CE 021 - Lecture 1.0-1. PDF

INTRODUCTION TO EARTHQUAKE ENGINEERING ENGR. PALAD  Intended Learning Outcomes At the of the course, the students shall be able to: 1. Describe earthquakes, their worldwide distribution, what causes them, their likely damage mechanisms, measuring scales, and current efforts on the...

INTRODUCTION TO EARTHQUAKE ENGINEERING ENGR. PALAD  Intended Learning Outcomes At the of the course, the students shall be able to: 1. Describe earthquakes, their worldwide distribution, what causes them, their likely damage mechanisms, measuring scales, and current efforts on the prediction of strong seismic ground motions. 2. Discuss the Philippine Fault System and how it differs from the United States (US) Fault System. What is an Earthquake? An earthquake is a sudden release of energy in the Earth's crust that creates seismic waves. Most earthquakes are produced when stress builds up along a fault over a long time, eventually causing the fault to slip. What causes Earthquakes? Most earthquakes occur due to the movement of tectonic plates, which are large pieces of the Earth's crust that fit together like a jigsaw puzzle. How Do Continents Differ from Ocean Basins? our planet is divided into continents and oceans. Continents and oceans differ in the types and thicknesses of the rocks they contain and, as we will learn later, form in very different ways. Within the oceans are major variations in the depth and character of the seafloor from place to place. The land also varies in elevation and character, such as higher, vegetation- covered mountains in eastern Australia than in the rest of the continent. What Is Inside Earth? Earth consists of concentric layers that have different compositions. The outermost layer is the crust, which includes continental crust and oceanic crust. Beneath the crust is the mantle, Earth’s most voluminous layer. The molten outer core and the solid inner core are at Earth’s center.  What Is Inside Earth? 1. Continental crust, the thin that averages 35 to 40 km (20–25 mi) in thickness. 2. Oceanic crust has an average thickness of about 7 km (4 mi). 3. The mantle extends from the base of the crust down 2,900 km (1,800 mi).  What Is Inside Earth? 4. The lower mantle has a composition similar to the upper mantle, but it contains minerals formed at very high pressures. Nearly all of the mantle is solid, not molten. 5. The outer core is molten, but the inner core is solid. What Is Inside 1. The crust and uppermost Earth? mantle together form an upper, rigid layer called the lithosphere (lithos means “stone” in Greek). 2. The asthenosphere, functions as a soft, weak zone over which the lithosphere may move. The word asthenosphere is from a Greek term for “not strong.” The asthenosphere is approximately 80 to 150 km thick, so its base can be as deep as about 250 km. Where Do Most Earthquakes Occur? Where Do Most Earthquakes Occur?  Earthquakes are not distributed uniformly across the planet. Most are concentrated in discrete belts, such as one that runs along the western coasts of North and South America.  Most earthquakes in the oceans occur along the winding crests of mid-ocean ridges. Where the ridges curve or zigzag, so do the patterns of earthquakes. Earthquakes are sparse in some continental interiors but are abundant in others, like the Middle East, China, and Tibet. Large areas of the seafloor, especially the abyssal plains, have few earthquakes. Volcanically active islands, like Hawaii, in the middle of the Pacific Ocean, do have earthquakes.  Some continental edges experience many earthquakes, but other edges have few. Earthquakes are common along the western coasts of South America and North America, and these edges also have narrow continental shelves. There are few earthquakes along the eastern coasts of the Americas, where the continental shelves are wide. Ocean trenches and associated island arcs have numerous earthquakes. In fact, many of the world’s largest and most deadly earthquakes occur near ocean trenches. Recent examples were the large earthquakes that produced deadly ocean waves (tsunamis) in the Indian Ocean in 2004 and in Japan in 2011. What Do Earthquake and Volcanic Activity Tell Us About Earth’s Lithosphere? Earthquakes, volcanoes, and other processes that deform the crust and mantle are called tectonic activity, or simply tectonics. The belts of yellow and orange on the map are areas of active tectonics. The regions between the belts are relatively stable. What Do Earthquake and Volcanic Activity Tell Us About Earth’s Lithosphere? Earth’s strong upper layer, the lithosphere, is broken into a dozen or so fairly rigid pieces, called tectonic plates. This map shows names and boundaries of the larger plates.  How Do Plates Move Relative to One Another? Plate boundaries have tectonic activity because plates are moving relative to one another Divergent Boundary Convergent Boundary Transform Boundary At a divergent boundary, two At a convergent boundary, At a transform boundary, two plates move apart relative to two plates move toward one plates move horizontally past one another. In most cases, another. A typical result is one another, as shown by the magma fills the space that one plate slides under the white arrows on the top between the plates. other. surface. Where Are the Three Types of Plate Boundaries?  What Happens at Mid-Ocean Ridges? Mid-ocean ridges are divergent plate boundaries where new oceanic lithosphere forms as two oceanic plates move apart. These boundaries are also called spreading centers because of the way the plates spread apart. The divergence and movement of fault blocks cause faulting, resulting in frequent small- to moderate- sized earthquakes. What Happens When Divergence Splits a Continent Apart? Most divergent plate boundaries are beneath oceans, but a divergent boundary may also form within a continent. This process, called continental rifting, creates a continental rift, such as the Great Rift Valley in East Africa. Rifting can lead to seafloor spreading and formation of a new ocean basin. What Happens When Divergence Splits a Continent Apart? A continental edge that lacks tectonic activity is called a passive margin. A long continental rift that begins near the Red Sea and extends into central Africa. Some parts of the rift contain large lakes. The Red Sea represents the early stages of seafloor spreading. It began forming about 50 million years ago. What Happens When Two Oceanic Plates Converge? Convergence of two oceanic plates forms an ocean-ocean convergent boundary. The process of one plate sliding beneath another plate is subduction. The zone around the downward-moving plate is a subduction zone where many large earthquakes occur  What Happens When Two Oceanic Plates Converge? An oceanic trench forms as the subducting plate bends down. Sediment and slices of oceanic crust collect in the trench, forming a wedge called an accretionary prism. The erupted lava and exploded volcanic fragments construct a curving belt of islands in an island arc. What Happens When an Oceanic Plate and a Continental Plate Converge? The convergence of an oceanic and a continental plate forms an ocean- continent convergent boundary. Compression associated with the convergent boundary squeezes the crust for hundreds of kilometers into the continent. The crust deforms and thickens, resulting in uplift of the region. What Causes the Pacific Ring of Fire? Volcanoes surround the Pacific Ocean, forming the Pacific Ring of Fire, as shown in the map below. The volcanoes extend from the southwestern Pacific, through the Philippine Islands, Japan, and Alaska, and then down the western coasts of the Americas. The Ring of Fire results from subduction on both sides of the Pacific Ocean. What Causes the Pacific Ring of Fire?  What Happens When Two Continents Collide? Two continental masses may converge along a continent-continent convergent boundary. This type of boundary is commonly called a continental collision, and it produces huge mountain ranges.  What Happens Along Transform Boundaries? Two continental masses may converge along a continent-continent convergent boundary. This type of boundary is commonly called a continental collision, and it produces huge mountain ranges.  What Happens Along Transform Boundaries? AT TRANSFORM BOUNDARIES, PLATES SLIP HORIZONTALLY past each other along transform faults. In the oceans, transform faults are associated with mid- ocean ridges. Transform faults combine with spreading centers to form a zigzag pattern on the seafloor. A transform fault can link different types of plate boundaries, such as a mid-ocean ridge and an ocean trench. What Happens Along Transform Boundaries? Transform faults along mid-ocean ridges are generally perpendicular to the axis of the ridge. A fracture zone is a former transform fault that now has no relative motion across it. Younger parts of the plate are warmer and higher than older parts. What Are Some Other Types of Transform Boundaries? What Are Some Other Types of Transform Boundaries?  END OF DISCUSSION ANY QUESTIONS? [email protected] C Consultation Hours: 6:00 - 7:00 pm T | TH @ CE Faculty No part of this material may be reproduced, distributed or transmitted in any form or by any means including photocopying or other means without prior written permission of the owner except for personal academic use and certain other non-commercial uses permitted by copyright law. How Do We Describe an Earthquake? When an earthquake occurs, it releases mechanical energy, some of which is transmitted through rocks as vibrations called seismic waves. These waves spread out from the site of the disturbance and travel through the interior or along the surface of Earth. Scientists record the waves using scientific instruments at seismic stations. How Do We Describe an Earthquake? The place where the earthquake is generated is called the hypocenter or focus. The epicenter is the point on Earth’s surface directly above where the earthquake occurs (directly above the hypocenter). If the seismic event happens on the surface, such as during a human- caused surface explosion, then the epicenter and hypocenter are the same.  What Causes Most Earthquakes? Most earthquakes are generated by movement along faults. Normal faults Reverse faults Strike-slip faults In a normal fault, the rocks In thrust and reverse faults, In strike-slip faults, the two above the fault (the hanging the hanging wall moves up sides of the fault slip wall) move down with respect with respect to the footwall. horizontally past each other. to rocks below the fault (the Such faults are formed by This can generate large footwall). compressional forces. earthquakes.  How Do Volcanoes and Magma Cause Earthquakes? Volcanoes generate seismic waves and cause the ground to shake through several processes. An explosive volcanic eruption causes compression, transmitting energy as seismic waves (shown here with yellow lines).  How Do Volcanoes and Magma Cause Earthquakes? Volcanism can be accompanied by faulting and associated earthquakes. Volcanoes add tremendous weight to the crust, and this loading can lead to faulting and earthquakes. The fault shown here caused an earthquake at depth, down dropping the volcano relative to its surroundings.  How Do Volcanoes and Magma Cause Earthquakes? Many volcanoes have steep, unstable slopes underlain by rocks altered and weakened by hot water heated by magma. The flanks of such volcanoes can fall apart catastrophically, causing landslides that shake the ground as they break away and travel down the flank of the volcano. Numerous small earthquakes also occur as the rocks break, prior to the actual landslide.  How Do Volcanoes and Magma Cause Earthquakes? As magma moves beneath a volcano, it can push rocks out of the way, causing earthquakes. Magma can push rocks sideways or open space by fracturing adjacent rocks and uplifting the earth’s surface. The emplacement of magma can cause a series of small and distinctive earthquakes, called volcanic tremors. All types of magma-related earthquakes are closely monitored by geologists and seismologists (scientists who study earthquakes), because they can signal an impending eruption.  What Are Some Other Causes of Seismic Waves? Catastrophic landslides, whether on land or beneath water, cause ground shaking. On the Big Island of Hawaii, lava flows form new crust that can become unstable and suddenly collapse into the ocean. Seismometers at the nearby Hawaii Volcanoes National Park often record seismic waves caused by such landslides and by fractures opening up on land in response to the sliding of the land toward the sea.  What Are Some Other Causes of Seismic Waves? Mine blasts and nuclear explosions compress Earth’s surface, producing seismic waves measurable by distant seismic instruments. Monitoring compliance with nuclear test-ban treaties is done in part using a worldwide array of seismic instruments. These instruments recorded detonation of a nuclear bomb. Seismic waves generated by a blast such as this are more abrupt than those caused by a natural earthquake. What Processes Precede and Follow Faulting? Before faulting, rocks change shape (i.e., they strain) slightly as they are squeezed, pulled, and sheared. Once stress builds up to a certain level, slippage along a fault generally happens in a sudden, discrete jump. Faulting reduces the stress on the rocks, allowing some of the strained rocks to return to their original shapes. This type of response, where rocks return to their original shape after being strained, is called elastic behavior.  Active strike-slip fault At the time shown here, the strength of the fault is greater than the tectonic forces working to slide the blocks past each other. With time, stress increases along the fault as depicted by the upward- sloping line on this graph which plots stress as a function of time. The rocks may deform elastically, changing shape slightly without breaking.  Slip and Earthquake Stress along the fault becomes so great that it exceeds the fault’s ability to resist it. As a result, the fault slips and the rocks on opposite sides of the fault rapidly move past each other. A large earthquake occurs, generating seismic waves that radiate outward from the fault. In the stress-versus-time graph, the point at which the earthquake occurred is shown as an orange dot. The rocks were no longer strong enough and there was not sufficient friction along the fault surface to prevent movement.  Slip and Earthquake With the stress partially relieved, the rocks next to the fault relax by elastic processes and largely return to their original, unstrained shape. However, the movement that has occurred along the fault is permanent. It is not elastic and is recorded by a new break in the topography. After the earthquake, stress again begins to slowly build up along the fault (as represented by the smaller yellow arrows). This sequence is called stick- The new, subtle break along the straight part slip behavior because the fault of the stream is a clue that something sticks (does not move) and happened here. then slips.  How Do Earthquake Ruptures Grow? Most earthquakes occur by slip on a preexisting fault, but the entire fault does not begin to slip at once. Instead, the earthquake rupture starts in a small area (the hypocenter) and expands over time. A rupture starts on a small section The rupture continues to grow along As the edge of the rupture migrates of the fault below Earth’s surface the fault plane and the fault scarp outward, it may eventually reach and begins to expand along the lengthens. The faulting relieves some Earth’s surface, causing a break preexisting fault plane. Some rocks of the stress, and rupturing will stop called a fault scarp. Seen from break adjacent to the fault, but when the remaining stress can no above, the rupture migrates in both most slip occurs on the actual fault longer overcome friction along the directions, but it may expand farther surface, which is weaker than fault surface. At that point, the in one direction than in the other. intact rock. earthquake stops.  Earthquake Ruptures in the Field In this photo, the scarp is cutting through granite. The fault had mostly strike-slip movement, with some vertical movement. The fault is part of a zone of strike-slip faults that are related to the San Andreas transform boundary, but farther into the continent. The zone is called the East California Shear Zone and poses a significant risk.  Earthquake Ruptures in the Field Movement along a normal fault ruptured the land surface during the 1983 Borah Peak earthquake, forming a fault scarp along the mountain front.  Earthquake Ruptures in the Field The 1959 Hebgen Lake earthquake in southern Montana just outside Yellowstone National Park formed a several-meter-high fault scarp. The earthquake and fault scarp were generated by slip along a normal fault. Scarps are most obvious soon after they form, but become more obscure over time. Erosion rounds off the top edge of the scarp, and sediment accumulates at the base of the scarp, producing a rounded step in the topography Where Do Earthquakes Occur in the Eastern Hemisphere? Where Do Earthquakes Occur in the Western Hemisphere and Atlantic Ocean? How Are Earthquakes Related to Mid-Ocean Ridges? How Are Earthquakes Related to Subduction Zones? How Are Earthquakes Related to Continental Collisions? How Are Earthquakes Generated Within Continents? How Do Earthquake Waves Travel? EARTHQUAKES GENERATE VIBRATIONS that travel through rocks as seismic waves. The word seismic comes from the Greek word for earthquake. Scientists who study earthquakes are seismologists. Geophysical instruments record and process information on seismic waves, and these data allow seismologists and geologists to understand where and how earthquakes occur. What Kinds of Seismic Waves Do Earthquakes Generate? 1. Shapes of waves – To describe seismic waves, we begin by defining waves in general. Most waves are a series of repeating crests and troughs. Whether moving through the ocean or through rocks, waves can travel, or propagate, for long distances. However, the material within the wave barely moves. Sound waves travel through the air and thin walls, but the wall does not move much. Think of a seismic wave as a pulse of energy moving through a nearly stationary material.  Body Waves Most earthquakes occur at depth, so they first produce seismic waves that travel through the Earth as body waves. The waves propagate (move outward) in all directions. There are two main types of body waves, P-waves and S-waves, which propagate in different ways.  Body Waves Most earthquakes occur at depth, so they first produce seismic waves that travel through the Earth as body waves. The waves propagate (move outward) in all directions. There are two main types of body waves, P-waves and S-waves, which propagate in different ways.  Surface Waves When body waves reach Earth’s surface, some energy is transformed into new waves that only travel on the surface (surface waves). There are two main kinds of surface waves: Rayleigh waves and Love waves. Surface waves cause the damage during an earthquake.  Surface Waves When body waves reach Earth’s surface, some energy is transformed into new waves that only travel on the surface (surface waves). There are two main kinds of surface waves: Rayleigh waves and Love waves. Surface waves cause the damage during an earthquake.  How Are Seismic Waves Recorded? Sensitive digital instruments called seismometers are able to precisely detect a wide range of earthquakes. The recorded seismic data are uploaded to computers that process signals from hundreds of instruments registering the same earthquake. These computers calculate the location of the hypocenter and the magnitude or strength of the earthquake. How Are Seismic Records Viewed? How Are Seismic Waves Recorded? How Are Seismic Waves Recorded? How Do We Locate Earthquakes? How Do We Locate Earthquakes? How Do We Measure the Size of an Earthquake? The magnitude of an earthquake is a measure of the released energy and is used to compare the sizes of earthquakes. There are several ways to calculate magnitude, depending on the earthquake’s depth. The most commonly mentioned scale, called the “Richter” or “Local” magnitude (Ml) scale, is illustrated here. How Do We Measure the Size of an Earthquake? How Do We Measure the Size of an Earthquake? How Do We Measure the Size of an Earthquake?  Magnitude of Magnitude is a measure of the energy released by an an Earthquake earthquake. The Richter scale is used to measure the magnitude of an earthquake, ranging from 0 to 10 or more. Each whole number increase on the scale represents a tenfold increase in the amplitude of the seismic waves. Energy of Earthquakes Intensity of Ground Shaking The Modified Mercalli Intensity Scale, abbreviated as MMI, describes the effects of shaking in everyday terms. A value of “I” reflects a barely felt earthquake. A value of “XII” indicates complete destruction of buildings, with visible surface waves throwing objects into the air. How Do We Measure the Size of an Earthquake? Major North American Earthquakes Alaska, 1964 A magnitude 9.2 (Mw) earthquake, one of the three or four largest earthquakes ever recorded, struck southern Alaska in 1964. It killed 128 people, triggered landslides, and collapsed parts of downtown Anchorage and nearby neighborhoods. This event was caused by thrust faults associated with the Aleutian Islands subduction zone. Most deaths and much damage were from a tsunami generated when a huge area of the seafloor was uplifted. The photograph above shows damage from the tsunami. Major North American Earthquakes San Francisco, 1906 A huge earthquake occurred when the San Andreas fault ruptured near San Francisco. The earthquake was likely a magnitude 7.7 to 7.8 (Mw) although not directly measured on seismometers. The earthquake ruptured the surface, leaving behind a series of cracks and open fissures. Within San Francisco, ground shaking destroyed most of the brick and mortar buildings. More than 3,000 people were killed and much of the city was devastated by fires that broke out after the earthquake. Geologists determined that 470 km (290 mi) of the fault ruptured during the event. Major North American Hebgen Lake, Earthquakes Yellowstone Area, 1959 This magnitude 7.3 (Mw) event was generated by slip along a normal fault northwest of Yellowstone National Park. Ground shaking set loose the massive Madison Canyon slide, which buried 28 campers and formed a new lake, aptly named Earthquake Lake. Recent Large Tohoku Earthquake of Earthquakes 2011 A huge and catastrophic earthquake struck off northeastern Japan on March 11, 2011. It had an extremely large magnitude of 9.0 (Mw), making it one of the five largest earthquakes ever measured. Ground shaking during the earthquake caused extensive damage, especially on the large island of Hokkaido, nearest to the epicenter. The earthquake and resulting tsunami destroyed 125,000 buildings, left 24,000 dead or missing, and caused more than $300 billion in economic damages, making it the most expensive natural disaster in history. Recent Large Tohoku Earthquake of Earthquakes 2011 The epicenter of the earthquake, shown here as a red dot, was on the seafloor east of Japan, along a oceanic trench that marks where the Pacific plate subducts beneath Hokkaido. The earthquake occurred at depth, along the subduction zone (plate boundary) that dips beneath Japan. The main hypocenter was 32 km deep, so this is classified as a shallow earthquake. The fault rupture grew upward from the hypocenter toward the seafloor, uplifting a large swath of seafloor by up to 3 m. The displaced water formed into an extremely damaging tsunami that locally was higher than 10 m (33 ft). Recent Large Earthquakes Haiti, 2010 The Haiti earthquake occurred on land, 25 km west of the capital, Port-au-Prince. The epicenter (shown as a red dot) is near, but not on, an active strike-slip fault that cuts east- west across the country. Aftershocks are yellow dots, green lines are strike-slip faults, and red lines have thrust movement. The earthquake flattened more than 300,000 buildings in and around Portau-Prince and killed perhaps 200,000 people. Recent Large Earthquakes New Zealand 2010 The two main earthquakes in New Zealand had epicenters (shown as red dots) on a broad coastal plain that lies east of the rugged Southern Alps and the Alpine fault, a mostly transform plate boundary that runs down the length of the island. Both earthquakes were very shallow (less than 15 km), were not on the plate boundary, and occurred on two different, but probably related, faults. The Canterbury quake was a magnitude 7.1 (Mw), caused moderate damage, and only injured two people. Recent Large Earthquakes New Zealand 2011 The 2011 Christchurch quake was smaller, but killed nearly 200 people. It destroyed or damaged 100,000 buildings, some by liquefaction of the soil and associated expulsion of water from the ground. The main difference in the amount of destruction was that the 2011 epicenter was very near Christchurch, New Zealand’s second largest city, and the quake had more vertical motion, destroying already weakened buildings. Recent Large Indian Ocean tsunami of Earthquakes 2004 On December 26, 2004, an undersea earthquake with a magnitude of 9.1 struck off the coast of the Indonesian island of Sumatra. Over the next seven hours, uplift of the seafloor caused a massive wave, called a tsunami, that spread across the Indian Ocean as a low wave. The tsunami increased in height as it approached the coasts of Indonesia, Thailand, Sri Lanka, India, east Africa, and various islands. Low coastal areas were inundated by as much as 20 to 30 m of water (65 to 100 ft) in Indonesia and 12 m (40 ft) in Sri Lanka. It was caused by movement on a fault, shown by the red Indian Ocean tsunami of line on this map. The red line shows the 2004 length of the fault that ruptured during the earthquake. The fault is part of a plate boundary where the Indian- Australian plate is subducting to the northeast beneath the Eurasian plate. Yellow dots nearby show the locations of smaller, related earthquakes. Destructive Earthquakes Casiguran Earthquake At 4:19 AM (local time) on August 02, 1968 an earthquake with an intensity of VIII in the Rossi-Forel Intensity Scale rocked the town of Casiguran, Aurora. This was considered the most severe and destructive earthquake experienced in the Philippines during the last 20 years. A six-storey building in Binondo, (Ruby Tower) Manila collapsed instantly during the quake while several major buildings near Binondo and Escolta area in Manila sustained varying levels of structural damages. How Do Seismic Waves Travel Through Materials? How Do Seismic Waves Travel Through Materials?  How Seismic Waves Refract Through Different Materials If a seismic wave passes into If a descending seismic ray If a rising seismic ray passes a material that causes it to passes from a slow material from a fast material to a slow down, it will be refracted to a faster one, it will be slower one, it will be refracted away from the interface at a refracted to a shallower upward toward the surface. steeper angle. angle. How Do Seismic Waves Travel Through Earth’s Crust and Mantle? How Do Seismic Waves Travel Through Earth’s Crust and Mantle? How Do Seismic Waves Travel Through Earth’s Crust and Mantle? DPWH DGCS The Need for a Preliminary GeoHazard Assessment The Philippine government proceeded to issue DENR AO2000-28 as its long-term response to the urgent need of protecting lives and property from destruction brought about by such geologic hazards. The Engineering Geology and GeoHazard Assessment (EGGA) process requires a land development project proponent to request the appropriate MGB office for a site geological scoping survey.  Conducted by: Practicing Geologist The Need for a Preliminary Qualified Engineer GeoHazard Assessment EGGAR Technical review by an MGB panel Revisions Endorsement to EMB Required for Issuance of ECC NATURAL AND MAN-MADE INFLUENCES Earthquakes: natural phenomena, but which can be triggered by large dam construction; Flooding: a natural event but which can be caused or exacerbated by man, as a result of deforestation, building on flood plains and so on. Contaminated Land: man-made but can be from naturally occurring substances such as arsenic, methane gas or radon gas. Seismicity In case of such a major earthquake structures, slopes and foundations will be subjected to seismic loading. Earthquakes can trigger other seismic hazards such as landslides, liquefaction, lateral spreading, differential settlement, tsunamis, seiches and even fires. Seismicity A Collapsed Building during the July 16, 1990 Northern Luzon Earthquake is shown in the figure. The Philippine Mobile Belt is sandwiched by trenches on both sides and traversed along its entire length by the Philippine Fault. Palawan and Zamboanga are in the Eurasian margin. Nearfault A fault within the 5 km distance is a nearfault Far-fault A fault beyond that distance is a far-fault, located in the far field. An active fault is one that has moved during the last 10,000 years. Faulting, whether through a seismic fault creep or through a catastrophic ground rupture, refers to actual displacement or dislocation along a fault. The Philippine Mobile Belt is therefore tectonically, seismically and volcanically active. Palawan and Zamboanga, on the other hand, are part of the Eurasian Margin and are therefore tectonically and seismically inactive. There are no earthquake generators within the margin, although it can experience earthquakes generated by bounding structures such as the Sindangan Fault or Cotabato Trench. The Preliminary For seismic design of GeoHazard vertical buildings, ASEP Assessment National Structural Code of the Philippines (2010) requires input of: Distance from active fault Soil type The Preliminary For bridges, requirements GeoHazard of DWPH Bridges Seismic Assessment Design Specifications (DPWH-BSDS), December 2013 JICA Study and the DGCS Volume 5 – Bridge Design. The Preliminary For earth retaining GeoHazard structures and earthworks, Assessment DGCS V olume 4 – Highway Design recommends designing using the quasi-static method, which will require a peak ground acceleration and then a reduction factor. At this stage the requirements are to identify the distance from active fault and peak ground acceleration at the site. The peak ground acceleration can also be obtained from the PHIVOLCS web site maps, and an example is shown in Figure. An estimate of the ground motion specific to a site can be calculated. In order to determine the peak ground acceleration that a site can experience in the case of a major earthquake, the attenuation model of Fukushima and Tanaka (1990) is applied. Correction factors are applied to the mean peak acceleration depending on the type of foundation material: rock =0.6 hard soil = 0.87 medium soil = 1.07 soft soil = 1.39.  Types of Earthquake Ground Rupture Hazards Deformation on the ground that marks, the intersection of the fault with the earth’s surface. It has the following effects: fissuring and displacement of the ground due to movement of the fault.  Types of Earthquake Ground Shaking Hazards Disruptive up, down and sideways vibration of the ground during an earthquake. It has the following effects: ground shaking may cause damage or collapse of structure; may consequently cause hazards such as liquefaction and landslide.  Types of Earthquake Liquefaction Hazards Phenomenon wherein sediments, especially near bodies of water, behave like liquid similar to a quicksand. It has the following effects: sinking and/ or tilting of structure above it; sandboil; fissuring.  Types of Earthquake-induced Earthquake Hazards Landslide Down slope movement of rocks, solid and other debris commonly triggered by strong shaking. It has the following effects: erosion; burial and blockage of roads and rivers.  Types of Earthquake Tsunami Hazards Series of waves caused commonly by an earthquake under the sea. It has the following effects: flooding; coastal erosion; drowning of people and damage to properties. EFFECT ON CIVIL ENGINEERING STRUCTURES Ground Condition Soft ground, based mostly on sediments such as those in flood plains, reclaimed land or former landfill, amplifies the effect of the earthquake vibrations, while harder rocks limit the amount of shaking. Building Design and Construction Poor construction technique, where slab walls and floors are not tied together correctly, for example, makes buildings far more vulnerable to earthquake damage; buildings where the bricks have been held in place with the correct mortar tend to survive much better. Materials Where buildings do collapse, the occupants are more likely to survive when the walls and roof are made of lightweight materials rather than heavy ones; rubble-masonry buildings, or brick buildings with low quality mortar, do not withstand earthquakes well; wooden or steel-framed buildings are generally much better, providing they are correctly braced. Design Buildings shake when the frequency of the seismic waves is close to the natural frequency of vibration of the building, an effect known as resonance. Resonance Frequency Resonance Frequency The resonant frequency depends on the height of the building: Low frequency shaking might cause tall buildings to shake violently while having little effect on low-rise buildings nearby. However, higher frequencies of vibration might have the opposite effect. Damage to tall buildings is often concentrated on the upper storeys, where the motion is greater. Another common cause of damage is 'pounding' by collisions with adjacent buildings. Tall structures can survive low frequency vibrations if they are designed to do so, however. This typically involves making sure that lower floors are stronger and heavier than upper floors, and avoiding large, unsupported spaces; it may also include extra reinforcement with steel cables, or even placing the building on a foundation which reduces the amount of shaking transmitted to the building structure. Large, unsupported spaces make buildings with ground floor car parks or viaducts particularly vulnerable. Resonance Frequency CIVIL ENGINEERING DESIGN CONSIDERATIONS Ground Condition The National Structural Code of the Philippines (NSCP) 2015 in Section 208: Earthquake Loads gives us the earthquake provisions to design seismic-resistant structures to safeguard against major structural damage that may lead to loss of life and property. These provisions are not intended to assure zero-damage to structures nor to maintain their functionality after a severe earthquake. Inspections and appropriate repairs must still be done to ascertain the safety of structure.  Site Seismic Hazard Characteristics The seismic hazard characteristics for the site are established based on the seismic zone and proximity of the site to active seismic sources, and other factors. The Philippine archipelago is divided into two seismic zones. Zone 2 covers the provinces of Palawan (except Busuanga), Sulu and Tawi-Tawi while the rest of the country is under Zone 4, as shown in the figure.  References https://www.britannica.com/event/Indian-Ocean-tsunami-of-2004 https://www.britannica.com/event/Japan-earthquake-and-tsunami-of-2011/Aftermath- of-the-disaster https://www.britannica.com/event/2010-Haiti-earthquake https://www.phivolcs.dost.gov.ph/index.php/earthquake/destructive-earthquake-of-the- philippines/17-earthquakeNSCP 2015 DPWH DGCS Volume 2 Exploring Geology Fifth Edition  END OF DISCUSSION ANY QUESTIONS? [email protected] C Consultation Hours: 6:00 - 7:00 pm T | TH @ CE Faculty No part of this material may be reproduced, distributed or transmitted in any form or by any means including photocopying or other means without prior written permission of the owner except for personal academic use and certain other non-commercial uses permitted by copyright law.