# Determine the Difference to get the Distance Say what? In class

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Determine the Difference to get the Distance Say what? In class

Determining Distance to Epicenter Determining Distance to Epicenter Must determine the difference between the P and S‐wave arrival times, then use ESRT (Page 11) to determine the distance. Say what? Determine the Difference to get the Distance between P and S-Wave arrival times to the Epicenter Dec 108:10 AM Determining Distance to Epicenter In class example: Dec 108:10 AM Determining Distance to Epicenter Step 1: Determine the Difference between the P and S-Wave arrival times. P(arrival) = 17:43:32 GMT Subract the S-Wave arrival (the higher number) from the P-Wave arrival S(arrival) = 17:45:21 GMT 17:45:21 17:43:32 00: Dec 108:10 AM Determining Distance to Epicenter Dec 108:10 AM Determining Distance to Epicenter Step 1: Determine the Difference between the P and S-Wave arrival times. Step 1: Determine the Difference between the P and S-Wave arrival times. Subract the S-Wave arrival (the higher number) from the P-Wave arrival Subract the S-Wave arrival (the higher number) from the P-Wave arrival 17:45:21 17:43:32 17:45:21 17:43:32 00: 02: 00: 02: -11 The negative value means we need to borrow 60 seconds (one minute) from the minutes. Dec 108:10 AM Dec 108:10 AM 1 Determining Distance to Epicenter Subract the S-Wave arrival (the higher number) from the P-Wave arrival Determining Distance to Epicenter Subract the S-Wave arrival (the higher number) from the P-Wave arrival 17:45:21 17:43:32 17:45:21 17:43:32 00: 02: -11 00: 02: -11 Reduce the minutes by 1 minute and then subtract the negative value from 60 seconds: Reduce the minutes by 1 minute and then subtract the negative value from 60 seconds: 17:45:21 17:43:32 17:45:21 17:43:32 00: 01: (60-11) 00: 01: (60-11) Dec 108:10 AM = 00:01:49 Dec 108:10 AM Determining Distance to Epicenter Determining Distance to Epicenter Now what? Now what? Take a piece of scrap paper (with a straight edge) and make a 'tic' mark at one minute and 49 seconds as read against the y-axis Dec 108:10 AM Dec 108:10 AM Determining Distance to Epicenter Determining Distance to Epicenter Now what? Take a piece of scrap paper (with a straight edge) and make a 'tic' mark at one minute and 49 seconds as read against the y-axis Dec 108:10 AM Now what? Take a piece of scrap paper (with a straight edge) and make a 'tic' mark at one minute and 49 seconds as read against the y-axis one minute Dec 108:10 AM 2 Determining Distance to Epicenter Now what? one minute; 20 seconds Take a piece of scrap paper (with a straight edge) and make a 'tic' mark at one minute and 49 seconds as read against the y-axis Determining Distance to Epicenter Dec 108:10 AM Now what? Take a piece of scrap paper (with a straight edge) and make a 'tic' mark at one minute and 49 seconds as read against the y-axis Dec 108:10 AM Determining Distance to Epicenter Step 2: Determine the Distance to the Epicenter. Use the ESRT (page 11) and the "Slip and Slide" method Dec 108:10 AM Take a piece of scrap paper (with a straight edge) and make a 'tic' mark at one minute and 49 seconds as read against the y-axis Dec 108:10 AM Determining Distance to Epicenter one minute; 49 seconds Now what? one minute; 40 seconds Determining Distance to Epicenter one minute; 49 seconds 'tic' mark Now what? Take a piece of scrap paper (with a straight edge) and make a 'tic' mark at one minute and 49 seconds as read against the y-axis Dec 108:10 AM Determining Distance to Epicenter Use the ESRT (page 11) and the "Slip and Slide" method: Slide the scrap paper with the 'tic' mark on it up and between the "P" and "S" curves (keeping it verticle) until the bottom of the paper is touching the "P" curve at the same time the "S" curve is touching the 'tic' mark. Dec 108:10 AM 3 Determining Distance to Epicenter 'tic' mark Determining Distance to Epicenter The greater the difference between the P and S-Wave arrival, the greater the distance to the Epicenter Slip and Slide to get the distance Epicenter Distance (x103 km) Dec 108:10 AM Dec 108:10 AM 4