Earthquake Engineering Lecture Notes PDF

BICOL UNIVERSITY COLLEGE OF ENGINEERING LEGAZPI CITY CE 413 EARTHQUAKE ENGINEERING LESSON 1: CAUSES OF EARTHQ...

BICOL UNIVERSITY COLLEGE OF ENGINEERING LEGAZPI CITY CE 413 EARTHQUAKE ENGINEERING LESSON 1: CAUSES OF EARTHQUAKES AND TECTONIC PLATES “This presentation is not for distribution outside this subject and to be used solely for this course subject – CE 413.” PREPARED BY: ANNA G. BILARO, MSCE Faculty ANNA G. BILARO, MSCE FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 1 Objectives After the discussion in this chapter, the student will be able to: 1. Explain the general causes/ effects of earthquakes on the built environment 2. Describe the main source of earthquakes. 3. List the different types of earthquakes. 4. Explain tectonic plate movement. 5. Learn the different fault mechanisms 6. Differentiate the different types of seismic waves. ANNA G. BILARO, MSCE FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 2  Earthquake Characteristics Causes of Earthquake Earthquake A weak to violent shaking of the ground produced by the sudden movement of rock materials below the earth’s surface (www.phivolcs.dost.gov.ph). Manifested as ground shaking caused by the sudden released of energy in the Earth's crust which may originate from different sources such as: a. dislocations of the crust b. volcanic eruptions c. man-made explosions d. collapse of underground cavities (e.g. mines or karst) Defined as natural/ Earth’s disturbance. ANNA G. BILARO, MSCE FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 3  Fig 1.0 Earth Disturbance ANNA G. BILARO, MSCE 4 FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 4 Source: Elnasahi and Di Sarno, 2008  2 Types of earthquakes: Tectonic earthquake – produced by sudden movement along faults and plate boundaries. Volcanic earthquake – induced by rising lava or magma beneath active volcanoes. ANNA G. BILARO, MSCE FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 5  Plate Tectonics Theory  The theory of Plate tectonics was proposed in 1960s based on the Earthquake occurrences theory of continental drift. may be explained by the theory of large-scale  This is the theory that explains the tectonic processes, formation and deformation of the referred as “plate Earth’s surface. tectonics” which is  According to this theory, continents derived from the theory are carried along on huge slabs of continental drift and (plates) on the Earth’s outermost sea-floor spreading. layer (Lithosphere).  Earth’s outermost layer is divided into 15 major Tectonic Plates (~80 km deep). These plates move relative to each other a few centimeters per year. Source: Lectures from Dr. G. Madhavi Latha ANNA G. BILARO, MSCE FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 6  Evidence for continental drift (Theory of Alfred Wegener, 1912) Matching coastlines Matching mountains Matching rock types and rock ages Matching glacier deposits Matching fossils ANNA G. BILARO, MSCE FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 7  Evidence for continental drift Matching coastlines Matching mountain ranges Source: Lectures from Dr. G. Madhavi Latha ANNA G. BILARO, MSCE FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 8  Evidence for continental drift Matching rock types and ages of rocks Matching glacier/ fossil deposits 300million years ago Source: Lectures from Dr. G. Madhavi Latha ANNA G. BILARO, MSCE FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 9  Earthquake are recognized to be the symptoms of active tectonic movements and as observed and confirmed that the intense activity occurs predominantly on plate boundaries (seismic belts). Add: Continental crust Oceanic crust Fig. 2.1 Tectonic Plates Source: Elnasahi and Di Sarno, 2008 ANNA G. BILARO, MSCE FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 10  Fig. 2.2 Tectonic Plates Source: Chen and Lui, 2006 ANNA G. BILARO, MSCE FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 11  Fig. 3.0 Earth’s Layer Earth’s Layer Plates – large and stable rigid rock slabs with a thickness of about 100km, forming the crust or lithosphere and part of the upper mantle. Crust – outer rock layer with non-uniform thickness of 25-60km under continents and 4- 6km under oceans. Mantle – portion of the Earth’s interior below Source: https://pubs.usgs.gov crust extending from 30km-2900km Large tectonic forces takes place at the plate edges due to the relative movement of the lithosphere-asthenosphere complex. The movement is caused by convection currents in the mantle. The velocity of movement is about 1 to 10cm/year. ANNA G. BILARO, MSCE FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 12  Principal types of plate boundaries : A. Divergent or rift zones – plates separates from one another either by effusion of magma occurrence or lithosphere diverges from interior of the Earth. A mid-ocean ridge may form by sea-floor spreading/ rifting marking a divergent boundary between two tectonic plates (e.g.Mid-Atlantic ridge). Tension - Plates move apart from each other. B. Convergent or subduction zones – adjacent plates converge and collide. There are two types: oceanic and continental lithosphere convergent boundaries (e.g. Circum- Pacific and Eurasian belts). - Plates come together. Compression C. Transform zones or transcurrent horizontal slip – two plates glide past one another but without subducting old lithosphere (e.g. San Andreas fault in California). Shearing - Plates slides past each other Image Source: Lectures from Dr. G. Madhavi Latha ANNA G. BILARO, MSCE FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 13  Fig. 4.0 Cross – section of the Earth with the main type plate boundaries ANNA G. BILARO, MSCE FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 14  Fig. 5.0 Tectonic mechanisms at plate boundaries. ANNA G. BILARO, MSCE FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 15  Faulting The distorted blocks snap back towards equilibrium and an earthquake ground motion is produced. This process is referred to as “elastic rebound”. The resulting fracture in the Earth’s crust is termed a “fault”. Fault zone – zone of the earth’s crust within which the two sides have moved – faults may be hundreds of miles long, from one to over hundred miles deep, sometimes not apparent on the ground surface. During the sudden rupture of the brittle crustal rock, seismic waves are generated. ANNA G. BILARO, MSCE FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 16  Source: www.slideshare.net (Lectures from Dr. G. Madhavi Latha Elastic Rebound Theory Rocks bend under stress while storing elastic energy. When the strain in the rocks exceeds their strength, breaking will occur along the fault. Stored elastic energy is released as the earthquake. Rocks “snap back”, or rebound to their original condition. ANNA G. BILARO, MSCE FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 17  Active faults may be classified on the basis of their geometry and the direction of relative slip. The parameters used to describe fault motion and its dimension are as follows: 1. Azimuth ( φ ): the angle between the trace of the fault, i.e. the intersection of the fault plane with the horizontal, and the northerly direction (0 ° ≤ φ ≤ 360 ° ). The angle is measured so that the fault plane dips to the right - hand side; 2. Dip ( δ ): the angle between the fault and the horizontal plane (0 ° ≤ δ ≤ 90 ° ); 3. Slip or rake ( λ ): the angle between the direction of relative displacement and the horizontal direction ( − 180 ° ≤ λ ≤ 180 Fig. 6.0 Parameters used to describe fault motion. ° ). It is measured on the fault plane; 4. Relative displacement ( Δ u ): the distance travelled by a The orientation of fault motion is defined by the point on either side of the fault plane. If Δ u varies along the three angles    and its dimensions are fault plane, its mean value is generally used; given by its area S as displayed in Fig. 6.0; the fault slip is measured by the relative 5. Area ( S ): surface area of the highly stressed region within displacement u. the fault plane. ANNA G. BILARO, MSCE FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 18  Parameters that used to describe the fault motion. 90˚ dip = vertical fault plane 0˚ strike = north parallel fault plane Fig. 6.0 Parameters used to describe fault motion. Image Source: www.slideshare.net (Lectures from Dr. G. Madhavi Latha ANNA G. BILARO, MSCE FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 19  Several fault mechanisms exist depending on how the plates move with respect to one another. The most common fault mechanisms of earthquake sources are: Dip-slip faults One block moves away vertically with respect to the other. If the block underlying the fault plane or “footwall” moves up the dip and away from the block overhanging the fault plane, or ‘hanging wall’, normal faults are obtained. Tensile forces cause the shearing failure of normal faults. When the hanging wall moves upward in relation to the footwall, the faults are reversed; compressive forces cause the failure. Thrusts faults are reverse faults characterized by a small dip. ANNA G. BILARO, MSCE FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 20  Image Source: Lectures from Dr. G. Madhavi Latha A Normal dip slip fault Fig. 7.0.1 Fundamental Fault Mechanisms A reverse dip-slip fault ANNA G. BILARO, MSCE 21 FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 21  Several fault mechanisms exist depending on how the plates move with respect to one another. The most common mechanisms of earthquake sources are: Strike-slip faults The adjacent blocks move horizontally past one another. Strike-slip can be right-lateral or left-lateral, depending on the sense of the relative motion of the blocks for an observer located on one side of the fault line. The slip takes place along an essentially vertical fault plane and can be caused by either compression or tension stresses. Typically, a transform zone. ANNA G. BILARO, MSCE FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 22  Image Source: Lectures from Dr. G. Madhavi Latha A strike-slip fault Fig. 7.0.2 Fundamental Fault Mechanisms Strike-slip right-lateral Strike-slip left-lateral ANNA G. BILARO, MSCE FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 23  Image Source: Lectures from Dr. G. Madhavi Latha Oblique slip  Combination of strike-slip and dip-slip movements.  Can be either normal or reverse and right – or – left-lateral movements. An oblique-slip fault Fig. 7.0.2 Fundamental Fault Mechanisms ANNA G. BILARO, MSCE FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 24  Focus or Hypocenter Point under the surface where the rupture originates. Located by geographical coordinates (latitude and longitude), focal depth and origin or occurrence of time. Earthquakes focal depth: shallow focus– 5-15km intermediate focus– 20-50km Fig. 8.0 Definition of source parameters deep focus– 300-700km Source parameters: Epicenter a. Epicentral distance Projection of the focus on the b. Hypocentral or focal distance surface. c. Focal depth ANNA G. BILARO, MSCE FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 25  Image Source: www.slideshare.net (Lectures from Dr. G. Madhavi Latha ANNA G. BILARO, MSCE FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 26  Seismic Waves Earthquake shaking is generated by two types of elastic seismic waves. The shaking is generally a combination of these waves at distance from the source or ‘near- field’. 1. Body waves a) P-waves b) S-waves 2. Surface waves a) Love (L or LQ-waves) b) Rayleigh (R or LR-waves) ANNA G. BILARO, MSCE FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 27 Body waves Also termed as ‘preliminary tremors’ because they are felt first and travels through the Earth’s interior layers. This waves includes: 1. P-waves – longitudinal or primary waves P-waves cause alternate push (compression) and pull (tension) in the rock thus, the waves propagate, the medium expands and contracts, while keeping the same form. P-waves are seismic waves with relatively little damage potential. Travel through solids, liquids or gases. Material movement is the same direction as wave movement. Arrival: They arrive first on a seismogram. Fig. 9.1 Travel path mechanisms of P-waves ANNA G. BILARO, MSCE FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 28  Body waves 2. S-waves - transverse or secondary waves S-waves causes vertical and horizontal side-to-side motion and introduces shear stresses in rocks along their paths also defined as ‘shear waves’. Their motion can be separated into horizontal (SH) and vertical (SV) components, both of which can cause significant damage Travel to solids only Arrival: Second on a seismogram. Fig. 9.2 Travel path mechanisms of S-waves ANNA G. BILARO, MSCE FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 29 Body waves P-waves travel faster (1.5 – 8km/s) than S-waves which travels 50% to 60% slower than P- waves. Body waves may be described by Navier’s equation for an infinite, homogeneous. Isotropic, elastic medium in the absence of body forces. The propagation velocities denoted as p and s are as follows: The ratio of P- and S-waves velocities: ANNA G. BILARO, MSCE FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 30  Table 1.0 Velocity of primary (P) and secondary (S) in Earth’s layer. ANNA G. BILARO, MSCE FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 31  Surface waves Propagate across the outer layers of the Earth’s crust, generated by constructive interference of body waves travelling parallel to the ground surface and various underlying boundaries. These waves induced large displacements, also called ‘principal motion’. Because of the long duration, cause severe damage to structural systems during earthquake. Slower than body waves; rolling and side-to-side movements. ANNA G. BILARO, MSCE FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 32  Fig. 9.3 Surface waves Source: www.slideshare.net (Lectures from Dr. G. Madhavi Latha ANNA G. BILARO, MSCE FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 33 Surface waves 1. Love waves (L- or LQ-waves) – G-waves Generated by constructive interference of SH body waves and cannot travel across fluids. The motion is horizontally oscillating and perpendicular to the direction of propagation which is parallel to the Earth’s surface. Have large amplitudes and long periods (60-300sec). Typical velocity: depends on earth structure, but less than the velocity of S-waves. Arrival: they usually arrive after the S-wave and before the Rayleigh wave. Fig. 9.1 Travel path mechanisms of Love waves ANNA G. BILARO, MSCE FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 34  Surface waves 2. Rayleigh waves (R- or LR-waves) Caused by constructive interference of body waves such as P and SV, as they pass by, particles of soil move in the form of a retrograde ellipse whose axis is perpendicular or vertically oscillating to the Earth’s surface. Causes back and forth horizontal motion. Motion is similar to that of being in a boat in the ocean. Exhibits very large amplitude and regular waveforms. Arrival: they usually arrive last on a seismogram. Fig. 9.2 Travel path mechanisms of Rayleigh waves ANNA G. BILARO, MSCE FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 35  Measurement of ground shaking Seismogram Seismogram is visual record of arrival time and magnitude of shaking associated with seismic wave, generated by a seismograph. Source: www.slideshare.net (Lectures from Dr. G. Madhavi Latha ANNA G. BILARO, MSCE FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 36  Foreshocks and Aftershocks Adjustments that follow a major earthquake often generate smaller earthquakes called aftershocks Small earthquakes, called foreshocks, often precede a major earthquake by days or, in some cases, by as much as several years ANNA G. BILARO, MSCE FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 37  HOMEWORK #1: 1. List down major historic earthquakes happened worldwide (in chronological order)*. 2. List down destructive earthquakes in the Philippines (in chronological order)*. *The oldest and the recent data that you can get. File must be in pdf format, to be submitted in Google Classroom. Deadline of submission: September 13, 2024. ANNA G. BILARO, MSCE FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 38 Reference Elnashai, Amr S. and Di Sarno, Luigi. 2008. Fundamentals of Earthquake Engineering. John Wiley & Sons Ltd, United Kingdom. Estrada, Hector and See, Luke S. 2017. Introduction to Earthquake Engineering. CRC Press, Taylor and Francis Group, Florida. Chen, W.F. and Lui, E.M. 2006. Earthquake Engineering for Structural Design. CRC Press, Taylor and Francis Group, Florida. Gioncu, Victor and Mazzolani, Federico M. 2011. Earthquake Engineering for Structural Design. Spon Press, New York, USA and Taylor & Francis Group e-Library. Lectures of Dr. Latha, G. Madhavi from Department of Civil Engineering, Indian Institute of Science. www.phivolcs.dost.gov.ph ANNA G. BILARO, MSCE FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 39  THANK YOU FOR LISTENING! ANNA G. BILARO, MSCE FACULTY CE 413 – EARTHQUAKE ENGINEERING Slide No. 40