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Seismic Waves NOTES.notebook January 05, 2016 Earthquake Seismic Waves lithosphere Earthquake: Release of the built‐up stress in the ________________ limit elastic once the ____________ __________ is passed elastic rebound Release of this energy is called ___________ ____________ fault Most earthquakes occur along a ____________ movement Fault __________: crack in the Earth’s crust where _____________ can occur. fault Energy is released at a _________ in the form of seismic waves _____________ ____________. Dec 108:10 AM Dec 108:10 AM Earthquake Seismic Waves Seismic waves focus ________________ ______________ originate at the ___________ all focus Move in _________ directions from the ___________. of the earthquake. Carry the energy of an earthquake away from the focus, Epicenter _____________________: the location on Earth’s surface directly interior surface through the Earth’s ____________, and across its ____________. focus above the ______________. Dec 108:10 AM Dec 108:10 AM Body Waves Seismic Waves strongest Felt the ___________________ at the epicenter. all Travel through the ground in __________ directions. Two categories of seismic waves: Primary ______________ Waves (P‐Waves) Body waves 1. ________________________________ First waves to arrive Surface waves 2. ________________________________ Produce __________________ waves compression Travel from one end to the other and back in a straight line Dec 108:10 AM Dec 108:10 AM 1 Seismic Waves NOTES.notebook January 05, 2016 Body Waves P‐Waves expanding contracting Series of ___________________ & ___________________ waves Push Pull Also known as “ _________ ‐ _________” waves solids liquids gases Travel through _____________, ______________, and __________ Secondary ______________________ Waves (S‐Waves) Second waves to arrive shear Produce ________________ waves up down Move ________ and ___________ solids Travel through _________________ only Dec 108:10 AM Dec 108:10 AM Body Waves Surface Waves surface Travel along ____________________ only Primary Waves Secondary Waves Fast, Arrive 1st Slow, Arrive 2nd Push - Pull Wave (Compression) Shear Wave Solids, Liquids & Gases Solids ONLY Slower _________________ than body waves earthquake (focus) While P and S‐waves are generated by the ____________________, P-Waves surface waves are made by _______________________. Dec 108:10 AM Dec 108:10 AM Surface Waves Surface Waves most severe Produce the____________ ________________ ground movements. Two ____________ wave actions at the same time: Rayleigh _________________ waves: causes ground to _________ roll like ocean waves Rayleigh side _________________ waves: shake ground from _________ Love Love side to __________ Dec 108:10 AM Dec 108:10 AM 2 Seismic Waves NOTES.notebook Earthquake Strength Seismograph: Records __________________ movements ground waves caused by _______________ ______________ . seismic January 05, 2016 Earthquake Strength MAGNITUDE Richter Scale: Measure of earthquake _____________________ (released energy from earthquake) Logarithm of the maximum wave amplitude upper No _________________ limit decimal Reported using ________________ numbers 2.0 – 3.0 : Felt by people (minor) 4.0 : Light 5.0 : Moderate (800/yr) Dec 108:10 AM Earthquake Strength Modern Moment Magnitude Scale: _________________ version of the Richter scale. In addition to the amplitude of the seismic waves, it also considers: surface movement 1. Amount of _______________ ________________ along the fault rocks 2. Strength of ____________ that were broken 6.0 : Strong 7.0 : Major (18/yr) 8.0 – 9.0: Great 10.0+ : Epic (Never) Dec 108:10 AM Earthquake Strength INTENSITY Mercalli Scale: Measure of _____________________ Not a precise measurement using instruments, but based on __________________ _____________________ human observations roman Scale of 1 to 12 using _____________ numerals: XII I _______ to ________ decimal (Also uses _________________ numbers) Dec 108:10 AM Earthquake Strength Dec 108:10 AM Determining Distance to Epicenter Seismograph records the arrival of P and S‐waves on a 24‐hour clock using Greenwich Mean Time (GMT) The prime meridian runs through Greenwich, England Greenwich, England is 5 hours ahead of New York State. May also be called Universal Coordinated Time (UTC) Dec 108:10 AM Dec 108:10 AM 3 Seismic Waves NOTES.notebook Determining Distance to Epicenter Seismograph records the arrival of P and S‐waves on a 24‐hour clock using Greenwich Mean Time (GMT) The prime meridian runs through Greenwich, England Greenwich, England is 5 hours ahead of New York State. January 05, 2016 Determining Distance to Epicenter Seismograph records the arrival of P and S‐waves on a 24‐hour clock using Greenwich Mean Time (GMT) Times reported as hh:mm:ss (uses a 'military time' format) Ex: 09:14:32 9:14:32 in the morning 14:52:17 2:52:17 in the afternoon May also be called Universal Coordinated Time (UTC) Dec 108:10 AM Dec 108:10 AM New York is GMT -5 (UTC -5): If it is 4:00:00 pm in New York, what is GMT? 4:00:00 pm + 5 hours = 9:00:00 pm If it is 4:00:00 pm in New York, what is the time in Chicago (central time zone)? 3:00:00 pm or, 21:00:00 GMT Dec 1012:29 PM Chicago is GMT -6 (UTC -6): If it is 3:00:00 pm in Chicago, what is GMT? Dec 1012:29 PM If a seismograph location records the arrival of a P-wave at 10:21:30 am (hours : minutes : seconds) ...and the earthquake occurred 8,000 km away, what time did the earthquake originate? 3:00:00 pm + 6 hours = 9:00:00 pm or, 21:00:00 GMT Dec 1012:29 PM Jan 52:26 PM 4 Seismic Waves NOTES.notebook Dec 147:25 AM January 05, 2016 Dec 147:25 AM 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. Determine the Difference to get the Distance Dec 147:25 AM between P and S-Wave arrival times to the Epicenter Dec 108:10 AM Determining Distance to Epicenter Determining Distance to Epicenter In class example: Say what? P(arrival) = 17:43:32 GMT S(arrival) = 17:45:21 GMT Dec 108:10 AM Dec 108:10 AM 5 Seismic Waves NOTES.notebook Determining Distance to Epicenter January 05, 2016 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 P-Wave arrival (the lower number) from the S-Wave arrival Subract the P-Wave arrival (the lower number) from the S-Wave arrival 17:45:21 17:43:32 17:45:21 17:43:32 00: 00: 02: Dec 108:10 AM Dec 108:10 AM Determining Distance to Epicenter Step 1: Determine the Difference between the P and S-Wave arrival times. Subract the P-Wave arrival (the lower number) from the S-Wave arrival The negative value means we need to borrow 60 seconds (one minute) from the minutes. Dec 108:10 AM 00: 02: -11 00:01: (60-11) Dec 108:10 AM Determining Distance to Epicenter Subract the P-Wave arrival (the lower number) from the S-Wave arrival 17:45:21 17:43:32 00: 02: -11 Reduce the minutes by 1 minute and then subtract the negative value from 60 seconds: Dec 108:10 AM 17:45:21 17:43:32 17:45:21 17:43:32 00: 02: -11 00: 01: (60-11) Subract the P-Wave arrival (the lower number) from the S-Wave arrival 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 Determining Distance to Epicenter Use some paper to supplement your notes: Find the difference between the following P and S-wave arrival times: 1. Parrival: 07:30:24 GMT Sarrival: 07:35:42 GMT 2. PA: 19:24:46 UTC SA: 19:27:02 UTC = 00:01:49 Dec 167:46 AM 6 Seismic Waves NOTES.notebook January 05, 2016 Dec 167:54 AM Dec 167:54 AM Dec 167:54 AM Dec 167:55 AM Dec 167:55 AM Dec 167:55 AM 7 Seismic Waves NOTES.notebook January 05, 2016 Dec 167:55 AM Dec 167:55 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 8 Seismic Waves NOTES.notebook January 05, 2016 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 9 Seismic Waves NOTES.notebook January 05, 2016 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 What is the time difference between these arrival times? Dec 1010:35 AM Dec 108:10 AM What is the distance to the epicenter? Dec 1010:35 AM Let's Practice...... Jan 58:51 AM 10