivity, fluid saturation and the porosity.

Archie's Law

Which of the following is a not a way seismic energy is lost during transmission?

Cavitation

The __________ array has the two current and two potential electrodes paired at a constant separation, with the distance between the electrode pairs increased by integer multiples of the separation distance.

Dipole-Dipole

A seismic survey is measuring subsurface variations in which physical property?

Acoustic wave velocity

__________ occurs when a signal is under sampled in either time or space.

Aliasing

to deduce the shape of a body producing an anomaly along a single traverse, a calculated result of model is compared in which the causative body that is uniform and horizontal, extending to an infinite distance on either side of the traverse. This is an example of:

Forward modeling in 2-D

_______ systems use a short EM signal called a chirp to produce high-resolution maps of the subsurface.

Ground Penetrating Radar

Which of the following statement is true about intensity scales?

Intensity is a subjective measure of the amount of damage caused by an earthquake.

Which of the following would not be a good application of magnetic methods?

Investigation of the depth and extent of the water table.

Which of the following travels at the greatest speed?

P-waves

This velocity is a weighted average that takes into account the refracted path a wave front travels along:

RMS velocity

John Fox first used the _____ method in _______ to locate a copper sulfide ore.

SP, 1830s

The __________ array has the potential electrodes close to each other near the center array and the current electrodes separated by a much larger distance.

Schlumberger

Which electrode array is best suited for Vertical Electrical Sounding surveys?

Schlumberger

If a P-wave hits a subsurface boundary normal (at 90°) to that boundary, which of the following statements is true?

The P-wave generates both reflected and transmitted P-waves.

Which of the following best defines "geological geophysics"?

The investigation of rocks and structures of the structures of the subsurface with the aim of complementing geologic investigations.

Part of processing gravity data is the application of a terrain correction to the data. Why is this done?

To correct for the fact that nearby elevations change radically.

Part of processing gravity data is the subtraction of Normal or Theoretical Gravity from the observed data. Why is this done?

To correct for the fact that the Earth is rotating and not a perfect sphere.

Part of processing gravity data is the application of the Free Air correction data. Why is this done?

To correct for the fact that the data are not acquired at sea level.

Part of processing gravity data is the application of the Bouguer correction to the data. Why is this done?

To correct for the fact that there is a mass between gravity station and sea level.

Which of the following best describes grain or electrode polarization?

When the current is turned on, conductive minerals become charged on the surface due to electron exchange and this charge attracts and holds oppositely charged ions from the solution.

Which of the following best describes membrane polarization?

When the current is turned on, mobile ions try to move in the proper direction (positive or negative); if clay particles line the channel, or the pore space is smaller than 10^-6 cm , the negative ions "pile up" in this space restricting the flow of both types of ions.

Where is 90% of the Earth's magnetic field generated?

Within the Earth's outer core

The geometric factor is _______.

a term that describes the geometry of the electrode array.

At a seismograph station, Rayleigh waves are recorded on the N-S seismograph. The earthquake occurred ___________.

along the line either north or south of the station.

Of the following Earth materials, which has the highest overall magnetic susceptibilities?

basic or mafic igneous rocks

The slope of a line in a T-X curve plotted for a refraction survey represents __________.

the reciprocal of the true velocity of that layer.

A gravity survey is measuring subsurface variations in which physical property?

density

The purpose of stacking is to

improve the signal-to-noise ratio

Interactions of objects with certain properties with the Earth's current magnetic field will produce a(n) __________ magnetic field.

induced

What are the units for wavelength?

meters

On a seismic reflection record, the reflections from shallower layers are ______ relative to reflections from deeper layers.

more hyperbolic and stronger

The process of migration ____________.

moves reflections back to their proper spatial and temporal location on a seismic section, collapses diffractions and removes "bow ties".

What type of faulting does the first motion diagram below represent (dark = compression)?

normal

What type of faulting does the first motion diagram below represent (dark = compression)?

reverse

The depth at which the EM field strength falls to 1/e is called the ______.

skin depth

This velocity is that which makes the final stacked seismic section look the "best":

stacking velocity

What type of faulting does the first motion diagram below represent (dark = compression)?

strike-slip

Which of the following best defines "environmental geophysics"?

the application of geophysical methods to the investigation near-surface physical and/or chemical phenomena which are likely to have implications for the management of the local environment.

The statement "it is a paramount importance that geophysical data are interpreted within a physically constrained or geological framework" is related to what property of all geophysical data?

the fundamental nonuniqueness of the data and its solutions.

Two bodies of the same size, shape, and susceptibility are buried at the same depth in the subsurface. If body A is located at 60° North magnetic latitude and body B at North magnetic pole, then...

the magnetic anomaly peak of body B will be larger and centered over the body.

Regarding the equatorial and polar radii of the Earth:

the polar radius is smaller than the equatorial radius.