2015/9/16 Chapter1 Chapter One 1.1 Causesand Types of Earthquake 1.2 Seismic Waves and Propagation Earthquake and 1.3 Earthquake Magnitude and Intensity Ground motions 14 Seismicity in the world 1.5 Seismic Fortification for Building Structures 1.1 Causes and Types of Earthquake Plate Tectonics Earth's crust.mantle earth Plate Tectonics Plate Tectonics Earth's crust,mantle,core 1
2015/9/16 1 Chapter One Earthquake and Ground motions 2015/9/16 Haibei XIONG College of Civil Engineering, Tongji University 1 1.1 Causes and Types of Earthquake 1.2 Seismic Waves and Propagation 1.3 Earthquake Magnitude and Intensity 1.4 Seismicity in the World 1.5 Seismic Fortification for Building Structures 2015/9/16 Haibei XIONG College of Civil Engineering, Tongji University 2 Chapter 1 • Earthquakes Causes Earthquakes may results from a number of natural and humaninduced phenomena. • Include - Plate Moving → Tectonic Earthquake (90%) - Volcanic Activity → Volcanic Earthquake - Collapse → Collapse Earthquake - Large Reservoir-induced Earthquake - Nuclear Explosion-induced Earthquake 1.1 Causes and Types of Earthquake 2015/9/16 Haibei XIONG College of Civil Engineering, Tongji University 3 Plate Tectonics Earth's crust, mantle, core http://en.wikipedia.org/wiki/Structure_of_the_Earth 2015/9/16 Haibei XIONG College of Civil Engineering, Tongji University 4 Crust Mantle Core • 16~40 km • most earthquakes occurred • rocks • 2900 km • 5/6 of the earth’s volume • transfer shear wave • solid • 3500 km • liquid + solid http://en.wikipedia.org/wiki/Structure_of_the_Earth 2015/9/16 Haibei XIONG College of Civil Engineering, Tongji University 5 Plate Tectonics Earth's crust, mantle, core http://edition.cnn.com/2012/10/01/tech/mantle-earth-drill-mission 2015/9/16 Haibei XIONG College of Civil Engineering, Tongji University 6 Plate Tectonics
2015/9/16 Plate Moving Plate Moving Flg-13 Fault Fg.1.2 Tech Fault ty in
2015/9/16 2 • Collisions between adjacent lithospheric plates, • destruction of the slab-like plate, • spreading along mid-oceanic ridges 7 Plate Moving 2015/9/16 Haibei XIONG College of Civil Engineering, Tongji University 8 Plate Moving Fig.1.3 Continued drift of the Indian plate towards Asian plate causes major Himalayan earthquakes 2015/9/16 熊海贝 同济大学 xionghaibei@tongji.edu.cn 9 Fig.1.2 Tectonic plate and world-wide distribution of earthquakes Earthquake Occurred Don’t look at me like that…, It’s not my fault! 2015/9/16 Haibei XIONG College of Civil Engineering, Tongji University 10 Fault In geology, a fault is a planar fracture or discontinuity in a volume of rock, across which there has been significant displacement along the fractures as a result of earth movement. Large faults within the Earth's crust result from the action of plate tectonic forces. Fracture: interrupt, break, or destroy Crust: the outer layer of the Earth Tectonic: relation to the structure or movement of the earth's crust 2015/9/16 Haibei XIONG College of Civil Engineering, Tongji University 11 Fault Fig.1.3 Sketch of the earth’s crust 2015/9/16 熊海贝 同济大学 xionghaibei@tongji.edu.cn 12 • Field observations show that abrupt changes in the structure of rocks are common. • Such offsets of geological structure are called faults. • Faults are causes rather than results of earthquakes
2015/9/16 Normal Fault Reverse Fault al fauit is one Strike-Slip Fault Can you distinguish the fault? 日 teral fault.inve Terminology Earthquakes are e classified as ng to focal dept focal depthkm 3
2015/9/16 3 • A normal fault is one in which the rock above the inclined fault surface moves downward relative to the underlying crust. 2015/9/16 Haibei XIONG College of Civil Engineering, Tongji University 13 Normal Fault A reverse fault is one in which the crust above the inclined fault surface moves upward relative to the block below the fault. 2015/9/16 Haibei XIONG College of Civil Engineering, Tongji University 14 Reverse Fault • A strike-slip fault ， sometimes called a transcurrent fault or lateral fault, involves displacements of rock laterally, parallel to the strike. 2015/9/16 熊海贝 同济大学 xionghaibei@tongji.edu.cn 15 Strike-Slip Fault The San Andreas Fault, a right-lateral strike-slip fault, caused the massive 1906 San Francisco earthquake Source From: http://en.wikipedia.org/wiki/Fault_(geology) Can you distinguish the fault? Himalaya Mountains 2015/9/16 Haibei XIONG College of Civil Engineering, Tongji University 16 Terminology 2015/9/16 熊海贝 同济大学 xionghaibei@tongji.edu.cn 17 震中 震 源 深 度 震源距 震中距 Earthquakes are classified as: （according to focal depth） • Shallow Earthquakes focal depth < 60 km • Intermediate Earthquakes 60km < focal depth < 300 km • Deep Earthquakes focal depth > 300 km 2015/9/16 Haibei XIONG College of Civil Engineering, Tongji University 18
2015/9/16 Earthquakes are also classified as: 1.2 Earthquake waves and propagation (according to time sequence) Body waves☐ P waves S waves A fe Body wa oture zone and within a body of solid rod 00980 0888 Pwaves☐ S waves P waves parellel to the direction of propagation of the wave v n of ware 密 Surface waves Rayleigh Waves R waves☐ Surface waves- L waves c movement
2015/9/16 4 Earthquakes are also classified as: (according to time sequence) • Foreshock A few earthquakes are proceeded by smaller from the source area, which can be used to predict the main shock. • Aftershock Large earthquakes are sometimes followed by incredible numbers of them, which can results the damaged building destructed. 2015/9/16 Haibei XIONG College of Civil Engineering, Tongji University 19 Body waves, originating at the rupture zone and traveling within a body of solid rock. 1.2 Earthquake waves and propagation 2015/9/16 熊海贝 同济大学 xionghaibei@tongji.edu.cn 20 Body waves P waves S waves Video 1 P waves parallel to the direction of propagation of the wave. •The motion of the P wave is the same as that of a sound wave, it alternately pushes (compresses) and pulls (dilates) the rock. • The P waves are able to travel through both solid rock and liquid material, such as volcanic magma or the water of the oceans. Direction of wave travel Direction of vibration 2015/9/16 熊海贝 同济大学 xionghaibei@tongji.edu.cn 21 P waves • P for Primary Direction of wave travel Direction of vibration •S waves produce an upand-down and side-toside motion of the earth that shakes the ground vertically and horizontally at right angles to the direction of wave travel. •S for Secondary •S waves cannot propagate in the liquid parts of the earth, such as the oceans, and their amplitude is significantly reduced in liquefied soil. 2015/9/16 Haibei XIONG College of Civil Engineering, Tongji University 22 S waves • Their motion of surface waves is mainly at or near ground surface. • two types: • Rayleigh waves or R waves • Love waves or L waves. 2015/9/16 熊海贝 同济大学 xionghaibei@tongji.edu.cn 23 Surface waves R waves L waves Surface waves Rayleigh Waves • Rayleigh wave move both vertically and horizontally in a vertical plane, in which the waves are traveling and exhibit elliptic movement. 2015/9/16 Haibei XIONG College of Civil Engineering, Tongji University 24
2015/9/16 Love waves□ 1.2 Earthquake waves and propagation -g-a-月 woi图 网 Q2:When we know>V What can we do? 8gonquaaPaetae Earthquake Warning System 上.20-万 Eg. g11-2y Strong Shaking Expected Early Warning 1.An earthquake warning system is a system of accelerometers.communication.computers.and alarms.that s devised for regional notification of a substantial V quake while it is in progress This is not the same as earthquake prediction,which is urrently inca of produding de before earthquake attack. Earthquake Records .ELCentro(US earthquake record) 5
2015/9/16 5 Love waves Love wave moves the ground side to side in a horizontal plane parallel to the earth’s surface. No vertical displacement. Q1: What can we observe from the different speed of the four kinds of waves? Q2: When we know VP>VS>VL>VR,What can we do? 2015/9/16 Haibei XIONG College of Civil Engineering, Tongji University 25 Video 1 • For general material, during earthquakes P waves travel faster than S waves. • The propagation velocities of P and S waves depend on the density and elastic properties of the rocks and soil through which they pass. 1.2 Earthquake waves and propagation E G Vp 2 (1 )(1 2 ) (1 ) E G Vs 2 (1 ) 1 2 2(1 ) s p V V 2015/9/16 Haibei XIONG College of Civil Engineering, Tongji University 26 1 2 2(1 ) s p V V 1. An earthquake warning system is a system of accelerometers, communication, computers, and alarms that is devised for regional notification of a substantial earthquake while it is in progress. 2. This is not the same as earthquake prediction, which is currently incapable of producing decisive event warnings. 3. Several seconds alarm before earthquake attack. Earthquake Warning System 2015/9/16 Haibei XIONG College of Civil Engineering, Tongji University 27 1 2 2(1 ) s p V Eq. V Early Warning Earthquake Records Displacement Time History Velocity Time History Acceleration Time History--- three features: Peak Ground Acceleration (PGA) Frequency spectrum Duration Time 2015/9/16 Haibei XIONG College of Civil Engineering, Tongji University 29 The duration time of the El Centro earthquake is 53.73s, with the PGA 341.7 in North-South, 210.1 in East-West, and 206.3 in vertical direction. The site classification is almost II-III. The earthquake magnitude is 6.7 degree with the epicenter distance is 11.5km. Elcentro -0.10 -0.08 -0.06 -0.04 -0.02 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0 10 20 30 40 50 60 Elcentro 0.0000 0.0002 0.0004 0.0006 0.0008 0.0010 0.0012 0.0014 0.0016 0.0018 0.0020 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 Acceleration history Power spectral density •EL Centro (US earthquake record) 2015/9/16 Haibei XIONG College of Civil Engineering, Tongji University 30