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- 1. Introduction to Seismology Introduction to Seismology-KFUPM Ali Oncel oncel@kfupm.edu.sa Department of Earth Sciences KFUPM Introduction to Seismology-KFUPM The What, Where and How of Earthquakes Purple dots, last 5 years Introduction to Seismology-KFUPM 1
- 2. Types of Plate Boundaries Introduction to Seismology-KFUPM Parks and Plates ©2005 Robert J. Lillie Introduction to Seismology-KFUPM Sea floor spreading Introduction to Seismology-KFUPM Mid-Atlantic ridge 2
- 3. Introduction to Seismology-KFUPM Introduction to Seismology-KFUPM Introduction to Seismology-KFUPM heat engine Internal 3
- 4. Introduction to Seismology-KFUPM Measuring plate motions Introduction to Seismology-KFUPM Velocities of the Arabian Plate with respect to the Eurasian Plate From: McClusky et al., 2003, GJI, 155, 126–138 Introduction to Seismology-KFUPM MICROEARTHQUAKES Western Arabia IN THE TIHAMAT-ASIR REGION BSSA, Vol 70, 70, No. 6, pp. 2291-2293, December 1980 4
- 5. Introduction to Seismology-KFUPM Crustal Earthquakes in NW Arabia From: AMBRASEYS and MELVILLE, 1989, BSSA, Vol. 79 Introduction to Seismology-KFUPM Mw=5.0 March 11 2002 From: Rodgers et al., 2006, Tectonophysics, 415 (2006) 57–64 Introduction to Seismology-KFUPM Faulting Mechanism Lillie, Figure 7.1 5
- 6. Introduction to Seismology-KFUPM Elastic Rebound (H.F.Reid, 1906) See pp. 398, Bullen and Bold Introduction to Seismology-KFUPM LOCATION OF EARTHQUAKE Focus Actual point of rupture within the Earth. Epicenter Point on Earth’s surface directly above the focus. An asperity is the roughness on the fault surface. It is a region of high shear strength. Parks and Plates ©2005 Robert J. Lillie Introduction to Seismology-KFUPM Parks and Plates ©2005 Robert J. Lillie 6
- 7. Introduction to Seismology-KFUPM Parks and Plates ©2005 Robert J. Lillie Introduction to Seismology-KFUPM Parks and Plates ©2005 Robert J. Lillie Release of Accumulate energy 7
- 8. Introduction to Seismology-KFUPM Introduction to Seismology-KFUPM Introduction to Seismology-KFUPM Lillie, Fig. 7.4 Distances ? How to determine 8
- 9. Introduction to Seismology-KFUPM http://www.geol.binghamton.edu/faculty/jones/eqlocate.html Introduction to Seismology Introduction to Seismology-KFUPM Ali Oncel oncel@kfupm.edu.sa Department of Earth Sciences KFUPM Introduction to Seismology-KFUPM Richter’s Local Magnitude •Measure log (A) in mm •Measure S-P in second •Measure Distance in km •Estimate Magnitude 9
- 10. Introduction to Seismology-KFUPM Earthquake Magnitude ML - Local (Richter) magnitude MW - Seismic Moment magnitude MS - Surface wave magnitude MB- Body wave magnitude Magnitude Saturation Introduction to Seismology-KFUPM Introduction to Seismology-KFUPM What Causes Saturation? The rupture process. Small earthquakes rupture small areas. Large earthquakes rupture large areas. 10
- 11. Introduction to Seismology-KFUPM Are mb and Ms still useful? YES! Many (most) earthquakes are small enough that saturation does not occur Empirical relations between energy release and mb and Ms exist The ratio of mb to Ms can indicate whether a given seismogram is from an earthquake or a nuclear explosion (verification seismology) Introduction to Seismology-KFUPM What is the better estimate of M? The seismic moment – Mo Invented in the 1960s to circumvent magnitude limitations Has physical units of energy (Nm, cal, J) Is the product of three factors that indicate the size of the earthquake: Mo = (shear modulus) x (rupture area) x (slip offset) Introduction to Seismology-KFUPM Moment Magnitude Moment-Magnitude Scale Seismic Moment = Strength of Rock x Fault Area x Total amount of Slip along Rupture M0 = µ A D Moment Magnitude Mw = 2/3 x [log10M0(dyne-cm) – 16] Measurement Analysis requires Time 11
- 12. Introduction to Seismology-KFUPM STRENGTH OF EARTHQUAKE Magnitude Relates to the amount of energy released by the earthquake. Intensity Relates to the effects (damage) observed at the surface. Logarithmic (not linear) scale. Increase 1 order of magnitude means: The seismic waves are 10 times as large. Parks and Plates ©2005 Robert J. Lillie Logarithmic (not linear) scale. Increase 1 order of magnitude means: The seismic waves are 10 times as large. 30 times as much seismic energy was released by the earthquake. Question: Compare M=6 EQ to M=7 EQ? Respond: Seismic waves 10 times as big. 30 times more energy. Parks and Plates ©2005 Robert J. Lillie Introduction to Seismology-KFUPM Compare M=6 EQ to M=7 EQ? Next Question: An M=8 EQ is equivalent how many M=6 EQ going off at the same time? Parks and Plates ©2005 Robert J. Lillie 12
- 13. Introduction to Seismology-KFUPM Compare M=6 EQ to M=8 EQ? Start with a magnitude 6 earthquake. A magnitude 7 earthquake releases 30 times the amount of seismic energy as a magnitude 6 earthquake. A magnitude 8 earthquake releases 30 times the amount of energy as a magnitude 7 earthquake. 30 x 30 = 900 It would take about 900 magnitude 6 earthquakes going off at the same time to pack the same wallop as a magnitude 8 earthquake! Parks and Plates ©2005 Robert J. Lillie Introduction to Seismology-KFUPM Seismic waves 100 times as big. Seismic Energy 900 times as big. Parks and Plates ©2005 Robert J. Lillie Introduction to Seismology-KFUPM Magnitude -Energy Correlation This figure was produced in cooperation with the US Geological Survey, and the University of Memphis private foundations 13
- 14. Introduction to Seismology-KFUPM For Tutorial and Download web.ics.purdue.edu/~braile/edumod/eqlocate/tutorial.pdf http://www.geol.binghamton.edu/faculty/jones/eqlocate.html Assignment: Estimate Location of One Earthquake Due to Next Wednesday Introduction to Seismology-KFUPM Step 1 Introduction to Seismology-KFUPM Step 2 14
- 15. Introduction to Seismology-KFUPM Multiple Window Seismogram Step 3 Seismogram in one window I played zooming and keys of arrow and arranged the location of above map. Good luck for rest of exercise. 15

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