CETS461 Topic 1 PDF

CETS461/STRUCTURAL PROFESSIONAL COURSE: SPECIALIZED 1 (EARTHQUAKE ENGINEERING) TOPIC 1 A. Y. 2 0 2 4 - 2 0 2 5 S E C O N D S E M E S T E R BY ENGR. ALJON M. MINDAÑA ...

CETS461/STRUCTURAL PROFESSIONAL COURSE: SPECIALIZED 1 (EARTHQUAKE ENGINEERING) TOPIC 1 A. Y. 2 0 2 4 - 2 0 2 5 S E C O N D S E M E S T E R BY ENGR. ALJON M. MINDAÑA  S E C O N D S E M E S T E R TOPIC 1: INTRODUCTION A. Y. 2 0 2 4 - 2 0 2 5 1. General Effects of Earthquakes 2. Main Source of Earthquakes 3. Types of Earthquakes 4. Tectonic Plate Movement 1 S P. C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E E A R T H Q U A K E E N G I N E E R I N G BY ENGR. ALJON M. MINDAÑA  S E C O N D S E M E S T E R General Effects of Earthquakes A. Y. 2 0 2 4 - 2 0 2 5 Generally, effects of earthquakes can be divided into three categories: ground failure, indirect effects, and ground shaking. Ground failure can be further subdivided into surface rupture, ground subsidence, ground cracking, soil liquefaction, and landslides. 1 S P. Indirect effects include tsunamis (tidal waves in the C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E oceans), seiches (tidal waves in an enclosed body of water, such as a lake), and fires, all of which can result in damage E A R T H Q U A K E E N G I N E E R I N G comparable to, or even larger than, ground shaking. BY ENGR. ALJON M. MINDAÑA  S E C O N D S E M E S T E R Ground Failures A. Y. 2 0 2 4 - 2 0 2 5 Ground failures are generally considered part of geotechnical earthquake engineering, and they involve the movement of the ground surface at a location where geological fissures or zones of weakness in the crust of the earth (faults) slip slowly or suddenly. 1 S P. C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E E A R T H Q U A K E E N G I N E E R I N G BY ENGR. ALJON M. MINDAÑA  S E C O N D S E M E S T E R Ground Failures A. Y. 2 0 2 4 - 2 0 2 5 Surface faulting occurs when the relative movement of rocks on the two sides of a fault takes place deep within the earth and breaks through to the surface; this can occur as slow movement in the form of fault creep or suddenly resulting in an earthquake. This type of ground failure typically follows a preexisting 1 S P. fault line. C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E E A R T H Q U A K E E N G I N E E R I N G BY ENGR. ALJON M. MINDAÑA  S E C O N D S E M E S T E R Ground Failures A. Y. 2 0 2 4 - 2 0 2 5 Ground subsidence occurs as loose soils rearrange and settle into a denser state during vibrations caused by earthquakes. In some cases, the compaction effect may amount to substantial settlement of the ground surface. 1 S P. C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E E A R T H Q U A K E E N G I N E E R I N G BY ENGR. ALJON M. MINDAÑA  C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E S P. 1 A. Y. 2 0 2 4 - 2 0 2 5 E A R T H Q U A K E E N G I N E E R I N G S E C O N D S E M E S T E R Ground Failures BY ENGR. ALJON M. MINDAÑA Anchorage, Alaska along Fourth Avenue during the Good Friday earthquake in 1964  S E C O N D S E M E S T E R Ground Failures A. Y. 2 0 2 4 - 2 0 2 5 Ground cracking is usually observed along the edges of ground subsidence; it may also be the result of slope failure or liquefaction, all of which cause the ground to lose its support and sink, with the ground surface breaking up into fissures, scarps, horsts, and grabens. 1 S P. C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E E A R T H Q U A K E E N G I N E E R I N G BY ENGR. ALJON M. MINDAÑA  S E C O N D S E M E S T E R Ground Failures A. Y. 2 0 2 4 - 2 0 2 5 Soil liquefaction occurs when loose, saturated granular soils temporarily change from a solid to a liquid state, losing their shear strength, which corresponds to a loss in effective stress between soil particles. Loose saturated (or moderately saturated) sands and nonplastic silts are most susceptible to this ground failure; 1 S P. however, in rare cases, gravel and clay can also experience C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E liquefaction. In all cases, poor drainage within the loose soil causes an E A R T H Q U A K E E N G I N E E R I N G increase in the pore water pressure as the soil is compressed by the vibratory effect of seismic waves. BY ENGR. ALJON M. MINDAÑA  C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E S P. 1 A. Y. 2 0 2 4 - 2 0 2 5 E A R T H Q U A K E E N G I N E E R I N G S E C O N D S E M E S T E R Ground Failures BY ENGR. ALJON M. MINDAÑA  S E C O N D S E M E S T E R Ground Failures A. Y. 2 0 2 4 - 2 0 2 5 In soil liquefaction, the load is transferred from soil to pore water pressure, the effective stress between particles is temporarily reduced, or eliminated, causing a corresponding decrease in shear strength. In some cases, the pore water pressure increases rapidly and a slurry (soil water mixture) forms that flows vertically to the surface, 1 S P. which can result in craters and sand boils. C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E E A R T H Q U A K E E N G I N E E R I N G BY ENGR. ALJON M. MINDAÑA  S E C O N D S E M E S T E R Indirect Effects of Earthquakes A. Y. 2 0 2 4 - 2 0 2 5 These include some of the most devastating and frightening impacts of earthquakes, such as tsunamis and fires. Designing structural systems to withstand the large magnitude forces resulting from water waves generated by a tsunami is challenging. Tsunamis are long-period sea waves that are generated 1 S P. when an earthquake causes the vertical movement of the C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E seafloor. Tsunamis travel far, at high speeds (over 500 mph) in the open ocean and are difficult to detect because of their E A R T H Q U A K E E N G I N E E R I N G small crest-to-trough height, and long wavelengths, which typically, are hundreds of miles long. BY ENGR. ALJON M. MINDAÑA  S E C O N D S E M E S T E R Indirect Effects of Earthquakes A. Y. 2 0 2 4 - 2 0 2 5 One of the most devastating tsunami events occurred in the Indian Ocean on December 26, 2004, which killed over 230,000 people in 14 different countries; the furthest fatality was in Port Elizabeth, South Africa, over 8000 km away 1 S P. C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E E A R T H Q U A K E E N G I N E E R I N G BY ENGR. ALJON M. MINDAÑA  S E C O N D S E M E S T E R Indirect Effects of Earthquakes A. Y. 2 0 2 4 - 2 0 2 5 Seiches are earthquake-induced waves in an enclosed body of water, such as a lake or a reservoir, or one that is partially enclosed, such as a bay. Seiches are caused when long-period seismic waves resonate with oscillations of the enclosed water and cause standing waves. 1 S P. C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E E A R T H Q U A K E E N G I N E E R I N G BY ENGR. ALJON M. MINDAÑA  S E C O N D S E M E S T E R Indirect Effects of Earthquakes A. Y. 2 0 2 4 - 2 0 2 5 Fire is probably the most terrifying indirect effect of earthquakes, particularly considering that people who survived in collapsed buildings, but were trapped in the debris, were burnt alive as the fire consumed everything in its path. 1 S P. C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E E A R T H Q U A K E E N G I N E E R I N G BY ENGR. ALJON M. MINDAÑA  S E C O N D S E M E S T E R Ground Shaking A. Y. 2 0 2 4 - 2 0 2 5 Ground shaking causes the majority of earthquake damage; additionally most of the aforementioned effects are caused by shaking. In fact, where the shaking intensity is low, the hazard of other effects can be minimal. Consequently, shaking is the only effect experienced by 1 everyone within an afflicted area, and intense shaking can S P. C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E produce widespread damage from various seismic hazards. For this reason, ground shaking is the main focus of E A R T H Q U A K E E N G I N E E R I N G earthquake engineering. BY ENGR. ALJON M. MINDAÑA  S E C O N D S E M E S T E R Ground Shaking A. Y. 2 0 2 4 - 2 0 2 5 Seismic waves that radiate from the location where a fault ruptures (the focus) quickly travel throughout the earth’s crust, producing ground shaking when they reach the ground surface. The intensity and duration of shaking experienced at a particular site during an earthquake are primarily because 1 S P. of three factors: earthquake size, location, and the C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E subsurface materials beneath the structure. E A R T H Q U A K E E N G I N E E R I N G BY ENGR. ALJON M. MINDAÑA  S E C O N D S E M E S T E R Ground Shaking A. Y. 2 0 2 4 - 2 0 2 5 Earthquake size (magnitude): It can be measured objectively or subjectively—larger earthquakes cause stronger shaking. A strong earthquake can cause ground shaking over widespread areas, suddenly affecting large numbers of structures. Even relatively small earthquakes can have a 1 S P. significant impact on large numbers of buildings. C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E E A R T H Q U A K E E N G I N E E R I N G BY ENGR. ALJON M. MINDAÑA  S E C O N D S E M E S T E R Ground Shaking A. Y. 2 0 2 4 - 2 0 2 5 Location (distance from the focus or epicenter): Generally, the closer to the epicenter, the stronger the shaking. Structures near the epicenter of a strong earthquake can experience extensive damage, in some cases partial or total collapse 1 S P. C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E E A R T H Q U A K E E N G I N E E R I N G BY ENGR. ALJON M. MINDAÑA  S E C O N D S E M E S T E R Ground Shaking A. Y. 2 0 2 4 - 2 0 2 5 The subsurface materials beneath the structure: Soft soils amplify the shaking, while rocks do not. This is the most insidious of the three factors because the site can be located at a long distance from the epicenter and still experience extensive ground shaking due to local soil conditions. 1 S P. C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E E A R T H Q U A K E E N G I N E E R I N G BY ENGR. ALJON M. MINDAÑA  S E C O N D S E M E S T E R Types of Earthquakes A. Y. 2 0 2 4 - 2 0 2 5 The majority of damaging earthquakes are produced by surface fault ruptures caused by the relative movement of the tectonic plates. However, a number of other sources, including man-made and volcanic, can produce measurable earthquakes. Volcanic earthquakes can be attributed to the same forces 1 S P. that are responsible for tectonic earthquakes. C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E E A R T H Q U A K E E N G I N E E R I N G BY ENGR. ALJON M. MINDAÑA  S E C O N D S E M E S T E R Man-Made Earthquakes A. Y. 2 0 2 4 - 2 0 2 5 These generally have a much smaller magnitude than the other two types of earthquakes, and thus have a lesser impact on infrastructure. However, man-made earthquakes can lead to earlier fault ruptures (tectonic earthquakes) because the shaking can increase critical stresses at the plate boundaries. 1 S P. One of the most intense cases is due to explosions, both C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E from conventional and nuclear weapons. E A R T H Q U A K E E N G I N E E R I N G BY ENGR. ALJON M. MINDAÑA  S E C O N D S E M E S T E R Man-Made Earthquakes A. Y. 2 0 2 4 - 2 0 2 5 Boxcar nuclear bomb explosion in 1968, with a yield of 1200,000 tons TNT equivalent, excited an earthquake of magnitude 5.0 that lasted 1 S P. for 10–12 s (Bolt, 2004). C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E E A R T H Q U A K E E N G I N E E R I N G BY ENGR. ALJON M. MINDAÑA  S E C O N D S E M E S T E R Man-Made Earthquakes A. Y. 2 0 2 4 - 2 0 2 5 Collapse earthquakes can be generated by landslides (those not generated by tectonic earth quakes) as well as collapse of mine/cavern roofs, or buildings. 1 S P. C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E E A R T H Q U A K E E N G I N E E R I N G BY ENGR. ALJON M. MINDAÑA  S E C O N D S E M E S T E R Man-Made Earthquakes A. Y. 2 0 2 4 - 2 0 2 5 Seismic activity near large artificial lakes has also been reported. It is believed that the weight of the water and the extra water pressure in rocks can change the stresses in existing rock fractures. The weight of the water increases the total stress by direct loading, while the extra pore water pressure decreases the 1 S P. effective stress (pushes the fracture planes apart); this can C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E lead to sliding along fracture planes where tectonic strain is already present, causing an earthquake. E A R T H Q U A K E E N G I N E E R I N G BY ENGR. ALJON M. MINDAÑA  S E C O N D S E M E S T E R Man-Made Earthquakes A. Y. 2 0 2 4 - 2 0 2 5 Earthquakes caused by energy production processes have been recorded for over 50 years, though recently the association of earthquakes and energy production has become contentious. This is particularly controversial with respect to the hydraulic fracturing (fracking) process. 1 S P. This technique for extracting oil and gas from low C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E permeability rocks involves fracturing rocks by injecting high E A R T H Q U A K E E N G I N E E R I N G pressure fluid into the rock. BY ENGR. ALJON M. MINDAÑA  S E C O N D S E M E S T E R Volcanic Earthquakes A. Y. 2 0 2 4 - 2 0 2 5 These are caused by the same energy source as tectonic earthquakes, which is the heat from the earth’s core. Volcanic seismicity affects limited areas near volcanic regions. 1 S P. C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E E A R T H Q U A K E E N G I N E E R I N G BY ENGR. ALJON M. MINDAÑA  S E C O N D S E M E S T E R Volcanic Earthquakes A. Y. 2 0 2 4 - 2 0 2 5 The movement of magma through tubes below the volcanic vents creates pressure changes in the surrounding rock that can rupture, releasing elastic strain energy as seismic waves. Other seismic waves can be induced by sudden, irregular movement of magma whose path has been obstructed, or by steady magma movement deep in the mantle. 1 S P. Damage from all these C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E earthquakes is relatively minor E A R T H Q U A K E E N G I N E E R I N G compared with that produced by tectonic earthquakes. BY ENGR. ALJON M. MINDAÑA  S E C O N D S E M E S T E R Tectonic Earthquakes A. Y. 2 0 2 4 - 2 0 2 5 These are caused by a sudden dislocation of segments of the earth’s crust, the structure of which is composed of plates (large and small) known as tectonic plates that float on a liquid layer, the mantle. This arrangement resulted from the formation of planet Earth five billion years ago, when hot gasses cooled into a 1 S P. semi-solid mass. It is estimated that after one to two billion C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E years of cooling, the crust solidified and cracked forming tectonic plates (different ones than those that exist today). E A R T H Q U A K E E N G I N E E R I N G BY ENGR. ALJON M. MINDAÑA  S E C O N D S E M E S T E R Tectonic Earthquakes A. Y. 2 0 2 4 - 2 0 2 5 From the beginning, the plates have been in constant motion forming and breaking up continents over time, including the formation of supercontinents that contained most of the landmass. The latest supercontinent, Pangea, started separating approximately 200 million years ago, and its parts have 1 S P. drifted apart to the current configuration of the earth’s C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E surface. This process was originally proposed by Alfred E A R T H Q U A K E E N G I N E E R I N G Wegener in the early 1900s. BY ENGR. ALJON M. MINDAÑA  S E C O N D S E M E S T E R Tectonic Earthquakes 1 S P. A. Y. 2 0 2 4 - 2 0 2 5 C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E E A R T H Q U A K E E N G I N E E R I N G Continental drift evidence; distribution of fossils across the southern continents of Pangea. (Courtesy of USGS.) BY ENGR. ALJON M. MINDAÑA  C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E S P. 1 A. Y. 2 0 2 4 - 2 0 2 5 E A R T H Q U A K E E N G I N E E R I N G S E C O N D S E M E S T E R Tectonic Earthquakes BY ENGR. ALJON M. MINDAÑA Tectonic plates and types of plate boundaries. (Courtesy of USGS.)  C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E S P. 1 A. Y. 2 0 2 4 - 2 0 2 5 E A R T H Q U A K E E N G I N E E R I N G S E C O N D S E M E S T E R Tectonic Earthquakes BY ENGR. ALJON M. MINDAÑA  C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E S P. 1 A. Y. 2 0 2 4 - 2 0 2 5 E A R T H Q U A K E E N G I N E E R I N G S E C O N D S E M E S T E R Tectonic Earthquakes BY ENGR. ALJON M. MINDAÑA Cross - section of the Earth with the main type plate boundaries. (Courtesy of USGS.)  C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E S P. 1 A. Y. 2 0 2 4 - 2 0 2 5 E A R T H Q U A K E E N G I N E E R I N G S E C O N D S E M E S T E R Tectonic Earthquakes BY ENGR. ALJON M. MINDAÑA Tectonic mechanisms at plate boundaries ( after Dewey, 1972 )  S E C O N D S E M E S T E R Tectonic Earthquakes A. Y. 2 0 2 4 - 2 0 2 5 At the boundaries of the plates, rocks fracture, usually at many locations, creating a web of smaller plates with edges that rub and push relative to each other; these edges are called faults. On average, these faults have the potential to displace approximately 2 inches per year. When the rubbing and 1 S P. pushing is prevented, elastic energy accumulates along the C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E edges of the plates. E A R T H Q U A K E E N G I N E E R I N G BY ENGR. ALJON M. MINDAÑA  C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E S P. 1 A. Y. 2 0 2 4 - 2 0 2 5 E A R T H Q U A K E E N G I N E E R I N G S E C O N D S E M E S T E R Tectonic Earthquakes BY ENGR. ALJON M. MINDAÑA Epicenters of 358,214 earthquakes, 1963–1998. (Courtesy of NASA.)  S E C O N D S E M E S T E R Tectonic Earthquakes A. Y. 2 0 2 4 - 2 0 2 5 When this energy is released with a sudden movement (slip), it causes brief strong ground vibrations. The specific location (generally a volume of rock) where the movement or energy release occurs is known as the focus, or hypocenter. The point on the earth’s surface directly above the 1 S P. hypocenter is called the epicenter. C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E Usually, the vibrations cause the rocks near the focus to become unstable; and as these rocks settle into a new E A R T H Q U A K E E N G I N E E R I N G equilibrium state they cause aftershocks. The discipline that studies seismic activity is known as seismology. BY ENGR. ALJON M. MINDAÑA  S E C O N D S E M E S T E R PLATE NO. 1: TECTONIC PLATES AND PLATE A. Y. 2 0 2 4 - 2 0 2 5 BOUNDARIES Instructions: Draw the following in a short bond paper: Tectonic plates and types of plate boundaries. Cross - section of the Earth with the main type plate boundaries. Tectonic mechanisms at plate boundaries. 1 S P. C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E E A R T H Q U A K E E N G I N E E R I N G BY ENGR. ALJON M. MINDAÑA  C E T S 4 6 1 – P R O F E S S I O N A L C O U R S E S P. 1 A. Y. 2 0 2 4 - 2 0 2 5 E A R T H Q U A K E E N G I N E E R I N G S E C O N D S E M E S T E R BY ENGR. ALJON M. MINDAÑA THANK YOU!