Earthquakes and The Earths Interior
Figure in text Northridge, CA earthquake, 1/17/94. Interstate 5 damage GLY Summer Lecture 14 1 Earthquake A sudden motion or trembling in the Earth caused by the abrupt release of slowly accumulated strain Strain is a change in the shape or volume of a body as a result of stress 2 Seattle Earthquake, 2/28/01 Movie of Microsoft laboratory during the earthquake Bill Gates was giving a presentation when the quake occurred Movie: MSQuake.WMV Source: 3 Focus, aka Hypocenter The initial rupture point of an earthquake, where strain energy is first converted to elastic wave energy The point within the Earth which is the center of an earthquake 4 Epicenter The point on the Earth's surface that is directly above the focus of an earthquake Focus Epicenter 5 Seismograph An instrument that detects, magnifies, and records vibrations of the Earth, especially earthquakes The resulting record is a seismogram 6 Principle of the Modern Seismograph
The vertical component of seismic wave motion is is recorded by a pendulum attached to a spring Two horizontal components (N-S and E-W) of seismic wave motion at right angles are recorded by pendulums hinged to swing like a gate Signals from the moving pendulums crate a current in the coil of wire, which is amplified and fed to a recording device, where the signal is plotted versus time Image: Modern_Seismograph.jpg 7 Seismograph Animation Example Seismogram Seismogram showing an earthquake - the three different traces represent vibrations in different directions First peaks are P waves, the second peaks the S waves Seismogram.jpg 9 Microearthquake Seismogram
Magnitude 1.8 quake, Japan N = North South Orientation E = East-West Orientation Z = Vertical orientation This earthquake had only P and S waves surface waves did not develop Earthquakes with magnitude of about 2.0 or less are usually call microearthquakes; they are not commonly felt by people and are generally recorded only on local seismographs. 10 Moderate Earthquake Seismogram
Magnitude 5.1 quake, Norwegian Sea Note well-developed surface waves (Love and Rayleigh) which have much greater amplitude than the P and S waves Events with magnitudes of about 4.5 or greater - there are several thousand such shocks annually - are strong enough to be recorded by sensitive seismographs all over the world. The seismograms were recorded in Germany because of the distance from the epicenter, the P and S waves are more attenuated than the surface waves The surface waves lasted more than five times as long as the P and S waves Rayleigh waves produce the well-known rolling motion associated with moderate to strong earthquakes Waves following the Rayleigh waves are a complex mix of P, S, Love, and Rayleigh waves arriving via different paths Image: Moderate_Quake_Seismogram, p_39_lower.jpg 11 Richter Scale Numerical scale of earthquake magnitude
Devised in 1935 by the seismologist C.F. Richter Defined local magnitude as the logarithm, to the base 10, of the amplitude in microns of the largest trace deflection that would be observed on a standard torsion seismograph at a distance of 100 km from the epicenter Very small earthquakes, or microearthquakes, can have negative magnitude values No upper limit to the magnitude of an earthquake, but the strength of Earth materials produces an actual upper limit of between 9 and 10 Logarithmic means an increase of 1 unit on the scale corresponds to an increase of 10 the trace deflection Photo: Richter_600dpi.jpg A short biography of Richter may be found at: 12 Richter Scale Continued
Measures the vibrational amplitude of the earth in response to seismic waves Does NOT measure the energy release 13 Mercalli Scale Arbitrary scale of earthquake intensity,ranging from I (detectable only instrumentally) to XII (causing almost total destruction) Based on human perception of the earthquake, and damage observed after the earthquake is over Named after Giuseppi Mercalli (d.1914), the Italian geologist who devised it in 1902 Its adaptation to North American conditions is known as the modified Mercalli scale Useful for comparing historical earthquakes, for which no instrumental records are available, with modern quakes Can be used on a map to show zones of maximum damage 14 Number of Earthquakes/Year
Only about one-third are strong enough to be felt by people, magnitude 3 or greater Damage begins to occur around magnitude 4.5 Table 14.2 in text 15 Isoseismal Map, Loma Prieta Earthquake, 1989
A different view This earthquake stopped the World Series of 1989 for several days Arabic numerals are Richter scale magnitudes Roman numerals indicate Mercalli scale intensity VI. Felt by all; many frightened and run outdoors. Some heavy furniture moved; a few instances of fallen plaster or damaged chimneys. Damage slight. VII. Everybody runs outdoors. Damage negligible in buildings of good design and construction slight to moderate in well built ordinary structures; considerable in poorly built or badly designed structures. Some chimneys broken. Noticed by persons driving motor cars. VIII. Damage slight in specially designed structures; considerable in ordinary substantial buildings, with partial collapse; great in poorly built structures. Panel walls thrown out of frame structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture overturned. Sand and mud ejected in small amounts. Changes in well water. Persons driving motor cars disturbed. Star shows epicenter Source: 16 Isoseismal Map of Prince William Sound Earthquake, 1964
Strongest recorded earthquake in the United States III. Felt quite noticeably indoors, especially on upper floors of buildings, but many people do not recognize it as an earthquake. Standing motor cars may rock slightly. Vibration like passing truck. Duration estimated. IV. During the day felt indoors by many, outdoors by few. At night some awakened. Dishes, windows, and doors disturbed; walls make creaking sound. Sensation like heavy truck striking building. Standing motorcars rock noticeably. V. Felt by nearly everyone; many awakened. Some dishes, windows, etc., broken; a few instances of cracked plaster; unstable objects overturned. Disturbance of trees, poles, and other tall objects sometimes noticed. Pendulum clocks may stop. VI. Felt by all; many frightened and run outdoors. Some heavy furniture moved; a few instances of fallen plaster or damaged chimneys. Damage slight. VII. Everybody runs outdoors. Damage negligible in buildings of good design and construction slight to moderate in well built ordinary structures; considerable in poorly built or badly designed structures. Some chimneys broken. Noticed by persons driving motor cars. VIII. Damage slight in specially designed structures; considerable in ordinary substantial buildings, with partial collapse; great in poorly built structures. Panel walls thrown out of frame structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture overturned. Sand and mud ejected in small amounts.Changes in well water. Persons driving motor cars disturbed. IX. Damage considerable in specially designed structures; well-designed frame structures thrown out of plumb; great in substantial buildings, with partial collapse. Buildings shifted off foundations. Ground cracked conspicuously. Underground pipes broken. X. Some well-built wooden structures destroyed; most masonry and frame structures destroyed with foundations; ground badly cracked. Rails bent. Landslides considerable from river banks and steep slopes. Shifted sand and mud. Water splashed over banks. Source: 17 Prince William Sound Earthquake Damage
Close-up of Government Hill elementary school, which was destroyed by the Government Hill landslide. Anchorage, Alaska. 125 dead, $311 million in damage Shock lasted 3 minutes! Photo source: Information: 18 Anchorage Building J.C. Penney building
Very little damage to adjacent building, with steel-frame construction 19 Energy Released by Earthquakes
A great earthquake releases the equivalent of 1 billion tons of TNT or more, over a period of 1-2 minutes Most intense energy release per unit time of any natural event, except meteorite impact 20 Catastrophic Event Energy Releases
A great earthquake releases almost as much energy in 1-2 minutes as a hurricane releases over 10 days The only larger natural event is the impact of a meteorite, which corresponds to a Richter magnitude of about 12.0 Note: Both scales are logarithmic an increase in one unit corresponds to a tenfold increase in the property Inset graph has a linear vertical scale The moment magnitude scale has been devised for more precise study of great earthquakes. Diagram: Catastrophic_Event_Energies.jpg 21 Areal Distribution of Earthquakes
Distribution of epicenters, color-coded to show the corresponding depth of focus Source: Photo #world.gif 22 Current US Seismicity Current as of 7/9/13 at 14:25 EDT 23
Image: Current_US_Quakes_ usa.gif 23 Seismicity of the United States, 1990 - 2000
Source: 24 Seismicity of Alaska, Source:http://earthquake.usgs.gov/regional/states/seismicity/images/alaska.gif Many earthquakes are associated with the Aleutian Island Volcanic Arc, located above a subduction zone 25 Seismicity of Hawaii, Source:http://earthquake.usgs.gov/regional/states/seismicity/images/hawaii.gif Most earthquakes on the the big island of Hawaii, associated with Hot Spot volcanism 26 Seismic Hazard 2008 Map Source: Image transformed to USpga500v4.jpg Peak Acceleration as a percent of g, with 2% probability of exceedence in 50 years 27 Western Hemisphere Seismic Risk
Image source: 28 Global Seismic Hazard From the Global Seismic Hazard Assessment Program (GSHAP), started in 1992 and terminated in 1999. Peak Acceleration as a percent of g, with 2% probability of exceedence in 50 years 29 Depth of Focus Earthquakes are classified by the depths of their foci below the surface, as follows: Shallow 0-70 kilometers Intermediate kilometers Deep kilometers Most earthquakes are shallow focus Deep focus, and most intermediate focus, earthquakes are associated with subduction zones 30 Indonesia Earthquake Depth: 33.0 km Magnitude 7.9Ms
70 miles (110 km) SSW of Bengkulu, Sumatera, Indonesia June 6, :28 EDT 4.73S E 31 Cause of Indonesian Earthquake
Map shows foci depth increase to the NE - Indication of subducting plate moving from SW to the NE Preliminary date indicate 120 killed, 1300 hundred injured. Thousands of homes and businesses in Bengkulu province have been damaged or destroyed.Seismologists have said more than 400 aftershocks followed the initial quake in Bengkulu province, home to 1.4 million people, a small population by Indonesian standards. Indonesias far-flung islands are regularly hit by earthquakes. At least 34 people died last month when an earthquake measuring 6.5 on the Richter scale hit central Sulawesi and some neighboring islands. The worst quake to hit Indonesia in the past decade was in 1992, when 2,200 people died in a string of eastern islands.(from MSNBC,- (As of 6/8/00) 32 Worldwide Recent Earthquakes
Source: Image from: This page will be updated before lectures. It serves as an example only, so changes will not affect any material on the exams. Tuesday, July 9, 2013 about 14:30 EDT 33 Afghanistan Seismicity
Source: Date-Time :08:06 UTC Location 36.44N 70.45E Depth kilometers Magnitude 7.3 Region HINDU KUSH REGION, AFGHANISTAN Reference 45 miles (75 km) SSW of Feyzabad, Afghanistan Source USGS NEIC The cross-section is typical of continent-continent collisions. This earthquake occurred near the boundary of the Eurasian and Indian tectonic plates. The two plates are converging towards each other at a rate of about 4.4 cm per year. The earthquake occurred in a subducted part of the Eurasian plate, at a depth of about 200 km. The faulting that produced the earthquake reflects internal deformation of the subducted Eurasian plate rather than slip on the boundary between the Eurasian and Indian plates. This earthquake occurred in the highly-seismic Hindu Kush region. On average, there are four magnitude 5 or greater earthquakes per year whose epicenters are within 60 km of this event. Earthquake depths in this region range from the surface to depths of 330 km. Although small near-surface earthquakes have been generated by human activity such as mining and reservoir loading, the depth and magnitude of this event preclude any connection with human activity including the recent bombing. 34 Earthquake Damage Earthquakes can cause damage in a number of ways
Building Collapse Tsunami waves Seiche waves Landslides Liquefaction Fire Disease Damage types discussed on following slides 35 Building Collapse Izmit, Turkey Earthquake, August 17, 1999
Magnitude 7.4 Click video to play (with sound) Source: clip3.wmv converted from 36 Collapse Studies Video from the Pacific Earthquake Research Center
Shake Table Demonstration of Column Collapse From KRON, Channel 4, San Francisco, CA KRON_broadcast.wmv 37 Tsunami Gravitational sea wave produced by any large-scale, short-duration disturbance of the ocean floor Disturbances caused principally by a shallow submarine earthquake, but also by submarine earth movement, subsidence, or volcanic eruption Characterized by: Great speed of propagation (up to 950 km/hr) Long wavelength (up to 200 km), Low observable amplitude on the open sea May pile up to heights of 30 m or more and cause much damage on entering shallow water along an exposed coast (often thousands of kilometers from the source) Etymology: Japanese, "harbor wave" 38 Tsunami Animation Indonesian Tsunami Animation of tsunami movement across Indian Ocean
Animation: Tsunami01.wmv Animation of tsunami movement across Indian Ocean 40 Tsunami Velocity Figure in text 41 Phuket, Thailand Video Home video of tsunami hitting 42
Video: tsunamiphuket_fix_low.wmv Home video of tsunami hitting 42 Tsunami Damage Seward, Alaska after Anchorage, Alaska earthquake, Mar. 27, 1964 Photo: Kirkpatrick Photo # S2586 (IMG0086.jpg) Steinbrugge Collection, Earthquake Engineering Research Center, University of California, Berkeley 43 Tsunami Harbor Damage Photo: Joseph Penzien, Steinbrugge Collection
Niigata, Japan earthquake, June 16, 1964 Magnitude 7.5 Steinbrugge Collection, Earthquake Engineering Research Center, University of California, Berkeley Photo # S3167 (IMG0051.jpg Photo: Joseph Penzien, Steinbrugge Collection 44 Sri Lanka - Before Photo: srilanka-before.jpg 45 Sri Lanka - After Photo: srilanka-after.jpg 46 Tohoku Earthquake, BBC News - Japan earthquake Footage of moment tsunami hit.wmv Seiche Free or standing-wave oscillation of the surface of water in an enclosed or semi-enclosed basin (as a lake, bay, or harbor) Varies in height from several centimeters to a few meters Initiated chiefly by local changes in atmospheric pressure, aided by winds, tidal currents, and small earthquakes Continues, pendulum fashion, for a time after cessation of the originating force Usually occurs in the direction of longest diameter of the basin, but occasionally it is transverse 48 Landslides Earthquakes may trigger mass movement of rock and sediment on unstable slopes Damage is most likely to occur after fire removes vegetation, or clear-cutting of forests 49 Quake Triggered Landslide Damage
Loma Prieta, California earthquake, 1989 Magnitude 7.1 Photo: Jeff Marshall Roadcut failure on Old Soquel-San Jose Highway, Santa Cruz Mountains This rockfall covers the southbound lane of Old Soquel-San Jose Highway Landslides on all three access roads, severely limited access to Santa Cruz 50 Landslide Damage, Continued
Loma Prieta, California earthquake, 1989 Magnitude 7.1 Photo by Jeff Marshall This landslide, initiated by the earthquake, covered both of the northbound lanes of Hwy 17, the major commuter route between Santa Cruz and San Jose The concrete wall in this photo is the highway center divider 51 House Destroyed by Landslide
Loma Prieta, California earthquake, 1989 Magnitude 7.1 Photo by Jeff Marshall Landslides have become a major public policy issue in the county Debate centers around whether to allow homeowners to rebuild on threatened property or not 52 Public Policy Rebuilding allowed if no immediate threat of injury or death Liability waiver mandatory Recently, the county board of supervisors approved rebuilding, if proper geologic investigation shows that there is no immediate threat of injury or death The homeowners must then sign a waiver releasing the county from any liability, and any geologic hazard must be clearly indicated in the deed for the property The average house in the Santa Cruz Mountains has a value of at least $200,000, which naturally introduces a number of interesting legal, economic, and emotional complications to this situation 53 Liquefaction Liquefaction is a physical process that takes place during some earthquakes that may lead to ground failure As a consequence of liquefaction, soft, young, water-saturated, well sorted, fine grain sands and silts behave as viscous fluids rather than solids Liquefaction takes place when seismic shear waves pass through a saturated granular soil layer, distort its granular structure, and cause some of its pore spaces to collapse The collapse of the granular structure increases pore space water pressure, and decreases the soil's shear strength Pore space water pressure increases to the point where the soil's shear strength can no longer support the weight of the overlyingsoil, buildings, roads, houses, etc. Soil will flow like a liquid and cause extensive surface damage 54 Liquefaction Animation Liquefaction Failure Steinbrugge Collection
Niigata, Japan earthquake, June 16, 1964, magnitude 7.5 Overturned building due to foundation failure No damage to interior (doors and windows still function) Failure reportedly took a considerable period of time Steinbrugge Collection, Earthquake Engineering Research Center, University of California, Berkeley. Picture #IMG0045.jpg Steinbrugge Collection 56 Liquefaction Failure Steinbrugge Collection Photo: Joseph Penzien
Overturned building due to foundation failure Niigata, Japan earthquake, June 16, 1964, magnitude 7.5 Steinbrugge Collection, Earthquake Engineering Research Center, University of California, Berkeley Steinbrugge Collection 57 Fire Fire often does more damage than the earthquake itself
Underground pipelines and tanks rupture Above ground tanks may rupture ortip over, spilling contents Water lines break Streets are blocked by debris Downed electrical lines may spark, setting off fires Fires are difficult to fight without water or equipment 58 Fire Photo: Arnold Genthe, Steinbrugge Collection
San Francisco earthquake of 1906 caused destruction, including cutting of water supply, and blocking of streets View down Sacramento Street, April 18, 1906, after the earthquakes but before fire spread Fire started and destroyed much of the city Photograph by Arnold Genthe Steinbrugge Collection, Earthquake Engineering Research Center, University of California, Berkeley. Picture #S3037 Photo: Arnold Genthe, Steinbrugge Collection 59 San Francisco, 1906 After the fire 60
View up Market Street after the fire Photo: 1906_SF_Quake_Market_Street_After_Fire, p_16_lower.jpg After the fire 60 Managua, Nicaragua Photo: Karl V. Steinbrugge
Managua, Nicaragua earthquake, Dec. 23, 1972, magnitude 6.2 Photo: Karl V. Steinbrugge, Dec the fires were still burning six days later Steinbrugge Collection, Earthquake Engineering Research Center, University of California, Berkeley Photo: Karl V. Steinbrugge 61 Tilted Gasoline Tank Steinbrugge Collection
Tilted tank at the Karumojima tank farm Note the ground cracking Kobe, Japan earthquake, Jan. 17, 1995, mag. 6.7 Steinbrugge Collection, Earthquake Engineering Research Center, University of California, Berkeley Photo #KG95 Steinbrugge Collection 62 Disease Earthquakes can cut underground sewer and water lines
No drinking water Only available water is contaminated Populations in less-developed countries may fare better than those in developed countries, because they may be routinely exposed to water-borne disease organisms from infancy on Immunizations against water-bourne diseases are used infrequently in developed countries 63 Broken Sewer Pipe, Chile
Chile earthquake, May 1960, magnitude 8.5 Two sewer pipe breaks occurred within 5 meters Steinbrugge Collection, Earthquake Engineering Research Center, University of California, Berkeley Photo # S1719 (IMG0080.jpg) Photo: Karl V. Steinbrugge 64 Seismic Wave Types There are several types of seismic waves
P(rimary) waves are the fastest S(econdary or shear) waves are the next fastest L (surface) waves are the slowest 65 P Wave Diagram Figure 14.7a from text
A type of body wave, it passes through the earth -through solid, liquid, or gas Talking, speakers, etc. produce compressional waves The earth is alternately compressed and dilated Wave travels in the same direction as the compression 66 S Wave Diagram Figure 14.7c in text
S waves are body waves, traveling through the earth Can travel only through solids, so they do not travel through the outer core They do travel through asthenosphere, so it cannot be a liquid (it behaves plastically) Shear waves vibrate in one direction, but travel in a direction perpendicular to the vibration direction Liquids do not have the rigidity to allow S waves to traverse them Pebbles or rocks thrown in water generate S waves 67 P and S Wave Animation To view this animation, click View and then Slide Show on the top navigation bar. Surface Waves Travel only along the surface, not through an object
Generated by P and S waves interacting with the surface Slowest type of seismic waves Cause the most damage to structures, and generally cause the most deaths 69 Rayleigh Waves Rayleigh waves are one type of surface waves 70 Rayleigh Waves First described by Lord Rayleigh in 1885
Rayleigh waves are created by rock particles moving forward, up, backward, and down in elliptical orbits oriented in a vertical plane that includes the direction of propagation This produces a distinct rolling motion of the surface Lord Rayleigh wasJohn William Strutt. A short biography may be found atHe won the 1904 Nobel Prize in Physics for work unrelated to seismology. Image: Surface Wave Motions.jpg (cropped) 71 Love Waves Love waves are the other type of surface wave 72 Love Wave Damage Love waves were named after A.E.H. Love, who first described them in 1912 The rock moves from side to side in a horizontal plane at right angles to the direction of travel A short biography of Augustus Love ( ) is at Image: Surface Wave Motions.jpg (cropped) 73 Seismic Wave Animation Reflection and Refraction
Seismic waves may be reflected or refracted when they encounter an interface between layers of different density Reflection occurs when the interface behaves like a mirror Refraction occurs when the wave enters the new layer, and is bent Both waves remain in the same plane The different paths traveled by waves, as well as their different velocities, account for their different arrival times at the seismograph stations The depth to the different layers can be determinedthat is how we know what the interior of the earth looks like 75 Wave Reflection and Refraction Haitian Earthquake On January 12, 2010 a magnitude 7.0 earthquake struck with epicenter near Logne, about 25 kilometers west of Port-au-Prince, Haiti An estimated three million people were affected by the quake Haitian Government reports estimated 230,000 people had died, 300,000 had been injured and 1,000,000 made homeless. Haiti Earthquake Location
Quake location was in the vicinity of the northern boundary where the Caribbean tectonic plate shifts eastwards by about 20 millimeters per year in relation to the North American plate. The location and focal mechanism suggest that the January 2010 quake was caused by a rupture of the Enriquillo-Plaintain Garden fault, which had been locked for 250 years, gathering stress The rupture was roughly 65 kilometerslong with mean slip of 1.8 meters Preliminary analysis of the slip distribution found amplitudes of up to about 4 meters using ground motion records from all over the world 2010 Chile Earthquake The 2010 Chilean earthquake occurred off the coast of the Maule Region of Chileon February 27, 2010 The earthquake triggered a tsunami which devastated several coastal towns in south-central Chile and damaged the port at Talcahuano Tsunami warnings were issued in 53 countries, causing minor damage in the San Diego area of California and in the To-hoku region of Japan, where damage to the fisheries business was estimated at US $66.7M Seismologists estimate that the earthquake was so powerful that it may have shortened the length of the day by 1.26 microseconds Precise GPS measurement indicated the telluric movement moved the entire city of Concepcin 3.04 metres to the west. The latest death toll as of May 15, 2010 is 521 victims Chile Earthquake Location
The earthquake took place along the boundary between the Nazcaand South American tectonic plates, at a location where they converge at a rate of 80 millimetersa year. This earthquake was characterized by a thrust-faultingfocal mechanism, caused by the subductionof the Nazca plate beneath the South American. Chile Earthquake Effects
Chile has been at a convergent plate boundary that generates megathrust earthquakes since the Paleozoic(500 million years ago) The segment of the fault zone which ruptured in this earthquake was estimated to be over 700 kmlong with a displacement of almost 10 meters GPSstudies indicate that the earthquake shifted Santiago 28 cm to the west-southwest and moved Concepcin at least at least 3 meters to the west