Teaching with Earthquake Lab

About these notes

Earthquake Lab is a made-up region, 700 kilometers across, with three seismograph stations and nine towns. Students draw a fault and break it, and watch the P and S waves spread out and reach each station, where a pen writes the seismogram. Then a quake is hidden, and they find it from the three seismograms alone: the classic epicenter worksheet, with the flags, the travel-time chart and the drawing compass on screen.

The waves travel at 6 and 3.5 kilometers a second, so the gap between them grows about one second for every 8.4 kilometers. The chart is drawn from those same speeds, so the chart and the waves always agree. A find within 15 kilometers of the real epicenter is a good one, and within 35 is close.

Period one: make quakes and watch the gap

1. The first break (10 minutes) Everyone drags across the map to draw a fault and presses Break the fault. Two rings leave the star together; the inner one falls behind. Under the map each pen writes its seismogram. Ask: which station's pen twitched first? Which waited longest between its twitch and its big swing?
2. Move a station (10 minutes) Drag a station far from the fault and break again, then drag it right next to the fault. The bench lists each station's gap and distance. Students find the rule: about 8 kilometers for every second of gap. Compare it to counting from a lightning flash to the thunder.
3. The side view (5 minutes) The side view cuts the ground open under the star: the focus at its depth, the epicenter on the map above it, the waves as round shells. Set the depth to 30 kilometers and break again. Ask why the station right above the quake still has a gap.
4. Size and the towns (10 minutes) Turn the magnitude up one step and break again: the swings grow about ten times, but the arrival times do not move. Open The towns: each town's shaking, from not felt to extreme, and its seconds of warning. Ask why the town nearest the quake got none.
5. Wrap up (10 minutes) Turn on Past quakes and let a hundred years play. Ask where most of them are, then Show the faults. The first questions on the sheet.

Period two: find a hidden quake

Press Hide a quake and find it, or pick Find a quake in the header. A quake breaks where nobody can see it, and the three strips fill. The bench walks the five steps of the worksheet, and each step lights when the one before is done.

1. Mark the arrivals Drag the P flag to where the quiet line first starts to wiggle and the S flag to where the wiggles suddenly jump. A loupe magnifies the trace beside the flag, and the arrow keys nudge the last flag a tenth of a second. The app never snaps a flag into place: deciding where the wiggle begins is part of the skill.
2. Find the gap S minus P for each station, typed in seconds. The app checks the subtraction and only the subtraction.
3. Read the distance On the travel-time chart, the paper's bottom mark rides the P line. Slide it until its top mark touches the S line and read the distance under its edge. Students who worked out the 8 km rule in period one can use it; a distance close enough either way is fine.
4. Draw the circles Drag the compass pencil along the ruler to a station's distance, click the station (or drag the compass onto it), and swing the pencil round. One circle per station.
5. Mark the epicenter Click where the three circles cross. They usually leave a small triangle; click its middle. Then Check my answer.

The check shows the real star, says how far off the click was, and lists what to look at again, from the student's own numbers. Fix my work and check again lets them correct it; Find another gives a new quake. The first find takes most of the period; the second goes much faster.

The mistakes the check names

These are the classic errors in the paper lab. The app finds each one from the student's own marks and numbers, and says it in a sentence on the result.

What students get wrong, and where the app answers it

What the app simplifies, on purpose

• The map is made up, and so is every quake on it. No real town's history is on it.
• The waves travel in straight lines through one kind of rock. In the real Earth they speed up with depth and bend, so the 8 km rule works best within about 200 kilometers.
• How deep a quake breaks does not change how hard the towns shake. In the real Earth a deeper quake usually shakes the ground above it less.
• The shaking comes from a relation fit to California quakes of magnitude 4.4 to 6.9 (Bakun and Wentworth, 1997). Above and below that it is a guess.
• The warning comes from one station, and the alert goes out five seconds after it feels the P wave. Real systems use several stations and do not alert towns that will barely feel it.
• The magnitude slider runs from 3 to 8 so a quake under the sea can reach the sizes that make a destructive tsunami. Richter's formula, which the high school level reads magnitude with, holds below about 7 and within a few hundred kilometers; the hidden quakes stay inside that, and seismologists now report moment magnitude.
• Strong shaking is said to come with the S wave. Surface waves carry strong shaking too.
• The tsunami has no heights in meters, no flooding and no damage. It always arrives crest first; a real sea sometimes pulls back first, which is itself a warning sign. A fault that slides sideways makes no wave in the app; in the real Earth it rarely makes much of one.
• Past quakes is a made-up sample: 220 quakes of magnitude 4 and up over a hundred years, spread evenly in time, with no aftershock clusters.

Fourth grade, middle school and high school

Code lets students write small functions for the lab to use. The first turns a gap into a distance: the starter multiplies by 5 and misses by about 100 kilometers, and the lab tries their rule on forty quakes and shows how far off it was until they land on 8.4. The second finds where the P wave starts in a list of numbers, the way automatic pickers begin.

The sheet and the setup

The Sheet in the app's header is the student's write-up: the quake they made with each station's gap and the towns' shaking, the quakes they found with their table of arrivals, gaps and distances, a picture of their circles, and the questions. They hand it in and it saves with the project, or print it.

Setup sets the level, whether each student gets their own hidden quakes or the class shares the same ones, which questions are on the sheet (this level's come first), up to ten of your own, and prints an answer key. With their own quakes no two answers match, and the app checks each one; with shared quakes everyone hunts the same ones in the same order, and the key lists the first five. Set it on a starter project and hand that out: the setup travels with it.

To give the whole class one quake you chose, make it in Make a quake, press Hide this one for a friend, and press Done in Setup. Every copy opens on that quake, and the answer key lists it. Students can do the same for each other.

Standards

No NGSS performance expectation names locating an epicenter. It is the classroom's way of doing the data work these ask for.

• MS-ESS3-2: analyze and interpret data on natural hazards to forecast future catastrophic events and inform the development of technologies to mitigate their effects (where quakes happen and how big, the towns' shaking, seconds of warning, the tsunami).
• MS-ESS2-2: geoscience processes at varying time and spatial scales (a fault that slips in seconds).
• MS-ESS2-3: patterns in rock and seafloor data as evidence of plate motion (Past quakes lining up along faults).
• MS-PS4-1: a wave model with speed and amplitude (two speeds, and swings about ten times bigger for each step of magnitude).
• 4-ESS2-2: patterns of Earth's features on maps, earthquakes among them (Past quakes).
• 4-ESS3-2: solutions that reduce the impacts of natural Earth processes, earthquakes and tsunamis named (drop, cover and hold on; high ground at the coast).
• HS-ESS2-3: seismic waves as evidence of the Earth's interior (origin time and magnitude from the records).

More help

Is something on this page wrong or not clear? Write to us.