How to Locate the Epicenter of an Earthquake: Lab Practical Guide

hi everyone today we're talking about station two of our lab practical and we're talking about how to locate the

epicenter of an earthquake so let's start with our directions right here and our directions packet so first of all it

says write the code number and distance from seismic Station 2 listed below in your answer booklet so down here it

tells me the epicenter code number which is two one so on here on my answer booklet I'm just going to write the code

number 21. the code numbers are important for when your teacher grades your work next is ask for the distance

from seismic Station 2 from the epicenter that's also given to me right here I'm just going to copy that number

down onto my answer booklet in this case it's 1700 kilometers so these two things are given to me in the beginning I'm

just copying it down number two says seismic station one is located on the map in your answer booklet the circle is

drawn around Science Station one and it represents the distance from station one to an earthquake epicenter so if I go to

my answer booklet I see that station one is already drawn for me and it's showing me the distance from station one to my

earthquake epicenter I know my earthquake might be somewhere around this circle but I don't know exactly

where my earthquake is so that's why I need the data from Station 2 here and station three here

now number three says seismic station two use the compass to draw a circle around station two on the map in your

answer booklet to represent the distance from seismic Station 2 to the epicenter provided for you so Megan can I have my

compass please I use my compass and it already gave me the answer it tells me that my distance from seismic Station 2

is 1700 kilometers I'm gonna go to my answer booklet and I'm going to measure 1700 kilometers with my compass I'm

going to put the metal part on zero and I'm just gonna measure out 1700 which should be somewhere around here notice

that each tiny increment is going up by 200. once I measured 1700 I'm going to keep

this distance since I'm measuring station two I'm going to put the middle part of my compass on station two and

I'm just gonna draw a circle around station two that's 1700 kilometers so let's see

[Music] there you go so now I have a circle around station two I hope it's visible

okay so finally number four on my instructions tells me that for station three I want to use the seismogram below

to determine the time difference between the P wave and S Wave so for this one they don't give me the distance and I

need to figure out the distance myself so first let's figure out what the time of the P wave was and the time of the S

Wave was most of the time you're going to be given a seismogram with increments of 20 seconds so in this case if this is

11 hours and 40 minutes this would be 11 hours 40 minutes and 20 seconds 11 hours 40 minutes and 40 seconds 11 hours 41

minutes so P where it would be 11 hours and 41 minutes so let's keep going S Wave if this is 11 45 11 hours and 45

minutes this would be 11 hours and 46 minutes 11 hours and 47 minutes 11 hours and 48 minutes and this would be 10

seconds because each of my small increments are 20 seconds so 45 46 47 48 11 hours 48 minutes and 10 seconds now I

know my RP wave arrival time and S Wave arrival time I just need to subtract them to find the time difference

so 48 11 hours 41 minutes 11 hours 48 minutes and 10 seconds minus 11 hours 41 minutes is

7 minutes and 10 seconds not that I have that I'm gonna go to my answer booklet and I'm gonna write down

the time difference which is seven minutes and 10 seconds lastly it swans the distance to from seismic Station 3

to the epicenter so I'm gonna go to my reference table page 11. this page will be given to you

during the lab practical so you don't need to bring with you but I'm going to use a piece of scrap paper in this case

I'm just going to use my boarding over here so it looks like my time difference is 7 minutes and 10 seconds I'm gonna

take my scrap paper and I'm gonna line it with my y-axis I'm gonna put a mark where the zero is I'm gonna put another

Mark at 7 minutes 10 seconds my time difference remember each small increment is 20 seconds this is seven minutes this

7 minutes 20 seconds so in between would be 7 minutes 10 seconds now I have my time difference marked to find the

distance I'm gonna keep my scrap paper vertical and I'm just gonna move it up until this Mark touches this line and

this Mark touches the bottom line so my answer I'm gonna stop somewhere around here it looks like here this Mark is

touching this one and this Mark is touching this slime now I'm going to stop here and just gonna I'm just gonna

move down to my what x-axis and I see that my distance is around five thousand

five thousand two hundred five thousand four hundred five thousand six hundred my distance is around five thousand

eight hundred kilometers and that's what I'm going to write in my answer booklet right here five thousand

eight hundred kilometers now that I have my distance I can now draw a circle around station three I'm gonna use my

compass again I'm gonna measure a distance of five thousand eight hundred so

you can see I always put the metal part at zero and I'm gonna measure five thousand eight hundred that's somewhere

around here remember each small increment is 200 I'm going to take my metal part again and I'm gonna put it

around three it's okay when you draw the circle it goes outside the map that's a very normal thing to happen but what I'm

gonna do is draw a circle around station three times you're gonna see all three circles

intercept but a lot of times you'll also see them almost intersect you don't have to do much here and they don't intersect

you just want to find the place where station one the circle around one two and three do connect and that's

somewhere around in this area so if I find that area I'm just gonna the last thing I'm gonna do if I look

back on my directions number five sorry number six says place an x on the map in your answer booklet

to Mark the location of the epicenter where all three circles intersect or nearly intercepts they almost nearly

intersect here so I'm going to draw a big x-ray here the x is very important because you will be graded on that part

and that's it for station two