6101, Fall 2022 Worksheet #5: Seismic Waves: distancel timing and velocity; calculating earthguake depth This worksheet is due by 11:59pm on Tuesday 10/25 For Part A of this worksheet you will work with the graph on ilearn titled "Graph of Earthquake Waves for worksheet #4." The graph shows the distance-time relationship for body waves generated by earthquakes. The lower left corner (0,0) indicates the earthquake Focus (point of origin). The Y axis provides the amount of time (in minutes) since the earthquake; the X axis provides the distance (in kilometers) the waves have travelled from the earthquake origin. For the X axis note that each whole number equals 1000km' The curves labelled "P\" and \"5" allow us to determine how long it takes the waves to travel a given distance. For examples of how to use the graph, see the pdf on ileorn titled \"Using the graph for Worksheet #4\" Use the graph and material from lecture to answer the following questions. Part A: Distancel timing and velocity of Body Waves 1. Why are P and S waves referred to as Body Waves? 2' At a distance of 400 km from an earthquake: How long will it take for the P-wave to arrive? How long for the S-wave to arrive? b. What is the time interval between P and S waves? 3. At a distance of 1200 km from an earthquake: How long will it take for the P-wave to arrive? How long for the S-wave to arrive? b. What is the time interval between P and S waves? 4. At a distance of 7600 km from an earthquake: How long will it take for the P-wave to arrive? How long for the S-wave to arrive? b. What is the time interval between P and S waves? 5. Take a close look at your answers for questions 2-4. As distance from the earthquake origin increases, what happens to the time interval between P and S waves? 6. Seismic Stations use the time interval between P and S waves to determine the distance ofthe station from an earthquake. It is an accurate measurement and allows the Station to determine distance without knowing when the earthquake occurred. We will use this method below: a. The Station measures the time interval between P and S waves at 4 minutes. How far away did the earthquake occur? b. The Station measures the time interval between P and S waves at 30 seconds. How far away did the earthquake occur? 7. Because the graph gives us Distance and Time from the earthquake origin, we can calculate the Velocity of the seismic waves using the following formula: Distance + Time = rate of travel (velocity) Calculate the velocity of the P and S waves at the following distances from the earthquake origin: Answers should be in kilometers per minute. (To get credit, you must show your calculations) Distance 1: 1600km Distance 2: 5000km Distance 3: 8800km Part B: Using the Properties of a Right Triangle for Earthquake Distances In this part, we will apply the properties of a Right Triangle to calculate earthquake depth. As we know from Pythagorean Theorem, if two sides of a triangle form a Right Angle {90}, the relationship between the three sides will be: a'+ b\": c' a'+ b'= r:2 allows us to determine the length of any side when the lengths of the two other sides are known. We are going to use this formula to determine the depth of an earthquake when given: 0 The distance from epicenter to Seismic Station along the surface (b side) a The distance from the earthquake focus (hypocenter) to Seismic Station (c side) To understand how this works, take a look at the diagram on the last page ofthis worksheet. Make sure you can identify the a, b, and c sides of the triangle. Remember, we are solving for depth, so you wiil' need to rearrange a24- b'z i:2 in your calculations. 9. Determine the depth of the earthquake focus for the three earthquakes numbered below (show your work): Earthquake #1: Epicenter to Seismic Station: 32 km Focus to Seismic Station: 49 km Earthquake #2: Epicenter to Seismic Station: 61 km Focus to Seismic Station: 74 km Earthquake #3: Epicenter to Seismic Station: 101 km Focus to Seismic Station: 103 km10. Let's assume that the Moment Magnitudes of the earthquakes in #9 are the same. Of the three (1, 2 or 3), which one will likely cause the most severe shaking at the surface? Explain why. Seismic Epicenter Station Earth's surface Distance from Epicenter (b) Depth (a) Distance from focus (c) Earthquake Focus (point of origin) a2 + 62 = c2Earthquake Waves: Time and Distance from origin Earthquake Waves: Time and Distance from origin 1. At a distance of 4000km, 1. At a distance of 4000km, How long for P-wave to arrive? 23- Using the Graph for 23 Using the Graph for 22 How long for S-wave to arrive? 22 How long for P-wave to arrive? 21- Worksheet #4 How long for S-wave to arrive? 21 - : Worksheet #4 What is the time interval 20 - What is the time interval 20- between P and S waves? 19- between P and S waves? 16- 15- S: 12 min 40 secs Travel Time (minutes) Travel Time (minutes) Time interval: 5:40 P: 7 minutes + ANWAU 5 6 8 9 10 3 5 6 7 8 9 10 Distance (1000s of km) Distance (1000s of km) 4000km Earthquake Waves: Time and Distance from origin Earthquake Waves: Time and Distance from origin 2. The Time Interval between P and 23 Using the Graph for 2. The Time Interval between P and 23 Using the Graph for S waves is 7 minutes; 40 seconds. 22 21- Worksheet #4 S waves is 7 minutes; 40 seconds. 22 21- Worksheet #4 How far away did the 20 - How far away did the earthquake occur? earthquake occur? 16- Time interval: Time (minutes) 7:40 Travel Time (minutes) Trave ANWAGON DANWAGON 6 Distance (1000s of km) Distance (1000s of km) Earthquake distance: 6200km3. Using this time/distance Earthquake Waves: Time and Distance from origin Seismic information, what is the velocity Station of the P wave at 4000km? What 23- Using the Graph for Epicenter Earth's surface Distance from Epicenter (b) 22- is the velocity of the S wave? :Worksheet #4 Depth (a) Use the formula we reviewed: Distance from focus (c) Distance/time = rate of travel S: 12 min 40 secs Earthquake Focus Travel Time (minutes) point of origin) a2 + 62 = c2 Part B of the worksheet: According to Pythagorean theorem, if the lengths of any two sides of a right P: 7 minutes triangle (where one angle is 90) are known, we can determine the length of the third side using the formula: a2 + b? = c? NW 5 10 Distance (1000s of km) 4000km Seismic Seismic Earth's surface Epicenter Station Station Distance from Epicenter (b) Earth's surface Epicenter Distance from Epicenter (b) Depth (a) Depth (a) Distance from focus (c) Distance from focus (c) Earthquake Focus Earthquake Focus point of origin) a2 + 62 = c 2 point of origin) a2 + 62 = c2 As an example, let's use the basic formula (a + b? = c?) to determine the length of "C" As an example, let's use the basic formula (a + b? = c?) to determine the length of "C" Depth (a): 15km Depth (a): 15km Distance from epicenter (b): 20km Distance from epicenter (b): 20km What is the distance from the Focus (c)? What is the distance from the Focus (c)? 152 + 202 = C2 225 + 400 = 625 V625 = 25km is the distance from earthquake origin (focus) to the Seismic Station For the worksheet you will be determining depth (a) when given Distance from Epicenter (b) and Distance from Focus (c), so think about how to rearrange the basic formula!2004 Sumatra Quake & Tsunami 2004-12-26 00:58 1 Tectonic Processes: Earthquakes Rotate Earth by dragging on it. Press @ to create an ear (part 2) Seismograms Distance (degree go 120 Mantle PET XMAS SSE GUMO Outer Core Inner Earth (draggable) G101: Physical Environment Graydon Creed Fall 2022 Earthquake Waves: Time and Distance from origin 2 Northridge, CA. 1994 3 Nisqually, WA. 2001 M6.7 M6.8 Travel Time (minutes km PLACEIN: Not felt Weak Light Moderate Strong Very strong Severe Violent Extreme OHHAlf! none none none Very light Light Moderate Moderate/Heavy Heavy Very Heavy Mercalli Scale PEAK ACC.($6g) <.17 .17-1.4>124 PEAK VEL (cm/s) 116 INSUREMENTAL 1 1-III IV V VI VII VIII Distance (1000s of km) Northridge, CA. 1994 4 Nisqually, WA. 2001 Northridge, CA. 1994 5 Nisqually, WA. 2001 M6.7 M6.8 M6.7 M6.8 km - Moron PERCEIVED Not felt Weak Light Moderate Strong Very strong Severe e Violent Extreme BAMade! none none none Very light Light Moderate Moderate/Heavy Heavy Very Heavy Port Dildosaden's Mercalli Scale PEAK ACC.($9) <.17 .17-1.4>124 Los Angeles PEAK VEL. (cm/s) 116 INTENSITY 1 11-111 IV V VI VII VIII Juan de Fucapt Both earthquakes were of a similar Moment Magnitude. What might account for differences in shaking intensity at the surface? Northridge, CA Nisqually, WA Focus depth: 17.5 km (10.8 miles) Focus depth 57 km (35 miles)Earthquake Waves: Time and Distance from origin 24 23 S Travel Time (minutes) - NWA VI O N OO D O N WA GONOGONN P 2 3 6 V- 8 10 Distance (1000s of km) The graph shows the distance-time relationship for body waves generated by earthquakes. The lower left corner (0,0) indicates the earthquake Focus (point of origin). The Y axis provides the amount of time (in minutes) since the earthquake; the X axis provides the distance (in kilometers) the waves have travelled from the earthquake origin. For the X axis note that each whole number equals 1000km. The curves labelled "P" and "S" allow us to determine how long it takes the waves to travel a given distance