Slide 1

Modes of Elastic Wave Propagation P-wave http://web.ics.purdue.edu/~braile/edumod/w aves/WaveDemo.htm

Slide 2

Modes of Elastic Wave Propagation S-wave http://web.ics.purdue.edu/~braile/edumod/w aves/WaveDemo.htm

Slide 3

Modes of Elastic Wave Propagation Rayleigh wave http://web.ics.purdue.edu/~braile/edumod/w aves/WaveDemo.htm

Slide 4

Modes of Elastic Wave Propagation Love wave http://web.ics.purdue.edu/~braile/edumod/w aves/WaveDemo.htm

Slide 5

What does a seismic signal look like? Broadband (short time) pulsed signal Superposition of many sine waves with different amplitude and frequency From Dobrin and Savit, 1988

Slide 6

Rayleigh Waves http://www.uwm.edu/~bketter/Research/Surf ace_Theory/Rayleigh/rayleigh_index.html

Slide 7

Modes of wave propagation

Slide 8

Slide 9

Location of Earthquakes Hypocenter or earthquake focus Epicenter Earthquakes do not occur at points but occur due to stress release within small volumes or along fault planes

Slide 10

Complications Earth is not homogeneous or flat P & S waves velocities are not constant Earthquakes dont normally occur at the surface Errors in traveltime measurement Precise solution requires many seismometers

Slide 11

Earthquake location Distance between epicenter and seismometer is called the epicentral distance Shortest distance between two points on a sphere is along the great circle connecting those two points Epicentral distance is the length of the great circle arc connecting the epicenter and seismometer With measurement of t s-p can estimate epicentral distance with compilation of global traveltimes

Slide 12

Slide 13

Slide 14

Classical Seismology Global Seismology Use energy released by earthquakes (or nuclear tests) to image Earths deep interior Source: http://www.mantleplumes.org

Slide 15

Earthquake magnitude and moment Concept of magnitude was first introduce by C.F. Richter in 1935 Based on local earthquakes in Southern California Based on amplitude of first arriving P-wave as measured on a particular seismograph (12Hz Wood-Anderson seismometer)

Slide 16

Earthquake magnitude and moment All magnitude scales are logarithmic and have the form

Slide 17

Richter MagnitudesDescriptionEarthquake EffectsFrequency of Occurrence Less than 2.0MicroMicroearthquakes, not felt.About 8,000 per day 2.0-2.9Minor Generally not felt, but recorded. About 1,000 per day 3.0-3.9Minor Often felt, but rarely causes damage. 49,000 per year (est.) 4.0-4.9Light Noticeable shaking of indoor items, rattling noises. Significant damage unlikely. 6,200 per year (est.) 5.0-5.9Moderate Can cause major damage to poorly constructed buildings over small regions. At most slight damage to well- designed buildings. 800 per year 6.0-6.9Strong Can be destructive in areas up to about 160 kilometres (100 mi) across in populated areas. 120 per year 7.0-7.9Major Can cause serious damage over larger areas. 18 per year 8.0-8.9Great Can cause serious damage in areas several hundred miles across. 1 per year 9.0-9.9Great Devastating in areas several thousand miles across. 1 per 20 years 10.0+Epic Never recorded; see below for equivalent seismic energy yield. Extremely rare (Unknown)

Slide 18

Richter Approximate Magnitude Approximate TNT for Seismic Energy Yield Joule equivalentExample 0.01 kg (2.2 lb)kglb4.2 MJ 0.55.6 kg (12.4 lb)23.5 MJLarge Hand grenadeHand grenade 1.032 kg (70 lb)134.4 MJConstruction site blast 1.5178 kg (392 lb)747.6 MJWWIIWWII conventional bombs 2.01 metric tonmetric ton4.2 GJLate WWII conventional bombs 2.55.6 metric tons23.5 GJWWII blockbuster bombblockbuster bomb 3.032 metric tons134.4 GJMassive Ordnance Air Blast bomb 3.5178 metric tons747.6 GJChernobyl nuclear disasterChernobyl nuclear disaster, 1986 4.01 kilotonkiloton4.2 TJSmall atomic bombatomic bomb 4.55.6 kilotons23.5 TJ 5.032 kilotons134.4 TJ Nagasaki atomic bombNagasaki atomic bomb (actual seismic yield was negligible since it detonated in the atmosphere. The Hiroshima atomic bomb was 15 kilotons ) Lincolnshire earthquake (UK), 2008Hiroshima atomic bomb Lincolnshire earthquake (UK), 2008 5.4150 kilotons625 TJ Chino Hills (Los Angeles) earthquake (CA, USA), 2008 5.5178 kilotons747.6 TJ Little Skull Mtn. earthquake (NV, USA), 1992 Alum Rock earthquake (CA, USA), 2007 6.01 megatonmegaton4.2 PJ Double Spring Flat earthquake (NV, USA), 1994 6.55.6 megatons23.5 PJRhodes (Greece), 2008 6.716.2 megatons67.9 PJNorthridge earthquake (CA, USA), 1994 6.926.8 megatons112.2 PJ San Francisco Bay Area earthquake (CA, USA), 1989 7.032 megatons134.4 PJ 7.150 megatons210 PJ Energy released was equivalent to that of Tsar Bomba, the largest thermonuclear weapon ever tested.Tsar Bomba 7.5178 megatons747.6 PJ Kashmir earthquake (Pakistan), 2005 Antofagasta earthquake (Chile), 2007 7.8600 megatons2.4 EJTangshan earthquake (China), 1976 8.01 gigatongigaton4.2 EJ Toba eruptionToba eruption 75,000 years ago; which, according to the Toba catastrophe theory, affected modern human evolution San Francisco earthquake (CA, USA), 1906 Queen Charlotte earthquake (BC, Canada), 1949 Mxico City earthquake (Mexico), 1985 Gujarat earthquake (India), 2001 Chincha Alta earthquake (Peru), 2007 Sumatra earthquake (Indonesia), 2007 Sichuan earthquake (China), 2008 (initial estimate: 7.8)Toba catastrophe theoryhuman evolution San Francisco earthquake (CA, USA), 1906 Queen Charlotte earthquake (BC, Canada), 1949 Mxico City earthquake (Mexico), 1985 Gujarat earthquake (India), 2001 Chincha Alta earthquake (Peru), 2007 Sumatra earthquake (Indonesia), 2007 Sichuan earthquake (China), 2008 8.55.6 gigatons23.5 EJ 9.032 gigatons134.4 EJ 9.290.7 gigatons379.7 EJAnchorage earthquake (AK, USA), 1964 9.3114 gigatons477 EJ Indian Ocean earthquake, 2004Indian Ocean earthquake, 2004 (40 ZJ in this case) 9.5178 gigatons747.6 EJ Valdivia earthquake (Chile), 1960Valdivia earthquake (Chile), 1960 (251 ZJ in this case) 10.01 teratonteraton4.2 ZJNever recorded.

Slide 19

Slide 20

Earthquake magnitude and moment Shallow focus (