Part 5 — Three Claims to Evaluate

Part 5 — Three Claims to Evaluate#

Each of the three claims below is a statement some geophysics student might write in a homework answer or report. Your job is to figure out — without your AI assistant’s help at first — whether each one is correct, and then ask your AI assistant to evaluate them and compare notes.

One of the three claims is wrong. The other two are essentially correct. The wrong one is wrong in a subtle way — it has the right shape of an equation but the wrong content.

Do not read the answer key (your instructor has it) until after you have submitted your worksheet.

Claim A#

Critically refracted head waves only exist when the lower layer has a higher seismic velocity than the upper layer (V₂ > V₁). If V₂ < V₁, the transmitted ray bends toward the normal upon entering the lower layer, and no critically refracted head wave can be generated along the interface.

Claim B#

In a flat two-layer refraction problem, the intercept time on the travel-time vs. offset plot — the time at which the refracted-wave linear branch would intersect the time axis if extended to x = 0 — equals 2h / V₁, where h is the depth to the refractor and V₁ is the velocity of the upper layer. This is the same as the vertical two-way travel time of a P-wave through the upper layer.

Claim C#

When a regional seismic network records a small crustal earthquake, the focal depth of the earthquake is typically more poorly constrained than its epicentral coordinates, because all stations are located near the Earth’s surface. The ray geometry from a shallow source to surface stations has poor vertical resolution compared to its horizontal resolution, particularly when no station is within roughly one focal depth of the epicenter.

Your task#

For each claim:

  1. Without using AI, write down whether you think it’s right or wrong, and why. (One or two sentences each, in your own words.)

  2. Then ask your AI assistant to evaluate each claim, one at a time, using the “Always push back” pattern from the AI Literacy Guide.

  3. Then cross-check the claim you suspect is wrong against Lowrie & Fichtner (Ch. 3 or 4), the relevant ESS 314 lecture, or your Lab 3 notebook. Quote the specific page, equation number, or notebook cell that confirms or rejects the claim.

  4. Document the verification in your ai_logs/error_log.md.

The point is not that you find the wrong claim — it’s that you articulate the reason it’s wrong with a specific primary-source citation.