Lecture 1 Page 1 Important Concepts Monday, August 17, 2009 1:05 PM Earthquake Engineering is a branch of Civil Engineering that requires expertise in geology, seismology, civil engineering and risk assessment. Project requiring earthquake engineering are best comprised of a multi-disciplinary team having 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 building, 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 resulting from moderate to larger earthquakes in earthquake prone regions. Earthquake hazards can be categorized as: Ground Shaking Hazards 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 Definitions: Ground Shaking 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
Lecture 1 Page 2 ground shaking. Structural collapse of poorly constructed buildings and bridges has caused a significant loss of life, especially in underdeveloped countries with no seismic provisions in building codes. 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 form of 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 Flow, 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 remains saturated. Tsunami and Seiche - Tsunami are very large, long-period waves produced in the ocean by fault rupture or crustal deformation during earthquakes. As the wave form approaches shore, decreasing water depth cause 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. 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.
Lecture 1 Page 3 Strong Motion - Building Damage Monday, August 17, 2009 2:29 PM "Earthquakes don't kill people, buildings do."
Lecture 1 Page 4 Strong Motion - Waves Monday, August 17, 2009 5:13 PM Primary wave animation Shear wave animation Love wave animation Rayleigh wave animation What is the difference between a Rayleigh wave and a water wave? Rayleigh wave animation Water wave
Lecture 1 Page 5 Strong Motion - Accelerograms Tuesday, August 18, 2009 12:33 PM 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 they different and why?
Lecture 1 Page 6 Strong Motion - Variation of pga Tuesday, August 18, 2009 2:30 PM Peak ground acceleration (g) for San Francisco Bay Area Why are the values of pga so variable on this map?
Lecture 1 Page 7 Strong Motion - Soil Effects Tuesday, August 18, 2009 2:37 PM Map of Bay Mud in San Francisco Bay
Are higher or lower pga values found where the Bay Mud is present? Lecture 1 Page 8
Changes in strong motion due to soil deposits are often called soil or site effects. Lecture 1 Page 9
Lecture 1 Page 10 Strong Motion - Structural Damage Tuesday, August 18, 2009 2:46 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 shattered What is the definition of unreinforced masonary?
Lecture 1 Page 11 Fault Rupture Tuesday, August 18, 2009 2:55 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. Lecture 1 Page 12