ASBOG Geophysics and Seismology 2

Question 1

Which seismic wave type travels exclusively along the Earth's surface and produces horizontal ground motion perpendicular to the direction of propagation?

Accepted Answer

Love wave

Answer

Love waves are surface waves that cause horizontal shear motion perpendicular to the propagation direction and cannot travel through water.

Question 2

The Mohorovičić discontinuity is defined by a seismic velocity increase to approximately what P-wave speed?

Accepted Answer

7.8–8.2 km/s

Answer

The Moho marks the crust-mantle boundary where P-wave velocities jump to approximately 7.8–8.2 km/s in the uppermost mantle.

Question 3

In gravity surveying, a Bouguer anomaly is calculated after applying the free-air correction plus a correction for which factor?

Accepted Answer

The mass of rock between the station and sea level

Answer

The Bouguer correction removes the gravitational effect of the rock mass between the observation point and the datum (sea level).

Question 4

Which electromagnetic method measures the ratio of induced electric field to the applied magnetic field and is commonly used to map conductive ore bodies?

Accepted Answer

Frequency-domain EM (FDEM)

Answer

Frequency-domain EM methods inject or induce an alternating magnetic field and measure both the primary and secondary (induced) fields to estimate conductivity.

Question 5

A geologist interprets a seismic reflection profile and notes an 'unconformity' as a truncation of reflectors below a surface. What does this indicate?

Accepted Answer

An erosional or non-depositional hiatus in the rock record

Answer

Reflector truncation below a surface on a seismic section indicates an unconformity — a gap in the stratigraphic record due to erosion or non-deposition.

ASBOG - Association of State Boards of Geology Practice Test

ASBOG - Association of State Boards of Geology Practice Test

ASBOG Geophysics and Seismology 2