LO1-3 List and describe the characteristics of the 4 main types of earthquake waves.

Transcription

1 Lecture 1 Page 1 Learning Objectives Saturday, August 22, :05 PM LO1-1 Know the characteristics of the major types of earthquakes hazards. 1. Strong motion and structural collapse 2. Fault rupture 3. Liquefaction 4. Earthquake-induced landslides, mudslides and debris flows 5. Embankment failure 6. Failure of retaining structures 7. Tsunami and Seiche LO1-2 Describe typical damage caused by earthquake hazards and give examples of historical earthquakes that have caused each type of damage listed above. LO1-3 List and describe the characteristics of the 4 main types of earthquake waves. 1. P wave 2. S wave 3. Rayleigh wave 4. Love wave LO1-4 Describe the characteristics of below types of liquefaction-induced failures. 1. flow failure 2. lateral spread 3. ground oscillation 4. bearing capacity failure 5. liquefaction-induced settlement LO1-5 Describe why the 1995 Kobe, Japan earthquakes was so damaging when compared with the 1994 Northridge, California earthquake. LO1-6 Discuss ways that seismic hazards can be reduced (via, education, planning, engineering design, emergency response, etc.).

2 Lecture 1 Page 2 Learning Objectives Saturday, August 22, :05 PM LO1-7 Describe how soil sites may significantly modify the characteristics of strong motion. LO1-8 Define the following: 1. Basin-generated surface waves. 2. Earthquake warning 3. Earthquake prediction 4. Seismology 5. Geotechnical earthquake engineering 6. Soil dynamics 7. Risk assessment 8. Seiches 9. Lifelines 10. Earthquake resistant design

3 Lecture 1 Page 3 Important Concepts Tuesday, August 18, :07 PM Earthquake Engineering is a branch of Civil Engineering that requires expertise in geology, seismology, civil engineering and risk assessment. Projects requiring earthquake engineering are comprised of a multi-disciplinary team with geologists, seismologists, geotechnical engineers, structural engineers, applied statisticians and planners. Geology - Science that deals with the study of the earth and the processes that formed and continue to shape the earth s interior and exterior. Seismology - Science that deals with the study of earthquake waves and other artificially produced vibrations and how these waves are propagated through the earth s interior and crust. Geotechnical Engineering - Discipline of civil engineering that deals with soil mechanics and the assessment and design of soil and foundation systems. Structural Engineering - Discipline of civil engineering that deals the design and construction of man-made structures such as buildings, bridges, etc. Earthquake hazards prose a significant risk to hundreds of millions of people worldwide. The health and prosperity of many local, regional, and nation economies are at risk from damage and loss of life and infrastructure resulting from moderate to larger earthquakes in earthquake prone regions. Earthquake hazards can be categorized as: Strong motion and Structural Collapse Fault Rupture Liquefaction Earthquake-Induced Landslide, Mud Flows and Debris Flows Failure of Embankments Failure of Earth Retaining Structures Tsunami and Seiche

4 Lecture 1 Page 4 Important Concepts Tuesday, August 18, :09 PM Definitions: Strong Motion and Structural Collapse - Strong ground shaking resulting from seismic waves can cause significant damage to, and even collapse of, constructed works. This is the most important of all seismic hazards, because most other seismic hazards are a consequence of strong ground shaking. Structural collapse of poorly constructed buildings and has caused significant loss of life, especially in underdeveloped countries that have no seismic provisions in building codes, or where the codes are poorly enforced. Fault Rupture - Fault rupture is a crack or fracture in the rock or soil caused by shifting of the earth s crust during earthquakes. Generally adjacent surfaces are differentially displace along the plane of fracture. Liquefaction - A form of earthquake-induced ground failure resulting from high pore pressures and a marked loss of shear strength in granular, saturated soils due to strong ground shaking. The term liquefaction generally encompasses several types of failure including: (1) flow failure, (2) lateral spread, (3) ground oscillation, (4) bearing capacity failure, (5) liquefaction- induced settlement. Earthquake-Induced Landslide, Mud Slides and Debris Flow - Slope failures in steep and saturated terrain, where the slope has been destabilized by strong ground shaking. Failure of Embankments and Retaining Structures - Earthen dams, embankments and other retaining structures (e.g., bulkheads, quay wall, retaining walls) are often damaged due to ground shaking or ground failure. These facilities may be particularly vulnerable to damage when in waterfront, port or harbor areas, where they retained earth is saturated. Tsunami and Seiche - Tsunami are very large, long-period ocean waves produced by fault rupture or crustal deformation during earthquakes. As the wave form approaches shore, decreasing water depth causes the wave speed to decrease and the height of the wave to increases. In some coastal areas, the shape of the sea floor may accentuate the height of the wave, producing a near vertical wall of water, which produces great destruction inland. Seiche are waves that oscillate in lakes, bays, or gulfs from a few minutes to a few hours as a result of seismic waves.

5 Lecture 1 Page 5 Important Concepts Tuesday, August 18, :11 PM Risk Analysis - Discipline of applied statistics that uses laws of probability to assess the potential loss and consequences due to either natural or man made events. Mitigation of seismic hazards requires proper planning, earthquake-resistant design and construction and rapid emergency response. What is the definition of risk? What is the total loss? What is the annual probability of the event?

6 Lecture 1 Page 6 Strong Motion - Structural Collapse Tuesday, August 18, :46 PM "Earthquakes don't kill people, buildings do." (The Day the Earth Shook) Building collapse for earthquakes is the major contributor to loss of life.

7 Lecture 1 Page 7 Strong Motion - Types of Waves Tuesday, August 18, :17 PM Primary ave animation Shear wave animation Love wave animation Rayleigh wave animation What is the difference between a Love wave and a Rayleigh wave in terms of particle motion? What is the difference between a Rayleigh wave and a water wave in terms of particle motion? Rayleigh wave animation Water wave

8 Lecture 1 Page 8 Strong Motion - Structural Damage Tuesday, August 18, :50 PM Damage to structures in San Francisco/Oakland (1989 Loma Prieta Earthquake): (a) Life-threatening collapse of unreinforced masonary building in Oakland City Center (b) Sporadic damage occurred to unreinforced masonary structures in San Francisco Note that the building remains standing, despite the loss of the bearing wall. (c) Extensive masonary loss and shear cracking was noted in this steel frame building in Oakland. (d) The masonary walls of this steel frame department store in Oakland had extensive damage.! Inside, many hollow clay tile partition walls have shattered.

9 Lecture 1 Page 9 Strong Motion - Measurement Tuesday, August 18, :52 PM An accelerogram or acceleration time history shows acceleration (g) as a function of time. It is measured by an accelerometer. These two accelerograms (i.e., acceleration time histories) were recorded from the same earthquake at approximately the same distance to the earthquake source. How are the recorded values different?

10 Lecture 1 Page 10 Strong Motion - Spatial Variation Tuesday, August 18, :00 PM Peak ground acceleration (g) for San Francisco Bay Area Why are the values of pga so variable on this map?

11 Lecture 1 Page 11 Strong Motion - Soil Effects Tuesday, August 18, :02 PM Map of Bay Mud in San Francisco Bay Are higher or lower pga values found where the Bay Mud is present? Variation in strong motion due to soil deposits are often called soil or site effects.

12 Lecture 1 Page 12 Fault Rupture Tuesday, August 18, :08 PM Fault rupture can be: (1) extensional, (2) compression or (3) strike-slip. Which type of faulting is shown above? Fissures in front of house near Summit Road (1989 Loma Prieta Earthquake) Significant extensional as well as vertical displacement shown.

13 Lecture 1 Page 13 Fault Rupture Tuesday, August 18, :10 PM Damage to diversion dam (1999 Chi Chi Taiwan Earthquake). Damage to highway bridge (1999 Chi Chi Taiwan Earthquake).

14 Lecture 1 Page 14 Liquefaction - Niigata Thursday, August 20, :21 PM Liquefaction is a process by which clay-free soil deposits, primarily sands and silts, temporarily lose strength and behave as a viscous liquid rather than as a solid. The actions in the soil which produce liquefaction are as follows: Seismic waves, primarily shear waves, passing through saturated granular layers, distort the granular structure, and cause loosely packed groups of particles to collapse. Disruptions to the particulate structure generated by these collapses cause transfer of load from grain-to-grain contacts in the soil to the interstitial pore water. This transfer of load increases pressure, in the pore water, causing drainage to occur. If drainage is restricted, a transient build up of pore-water pressure will occur. If the pore-water pressure rises to a level approaching the overburden pressure grain-to-grain contact stresses approach zero and the granular layer temporarily behaves as a viscous liquid rather than as a solid and liquefaction has occurred. In the liquefied condition, soil deformation: may occur with little shear resistance. Deformations large enough to cause damage to constructed works (usually more than 0.1 m) are called ground failure. Pasted from < Liquefaction during 1964 Niigata, Japan Earthquake (Video) The Niigata earthquake of June 16, 1964 had a magnitude of 7.5 and caused severe damage to many structures in Niigata. The destruction was observed to be largely limited to buildings that were founded on top of loose, saturated soil deposits. Even though about 2000 houses were totally destroyed, only 28 lives were lost Pasted from < ~liquefaction/html/quakes/niigata/niigata.html> Sand boils (right, SC) and ground fissures were observed at various sites in Niigata. Pasted from < hington.edu/ ~liquefaction/html/q uakes/niigata/niigata.html> Pasted from < ~liquefaction/selectpiclique/nigata64/sandboils.jpg>

15 Lecture 1 Page 15 Liquefaction - Niigata Thursday, August 20, :21 PM

16 Lecture 1 Page 16 Liquefaction - Niigata Thursday, August 20, :21 PM

17 Lecture 1 Page 17 Liquefaction - Niigata Thursday, August 20, :21 PM

18 Lecture 1 Page 18 Liquefaction - Niigata Thursday, August 20, :21 PM

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20 Lecture 1 Page 20 Liquefaction - Niigata Thursday, August 20, :21 PM

21 Lecture 1 Page 21 Liquefaction - Niigata Thursday, August 20, :21 PM

22 Lecture 1 Page 22 Flow Failure Thursday, August 20, :21 PM Flow failures are the most catastrophic ground failure caused by liquefaction. These failures commonly displace large masses of soil tens of meters and in a few instances, large masses of soil have traveled tens of kilometers down long slopes at velocities ranging up to tens of kilometers per hour. Flows may be comprised of completely liquefied soil or blocks of intact material riding on a layer of liquefied soil. Flows usually develop in loose saturated sands or silts on slopes greater than 5 degrees. Pasted from <

23 Lecture 1 Page 23 Lateral Spread Lateral spreads involve lateral displacement of large, surficial blocks of soil as a result of liquefaction of a subsurface layer. Displacement occurs in response to combination of gravitational forces and inertial forces generated by an earthquake. Lateral spreads generally develop on gentle slopes (most commonly less than 5 degrees) and move toward a free face such as an incised river channel. Pasted from <

24 Lecture 1 Page 24 Ground Oscillation Thursday, August 20, :21 PM Ground Oscillation Where the ground is flat or the slope is too gentle to allow lateral displacement, liquefaction at depth may decouple overlying soil layers from the underlying ground, allowing the upper soil to oscillate back and forth and up and down in the form of ground waves. These oscillations are usually accompanied by opening and closing fissures and fracture of rigid structures such as pavements and pipelines. Pasted from < Pasted from < /osc_loma5.html> The Marina District of San Francisco suffered from relatively intense shaking and liquefaction in the 1989 Loma Prieta earthquake. The soft bay and marsh soils in the area, which were covered by dredged sand in the early 1900s, amplified earthquake shaking. The sandy fill material liquefied, causing disruption of streets, sidewalks, telephone and power poles and homes. Here, the liquefied sand decoupled the overlying fill and structures from the underlying sediment, allowing the overlying materials to oscillate with shaking that continued after the fill material liquefied. In such "ground oscillation" permanent deformations may be small, but displacements during earthquake shaking may be damaging (Youd, 1995). Pasted from < pages/osc_loma5.html>

25 Lecture 1 Page 25 Bearing Capacity Failure Thursday, August 20, :23 PM When the soil supporting a building or other structure liquefies and loses strength, large deformations can occur within the soil which may allow the structure to settle and tip. Conversely, buried tanks and piles may rise buoyantly through the liquefied soil. For example, many buildings settled and tipped during the 1964 Niigata, Japan earthquake. The most spectacular bearing failures during that event were in the Kwangishicho apartment complex where several four-story buildings tipped as much as 60 degrees. Apparently, liquefaction first developed in a sand layer several meters below ground surface and then propagated upward through overlying sand layers. The rising wave of liquefaction weakened the soil supporting the buildings and allowed the structures to slowly settle and tip. Pasted from <

26 Lecture 1 Page 26 Settlement Thursday, August 20, :23 PM Pasted from < Photograph looking up Dore Street (likely between Brannan and Bryant streets) in San Francisco, showing liquefaction-related damage from the 1906 earthquake. The undulations in the road show the effects of settlement and lateral spreading. Damage to the wood-frame houses likely resulted from a combination of lateral spreading and loss of soil strength (loss of bearing capacity) from liquefaction. This area was once marshland with a tributary to Mission Creek bisecting the marsh and flowing southeast toward Mission creek. The marsh and creek was filled in the middle to late 1800s, likely with dune sand (O'Rourke and others, 1992). Such areas are subject to amplified shaking, because of the underlying soft soils, and liquefaction of the poorly engineered, sandy artificial fill. (Photograph courtesy of the Bancroft Library) Pasted from <

27 Lecture 1 Page 27 Earthquake Induced Landslides, Mudflows and Debris Flows Thursday, August 20, :23 PM Landslides in Anchorage caused heavy damage. Huge slides occurred in the downtown business section, at Government Hill, and at Turnagain Heights. The largest and most devastating landslide occurred at Turnagain Heights. An area of about 130 acres was devasted by displacements that broke the ground into many deranged blocks that were collapsed and tilted at all angles. This slide destroyed about 75 private houses. Water mains and gas, sewer, telephone, and electrical systems were disrupted throughout the area. Pasted from < al/states/events/1964_03_28.php>

28 Lecture 1 Page 28 Failure of Embankment Thursday, August 20, :23 PM Embankment failure due to liquefaction on the Pan-American Highway near the Pacific Ocean about 190 km south of Lima, Peru Pasted from < n/07/21-03/05peru.asp> Pasted from < Aznalcóllar, Spain tailings dam rupture, April 25, 1998 Tailings dam failure during shaking Landslides that can cause dams failure Landslides that can deposit material within the dam, causing tailings overflow Subsidence near underground mine workings, allowing water to enter and potentially release acid mine drainage Pasted from < /seismic_risk.html> Pasted from <

29 Lecture 1 Page 29 Failure of Earth Retaining Structures Thursday, August 20, :23 PM Pasted from < Example of retaining wall failure during earthquake in El Salvador (January, 2001).

30 Lecture 1 Page 30 Tsunami and Seiche Saturday, August 22, :05 PM Tsunami damage from the 1964 Alaska earthquake 2004 Indonsian Earthquake (Video 1) 2004 Indonsian Earthquake (Video 2)