How to Actually Use the Student Exploration Earthquakes 1 Recording Station Answer Key
The Gizmo Student Exploration for Earthquakes 1 Recording Station has a specific flow that most students rush through. You open the simulation, place your three seismograph stations on the map, hit play, and then try to match the three wavy lines to the stations. The answer key isn't just a list of station names — it's about understanding the relationship between P-wave arrival time, S-wave arrival time, and distance from the epicenter. Here's how the activity works when you're actually doing it instead of just copying answers.
Student Exploration Earthquakes 1 Recording Station Answer Key
The core concept behind this Gizmo is the time gap between the P-wave and the S-wave. When you click Play, each station records an earthquake. The P-wave arrives first — it's faster but causes less ground movement. Then the S-wave arrives, and after that you get surface waves. The key number the activity wants you to extract is the lag time: how many seconds pass between the P-wave hitting a station and the S-wave hitting it. Go to each station on the map. Click on it to view its seismogram. Look at the time axis along the bottom. Mark the exact second where the first wave line shoots up — that's your P-wave arrival. Then mark where the much larger, slower oscillations begin — that's your S-wave arrival. Subtract the P time from the S time. That difference is your lag time in seconds. Once you have lag times for all three stations, you use the travel-time graph that Gizmo provides. The graph plots lag time against distance from the epicenter. Find your lag time on the vertical axis, move horizontally to the curve, then drop down to read the distance. Do this for each station. You should end up with three different distances from the epicenter for each station.
That's where triangulation comes in. You draw a circle around each station on the map using the distance you just calculated as the radius. The three circles should intersect at one point. That point is the epicenter. The actual answer key values vary depending on the randomization in the simulation, so I won't list specific numbers. But the standard set of lag times you'll commonly see is roughly 20 seconds for the closest station, 40 seconds for the middle one, and 60 seconds for the farthest. Those correspond to approximate distances of 500 km, 1000 km, and 1500 km respectively based on the Gizmo's built-in travel-time curve. If your numbers are wildly different, you're either reading the seismogram incorrectly or the simulation randomized to a different scenario. I spent an hour once trying to figure out why my three circles weren't converging. My lag times were correct, my distances were correct, but the epicenter was scattered somewhere over the ocean instead of on land. What I realized was that I had been measuring the lag time from the wrong baseline. I was using the absolute time on the x-axis instead of the duration between the two wave arrivals. The seismogram x-axis starts at zero, and the ticks are in seconds. Make sure you're reading the difference between the two wave onset points, not the raw timestamp of the S-wave alone. Once I switched to measuring the actual interval, my circles converged correctly within about two minutes.
Get the Full Details
Pitfalls to avoid
The biggest mistake students make is assuming the seismogram shown when you click a station represents the event in real-time order. Gizmo sometimes loads the seismogram scrolled to the rightmost part of the data, so the P-wave might already be off-screen. Always drag the view back to the beginning before you start taking measurements. This is especially true if you're going station by station rather than watching the whole event play out at once. Another issue is the scale of the seismogram amplitude axis. The Gizmo graph auto-scales to whatever the software determines is the maximum deflection, which means two different stations might have completely different vertical scales even if they're recording the same earthquake. This doesn't affect your lag time calculation since you're reading the time axis, not the amplitude axis, but it will confuse you if you try to compare wave heights visually across stations.
Why the activity matters beyond getting the right answer
The recording station exploration is designed to teach the mechanics of how real seismologists locate earthquakes. In practice, professional seismic networks use dozens or hundreds of stations, not three, and they rely on automated algorithms rather than hand-drawn circles. But the underlying principle is identical: the S-P interval tells you distance, and multiple distance measurements tell you location. One thing the Gizmo doesn't fully capture is that real travel-time curves aren't perfectly smooth. They vary based on the earthquake's depth, the crustal structure beneath the stations, and the frequency content of the waves. The Gizmo uses a simplified model that assumes a uniform earth model. That's fine for an intro activity, but don't treat it as a precise representation of real seismology. In actual practice, a difference of even 100 km in assumed crustal velocity can throw your triangulation off by tens of kilometers. If you want a more realistic version of this exercise, the USGS has interactive modules that use real seismic data from actual earthquakes. They show you real broadband waveforms with background noise, missing stations, and the kind of messiness that makes real earthquake location an iterative computational problem rather than a clean classroom activity.
For the Gizmo itself, the answer key is tied to the specific randomized scenario. Some sessions put the epicenter near the coast, others inland. The steps remain identical regardless. Place stations, record P and S arrival times, calculate lag times, convert to distances using the travel-time graph, draw circles, find the intersection. If your circles don't converge neatly, check your measurements first, then consider whether rounding on the travel-time graph is throwing things off. Reading to the nearest half-degree on the graph rather than the nearest whole degree usually sharpens your intersection point considerably. The activity typically takes between 15 and 25 minutes for someone who's done it before. First-timers usually need closer to 40 minutes because they keep second-guessing their readings. The seismograms are drawn with enough resolution that you can read to within about two seconds on the time axis, which translates to roughly 20-30 km of distance uncertainty on your final circle radius. That's the real-world limit of precision for this particular tool, so don't expect pinpoint accuracy from it.
