An introduction to probabilistic seismic hazard analysis. Basis of the seismic method is the timing of artificially generated pulses of elastic wave energy that propagates through the ground. A seismograph is an instrument that records and measures. Seismic rays are used instead of the wave front to describe the wave propagation. A related powerpoint presentation for seismic waves and the slinky is. Seismic waves are usually generated by movements of the earths tectonic plates but may also be caused by explosions, volcanoes and landslides. Deep inside the earth, rocks are constantly being pressured to move until the strain is so great the rocks can no longer bear the tension. Seismology is the study of earthquakes and seismic waves that move through and around the. Reflection and refraction are the most commonly used seismic techniques. Lecture 11 chapter 16 waves i university of virginia.
Seismic techniques are commonly used to determine site geology, stratigraphy, and rock quality. They create most of the damage at the surface because they are the waves that produce the most ground movement and pass through an area the most slowly. The p wave can move through solid rock and fluids, like water or the liquid layers of the earth. The division of the earth into the earths crust, mantle and core, the later division into socalled bullen zones, or the latest laterally inhomogeneous models of the earth are all based predominantly on studies of seismic body waves. The earthquake waves travel in all directions, but they have highest intensity at the epicenter. Principles of the seismology and seismic engineering. Normal incidence reflection seismogram the principles of the normal incidence reflection seismogram are illustrated in the diagrams below. Body waves are generated by the energy released at the focus hypocenter.
It pushes and pulls the rock it moves through just like sound waves push and pull the. Reflections recorded at late times have lower amplitude than those at early times. The precise speed that a seismic wave travels depends on several factors. Seismographs are equipped with electromagnetic sensors that translate ground motions into electrical changes, which are processed and recorded by the instruments analog or digital circuits. These techniques provide detailed information about subsurface layering and rock geomechanical properties using seismic acoustical waves. A seismologist is a scientist who studies earthquakes and seismic waves. Electromagnetic waves do not need a medium to travel from place to place.
The relative amplitudes of the transmitted and reflected waves depend on. Reflection frequencies decrease with depth because of attenuation of seismic waves, and this also decreases the resolution at depth. In other words, the material was not and is not intended as a standard introductory text on theoretical seismology. Despite some similarities which water waves and seismic surface waves. Earthquakes and the earths interior earthquakes earthquakes occur when energy stored in elastically strained rocks is suddenly released. Traveling through the interior of the earth, body waves arrive before the surface waves emitted by an earthquake. Lecture notes nearsurface geophysical imaging earth. The earth consists of a crust, a mantle, a liquid outer core, and a solid inner core. There are 2 types of waves mechanical waves need a physical medium to move through examples include waves in water, seismic waves, sound waves, and vibrations in strings the energy of a mechanical wave is a function of its amplitude.
Temperature tends to lower the speed of seismic waves and pressure tends to increase the speed. The seismic waves that emanate from earthquakes include body waves and surface waves. Examples of wave motion include waves on strings, water waves, seismic waves, sound, all electromagnetic radiation including light, heat, xrays, etc. This product includes cornell notes, an activity, a presentation on the lesson, and a mini quiz built into the presentation on how seismic waves pass through earths interior. The seismic wave equation x 1 x 2 x 3 t x 1 t x 1 dx 1 dx 2 dx 3 figure 3. Seismograph instrument for recording the earthquakes if ground acceleration is measured accelerograph seismogram earthquake record in case of ground acceleration recording the accelerogram magnitude c. Mechanical waves need a medium to pass through in order to move. Measure earthquakes with your own seismograph one stop science shop duration. Complete the quick lab on page 505 of your text book. Seismic waves decrease in amplitude as they propagate further into the earth. The lecture notes are just transcription of what i originally handwrote on transparencies for students of the course theory of seismic waves at universit. Periodic waves are reflected and inverted and interfere with one another creating standing waves. If you can collect a bunch of slinkys, each small group can try it.
Powerpoint includes 9 slides with activator, daily objectives, an embedded youtube video. In the open ocean, height is usually less than 1 meter. From source to detector sound from an instrument to ear cell phone to cell tower and vice versa em waves water waves a disturbance in the water moves outward. Surface waves are the slowest seismic waves and travel outward on the earths surface from the epicenter much like ripples do from a stone thrown into water figure 3. Simply stated, seismic methods involve estimation of the shapes and physical properties of earths subsurface layers from the returns of sound waves that are propagated through the earth. This article talks about earthquakes, its magnitude scale, causes, types, etc. An important concept not covered in these web notes is the optimumoffset method of seismic reflection data acquisition. Earthquake and seismic waves geography study material. Basically, use a compressional wave for pwave, a sidetoside snake motion for s waves, and upanddown wave motion for l waves.
Seismic wave speed seismic waves travel fast, on the order of kilometers per second kms. This release of energy causes intense ground shaking in the area near the source of the earthquake and sends waves of elastic energy, called seismic waves, throughout the earth. A the focus of the earthquake is directly below the epicenter. This is the fastest kind of seismic wave, and, consequently, the first to arrive at a seismic station. The dangers of earthquakes are presented as well as the necessity for engineers to design structures for earthquakeprone areas that are able to withstand the forces of seismic waves. When an earthquake occurs, the shockwaves of released energy that shake the earth and temporarily turn soft deposits, such as clay, into jelly liquefaction are called seismic waves, from the greek. Principles of the seismology and seismic engineering assoc. As they pass through the different mediums, they are defracted.
The most familiar type of waves such as waves on a string, water waves, sound waves, seismic waves, etc. Synthetic full wavefield finitedifference simulation shall be demonstrated for the following situations. These waves require a medium for propagation, they cannot propagate through vacuum. The p and s waves help determine where the epicenter is located. In 2003, a convergence of interests in making precast diaphragms safer, in spreading the advantages of precast construction to seismic zones, and in generating the scientific knowledge needed to enable these advancementsgave rise to the dsdm project. An earthquakes magnitude is a number that geologists assign to an earthquake based on the earthquakes strength. They travel through solids and liquids and are fast. Earthquakes and seismic waves barren county schools.
Seismic notes basis of the seismic method is the timing of artificially generated pulses of elastic wave energy that propagates through the ground. Seismic wave demonstrations and animations 1 purdue university. Gy 112 lecture note series university of south alabama. Nov 07, 20 seismic waves blue primary waves followed by red secondary waves move outward in concentric circles from the epicenter of an earthquake off british columbia and washington state. The seismic waves produced by an earthquake are monitored and tracked. P waves in a liquid or gas are pressure waves, including sound waves. They involve oscillations of constituent particles and depend on the elastic properties of the medium. However, when the waves reach shallower coastal waters, the water piles up to heights that occasionally exceed 30 meters. The roll the ground like waves in an ocean but only travel on the surface of the earth, they do not travel through the earth 3. Elevation statics vertical travel time through the nearsurface layer varies due to changes in elevation of shot or receiver. Students learn about the types of seismic waves produced by earthquakes and how they move the earth. Most of the materials for this book originated as lecture notes for graduate courses in. Among the many types of seismic waves, one can make a broad distinction between body waves, which travel through the earth, and surface waves, which travel at the earths surface 4850. Find materials for this course in the pages linked along the left.
Standing seismic waves, known as the free oscillations of the earth, represent vibrations of the. Powerpoint and guided notes i use to teach about seismic waves including p waves, s waves, and surface waves, as well as how a seismograph measures waves. Types of seismic waves there are several different kinds of seismic waves, and they all move in different ways. Seismic resolution is controlled by the bandwidth of the signal, which is typically f30140 hz.
Seismic energy is provided by a source shot located on the surface. The intensity of earthquake decreases as one moves away from the epicentre. Students learn how engineers build shake tables that simulate the ground motions of the earth caused by seismic. S, shear, secondary, transverse alternating transverse motions perpendicular to the direction of propagation, and the raypath. Using directional waves is advantageous in subsurface. The terms seismograph and seismometer are often used interchangeably.
Preface the lecture notes are just transcription of what i originally handwrote on transparencies for students of the course theory of seismic waves at universit. The richter scale is a rating of an earthquakes magnitude based on the size of the earthquakes seismic waves. P waves travel the quickest and can go through the liquid and solid cores. Powerpoint and guided notes i use to teach about seismic waves including pwaves, swaves, and surface waves, as well as how a seismograph measures waves. Czech technical university in praha content introduction earthquake causes earthquake characteristics earthquake impacts and their consequences seismic regime seismological characteristic of europe. Seismograph, instrument that makes a record of seismic waves caused by an earthquake, explosion, or other earthshaking phenomenon. Intrinsic attenuation andas waves pass into different materials, partitioning of.
Similar waves, which are generated by earthquakes, artificial explosions and analogous sources, and prpagate along the earths surface, are referred to as seismic surface waves. They are the energy that travels through the earth and is recorded on seismographs. Seismic waves, shadow zone of pwaves and swaves pmf ias. Ncert notes on important topics for the upsc civil services exam. Elasticity and seismic waves seismic waves and travel times in the earth evidence from seismic velocities for the existence of the core plate tectonics lithosphere, asthenosphere primary chemical layering of the earth crust, mantle, core materials. Nov 15, 2014 demonstrating p and s seismic waves duration. A seismograph, or seismometer, is an instrument used to detect. The total energy of the transmitted and reflected waves must be equal to the energy of the incident ray. Probabilistic seismic hazard analysis psha aims to quantify these uncertainties, and combine them to produce an explicit. Seismic waves come in two types, s waves and p waves. Notes,whiteboard,whiteboard page,notebook software,notebook, pdf,smart,smart technologies ulc,smart board interactive whiteboard created date. Electromagnetic waves do not need a physical medium.
Seismic waves seismology is the study of earthquakes and seismic waves that move through and around the earth. Notes,whiteboard,whiteboard page,notebook software,notebook,pdf,smart,smart technologies ulc,smart board interactive whiteboard created date. For shallow applications this normally comprises a hammer and plate, weight drop or small explosive. However, when the waves reach shallower coastal waters, the water piles. Dec 25, 2019 earthquakes an earthquake is shaking or trembling of the earths surface, caused by the seismic waves or earthquake waves that are generated due to a sudden movement sudden release of energy in the earths crust shallowfocus earthquakes or upper mantle some shallowfocus and all intermediate and deepfocus earthquakes. Seismic waves can be defined as, the waves of energy caused by the sudden breaking of rock within the earth or an explosion1. There are many common elements to all the various types of wave motion that can be described and these will be pointed out. Using the stress and strain theory developed in the previous chapter, we now con struct and solve the seismic wave equation for elastic wave propagation in a. Click here for one website that discusses how to demo seismic waves. Focus also known as the hypocenter, it is the place within earth where earthquake waves.
Every point on the wave front is a source of a new wave that travels out of it in the form of spherical shells. The seismic refraction method is based on the measurement of the travel time of seismic waves refracted at the interfaces between subsurface layers of different velocity. Seismic waves are fundamentally of two types, compressional, longitudinal waves or shear, transverse waves. Earths interior structure page 1 of 22 purdue university. These notes will also be useful for other competitive exams like banking po, ssc, and so on. In these lecture notes, we shall deal only with this type of waves. Propagation in a simple onelayer over half a space model.
Traveling waves waves propagate from one place to another. These pulses of elastic wave energy or seismic waves are detected using electromagnetic transducers called geophones. The first kind of body wave is the p wave or primary wave. A wave is a disturbance that moves energy from one place to another. This product is part of my earthquake interactive notebook bundle.
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