Question

triangulation scenario
for this part of the activity, you will use s - p arrival intervals from three seismic stations to determine how far each station is from the epicenter. use the travel - time curve to find the distance for each s - p interval. record your answers below.

1. corvallis, oregon (iu - cor)

• location: 44.5859°n, - 123.3046°w
• s - p arrival interval: 6 minutes 15 seconds
• distance from epicenter: ____________ km

1. tucson, arizona (iu - tuc)

• location: 32.3098°n, - 110.7847°w
• s - p arrival interval: 8 minutes 15 seconds
• distance from epicenter: ____________ km

1. black hills, south dakota (iu - rssd)

• location: 44.1212°n, - 104.0359°w
• s - p arrival interval: 10 minutes
• distance from epicenter: ____________ km

epicenter location

• where was the epicenter of this earthquake located (near what city or region)?

accuracy of triangulation

• why do we need at least three seismic stations to determine the exact epicenter?
• what would happen if we only had data from two stations?

travel - time curve interpretation

Explanation:

Step1: Convert S - P arrival intervals to seconds for Corvallis

6 minutes 15 seconds = 6*60 + 15 = 375 seconds.

Step2: Read distance from travel - time curve for Corvallis

From the curve, for 375 seconds S - P interval, distance ≈ 3200 km.

Step3: Convert S - P arrival intervals to seconds for Tucson

8 minutes 15 seconds = 8*60+15 = 495 seconds.

Step4: Read distance from travel - time curve for Tucson

From the curve, for 495 seconds S - P interval, distance ≈ 4400 km.

Step5: Convert S - P arrival intervals to seconds for Black Hills

10 minutes = 10*60 = 600 seconds.

Step6: Read distance from travel - time curve for Black Hills

From the curve, for 600 seconds S - P interval, distance ≈ 5200 km.

For the questions about triangulation:

• Why we need at least three seismic stations to determine the exact epicenter: Each seismic station gives a distance from the epicenter. With two stations, the possible locations of the epicenter lie on the intersection of two circles (centered at the stations with radii equal to the distances), which gives two possible points. With three stations, the three circles (centered at the three stations with radii equal to the respective distances) intersect at a single point, determining the exact epicenter.
• What would happen if we only had data from two stations: We would have two possible locations for the epicenter, as the intersection of two circles centered at the two stations with radii equal to the distances from the epicenter gives two intersection points.

To find the epicenter location precisely would require further geographical and triangulation techniques using the three - station distances calculated above, but without additional tools like a map and more detailed triangulation methods, we can't give a specific city or region here.

Answer:

1. Distance from epicenter for Corvallis: 3200 km
2. Distance from epicenter for Tucson: 4400 km
3. Distance from epicenter for Black Hills: 5200 km

Why we need at least three seismic stations to determine the exact epicenter: Three circles intersect at a single point.
What would happen if we only had data from two stations: Two possible epicenter locations.