EARTHQUAKE ENGINEERING LEC.docx

**EARTHQUAKE ENGINEERING** LEC1\_ **Introduction to Earthquke Engineering** **Earthquake** - A phenomenon resulting from the sudden release of stored energy in the Earth's crust which creates seismic waves. - A broad-banded vibratory ground motions, resulting from several causes incl...

**EARTHQUAKE ENGINEERING** LEC1\_ **Introduction to Earthquke Engineering** **Earthquake** - A phenomenon resulting from the sudden release of stored energy in the Earth's crust which creates seismic waves. - A broad-banded vibratory ground motions, resulting from several causes including tectonic ground motions, volcanism, and man-made explosions - Generates horizontal ground motion **Damaging Effects of Earthquake** Can damage in 3 different ways: 1. By causing ground failure 2. By producing other effects that may indirectly affect the structure, e.g., ground cracking, landslides or tsunami 3. By shaking the ground on which the structure rests. 1. Ground Failure **Type: GROUND CRACKING** - when the soil at the surface loses its support and sinks, or when it is transported to a different location - when displaced, a soil layer breaks causing fissures, scarps, horsts and grabens on the ground surface. **Type: GROUND SUBSIDENCE** - A phenomenon in which the ground surface of a site settles or depresses as a result of compaction induced by an earthquake's vibrations. - Sites with loose or compressible soils are susceptible - Damage: cracks and/or tilting of building - Pipelines, channels and road embarkments may damage **Type: LANDSLIDE** - represent the failure of slopes that are marginally stable before the earthquake and become unstable as a result of the violent shaking generated by the earthquake. **Type: SOIL LIQUEFACTION** - a phenomenon by which fine saturated granular soils temporarily change from a solid to a liquid state and as a result lose their ability to carry loads or remain stable - when a loose soil is vigorously shaken or vibrated 2. Indirect Affects To Structure: **TSUNAMIS** - It is a large sea wave generated mostly by an undersea earthquake. **SEICHES** - long-period oscillating waves generated by distant earthquakes in enclosed bodies of water such as bays, lakes, reservoirs, and even swimming pools - Occurs when the natural frequency of a water body matches the frequency of the incoming earthquake waves 3. Ground Shaking - a structure lying on the shaking ground oscillate back and forth and up and down and makes the structure experience large stresses and deformations in the process. **BRIEF HISTORY OF EARTHQUAKE** - **ROBERT MALLET** - - - Modern research on **earthquake-resistant structures:** - - - - study the earthquake and the formulation of practical recommendations for the seismic design of buildings - recommended buildings were to be designed for horizontal forces equal to fractions of the building weight based on different story levels - The 20th Century can be divided into three very distinct periods: - - - LEC2\_**Elements of Seismology** **SEISMOLOGY** - It is the scientific study of earthquakes and the propagation of elastic waves through the Earth. - The field also includes studies of earthquake environmental effects such as tsunamis as well as diverse seismic sources such as volcanic, tectonic, oceanic, atmospheric, and artificial processes such as explosions. - A related field that uses geology to infer information regarding past earthquakes is paleoseismology **Engineering Seismology** - the study and application of seismology for engineering purposes. It generally applied to the branch of seismology that deals with the assessment of the seismic hazard of a site or region for the purposes of earthquake engineering. **Elements of Engineering Seismology** 1. Studying earthquake history and tectonics to assess the earthquakes that could occur in a region and their characteristics and frequency of occurrence. 2. Studying strong ground motions generated by earthquakes to assess the expected shaking from future earthquakes with similar characteristics. These strong ground motions could either be observations from accelerometers or seismometers or those simulated by computers using various techniques. **Theory of Plate Tectonics** - derives from the theory of continental drift and floor spreading.  **PLATE BOUNDARIES MOVEMENT** - The lateral movement of the plates is mainly at the speeds of 50-100 mm annually. - Earthquakes, volcanoes, mountain and oceanic trench formation normally occur along these boundaries **DIVERGENT** **CONVERGENT**  **TRANSFORM** **SUBDUCTION ZONE**  SUBDUCTION occurs along the following: \- west coast of South America at the boundary of the Nazca and South American Plate \- Central America (boundary of the Cocos and Caribbean plates), \- Taiwan and Japan (boundary of the Philippines and Eurasian plates), \- North American Pacific Northwest (boundary of the Juan de Fuca and North American Plates) **Ring of Fire** \- Stretching 40,000 km (24,000 miles) around the circumference of the Pacific Ocean \- Plates that make up the Pacific basin are generally subducting beneath continental plates, causing subduction-zones volcanism in the surface. \- Nearly 80% of the earth's volcanoes are found near the tectonic plate boundaries of the Pacific Ocean. **Tectonic Plate** \- Tectonic Plates move relatively slowly (5 cm per year is relatively fast) and irregularly, with relatively frequent small and only occasional large earthquakes. \- violent motions produce the shaking that is felt as an earthquake **FAULT** \- a zone of the earth's crust within which the two sides have moved. Faults may be hundreds of miles long, from one to over one hundred miles deep, and are sometimes not readily apparent on the ground zone. **Types of Earthquake Fault:** 1. ***STRIKE-SLIP FAULT*** - - 2. ***NORMAL FAULT (DIP-SLIP)*** - - 3. ***THRUST OR REVERSE FAULT*** - - 4. ***OBLIQUE-SLIP FAULT*** - - Generally, earthquakes will be concentrated in the vicinityof faults. - Faults that are moving more rapidly than others will tend to have a higher rates of seismicity, - Larger faults are more likely to produce a large events than others. - However, earthquakes continue to occur on \"unknown\" or \"inactive\" fault.  LEC3\_**Propagation of Seismic Disturbances** \- For most earthquakes, shaking is the dominant and most widespread agent of damage. **Shaking** near the actual earthquake rupture lasts only during the time when the fault ruptures, a process that takes second or at most a few minutes. The **seismic waves** generated by the rupture propagate long after the movement on the fault has stopped, however, spanning the globe in about 20 minutes. **Earthquake ground motions** \- powerful motions to cause damage only in the near field (i.e., within a few tens of kilometers from the causative fault) \- long period motions have caused significant damage at great distances, to selected lightly damped structures. - **FOCUS OR HYPOCENTER** - point within the Earth along the rupturing geological fault where in earthquake originates - **EPICENTER** - point on the Earth\'s surface directly above the focus. - **Near-field** means within one source dimension of the epicenter. - **Source dimension** refers to the width or length of faulting. - **Far-field** means beyond near-field. - **Meizoseismal** means the area of strong shaking and damage **Energy** is radiated over a broad spectrum of frequencies through the earth, in body waves and surface waves. **Body waves** are two types: 1\. **P waves** means transmitting energy via push-pull motion 2\. **S waves** means transmitting energy via shear action at right angles to the direction of motion **Surface waves** are also of two types: 1\. Love waves means horizontally oscillating (analogous to body s waves) 2\. Rayleigh waves means vertically oscillating    LEC4\_**Major Earthquake Zones in the Philippines** **PHILIPPINE FAULT ZONE (PFZ)** \- 1,200 km long \- major tectonic that transects the whole Philippine archipelago from southeastern Mindanao to northwestern Luzon. \- Nueva Ecija up to the Ilocos region in northwest Luzon \- Quezon province in eastern Luzon \- Caraga region at the Agusan River basin, crosses to Leyte and Masbate islands, \- Davao Gulf in the south - This arc-parallel, left-lateral strike slip fault is divided into several segments and has been the source of large-magnitude earthquakes in recent years, such as: - 1968 Casiguran earthquake in Aurora, Quezon (Mw 7.6) - 1976 Moro Gulf earthquake in Sulu and Mindanao Islands (Mw 8.0) - 1990 Luzon earthquake (Mw 7.7) - 1994 Mindoro earthquake (Mw 7.1) - 2002 Mindanao earthquake (Mw 7.5) - 2013 Bohol earthquake (Mw 7.2)  **FAULTS IN THE PHILIPPINES** - The Philippines is located in latitude 5° to 19°45\' N. and longitude 116° to 128° E. - Metropolitan Manila is located in the center of Luzon Island, between Manila Bay, which extends to the South China Sea, and Laguna de Bay. - Many earthquake generators are distributed all over the country. **THE CENTRAL PHILIPPINE FAULT ZONE: Location of Great Earthquakes, Slow Events, and Creep Activity** \- The central Philippine Fault Zone is found to be the locus of great earthquakes, a transition zone with slow slip and creep activity. \- ***Guinyangan fault*** - northern locked portion with recurrence interval of as short as 65 years. \- ***Masbate fault*** - central part with large and medium earthquakes accompanied by unusually large ground rupture. \- ***North Central Leyte fault*** - a seismic creep \- ***Central Leyte fault*** - medium-sized event with clusters of foreshock Since 2003, Kyoto University and PHIVOLCS-DOST have been mapping the Philippine Fault. At present, approximately 90% of on-land-stretch of the PFZ has been mapped. This delineation is based on interpretation of available large-scale (at least 1:30,000) aerial photographs. In areas where there are no available aerial photographs, various satellite images are used to map the fault zone. **THE BIG ONE** an earthquake of no less than 7.2 in the Richter scale may be experienced in our lifetime (DOST-PHILVOCS). 4 major earthquakes have taken place in the last 1400 years with recurrence interval of 400 to 500 years. Last major earthquake - 1658 or 357 years ago The areas traversed by the West Valley Fault may experience earthquakes of up to magnitude 7.2 while areas in the East Valley Fault with 6.2 magnitude **MARIKINA VALLEY FAULT SYSTEM** The Marikina Valley Fault System or Valley Fault System (VFS) is a dominantly dextral strike-slip fault system in Luzon. It extends from Dingalan, Aurora in the north and runs through the provinces of Nueva Ecija, Bulacan and Rizal, and the Metro Manila Cities of Quezon, Marikina, Pasig, Makati, Parañaque, Taguig and Muntinlupa, and the provinces of Cavite and Laguna that ends in Canlubang. The **West Valley Fault** is a 100-km long fault that moves in a dominantly dextral strike-slip motion which is capable of producing large scale earthquakes on its active phases with a magnitude of 7 or higher. The **East Valley Faul**t is a 10-km long fault that moves in an oblique dextral motion which is capable of producing earthquakes with a magnitude of about 6. The **West Valley Fault** transects portions of: - Quezon City - Marikina - Makati - Pasig - Parañaque - Taguig - Muntinlupa - Bulacan (Doña Remedios Trinidad, Norzagaray, San Jose Del Monte City) - Rizal (Rodriguez) - Laguna (San Pedro City, Biñan, Sta. Rosa, Cabuyao, Calamba) - Cavite (Carmona, General Mariano Alvarez, Silang) The **East Valley Fault** transects portions of: - Rodriquez, Rizal - San Mateo, Rizal