Final Set for Earthquakes
If an Earthquake were to happen in Berkeley:
-The campus would shut down for 1 semester at least, but possibly one year if no retrofit -Students wouldn't be here - transfer students, teachers would also transfer -NO UCB just like new orleans wouldn't come back :O the END of UCB -Invest in improving buildings so that the city and University wouldn't collapse and be able to get up after an earthquake. -Losses if repeat of 1906 EQ-$54 B (buildings only) $170 - 225 B total losses -Losses if Hayward Fault EQ: M6.9 $23 B (buildings only)
Three Types of Boundaries: 1) Divergent Boundary 2) Convergent Boundary 3) Transform Boundary
Boundaries have to do with two different tetonic plates sliding past each other. Example Pacific Plate with North American Plate. The BOUNDARY (gap) between the two plates. 1) Divergent: tension stress, spreading, constructive (oceanic lithosphere created), Ridge/Rift, Volcanic Activity 2) Convergent: compression stress, subduction zone, destruction (oceanic lithosphere destroyed), Trench, Volcanic Activity 3) Transform: shear stress, lateral sliding, conservative (oceanic lithosphere neither created or destroyed), no major effect, No Volcanic Activity, San Andreas Fault is an example.
Earthquake Early Warning:
1) California: i) Earthquake's Early Warning Law: statewide, develop standards for system & review compliance - need to get general fund (not from taxes) ii) The Earthquake Early Warning System: predicts earthquake a few seconds to tens of seconds before an earthquake hits. iii) CA Shake Alert status: -400 seismic stations -5 seismic stations -3 processing centers. iiii) Alert systems in CA provide: •Personal safety (time to prepare) -Schools -Mental preparedness, protection (from falling shelves, machinery) •Automated control -$15M -> $200K in losses after investment in early warning and shear walls -From 2 weeks of loss of productivity to ~4 weeks -Automatically stopping/slowing down trains, an example would be the BART •Situation awareness (initiating response before shaking) -Re-routing power or communications -Preventing cascading failures -Initiating emergency response -Information available before communications are lost iV) Future Plans for Earthquake Warning System: •Today: UserDipslay •2 years from now: build rototype warning system for West Coast •By the year 2015: build early public warning system for EVERYONE. 2) Elsewhere: i) Japan's Earthquake Warning System: March 11, 2011 Tohoku-Oki, Japan earthquake. TV & Radio announcements, J-alert systems, cellphones, dedicated providers serve. E-mail (58%) & EQ apps (25%) most useful
Strike Slip vs Transform Fault: (Be able to distinguish)
All transform faults are strike-slip faults because rocks on either side of the fault move parallel to the fault itself. But not all strike-slip faults are transform faults -- transform faults only occur at the boundary between two plates. For example, a strike-slip fault in the middle of a plate is not a transform fault, but a strike-slip fault at the boundary between two plates is indeed a transform fault. **key: boundary vs middle of a tectonic plate
Seven Total Bay area faults:
Bay Area faults (7): 1) San Andreas Fault: North American and Pacific Plate touch. Right lateral transform fault (Meaning it is a Strike Slip fault but since it is specific to within two plate boundaries it is also Transform). Approximately 800 miles long and 10 miles deep. 2) Hayward Fault: The Hayward fault is apart of the San Andreas fault system. It runs along the foot of the East Bay hills (approximately 74 miles long). They have found that the most recent 5 major earthquakes happened on average every 140 years. Since it has been more than 144 years since the last major earthquake, the clock is ticking. It is very likely that the Hayward fault will rupture and produce a significant earthquake within the next 30 years. **Most Important San Andreas/Hayward 3) Calaveras 4) Concord-Green Valley 5) Greenville 6) Rodgers Creek 7) San Gregorio Faults
Earthquake History/Important Dates:
Earliest Seismicity Record: 1868 (southern half of Hayward Fault). First seismograph in Western Hemisphere: 1887 Astronomy installation (San Jose) it was sensitive to motion so they had to keep track of it for precision in planet movement Lawson Report published: 1906 Mercalli Scale developed: 1902 Mercalli Scale modified: 1931 Ritcher Scale: 1934 Moment Magnitude Scale: 1979 Earthquake Early Warning Law: 2012 Earthquake Early Warning System: 2012 CA Shake Alert: January 2012 Uniform Building code: 1991 First continuous digital broadband network in US: 1991 First automated response to EQ alerts: 2012 Great SF earthquake I: 1868 Great SF earthquake II: 1906 Loma Prieta: 1989 Northridge: 1994 Kobe: 1995 Chi Chi: 1999 Tohoku-Oki: 2011 World Wide Standard Seismographic Network established in Beverly Hills: 1961 o cold war o world wide seismic network o put together for monitored nuclear testing Tombstone Diagram: Past earthquake history in Northern CA. No large earthquakes after big one (1906) happens.
Four Types of Faults: 1) Dip-Slip Fault (Normal vs. Reverse) 2) Strike Slip Fault (Right vs. Left lateral) 3) Oblique Fault (Mix both Dip and Strike) 4) Thrust Fault (Thrust vs. Blind Thrust)
Faults can be classified according to which of the three directions of space the rocks on either side move. 1) Dip-Slip: When the motion is predominantly vertical, they are called dip slip faults. Two Types of Dip-Slip Faults: i) Normal: hanging wall (above) moves down footwall (below) moves up. Normal fault is an example of tension stress. ii) Reverse: hanging wall (above) moves up footwall (below) moves down. Reverse fault is an example of compression stress. **Hanging wall is the part that is above whereas Footwall is the part that is below. "Above or below" depends on the angle of the fault line. Normal fault = divergent boundaries (mid oceanic ridge, rift) = Extension (dip slip motion, hanging wall moves down) 2) Strike Slip: If the motion is mostly horizontal and parallel to the fault plane, the fault is called a strike slip fault. Two Types of Strike Slip Faults: i) Left Lateral: if you are standing and you look in front of you and everything (such as trees for example) has shifted LEFT, then it is left lateral. ii) Right Lateral: if you are standing and you look in front of you and everything (such as trees for example) has shifted RIGHT, then it is right lateral. Strike Slip faults are an example of Shear Stress **Can be Transform boundary and Strike slip if occurs at plate boundary. Transform is always Strike slip but Strike slip isn't always transform. 3) Oblique Strike: have both a vertical and horizontal component of motion along the fault. Thus, adjacent points on different sides of the fault have moved up or down and back or forward relative to each other. They are essentially a combination of strike-slip and dip-slip motion. neither slip component dominates the other -- the slip of the fault is referred to with a combination of slip terms. The sense of strike slip is used first, followed by the sense of dip slip. For example, if the slip on a fault were such that the hanging wall (above) moved up with respect to the footwall (below), and the two sides slipped laterally right with respect to each other, you would call this sense of slip "right-lateral reverse", which is sometimes shortened to "right-reverse". 4) Thrust Fault: Move in the same motion as a Dip slip reverse faults with dips less than 45 degrees Thrust faults occur mainly at convergent plate boundaries. Hanging wall (above) moves up footwall (below) moves down. Thrust fault is an example of compression stress. i) If dips more than 45 degrees than no longer thrust it would be considered a Reverse Fault. ii) Blind thrust fault: does not rupture all the way to the top of the surface **Thrust faults occur in LA area because bending of San Andreas fault. Thrust faults put older rocks above younger rocks. **A reverse fault occurs primarily across lithological units (anywhere on a plate) whereas a thrust usually occurs within or at a low angle to lithological units (between two different plates).
Loma Prieta Earthquake •1989 •Right lateral Strike Slip transform fault •San Andreas Fault-locked •Magnitude 6.9
Year: 1989 Location/Fault: 50 miles away from SF, In Santa Cruz Mountains near Loma Prieta Peak, San Andreas Fault Magnitude: 6.9 Example of damage: The shock was centered in a sparsely populated area approximately 10 mi (16 km) northeast of Santa Cruz on a section of the San Andreas Fault System and was named for the nearby Loma Prieta peak in the Santa Cruz Mountains. broke bay bridge-took 25 years to fix, Mountains
Locked Fault vs. Creep Fault:
Locked: A locked fault is a fault that is not slipping because frictional resistance on the fault is greater than the shear stress across the fault (it is stuck). Such faults may store strain for extended periods that is eventually released in an earthquake when frictional resistance is overcome. Locked = s-shape (bay area) Example: The San Andreas Fault is locked. Creep: due to low frictional strength on the fault. Fault creep occurs when some or all of the fault plane is not locked by friction, and rocks on either side of the fault are able to slide along slowly in response to the forces driving the fault. Creeping = arrows go same way Example: Hayward Fault creeping occurs in spots along the Hayward Fault. The ground consistently moves a few millimeters each year, pulling apart sidewalks, pipelines and other structures that sit astride the fault. **Creep accounts for a small part of the total motion that takes place on a fault over geologic time; earthquakes account for the rest.
Two types of Seismic Waves: 1) Surface Wave (S-wave and Rayleigh wave) 2) Body Wave (P-wave)
Seismic waves: are the waves of energy caused by the sudden breaking of rock within the earth or an explosion. They are the energy that travels through the earth and is recorded on seismographs. Earthquakes radiate seismic energy as both body and surface waves. The results of seismic waves can provide a snapshot of the Earth's internal structure and help us to locate and understand fault planes and the stresses and strains acting on them 1) Surface wave: Surface waves can only move along the surface of the planet like ripples on water. Travelling only through the crust, surface waves are of a lower frequency than body waves, and are easily distinguished on a seismogram as a result. Though they arrive after body waves, it is surface waves that are almost enitrely responsible for the damage and destruction associated with earthquakes. This damage and the strength of the surface waves are reduced in deeper earthquakes. i) S-wave (up and down, looks like the movement of a snake): The second type of body wave is the S wave or secondary wave, which is the second wave you feel in an earthquake. An S wave is slower than a P wave and can only move through solid rock, not through any liquid medium. It is this property of S waves that led seismologists to conclude that the Earth's outer core is a liquid. S waves move rock particles up and down, or side-to-side--perpindicular to the direction that the wave is traveling in (the direction of wave propagation). ii) Rayleigh wave (rolling, looks like a huge bump traveling through the surface): rolls along the ground just like a wave rolls across a lake or an ocean. Because it rolls, it moves the ground up and down, and side-to-side in the same direction that the wave is moving. Most of the shaking felt from an earthquake is due to the Rayleigh wave, which can be much larger than the other waves. 2) Body wave: Body waves can travel through the earth's inner layers. Traveling through the interior of the earth, body waves arrive before the surface waves emitted by an earthquake. These waves are of a higher frequency than surface waves. i) P-wave (left to right, push-pull particles): The first kind of body wave is the P wave or primary wave. This is the fastest kind of seismic wave. The first to arrive at a seismic station. The P wave can move through solid rock and fluids, like water or the liquid layers of the earth. It pushes and pulls the rock it moves through. P waves are also known as compressional waves, because of the pushing and pulling they do. Subjected to a P wave, particles move in the same direction that the the wave is moving in, which is the direction that the energy is traveling in, and is sometimes called the 'direction of wave propagation'.
How do earthquakes happen?
Seismology: is the study of earthquakes and seismic waves that move through and around the earth. A seismologist is a scientist who studies earthquakes and seismic waves. The plates are continually moving but where they touch each other, they get stuck. As the rest of the plates moves, the stuck parts deform like compressing a spring so they build up stress in the rocks along the fault. When the rock breaks or slips, then suddenly plates move, causing an earthquake. The entire process is called elastic rebound. As they break and scrape by one another, they produce seismic waves that travel through the ground and shake the surface. Rupture- The rupture front is the instantaneous boundary between the slipping and locked parts of a fault during an earthquake. Rupture in one direction on the fault is referred to as unilateral. Rupture may radiate outward in a circular manner or it may radiate toward the two ends of the fault from an interior point, behavior referred to as bilateral.
Three Different Types of Stress: 1) Tension 2) Compression 3) Shear
Tension stress: <- -> Compression stress: -><- Shear stress: -> <-
Earthquake Statistics:
Within 30 years: San Andreas - 4.7% San Andreas, Peninsula segment - 4.4% San Andreas, South segment - 2.6% N & S Hayward - 8.5%, 21% in North Probability for Earthquake Today: .0009% today 1% next semester 12% by the time we graduate M6.7+ = 37-87% range probability but say 62% by 2032 M6-6.6 = 80% by 2032
Great SF Earthquake I •1868 •Right Lateral Strike Slip •Hayward Fault-creeping •Magnitude 6.8
Year: 1868 Location/Fault information: San Francisco, Hayward Fault-- Magnitude: 6.8 Money to fix: $350,000 Example of damage: -Property loss was extensive and 30 people were killed. Five deaths were reported in San Francisco, out of a population of 150,000. -The cracking of the ground along the Hayward Fault was traced about 20 miles -Damage most severe in Hayward. -During this time in history it was known as one of the most biggest to ever be felt.
Great SF II Earthquake •1906 •Right lateral transform fault •San Andreas Fault-locked •Magnitude 7.9
Year: 1906 Location/Fault: San Francisco, San Andreas Fault--(Right lateral transform fault meaning it is a Strike Slip fault that shifted everything right but since it is specific to within two plate boundaries it is also Transform). Magnitude: 7.9 Money to fix: $90 million on reconstruction. Example of damage: -The earthquake was felt from southern Oregon to south of Los Angeles and inland as far as central Nevada. -Though the quake lasted less than a minute, its immediate impact was disastrous. The earthquake also ignited several fires around the city that burned for three days and destroyed nearly 500 city blocks. -The earthquake and fires killed an estimated 3,000 people and left half of the city's 400,000 residents homeless.
Northridge Earthquake •1994 •Blind Thrust Fault •Magnitude 6.7
Year: 1994 Location/Fault: Northridge, Northridge Blind Thrust Fault Magnitude: 6.7 Money to fix: 15 B Example of damage: 56 reported dead, Blind thrust fault. he earthquake occurred on a blind thrust fault, and produced the strongest ground motions ever instrumentally recorded in an urban setting in North America. Damage was wide-spread, sections of major freeways collapsed, parking structures and office buildings collapsed, and numerous apartment buildings suffered irreparable damage. Damage to wood-frame apartment houses was very widespread
Kobe Earthquake •1995 •Right Lateral Strike Slip •Magnitude 6.9
Year: 1995 Location/Fault: Also known as Great Hanshin, Located in South east of Japan Magnitude: 6.9 Money to fix: 200 B Example of damage: moderate earthquake in modern setting, old buildings collapsed. was one of the most devastating earthquakes ever to hit Japan; more than 5,500 were killed and over 26,000 injured. The economic loss has been estimated at about $US 200 billion.
Chi Chi Earthquake •1999 •Reverse-Thrust •Magnitude 7.6
Year: 1999 Location/Fault: Taiwan in city of Chi Chi is where Epicenter was Magnitude: 7.6 Money to fix: Example of damage: Thrust - 9m vertical offset 2100 deaths with 8000 people injured.
Tohoku-Oki Earthquake •2011 •Dip-Slip Reverse Fault •Magnitude 9.0
Year: March 11, 2011 Location/Fault: Japan, Subuction zone of Pacific plate and Eurasian Plate, Tohoku fault. Magnitude: 9.0 Money to fix: Example of damage: -one of largest recorded in history -triggered a devastating tsunami that killed more than 20,000 people -an ongoing nuclear disaster at the Fukushima Daiichi power plant. -The Tohoku-Oki earthquake occurred in a "subduction zone," a boundary between two tectonic plates where one plate is diving beneath another--in this case, the Pacific plate dives beneath the Eurasian plate just east of Japan. -in addition to the 50 meters of slip, was that the fault ruptured all the way to the surface of the seafloor. -The large slip at shallow depths contributed to the tsumani
Important Earthquake Terms:
•Earth structure: In the early part of the 20th century, geologists studied the vibrations (seismic waves) generated by earthquakes to learn more about the structure of the earth's interior. -Inner core: extremely hot solid sphere, iron and nickel -Outer core: the only liquid layer. -Mantle: upper and lower mantle, dense layer made of hot semisolid rock. -Crust: hard and rigid, outermost thinnest layer. •Fault: a fracture along which the blocks of crust on either side have moved relative to one another parallel to the fracture. There are four types: Dip-slip (normal vs reverse), Strike slip (right lateral vs. left lateral), thrust (thrust vs. blind thrust), oblique (mixture of both dipslip and strike slip) •Epicenter: the point on the earth's surface vertically above the focus of an earthquake. Where the ripples start, the focal point of the ripples. •Intensity: The effect of an earthquake on the Earth's surface is called the intensity. •Magnitude: based on a logarithmic scale (base 10). What this means is that for each whole number you go up on the magnitude scale, the amplitude of the ground motion recorded by a seismograph goes up ten times. Using this scale, a magnitude 5 earthquake would result in ten times the level of ground shaking as a magnitude 4 earthquake. The magnitude is the most often cited measure of an earthquake's size. •Amplitude: The amplitude is the size of the wiggles on an earthquake recording. Low Medium or High. The maximum or "peak" ground motion is defined as the largest absolute value of ground motion recorded on a seismogram, measured from the position of equilibrium. •Subduction zone: subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate and sinks into the mantle as the plates converge. Occur all around the Pacific Ocean. Oceanic Crust denser than continental crust and will sink into mantle when these two kind of crusts meet in a subduction zone. Because of subduction zones after Earthquakes usually Tsunamis happen. Subduction zone earthquakes are the biggest of the world because size of earthquake is related to size of fault and subduction zone faults are are the longest and widest of the world. Largest Earthquakes ever recorded were on Subduction zones. •Trench: In Convergent Boundaries when there is compression stress (-><-) between two plates a subduction zone happens (one tectonic plate moves under another tectonic plate) leading to destruction of oceanic lithosphere (oceanic lithosphere goes underneath continental lithosphere) which forms a Trench (linear depression of the sea floor). Trench marks the line where subduction begins. Sometimes there can be Volcanic activity. Earthquakes in and around deep ocean trenches are principally produced by motions on thrust faults, indicating compression (converging plates). The farther from the trench, the deeper the earthquakes are. •Ridge/Rift: In Divergent Boundaries when there is tension stress (<-->) between two tectonic plates a constructive (oceanic lithosphere created Tension Stress •Lithosphere: is the rigid, outermost shell of a rocky planet. Right underneath the continental and oceanic crust. •Liquefaction: a phenomenon in which the strength and stiffness of a soil is reduced by earthquake shaking or other rapid loading. •Stress Shadow: Earthquakes may trigger or silence quakes on nearby faults, but such relationships are difficult to verify. An example would be the San Andreas fault, because most major faults in the area are nearly parallel to the San Andreas fault, in 1906 the change in stress tended to be in a sense to relax these faults. (If one of two side-by-side faults fails, the other will generally be relaxed; if the two faults are end-to-end, the second will become more stressed by the failure of the first.) New Madrid Seismic Zone: The New Madrid Seismic Zone (NMSZ) is the most active seismic area in the United States east of the Rocky Mountains. 1811-1812, Midwest (Missouri) M8 earthquakes. There has been small earthquakes since then, therefore, it is reasonable to expect earthquakes in area.
Laws/Standards put in place for Earthquake safety and preparedness:
1) Earthquake's Early Warning Law: statewide, develop standards for system & review compliance, need to get general fund (not from taxes) 2) The Earthquake Early Warning System: Today, the technology exists to detect earthquakes, so quickly, that an alert can reach some areas before strong shaking arrives. The purpose of an EEW system is to identify and characterize an earthquake a few seconds after it begins, calculate the likely intensity of ground shaking that will result, and deliver warnings to people and infrastructure in harm's way. This can be done by detecting the first energy to radiate from an earthquake, the P-wave energy, which rarely causes damage. Using P-wave information, we first estimate the location and the magnitude of the earthquake. Then, the anticipated ground shaking across the region to be affected is estimated and a warning is provided to local populations. The method can provide warning before the S-wave arrives, bringing the strong shaking that usually causes most of the damage. Messages sent through CA Shake Alert 4) Uniform Building Code (1991): M6.2 Morgan Hill. New buildings have to fit standards, existing buildings don't have to be modified. 5) Changes to building codes (2): 1973: '64 Alaska, '67 Caracas, '71 San Fernando 1997: '94 Northridge & '95 Kobe 6) Mary Comerio: economic benefits of retrofitted university 7) Arietta Chakos: improve buildings & schools in whole city
Three Earthquake Scales: 1) Mercalli Scale (intensity) 2) Richter Scale (Magnitude, local) 3) Moment Magnitude Scale (Magnitude, more reliable)
1) Mercalli Scale (Intensity): developed in 1902 (originally scale of 1-10) but modified in 1931 (now, scale of 1-12) by the American seismologists Harry Wood and Frank Neumann. The Mercalli scale measures intensity based on OBSERVED effects of those who have experienced earthquake. **The Modified Mercalli Intensity value assigned to a specific site after an earthquake has a more meaningful measure of severity to a person than the magnitude because intensity refers to the effects actually experienced at that place. 2) Richter scale (Magnitude, less reliable): First earthquake magnitude scale. A diagram of peak ground motion versus distance developed by Charles F. Richter in 1934. It used a formula based on amplitude of the largest wave recorded on a specific type of seismometer and the distance between the earthquake and the seismometer. Assigns a magnitude number to quantify the energy released by an earthquake. The Richter scale is a base-10 logarithmic scale. **Richter's scale was specifically designed for application in southern California. Richter's method became widely used because it was simple, required only the location of the earthquake (to get the distance) and a quick measure of the peak ground motion, Many scales, such as the Richter scale, do not provide accurate estimates for large magnitude earthquakes. Today the Moment Magnitude scale, abbreviated MW, is preferred because it works over a wider range of earthquake sizes and is applicable globally. 3) Moment Magnitude Scale (Magnitude, more reliable): preferred because it works over a wider range of earthquake sizes and is applicable globally. The moment magnitude scale is based on the total moment release of the earthquake. Moment is a product of the distance a fault moved and the force required to move it. It is derived from modeling recordings of the earthquake at multiple stations. Moment magnitude estimates are about the same as Richter magnitudes for small to large earthquakes. But only the moment magnitude scale is capable of measuring M8 and greater events accurately.
Earthquake Preparedness:
1) Prediction: i) What does a useful prediction include? • interval of time when it will occur • area of the location • magnitude range • probability earthquake will occur by chance ii) Earthquake precursors (Predictions): •P-velocity variations •ground uplift & tilt •radon gas •electrical conductivity •swarms of local earthquakes •animal behavior 2) Forecasting: i) Where do forecasts come from? •Balance scale: Plate tectonics motion (strain) vs. Slip releasing stress (Earthquake) ii) Which earthquakes matter for forecasting? • Only the BIG earthquakes count because the smaller ones are on a logarithmic scale while LARGE earthquakes cover large areas of slip. iii) Elastic Rebound: •Displacement over 50 year prior/ Displacement during earthquake x 50 years = next event **Assumption: everything is constant, (rate of plate motion & phys. properties of fault) iiii) 2003 vs. 2008 forecasts (different reports, same answers) 2003: • 99% chance of M >_ 6.7 STATEWIDE • 63% M>_ 6.7 SF REGION • 67% M>_ 6.7 LA REGION 2008: • 62% chance of one or more M>_6.7 EQs by 2032 • 27% on Hayward-Rodgers Creek fault • 21% chance on San Andreas fault 3) Early Warning System ✓ 4) Comprehensive solution: i) Educate the public on risk (high risk perception) ii) Clear explanations of what needs to be done (widespread knowledge of what to do - higher education, neighbors retrofit, Earthquake Preparedness) iii) Financial incentives (city programs, funds)
Ways in which Seismologist monitor/understand Earthquakes:
1) Terrashake Simulations: to help understand earthquakes 2) Moment Tensors: Identify which fault is active Use first motion to calculate it (speed>accuracy) SO use different stations at different locations using Annual Moment Tensor Maps. 3) Annual Moment Tensor Maps: o regional stress emerges o beach balls disappear in big earthquakes but appear where there were gaps o used for forecasting models 4) Nuclear Bomb vs. Earthquake (Discrimination) -Waves look different -Magnitudes of body waves & surface waves are different -Moment Tensors are different 5) How do we know what's inside earth? Digging, samples Indirect probes: Potential fields (magnetic fields, gravity), electromagnetic (but lose resolution w/ depth), seismic (not enough stations to provide images)
Damage of different types of buildings:
1) Things that affect the amount of damage that occurs are: i) The building/road designs •Brick Masonry-Masonry buildings are brittle structures and one of the most vulnerable of the entire building stock under strong earthquake shaking. Furthermore, they are slender due to small thickness, causing it to overturn during earthquake. When unreinforced masonry buildings begin to come apart in earthquakes, heavy debris can fall on adjacent buildings or onto the exterior where pedestrians are located. Example is downtown Berkeley Shattuck street and Telegraph. •Concrete, although technically different from bricks displays many of the same characteristics. Neither one of them can handle the lateral forces of the earthquake. Concrete, as is brick, is not ductile; it has no flexibility to it, rather it is brittle. Therefore, the concrete walls are likely to break apart and fall over when upset by an earthquake. •Wood frame- relatively safe. Type generally built in the United States, can stand up far better in quakes than the outwardly solid masonry homes. They are able to sway with the motion of an earthquake due to their flexibility. One common reason houses are destroyed is the quality and type of the foundation is not appropriate. •Soft Story-extremely dangerous everything will collapse on top of each other. A lot of apartment in Berkeley are Soft Story. Bottom layer is that of a garage for parking cars for example. •Steel framed buildings- such as skyscrapers, on the other hand are generally much more stable in an earthquake. Steel is more ductile, and can be stretched or bent without breaking. Damage is typically limited to localized damage (Yanev 108). Most of the damage that happens to steel framed buildings is caused by not having connections between the horizontal and vertical framing elements.they are designed to have enough flexibility •Older overpasses- are supported by vertical steel rods embedded in the concrete of the pillars holding up the highway. If these rods are bent by the pressure of the freeway rocking above them, they lose their strength and continue to bend outward. Ultimately, the pillar can collapse. ii) The distance from the epicenter •Further from epicenter less you will get affected by the Earthquake. iii) The type of surface material (rock or dirt) the buildings rest on •Solid rock usually shakes less than sand, so a building built on top of solid rock shouldn't be as damaged as it might if it was sitting on a sandy lot 2) Modes of building failure: Soft-story building (Kobe, Northridge) Inadequate connection to foundation (Loma P, NR) Column failure (freeways, NR) Soil failure, liquefaction (Nigata '64) Narrow base structure (Kobe) Bending (Northridge) Partial Wall Collapse (LP, masonry buildings) Fallen objects
Discuss ways buildings can be retrofitted:
1) Wooden houses: •Shear Wall: structural system composed of braced panels (also known as shear panels) to counter the effects of lateral load acting on a structure. Wind and seismic loads are the most common loads that shear walls are designed to carry. homes need to have what are known as shear walls, which are normally made from plywood fastened between the upright wooden beams to help withstand side-to-side forces. •Concrete slab foundation under houses •nailing plywood to the framing to prevent wall from falling over •On the exterior of a house, stucco backed with mesh is another way to provide shear support. However, stucco siding should not be used as a replacement for plywood sheathing. If the stucco cracks it loses almost all of its shear strength (Helfant 32). Having both stucco and plywood sheathing is a good choice for earthquake resistance. •Continuous perimeter footing: really good foundation for wood frame houses. Anchor bolts. •Do not have heavy material on roof of wooden frame homes, such as heavy tile. •If multiple story make sure floors are secureed to each other well. 2) Brick Masonry: •thicker walls •steel reinforcing bars embedded within them •Improving the grout condition •Fill minor cracks with epoxy to restore composite action •Anchoring and tying the floor/roof to the wall •Anchor unsupported masonry walls •Filling any hollows in the brick or concrete is important 3) Concrete: •steel bars inside in concrete walls it must be done at the time of construction, before the concrete is formed. This helps to hold the concrete together even if it cracks, and to hold the walls up. •To provide adequate support the rods must run both horizontally and vertically 3) Soft story: •should not exist 4) Steel Buildings: •seismic isolation. The technique, which can also be used on other types of buildings, is to keep the building from moving with the ground. By adding layers of rubber and steel to the foundation the stress on the building in an earthquake can be reduced to one tenth of what it would be without 5) freeway structure: •support columns of existing bridges in a dapper jacket of thick steel that kept them standing during the quake. •steel casing •grout •support collumns •bridge's footings and anchor the footings more securely into the ground. •Thick cables hold sections of the freeway together and secure it to the support pillars. 6) suspension bridges: •Strengthening the existing foundations •steel towers and strengthening •Replacement and addition of top and bottom lateral bracing and strengthening vertical truss members and truss connections •Installing seismic expansion joints Memorial Stadium and Stanley having the X structure across windows and frame. Solid rock usually shakes less than sand, so a building built on top of solid rock shouldn't be as damaged as it might if it was sitting on a sandy lot Tall building design: design to sway to release energy
Mercalli Scale (intensity), be able to talk about potential destruction an earthquake can cause at the different magnitudes, WILL BE ON TEST:
Mercalli Scale 1-12 (measures intensity): 1) Not felt except by a very few under especially favorable circumstances. 2) Felt only by a few persons at rest, especially on upper floors of buildings. Delicately suspended objects may swing. 3) Felt quite noticeably indoors, especially on upper floors of buildings, but many people do not recognize it as an earthquake. Standing motorcars may rock slightly. Vibration like passing truck. Duration estimated. 4) 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 rocked noticeably. 5) 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. 6) Felt by all; many frightened and run outdoors. Some heavy furniture moved; a few instances of fallen plaster or damaged chimneys. Damage slight. 7) 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 motorcars. 8) 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 motorcars disturbed. 9) 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. 10) 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 (slopped) over banks. 11) Few, if any (masonry), structures remain standing. Bridges destroyed. Broad fissures in ground. Underground pipelines completely out of service. Earth slumps and land slips in soft ground. Rails bent greatly. 12) Damage total. Waves seen on ground surfaces. Lines of sight and level distorted. Objects thrown upward into the air.
