GEO100 Midterm

Student Name________________________ Prof. Robert J. Sager

GEOLOGY 100 – MIDTERM EXAM (20% of course grade)


Purpose: Apply the scientific method to interpret geologic data/information in this exercise. The student should review the topics covered on rocks (igneous, sedimentary, and metamorphic rocks) and geologic time from your previous assignments, the course “Webliography”, and online geologic research sources. Your research sources must be listed in proper APA-style citations at the end of the questions.


Figure 1.

Answer the following questions based on your interpretation of the geologic cross-section above (Page 1).

1) How would you apply the “principle of original horizontality” to the layers (strata) in Fig. 1? Use the strata from B to M (includes B-K-N-J-D-M). Explain.

2) How would you apply the “principle of superposition” to the layers (strata) in Fig. 1? Use the strata from B to M

(includes B-K-N-J-D-M). Which is the oldest strata and which is the youngest strata (identify by letter)? Explain.

3) Which is the surface cover (identify by letter)? What would this be composed of? What are the possible sources of this material? Why is this not considered part of the sedimentary rock strata? Explain.

4) What is a geologic “unconformity”? Are there any unconformities in this strata sequence? If so, what type of unconformity are they? Describe in the stratigraphy (between letters) where at least two (2) unconformities are located, if any.

5) If rock region A is composed of igneous rock, would it be intrusive or extrusive igneous rock? What type of common igneous rock would it most likely be composed of? What is this large igneous feature called?

6) If the sedimentary strata from B to M had some metamorphic rock in it, which strata (identify by letter) would most likely have had the most contact metamorphism? Explain.

APA citations:


Purpose: Apply the scientific method to interpret geologic data/information in this exercise. The student should review the topics covered on Plate Tectonics from your previous assignments, the course “Webliography”, and other online geologic research sources that cover earthquake distribution. Your research sources must be listed in proper APA-style citations, including any websites you used.

Earthquake data has been collected over a 32-month period from a local seismograph network. A total of 2,476 seismic events were recorded, of which, 205 are chosen to serve as the master data set (earthquakes with the most reliable locations).

The master data set is provided in Table 2, which shows only the earthquake foci locations that occur within the line of the cross section in Figure 1 at latitude 20ºS. The focus (pl. foci) of an earthquake is the point of the earthquake source below the surface, while the epicenter is the point directly above the focus and located at the surface.

Plot the earthquake data from Table 2 on the cross-section of Figure 2 by placing a dot on the cross-section at the correct location for each earthquake focus.

Longitude, ºW Depth (km) Longitude, ºW Depth (km) Longitude, ºW Depth (km)
68 -18 66 -24 69 -15
65 -29 68 -28 65 -25
71 -15 67 -21 73 -8
67 -20 68 -20 63 -33
70 -12 72 -6 67 -23
72 -9 66 -26 66 -22
68 -23 69 -20 72 -12
71 -10 67 -25 64 -30
65 -27 70 -14 71 -9
64 -32 70 -17 69 -17

Table 2. Earthquake foci data recorded along the plane of the cross section of Figure 2.




Figure 2: Cross-section along the 20ºS latitude (20S) parallel (X-axis=latitude, Y-axis=depth).

Interpret the data (Pages 3 and 4) by answering the following questions:

1) Based on the pattern that emerged when you plotted the earthquake foci data, determine the plate tectonic boundary type for this region. Indicate this by drawing a possible plate boundary on the cross-section, and show the direction of motion of the plates with arrows.

2) Describe the geologic processes and activity associated with this type of tectonic boundary.

3) Assess this region for geologic hazards. Name three geologic hazards that could be expected in this region.




4) Based on the latitude and longitude from Figure 2, where is this plate boundary located?

APA Citations:


Updated 09.12.18











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