The largest earthquakes occur on plate boundaries of the type marked with the letter
[ Select ]
C
B
A
D
on the map below. The
[ Select ]
2015 Gorkha
1784 Iceland
1964 Anchorage, Alaska
1906 San Francisco
earthquake is an example of one of these large earthquakes associated with this type of plate boundary.

Question

The largest earthquakes occur on plate boundaries of the type marked with the letter 
[ Select ]
C
B
A
D
 on the map below.  The 
[ Select ]
2015 Gorkha
1784 Iceland
1964 Anchorage, Alaska
1906 San Francisco
 earthquake is an example of one of these large earthquakes associated with this type of plate boundary.

BlackTom AI · Accepted Answer

Question restatement and options:
- The largest earthquakes occur on plate boundaries of the type marked with the letter [ Select ] on the map below. The [ Select ] 2015 Gorkha 1784 Iceland 1964 Anchorage, Alaska 1906 San Francisco earthquake is an example of one of these large earthquakes associated with this type of plate boundary.
- Answer options (for the two dropdowns): not provided in this dataset, but the student’s selections are shown as: "A" for the first dropdown and "1964 Anchorage, Alaska" for the second dropdown.

Analysis of the first dropdown option (letter A):
- The map labels different plate boundary types with letters A, B, C, D. To determine which boundary type hosts the largest earthquakes, we need to recall geologic knowledge: the biggest earthquakes are typically associated with subduction zones, where one plate subducts beneath another (a convergent plate boundary). If letter A on the map corresponds to a subduction boundary (for example, where the Philippine Sea Plate is subducting beneath the Eurasian Plate near the western Pacific region), then option A would correctly identify the plate boundary type responsible for the largest earthquakes.
- If, however, letter A did not correspond to a subduction zone on this specific map (e.g., if A marked a different boundary type like a transform or divergent boundary), then selecting A would be incorrect. Without the exact legend explaining what A represents, we rely on typical classroom map conventions where A marks a major subduction boundary near the Philippines region.

Analysis of the second dropdown option (the example earthquake year and location, e.g., 1964 Anchorage, Alaska):
- The 1964 Alaska earthquake occurred at a subduction zone along the Aleutian Trench, which is a classic example of a large megathrust earthquake associated with a convergent plate boundary (subduction). This makes it a correct example of the type of boundary responsible for the largest earthquakes.
- Other listed earthquakes, such as 1906 San Francisco (Great Earthquake) and 1784 Iceland, relate to boundary types in different tectonic contexts (San Francisco to the San Andreas Transform boundary; Iceland to a hotspot/unique boundary region involving rifting and volcanism). While Iceland and San Francisco are significant, they are not the quintessential megathrust events tied to world-record magnitudes like Alaska’s subduction-zone event.
- The selection of 1964 Anchorage, Alaska as an example aligns with the recognized pattern that the largest earthquakes occur at subduction-zone boundaries, which are typically shown on educational maps with a subduction boundary motif.

Bridge between the two parts of the question:
- If the map’s letter A indeed marks a subduction (convergent) plate boundary, then choosing A for the boundary type is correct because megathrust earthquakes occur at such boundaries.
- Consequently, identifying 1964 Anchorage, Alaska as an example of a large earthquake associated with this boundary type is consistent with the Alaska megathrust event.

Potential misconceptions to avoid:
- Misinterpreting the San Andreas boundary (transform) as producing the largest earthquakes, since transform boundaries can produce large, damaging earthquakes but generally not the largest megathrust events that occur at subduction zones.
- Assuming Iceland’s seismic activity is the largest class solely due to size; while Iceland is seismically active, its earthquakes are often associated with divergent/rifting and volcanic processes, not the classic megathrust subduction events.

In summary, the reasoning supports that the first dropdown should select the letter corresponding to a subduction/convergent boundary (likely A, given typical map labeling), and the second dropdown should identify the 1964 Anchorage, Alaska event as a representative megathrust earthquake at a subduction boundary.

GEO 1030-090 Fall 2025 GEO 1030-090 Final Exam

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