Lab locating epicenters | PDF - Free Printable

Since I can't view or access uploaded images directly, I can’t see the specific details of your image (such as the seismograms or map). However, based on the text you've provided, I can help you solve the earthquake problem step by step and explain how to approach it. This appears to be a standard seismology exercise involving interpreting seismograms to locate an earthquake epicenter.

Let’s walk through each part of the task using general principles and typical data formats for such problems.

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Problem: Earthquake 1 – Determining Epicenter Location

#### Step 1: Analyze Seismograms
You are given three seismograms from three stations:
- Denver
- Dallas
- Salt Lake City

Each shows P-waves (primary waves) and S-waves (secondary waves). The arrival times of these waves are used to determine the distance to the earthquake's epicenter.

##### Procedure:
1. Determine arrival times of P-wave and S-wave at each station.
2. Calculate time difference between P-wave and S-wave arrivals.
3. Use the time difference to find the distance from the station to the epicenter using a travel-time graph (which is typically provided in textbooks or lab manuals).
4. Repeat for all three stations.
5. Use triangulation to locate the epicenter on a map.

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Step-by-Step Solution

#### Step 1: Arrival Times
Assume the following (you'll need to read these from your actual seismograms):

| Station | P-wave Arrival Time (sec) | S-wave Arrival Time (sec) | Time Difference (S-P) |
|---------------|----------------------------|-----------------------------|------------------------|
| Denver | 3.0 | 7.0 | 4.0 sec |
| Dallas | 4.5 | 9.5 | 5.0 sec |
| Salt Lake City| 2.5 | 6.0 | 3.5 sec |

*(Note: These values are illustrative. You must extract real values from your seismograms.)*

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#### Step 2: Use Travel-Time Graph
On a typical P-wave/S-wave travel-time graph, you plot the time difference (S-P) on the x-axis and read off the corresponding distance from the epicenter.

For example:
- A 4.0-second difference → ~300 km
- A 5.0-second difference → ~400 km
- A 3.5-second difference → ~250 km

So:
| Station | Distance to Epicenter (km) |
|---------------|----------------------------|
| Denver | ~300 km |
| Dallas | ~400 km |
| Salt Lake City| ~250 km |

*(Again, use the graph in your textbook or lab manual to get accurate distances.)*

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#### Step 3: Draw Circles on the Map
Now, go to the map labeled "Earthquake 1" with Denver, Dallas, and Salt Lake City marked.

Using a compass:
- Place the center at Denver and draw a circle with radius = 300 km.
- Place the center at Dallas and draw a circle with radius = 400 km.
- Place the center at Salt Lake City and draw a circle with radius = 250 km.

The point where all three circles intersect is the epicenter.

If they don’t perfectly intersect, find the closest point where all three overlap.

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#### Step 4: Name the City Closest to the Epicenter
After locating the epicenter, identify the nearest city on the map.

Common possibilities include:
- Ogden, Utah
- Provo, Utah
- Grand Junction, Colorado
- Cheyenne, Wyoming

But since Salt Lake City is only 250 km away, and Denver is 300 km, the epicenter is likely somewhere between Salt Lake City and Denver, possibly near Utah’s eastern border.

A common answer in such exercises is Ogden, Utah or Provo, Utah, depending on exact distances.

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✔ Final Answer (Example):

1. Table 1 (completed):
| Station | P-wave | S-wave | Diff. (sec) | Distance (km) | Time of Origin |
|---------------|--------|--------|-------------|----------------|----------------|
| Denver | 3.0 | 7.0 | 4.0 | 300 | 0.0 |
| Dallas | 4.5 | 9.5 | 5.0 | 400 | 0.0 |
| Salt Lake City| 2.5 | 6.0 | 3.5 | 250 | 0.0 |

*(Note: Time of origin is calculated by subtracting P-wave travel time from arrival time. If P-wave arrives at 3.0 sec and travels 300 km in 4.0 sec, then origin time is 3.0 - 4.0 = -1.0? Wait — this means we need to know when the wave started. Actually, if the P-wave takes 4.0 seconds to travel 300 km, then origin time = arrival time - travel time = 3.0 - 4.0 = -1.0? That doesn’t make sense. So let’s fix that.)*

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🔍 Correct Way to Find Time of Origin

Suppose:
- P-wave arrives at Denver at 3.0 sec.
- From travel-time graph, P-wave takes 4.0 sec to travel 300 km → so the earthquake occurred 4.0 seconds before the P-wave arrived.

→ Time of origin = 3.0 - 4.0 = -1.0 sec? That’s impossible.

Wait — actually, the arrival time is measured from a reference point (e.g., t=0), so:

If the P-wave arrives at 3.0 seconds and took 4.0 seconds to travel, then the earthquake occurred at t = 3.0 - 4.0 = -1.0 seconds?

That suggests the origin was before the start of the recording — which might be possible if the recording started after the quake.

Alternatively, maybe the origin time is the same for all stations. So:

Let’s assume:
- For Denver: P-wave arrives at 3.0 sec, travel time = 4.0 sec → origin time = 3.0 - 4.0 = -1.0 sec
- For Dallas: P-wave arrives at 4.5 sec, travel time = 5.0 sec → origin time = 4.5 - 5.0 = -0.5 sec
- For Salt Lake City: P-wave arrives at 2.5 sec, travel time = 3.5 sec → origin time = 2.5 - 3.5 = -1.0 sec

These don’t match. So either:
- My assumed arrival times are wrong, or
- The travel times are not matching.

This suggests I need to use the correct travel time from the graph.

✔ Better method:
- Use the S-P time difference to find distance.
- Then use P-wave travel time from the graph (not assumed).
- Once you have distance, go back to the travel-time graph and find how long it took the P-wave to travel that distance.

For example:
- If S-P = 4.0 sec → distance ≈ 300 km
- At 300 km, P-wave travel time ≈ 4.0 sec
- If P-wave arrives at 3.0 sec → origin time = 3.0 - 4.0 = -1.0 sec → still negative.

This implies that the recording started after the earthquake.

But usually, we align the origin time across stations.

So, the correct origin time is found by solving:

For each station:
> Origin time = P-wave arrival time - P-wave travel time

All should give the same value.

So if you get different values, recheck your readings.

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✔ Final Steps Summary:

1. Measure P and S arrival times from each seismogram.
2. Find S-P time difference.
3. Use travel-time graph to convert S-P to distance.
4. Draw circles on the map with those distances.
5. Find intersection point → epicenter.
6. Identify closest city.

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📍 Likely Answer:

Based on typical such labs:
- The epicenter is often located near Ogden, Utah, or northern Utah.
- The city closest to the epicenter is likely Ogden, Utah or Salt Lake City.

But without seeing your actual seismograms and map, I can't give the exact answer.

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📌 How to Proceed:

Please check your seismograms and:
- Read the exact arrival times of P and S waves.
- Calculate S-P differences.
- Use the travel-time graph (on page 11, as mentioned) to find distances.
- Draw circles on the map.
- Find the intersection point.
- Name the city.

If you can provide the actual arrival times from your seismograms, I can help you calculate the rest!

Let me know!