Grading Note: Accept synonymous descriptions (e.g., "colliding" for convergent, "pulling apart" for divergent, "sliding laterally" for transform). For the reason column, award full credit if student mentions the presence/absence of vertical water displacement.
Futura Geohazards Engineering Internship • Answer Key Page 1 of 2
Chapter 3 Assessment — Answer Key (Continued)
Parts 3 & 4 Rubrics & Model Responses
Part 3: Subduction Diagram Analysis Answers 4 Points Total (2 pts each)
Model Answer: Subduction is the geological process where one tectonic plate (the denser oceanic plate) moves under another plate into the mantle. At the ocean trench, seafloor crust is destroyed as it gets pushed downward into Earth's interior.
• 1 pt: One plate sinks under another • 1 pt: Crust is destroyed at trench
Model Answer: As plates lock, friction creates immense pressure. An earthquake suddenly releases this pressure, causing a rapid vertical movement of the plate. This snaps the seafloor upward and violently displaces the ocean water column above it, generating the tsunami wave.
• 1 pt: Locked pressure release • 1 pt: Vertical seafloor uplift displacing water column
Part 4: Engineering Case Scenarios Model Answers 8 Points Total
Scenario A: Transform Fault Offshore (Mw 7.4) — Low Tsunami Risk 3 Points
Model Answer: Although the magnitude exceeds 7.0 under the ocean, transform boundaries slide sideways (horizontally). Horizontal motion does not raise or lower the seafloor or displace the water column vertically. Without vertical water displacement, an ocean-wide tsunami is very unlikely.
Scoring: 1 pt for horizontal plate motion • 1 pt for lack of vertical seafloor shift • 1 pt for no vertical water displacement.
Scenario B: Subduction Zone Event (Mw 6.1) — No Ocean-Wide Warning 3 Points
Model Answer: While subduction zones have the proper vertical motion, Chapter 3 notes an earthquake must have a magnitude larger than 7.0 to release sufficient energy for a tsunami. At magnitude 6.1, shaking is strong but the energy released is insufficient to generate an ocean-wide wave.
Scoring: 1 pt for Mw < 7.0 threshold • 1 pt for insufficient energy released • 1 pt for recognizing boundary type alone is not enough.
Scenario C: Divergent Boundary Behavior 2 Points
Model Answer: According to Chapter 3 (p. 9), divergent earthquakes typically do not cause tsunamis because: (1) they are not strong enough, and (2) they do not generate enough vertical shift in the seafloor.
Scoring: 1 pt for earthquakes not strong enough • 1 pt for insufficient vertical seafloor shift.
Performance Bands:
Advanced: 23–25 pts (92–100%) Proficient: 18–22 pts (72–88%) Developing: 14–17 pts (56–68%) Novice: < 14 pts
Futura Geohazards Engineering Internship • Answer Key Page 2 of 2
