Question

which statement best describes what information can be gained from the s-p interval of seismic waves?

the s-p interval relies on the number of aftershocks following the main earthquake event and does not provide information about distance.

the s-p interval measures the time between the arrival of the primary (p) and secondary (s) seismic waves, with a longer s-p interval indicating a closer earthquake epicenter.

the s-p interval is based on the difference in speed between p and s waves, with a shorter interval suggesting a closer epicenter.

the s-p interval is irrelevant for determining earthquake distance; instead, it is used to estimate the earthquakes magnitude.

Explanation:

Define the S-P interval and wave speeds

Primary (P) waves travel faster than secondary (S) waves. The S-P interval is the time difference between the arrival of these two waves at a seismograph station.

Relate interval duration to epicenter distance

Because P-waves travel faster, the gap in arrival time (S-P interval) increases as the waves travel farther from the origin. Therefore, a shorter S-P interval indicates a closer epicenter, while a longer interval indicates a more distant epicenter.

Evaluate the given options

• Option 1: Incorrect. The S-P interval is directly related to distance and does not rely on the number of aftershocks.
• Option 2: Incorrect. A longer S-P interval indicates a farther epicenter, not a closer one.
• Option 3: Correct. It correctly states that the interval is based on the speed difference, with a shorter interval suggesting a closer epicenter.
• Option 4: Incorrect. The S-P interval is the primary tool for determining distance to the epicenter, not magnitude.

Answer:

• (A) The S-P interval relies on the number of aftershocks following the main earthquake event and does not provide information about distance.
• (B) The S-P interval measures the time between the arrival of the primary (P) and secondary (S) seismic waves, with a longer S-P interval indicating a closer earthquake epicenter.
• (C) The S-P interval is based on the difference in speed between P and S waves, with a shorter interval suggesting a closer epicenter. (Correct answer)
• (D) The S-P interval is irrelevant for determining earthquake distance; instead, it is used to estimate the earthquake's magnitude.