Epicenter Lab (2/2)

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SWBAT interpret a seismograph reading and triangulate the epicenter of an earthquake using a drawing compass and the 'P & S Wave Travel Time Chart' in the Earth Science Reference Tables

Big Idea

This second-day lab focuses on the culmination of the previous day's material - students triangulate the distance to an epicenter by analyzing seismograph readings

Lesson Introduction

[Note: Usually, my lessons have embedded comments as part of a Word document. While the original lessons are still included in Word format (Whole lesson w/comments) and in PDF (Whole lesson [PDF]), I don't readily have embedded comments for this lesson. This is partly because I have this so deeply internalized that I don't really need them, partly because I find the pace and understanding of each class changes each time I teach it, and partly because some of the teacher moves are so complex that I included an additional resource in the "Trial 1" section below. Definitely consult that for any particular content/process questions you might have!]

Materials Needed:

  • Drawing Compass (I recommend the ones linked here. They're cheap and relatively easy to use). 
  • Blank piece of paper for determining the time difference for the P-waves and S-waves on the ESRT. 


In terms of specific introductions, this is the second part of a lesson that began yesterday with lesson 2.7. While there was a lot of practicing of disparate skills, they all "come together" in this lab. It is one of my favorite lessons, but there are a few sticking points where student misunderstanding can emerge. This is a best practice anyway, but I strongly recommend you do this lab in its entirety beforehand and have a working key you can refer to when teaching. Again, much of the content is fairly complex and takes a while to actually figure out, which would be difficult to do on the fly with a class full of students, especially if you haven't taught it before. 

Do Now & Objective(s)

10 minutes

Students come in silently and complete the (attached) Do Now. In this case, the Do Now is a review of material and some "hot standards" from earlier in the unit. After time expires (anywhere from 2-4 minutes depending on the type of Do Now and number of questions), we collectively go over the responses (usually involving a series of cold calls and/or volunteers), before I call on a student and ask them to read the objective out loud to start the lesson.

As a general note, the Do Now serves a few purposes:

  1. It serves as a general review of the previous day's material;
  2. It is a re-activation of student knowledge to get them back into "student mode" and get them thinking about science after transitioning from another content area or alternate class;
  3. As a strategy for reviewing material students have struggled with (for example, using this as a focused review for material that they have struggled with on unit assessments or recent quizzes); and,

It is an efficient and established routine for entering the classroom that is repeated each day with fidelity (I never let students enter the classroom talking. While it may seem potentially severe to have students enter silently each day, this is both a school wide expectation and a key component of my classroom. In many respects, I find that students readily enjoy the focus that starting with a quiet classrooms brings each day).


Trial 1: Finding Epicenters

25 minutes

For Trial 1, I approach this like a very traditional lesson format - there are three (3) seismic stations necessary to triangulate the epicenter using a drawing compass, so I set up the lesson in a very "I do, we do, you do" format. The first trial, Chicago, I do a model of. Using the Earth Science Reference Tables [ESRT] (page 11), I fill in the table and ask students to follow along. I then transition to the map of North America and create the circle with a drawing compass using the associated scale.

[Note: Similarly to the previous unit, the teacher directions in this lesson are fairly complex. I didn't use lesson comments here, but I did want to include this section from an Earth Science textbook - Triangulating Earthquake Epicenter Teacher Directions. This very clearly explains the exact step-by-step directions necessary for reading a seismograph, calculating P and S-wave travel time, and then creating the actual epicenter distance on a map using the drawing compass. Please read this over carefully if you find yourself confused or unsure about how to proceed]

For the next step, Tampa, I approach in more of a guided way. I generally ask around the room for student input in filling in the data table on the P-wave arrival time, S-wave arrival time, time difference, and epicenter distance. Similarly, I do the same thing for my measurements involving the drawing compass, and the creation of the epicenter circle away from Tampa.

With the exposure to two mini-trials from start to finish, I find that most students are equipped and ready to try Wink, Texas on their own. I give them a few minutes to try it out before we reconvene to go over the answers. 

[Note: It's totally okay if the three circles don't meet perfectly. There's often a small triangle/gap between them. That is normal and expected!]

Trial 2: Finding Earthquake Epicenters

15 minutes

Given that students have had a good amount of careful practice and modeling with Trial 1, I ask for students to independently tackle Trial 2, again using Page 11 on their Earth Science Reference Tables [ESRT]. Usually during the independent work time, I'm able to circulate and round up an idea on who is struggling and where. Traditionally, since this is the first time many of them are doing it, they need a bit of support with the concentric circles via the drawing compass. Trial 2 should allow them a fresh opportunity to work this out from start to finish - I again, usually circulate and try to help students individually, occasionally briefing students to check their answers to specific sections with my document camera. 


5 minutes

Since this lesson does not have a traditional exit ticket like most lessons, the closing and clean up process necessarily takes less time today. However, in the last few minutes of class, I definitely want to make sure have the room ready for either my next period, or an alternate class that might be using the room (I share a room with another science teacher, which makes clean up all the more important at the end of the period). Since this lab isn't super materials-intensive, I only give students 2-3 minutes to make sure all the materials have been accounted for and put away (usually by a 'Materials Manager' or someone designated to do so). As I've mentioned several times in previous lessons, I put a strong emphasis on this time, and very directly manage this process, although it is completely done by the students themselves. As a quick tip, I find it always helpful to: 1.) save more time than you think you need and 2.) have a hard stop at the end of a lab. Once that time is reached, no lab work can continue. You have to begin the process of cleaning up. Since, as mentioned above, I also share a classroom, I also give them some time to make sure all the desks have been put back into a normal classroom arrangement and students are prepared for transitioning out of the room. 

In the last minute or so, I do utilize the same procedure I do on non-lab days, which is to ask the students time to think about their self-mastery of the objective (which is posted on the whiteboard), through some guided questions:

  1. Do you feel that you mastered the objective for the day?
  2. Can you reiterate one thing you learned about ____________ (in this case, something like "How was it modeling the process of epicenter distance?" or a procedural question like "How was it working together today?", etc.)

Once I take 2-3 individual responses (sometimes I'll ask for a binary "thumbs up/thumbs down" or something similar), I have students leave once the bell rings.