How do we find the distance to the epicenter from a station?

Based on studying many earthquakes… Scientists were able to come up with a distance travel-time graph for earthquakes ESRT.Slides.pdf This graph tells you at varying distances to the epicenter how long it would take a P wave or S wave to get to that station

WHAT YOU NEED A seismogram which tells you the arrival time of P and S waves The lag time ( difference in arrival time between P and S waves ESRT

From the seismogram figure out the arrival time of the P and S wave WHAT YOU DO From the seismogram figure out the arrival time of the P and S wave                                                                    

Subtract the P wave arrival time from the S wave arrival time To get the lag time… Subtract the P wave arrival time from the S wave arrival time              

Represent the lag time on paper

Fit the paper between the lines and read down New York State High School Regents Exam Prep Center: Earth Science                                                                                                                                                                                                                                                                                                                 . Fit the paper between the lines and read down

TRY THESE A P wave came into a station at 02:05:00. The S wave came in at 02:10:00. What is the distance from the epicenter of an earthquake for this station?

02:08:00- 02:05:00=5 minute lag time LOOK back to slide 6

A P wave came in at 1:05:30. The S wave came in at 1:08:50 A P wave came in at 1:05:30. The S wave came in at 1:08:50. How far is this station from the epicenter of the earthquake?

If a station is 2000 km from an earthquake epicenter, how long would it take a P wave to get to that station? What about the S wave?

A P wave came into a station at 03:10:00 A P wave came into a station at 03:10:00. The S wave came in at 03:17:00. How far is this station from the epicenter of the earthquake? What is the lag time?

7 minutes Represent it on paper- slide the paper between the lines- line it up and read down- that is your distance Remember units

How do we find an epicenter? You must have 3 seismograms b/c one seismogram only gives you the distance to the epicenter it does not pin point the exact location.

Drawing Circles to represent distance to the epicenter Use the distance to the epicenter provided by one seismogram and scale to set your compass Draw a circle around your given city with that radius. Repeat this for 2 more stations The Epicenter could be at any point on this circle to narrow down the location you need 2 more circles Distance to the epicenter

Epicenter – will be where the 3 circles intersect