ASBOG - Association of State Boards of Geology Geophysics and Seismology Questions and Answers

Question 1

An airborne magnetic survey is being used for regional geologic mapping. Which of the following geologic features is most likely to produce a strong, positive magnetic anomaly?

Accepted Answer

A buried granite batholith intruding into sedimentary rocks.

Answer

A thick sequence of limestone and shale.

Answer

A syncline composed of folded sandstone beds.

Answer

A salt dome (diapir) that has pierced overlying strata.

Question 2

The Mohorovičić discontinuity (Moho) is a major seismic boundary within the Earth. What does it represent?

Accepted Answer

The boundary between the crust and the mantle.

Answer

The boundary between the lithosphere and the asthenosphere.

Answer

The boundary between the mantle and the outer core.

Answer

The boundary between the liquid outer core and the solid inner core.

Question 3

A seismologist is analyzing seismograms from three different stations (A, B, and C) to locate an earthquake's epicenter. The S-P time interval is smallest for station A, larger for station B, and largest for station C. What can be concluded about the earthquake's location?

Accepted Answer

The earthquake's epicenter is closest to station A.

Answer

The earthquake occurred an equal distance from all three stations.

Answer

The earthquake's epicenter is closest to station C.

Answer

The S-P time interval is unrelated to the distance from the epicenter.

Question 4

Which of the following statements most accurately describes the key difference between primary (P) waves and secondary (S) waves?

Accepted Answer

P-waves are compressional and can travel through solids and liquids, while S-waves are shear waves and can only travel through solids.

Answer

S-waves have a higher velocity than P-waves and are the first to arrive at a seismograph station.

Answer

P-waves cause particle motion perpendicular to the direction of wave propagation, while S-waves cause particle motion parallel to it.

Answer

S-waves are a type of surface wave, while P-waves are a type of body wave.

Question 5

A gravity survey is conducted over a buried, high-density ore body surrounded by lower-density host rock. After applying the standard Free-Air, Bouguer, and terrain corrections, which of the following would be the expected gravity anomaly directly over the ore body?

Accepted Answer

A positive Bouguer anomaly.

Answer

A negative Bouguer anomaly.

Answer

No significant anomaly because the corrections remove all local effects.

Answer

A positive Free-Air anomaly but a negative Bouguer anomaly.

Question 6

A seismic refraction survey is performed to determine the depth to bedrock. The resulting travel-time graph for the first arrivals shows two distinct linear segments. The first segment has a steep slope (low velocity), and the second has a shallower slope (high velocity). What does the 'crossover distance' on this graph represent?

Accepted Answer

The distance from the source where the refracted wave from the bedrock becomes the first arrival at the geophone.

Answer

The point where the direct wave and the reflected wave arrive at the same time.

Answer

The shallowest depth at which the bedrock can be detected.

Answer

The point where the S-wave from the bedrock first arrives.

An airborne magnetic survey is being used for regional geologic mapping.Which of the following geologic features is most likely to produce a strong, positive magnetic anomaly?

An airborne magnetic survey is being used for regional geologic mapping.
Which of the following geologic features is most likely to produce a strong, positive magnetic anomaly?