There are three major kinds of seismic waves: P, S, and surface waves. In every building, there is a natural frequency of swaying depending on the shape, height and material of it. Seismic waves. Which seismic wave refracts and cannot penetrate the core? They usually result from an earthquake, volcanic eruption or other explosion. I am sure that you are familiar with reflected sound waves; we call them echoes. epicenter: The point on Earth's surface directly above an earthquake's focus. Describe the layers of earth. Those that travel through the slow region are slowed down, and hence will be recorded later on the a seismogram. Seismic waves may travel either along or near the earth's surface (Rayleigh and Love waves) or through the earth's interior (P and S waves). Near an earthquake the shaking is large and dominated by shear-waves and short-period surface waves. The next map shows the variations at 2,880 km depth , in the mantle just above the core-mantle boundary. B 25. The shallow part of the mantle is different; it contains several important well-established and relatively abrupt velocity changes. We can measure that difference from a seismogram and if we also know the speed that the waves travel, we could calculate the distance by equating the measured time difference and the expression. When a tsunami breaks, the water does not go back until all the water has come to shore. S wave: A type of seismic wave that moves the ground up and down or side to side. I mentioned above that surface waves are dispersive - which means that different periods travel at different velocities. Like the velocity the rate of amplitude decrease with depth also depends on the period. Love wave: A surface seismic wave that cause horizontal shifting of the Earth during an earthquake. Slowest. The main regions of Earth and important boundaries are labeled. Pressure increases with depth in Earth because the weight of the rocks above gets larger with increasing depth. The difference in the arrival times of the waves is. (skin-effect) represent another type of surface waves. The epicenter of the earthquake is directly below the focus. Ultrasound imaging is identical to P-wave tomography, it's just that in seismology we don't have the choice of where are wave sources are located - we just exploit earthquakes. The diagram below is an example of the paths P-waves generated by an earthquake near Earth's surface would follow. The vibration caused by P waves is a volume change, alternating from compression to expansion in the direction that the wave is traveling. S waves are called secondary waves because they always arrive after P waves at seismic recording stations. Seismic tomography is like an x-ray of Earth's interior, except that it uses earthquakes for the illumination. Love waves are transverse and restricted to horizontal movement - they are recorded only on seismometers that measure the horizontal ground motion. Perhaps you recall from high school a principle called Snell's law, which is the mathematical expression that allows us to determine the path a wave takes as it is transmitted from one rock layer into another. One of the results of an earthquake can be _____. In fact, we often divide the mantle into two regions, upper and lower, based on the level of velocity heterogeneity. The PREM model is a useful reference for understanding the main features of Earth. An earthquake is a more complicated process than a stone splashing into water, and the seismic waves that are set up during an earthquake are more varied than those on the pond. We have already discussed the main elements in Earth's interior, the core, the mantle, and the crust. Unlike P waves, S waves can travel only through solid materials. that the wave took to complete its journey. By studying the propagation characteristics (travel times, reflection amplitudes, dispersion characteristics, etc.) A P wave (primary wave or pressure wave) is one of the two main types of elastic body waves, called seismic waves in seismology. Thus, if we look at a seismogram, we expect to see the first wave to arrive to be a P-wave (the fastest), then the S-wave, and finally, the Love and Rayleigh (the slowest) waves. S-waves are transverse waves. Thus the simple rule of thumb for earthquakes in this distance range is the distance is about eight times the arrival time of S-wave less the arrival time of the P-wave. At a seismic station the second waves to arrive are _____. Tsunami waves are caused by an undersea earthquake that occurs in a tectonic plate far put to sea on the ocean floor. up . In the crust, the variations are larger and can reach tens of percent. Other waves such as surface waves and body waves reflecting off the surface are recorded in the "shadow" region, but the P-wave "dies out" near 100°. Su, R. L. Woodward and A. M. Dziewonski, Degree-12 Model of Shear Velocity Heterogeneity in the Mantle, Journal of Geophysical Research, vol. 10. Now, there's two fundamentally different types of the seismic waves. Map of the variations in seismic shear-wave speed with respect to the value in PREM at 100 km depth. Which seismic wave can penetrate the core but refracts? D 26. S-waves also travel fast and through earth but not through the core. The velocities deeper in the Earth have also be imaged. Crust is the thinnest layer and mostly made of rocks. Surface waves are similar in nature to water waves and travel just under the Earth’s surface. Since the earthquake location since it must lie on each circle centered on a seismometer, if we plot three or more circles on a map we could find that the three circles will intersect at a single location - the earthquake's epicenter. When a wave encounters a change in material properties (seismic velocities and or density) its energy is split into reflected and refracted waves. Which type of wave can penetrate the outer and inner core? Earthquakes are imperfect illuminators because they are clustered on plate boundaries, leaving much of the interior in the shadows. A tsunami wave is one big wave with all the water behind it. Typical S-wave propagation speeds are on the order of 1 to 8 km/sec. Secondary , or S waves, travel slower than P waves and are also called "shear" waves because they don't change the volume of the material through which they propagate, they shear it. They are formed by the interaction of S waves with Earth's surface and shallow structure and are dispersive waves. In practice we use better estimates of the speed than our simple rule of thumb and solve the problem using algebra instead of geometry. In general, earthquakes generate Love waves over a range of periods from 1000 to a fraction of a second, and each period travels at a different velocity but the typical range of velocities is between 2 and 6 km/second. Like Love waves they are dispersive so the particular speed at which they travel depends on the wave period and the near-surface geologic structure, and they also decrease in amplitude with depth. Key 21. (Model S12 WM13, from W.-J. Can travel through Earth. Surface waves can cause the ground to move sideways and up and down like ocean waves. 9. D 24. P-waves travel through all types of media - solid, liquid, or gas. Faster waves will travel the distance quicker and show up on the seismogram first. Another important characteristic of Love waves is that the amplitude of ground vibration caused by a Love wave decreases with depth - they're surface waves. perpendicular: Meeting at a right (90 degree) angle. Although surface waves travel more slowly than S-waves, they can be much larger in amplitude and can be the most destructive type of seismic wave. S-Wave (up and down) P-Wave (sideways) Surface Wave (rolling motion) In what directions do the S, P, and Surface waves move? The decrease in velocity from the lower mantle to the outer core casts a "shadow" on the P-waves that extends from about 100° to 140° distance. We'll examine the two simplest types of interaction refraction and reflection. Similar waves, which are generated by earthquakes, artificial explosions and analogous sources, and pr~pagate along the Earth's surface, are referred to as seismic surface waves. T/F. Which seismic waves stay on earth's surface? Other waves such as surface waves and body waves reflecting off the surface are recorded in the "shadow" region, but the P-wave "dies out" near 100°. Earthquakes can happen when there is a large amount of _____. (solid, liquid, thick, thin, iron, rocks). Can travel through Earth, but not through the core. The amplitude of Rayleigh-wave shaking decreases with depth. Seismographs record the amplitude and frequency of seismic waves and yield information … Seismic waves travel through the layers of the Earth. 13. The point on the surface of the Earth at which a seismic wave first hits is called the epicenter. The latter two are called surface waves they the travel along Earth’s surface and their amplitude decreases with depth into Earth. The Earth is almost a sphere. to the mantle, not the core? Here's an example to illustrate the difference: if two earthquakes occurred at the same place but exactly 24 hours apart, the wave travel times would be the same but the arrival times would differ by one day. A 23. secondary. In this case, we're talking about the surface of the ground. Great progress was made quickly because for the most part Earth's interior is relatively simple, divided into a sphere (the inner core) surrounded by roughly uniform shells of iron and rock. We are fortunate that the speed depends on the rock type because it allows us to use observations recorded on seismograms to infer the composition or range of compositions of the planet. Fastest. In some instances reflections from the boundary between the mantle and crust may induce strong shaking that causes damage about 100 km from an earthquake (we call that boundary the "Moho" in honor of Mohorovicic, the scientist who discovered it). The actual interaction between a seismic wave and a contrast in rock properties is more complicated because an incident P wave generates transmitted and reflected P- and S-waves and so five waves are involved. In the two decades tomography has been applied to Earth studies on many scales, from looking at small regions of Earth's crust that may contain petroleum, to imaging the entire planet. Seismic waves travel from the focus outwards in all directions. To apply those ideas to earthquake studies, think of the earthquake location as the starting point for the trip and the seismometer as the place where the trip concludes. Likewise, when an S-wave interacts with a boundary in rock properties, it too generates reflected and refracted P- and S-waves. S-Wave. As you might expect, the difference in wave speed has a profound influence on the nature of seismograms. B 22. Although we have neglected differences in the travel path (which correspond to differences in travel distance) and the abundance waves that reverberate within Earth, the overall character is as we have described. parallel: Having the same direction. The two major types are body waves (S and P waves) and surface waves. (Recorded during a … Seismologist have reasoned that earths outer core must be liquid based on the disappearance of S-waves (T or F) True Studies of how waves reflect deep inside earth show that earths … Properties of seismic waves. In regions where material is rising from the mantle, it should be warmer, and the velocity should be lower, in regions that are old and cold, such as beneath many of the old parts of continents, we would expect to see faster regions (assuming that temperature is the only difference). P wave: A type of seismic wave that compresses and expands the ground. In general, the seismic velocity in Earth increases with depth (there are some important exceptions to this trend) and refraction of waves causes the path followed by body waves to curve upward. Other articles where Love wave is discussed: Augustus Edward Hough Love: …a method—based on measurements of Love waves—to measure the thickness of the Earth’s crust. That means that we can estimate the distance an earthquake is from a seismometer. And your reflection in a mirror or pool of water is composed of reflected light waves. Seismic waves travel at a speed of 5 miles per second or 8 kilometers per second. The machine that measures the strength of an earthquake is called _____. Analogously, surface elastic waves can propagate along the surface of an elastic substance. If we have two other seismometers which recorded the same earthquake, we could make a similar measurement and construct a circle of possible locations for each seismometer. Which seismic wave can travel through earth? T/F, Waves move out through the ground from the source of an earthquake. In seismology, reflections are used to prospect for petroleum and investigate Earth's internal structure. And we're going to focus on one more than the other. Structure of the Earth. For example, on a striped shirt, the stripes are parallel. P waves travel faster than other seismic waves and hence are the first signal from an earthquake to arrive at any affected location or at a seismograph.P waves may be transmitted through gases, liquids, or solids. Map of the variations in seismic shear-wave speed with respect to the value in PREM at 2,880 km depth, just above the core mantle boundary. Typical speeds for Rayleigh waves are on the order of 1 to 5 km/s. The basic idea is to use observed delayed (or early) arrival times (delayed with respect to the reference model) to locate regions of relatively fast and relatively slow seismic wave speed. As a wave travels through Earth, the path it takes depends on the velocity. A dispersed Rayleigh wave generated by an earthquake in Alabama near the Gulf coast, and recorded in Missouri. At all distances from the focus, mechanical properties of the rocks, such as incompressibility, rigidity, and density, play a role in the speed with which the waves travel and the shape and duration of the wave trains.The layering of the rocks and the physical properties of surface soil also affect wave characteristics. Assume a seismometer are is far enough from the earthquake that the waves travel roughly horizontally, which is about 50 to 500 km for shallow earthquakes. We can solve these equations or an appropriate approximation to them to compute the paths that seismic waves follow in Earth. Which seismic wave can travel to the mantle, not the outer core (liquid iron)? Even in large earthquakes the intense shaking generally lasts only a few tens of seconds, but it can last for minutes in the greatest earthquakes. The value in parentheses is then equal to about (1/3.45 - 1/8) or about 1/8. Seismic waves can be distinguished by a number of properties including the speed the waves travel, the direction that the waves move particles as they pass by, where and where they don't propagate. Since the outer core is fluid, and S-waves cannot travel through a fluid, the "S-wave shadow zone" is even larger, extending from about 100° to 180°. A notable exception is caused by the decrease in velocity from the mantle to the core. Both are compositional boundaries and the core-mantle boundary is the larger contrast. After both P and S waves have moved through the body of Earth, they are followed by surface waves, which travel along Earth’s surface. Usually, the long periods arrive first since they are sensitive to the speeds deeper in Earth, and the deeper regions are generally faster. For the distance range 50 to 500 km, the S-waves travel about 3.45 km/s and the P-waves around 8 km/s. Love waves are transverse waves that vibrate the ground in the horizontal direction perpendicular to the direction that the waves are traveling. When a regular wave breaks, most water goes back into the ocean. The are many different seismic waves, but all of basically of four types: An earthquake radiates P and S waves in all directions and the interaction of the P and S waves with Earth's surface and shallow structure produces surface waves. As a transverse wave passes the ground perpendicular to the direction that the wave is propagating. These usually cause the most destruction because they cause the most movement of the ground and they take the longest to pass. For example, the bulk modulus is a measure of how a material changes volume when pressure is applied and is a characteristic of a material. The fact that the waves travel at speeds which depend on the material properties (elastic moduli and density) allows us to use seismic wave observations to investigate the interior structure of the planet. The paths of P-wave energy for a shallow earthquake located at the top of the diagram. Seismic waves are essentially just the jiggling of the ground in response to the force put on the ground by the earthquake, similar to the way the jello in a bowl responds to a tap to the side of the bowl. The main chemical shells of Earth are shown by different colors and regions with relatively abrupt velocity changes are shown by dashed lines. Body waves are of two types: compressional or primary (P) waves and shear or secondary (S) waves. The transmitted wave travels in a different direction which depends on the ratio of velocities of the two rock types. When I describe the different seismic wave types below I'll quote ranges of speed to indicate the range of values we observe in common terrestrial rocks. A 29. B 27. We can look at the travel times, or the travel times and the amplitudes of waves to infer the existence of features within the planet, and this is a active area of seismological research. The atoms in these rocks rearrange themselves into compact structures that are stable at the high pressures and the result of the rearrangement is an increase in density and elastic moduli, producing an overall increase in wave speed. The lower value corresponds to the wave speed in loose, unconsolidated sediment, the higher value is near the base of Earth's mantle. They travel more slowly than seismic body waves (P and S). Also with increasing distance from the earthquake, the waves are separated apart in time and dispersed because P, S, and surface waves travel at different speeds. Seismic waves travel fast, on the order of kilometers per second (km/s). Fast. What happens to S and P waves as they travel inside earth? As a Rayleigh wave passes, a particle moves in an elliptical trajectory that is counterclockwise (if the wave is traveling to your right). Part of the energy carried by the incident wave is transmitted through the material (that's the refracted wave described above) and part is reflected back into the medium that contained the incident wave. Seismic waves are recorded by a machine called a seismograph, which tells us about the strength and speed of the seismic waves.These recordings made by a seismograph are called seismograms.Seismic waves travel at different speeds when they pass through different types of material, so by studying seismograms, scientists can learn a lot about Earth's internal structure. When an earthquake occurs the P and S waves travel outward from the region of the fault that ruptured and the P waves arrive at the seismometer first, followed by the S-wave. 99(4) 4945-4980, 1994). The actual variations are influenced by both temperature and composition variations, but they agree well with the ideas of plate tectonics, particularly at the divergent boundaries or oceanic spreading ridges. Once the S-wave arrives we can measure the time interval between the onset of P-wave and the onset of S-wave shaking. The mantle is the thickest layer. A seismic wave is a wave that travels through the Earth, most often as the result of a tectonic earthquake, sometimes from an explosion. Surface Waves. The amplitude of the reflection depends strongly on the angle that the incidence wave makes with the boundary and the contrast in material properties across the boundary. Travel times are best conceptualized of with an analogy of an auto trip. Models that assume the Earth is perfectly symmetric can be used to predict travel times of P-waves that are accurate to a few seconds for a trip all the way across the planet. P-wave: A seismic pressure wave that travel through the body of the Earth. True or false: s waves do not travel through earths mantle. Seismic waves have a particular frequency in which they travel at through the ground. The curves show the paths of waves, and the lines crossing the rays show mark the wavefront at one minute intervals. Slowest type of waves which travel only along the Earth's surface. Velocity and density variations within Earth based on seismic observations. false. The precise speed that a seismic wave travels depends on several factors, most important is the composition of the rock. At a seismic station the last waves to arrive are _____. The warm colors (red, orange, and yellow) show regions with slower than normal speeds, the darker regions are faster than normal. In addition to his work on geophysical theory, Love studied elasticity and wrote A Treatise on the Mathematical Theory of Elasticity, 2 vol. This model was developed in the early 1980's and is called PREM for Preliminary Earth Reference Model. The S-wave speed, call it b, depends on the shear modulus and the density. 11. You need at least three stations and some idea of the P and S velocities between the earthquake and the seismometers. They are called surface waves, as they diminish as they get further from the surface. the rocks) are commonly observable on seismograms. These variations are actually quite small, on the order of a few percent, so the basic idea of Earth being a spherically stratified planet are well founded. Earthquakes generate four principal types of elastic waves; two, known as body waves, travel within the Earth, whereas the other two, called surface waves, travel along its surface. Seismic Waves. The second wave interaction with variations in rock type is reflection. A The focus of the earthquake is directly below the epicenter. The mathematical formula we use in this problem is. S-waves are transverse waves because they vibrate the ground in a the direction "transverse", or perpendicular, to the direction that the wave is traveling. B 28. Which seismic waves stay on earth's surface? The increase is a result of the effects of pressure on the seismic wave speed. We also can include the earthquake depth and the time that earthquake rupture initiated (called the "origin time") into the problem. An important distinguishing characteristic of an S-wave is its inability to propagate through a fluid or a gas because a fluids and gasses cannot transmit a shear stress and S-waves are waves that shear the material. A seismic wave is an elastic wave generated by an impulse such as an earthquake or an explosion. The earthquake can be in any direction, but must be the estimated distance away. Geometrically that means that the earthquake must be located on a circle surrounding the seismometer, and the radius of the circle is about eight times the observed wave travel-time difference (in kilometers). On a global scale, we might expect that the shallow parts of the mantle would correlate with the major structural features we can observe at the surface - the plate boundaries. The region from near 400 to 1000 km depth is called the transition zone and strongly affects body waves that "turn" at this depth and arrive about 20°-30° distant from a shallow earthquake. A seismic reflection occurs when a wave impinges on a change in rock type (which usually is accompanied by a change in seismic wave speed). 12. S-waves. Rayleigh waves move along the surface of the Earth forming a wave that is much like: (a) a skier moving down a mountain hill, The crust is the material extracted from the mantle over the last 4.5 billion years and it contains a great diversity of structures that are often apparent when you study the rocks exposed at the surface. P-waves are sound waves, it's just that in seismology we are interested in frequencies that are lower than humans' range of hearing (the speed of sound in air is about 0.3 km/sec). Faults are only found near the edges of tectonic plates. For some angles all the energy can be returned into the medium containing the incident wave. Seismographs record the amplitude and frequency of seismic waves and yield information about the Earth and its subsurface structure. In this depth range the minerals that make up the mantle silicate rocks are transformed by the increasing pressure. They typically travel at speeds between ~1 and ~14 km/sec. These are the waves that do the most damage to our buildings, highways, etc. Even though they are slower than P-waves, the S-waves move quickly. Type of seismic wave: causes rock to move both up and down and side to side. Travel time is a relative time, it is the number of minutes, seconds, etc. You can picture this concept by recalling the circular waves that spread over the surface of a pond when a stone is thrown into the water. Which seismic wave refracts and cannot penetrate the core? 5. Earthquake foci (focus, singular) are _____. We can use the fact that P and S waves travel at different speeds to locate earthquakes. Temperature tends to lower the speed of seismic waves and pressure tends to increase the speed. We'll go through each wave type individually to expound upon the differences. false. There are different types of seismic waves based on the movement. For example, foam rubber has a lower bulk modulus than steel. are produced by Earthquakes. Also, note that the correlation with surface tectonics is gone, as you would expect for a complex convective system such as Earth's mantle. Note the correlation with plate boundaries and surface heat flow. There are instruments throughout the world that detect earthquakes called seismometers and seismographs. At farther distances the amplitude of the seismic waves decreases as the energy released by the earthquake spreads throughout a larger volume of Earth. P-Wave. Many earthquakes happen along the borders of _____. The focus is the origin of the earthquake P-waves are the fastest and travel through earth. In what directions do the S, P, and Surface waves move? surface waves are slowest and travel the earth's surface. The top of the Earth is located at 0 km depth, the center of the planet is at 6371 km. Seismic surface waves travel along the Earth's surface. The two largest contrasts in material properties in the Earth system are located near the surface and the core-mantle boundary. Other sharp contrasts are observable, the inner-core outer-core boundary is relatively sharp, and velocities increase from the liquid to the solid. If we let k represent the bulk modulus of a material, m the shear-modulus, and r the density, then the P-wave velocity, which we represent by a, is defined by: A modulus is a measure of how easy or difficulty it is to deforms a material. Which seismic wave can penetrate the core but refracts? Usually, the effect of pressure is the larger and in regions of uniform composition, the velocity generally increases with depth, despite the fact that the increase of temperature with depth works to lower the wave velocity. Note the curvature of the rays in the mantle, the complexities in the upper mantle, and the dramatic impact of the core on the wavefronts. The mathematics behind wave propagation is elegant and relatively simple, considering the fact that similar mathematical tools are useful for studying light, sound, and seismic waves. The speed at which a dispersive wave travels depends on the wave's period. One is surface waves. Those waves that are the most destructive are the surface waves which generally have the strongest vibration. The point beneath Earth's surface where rock breaks under stress and causes an earthquake. Rayleigh waves are the slowest of all the seismic wave types and in some ways the most complicated. The color scale is the same but note how the lower-mantle velocity variations are more subdued than those in the more heterogeneous upper mantle. The change in direction depends on the ratio of the wave velocities of the two different rocks. More recent efforts have focused on estimating the lateral variations in wave speed within the shells that make up the reference model. Although temperature also increases with depth, the pressure increase resulting from the weight of the rocks above has a greater impact and the speed increases smoothly in these regions of uniform composition. T/F. Since the outer core is fluid, and S-waves cannot travel through a fluid, the "S-wave shadow zone" is even larger, extending from about 100° to 180°. The edges of tectonic plates that pass through the layers of the is! Rocks forces them to topple strongest vibration diagram below is an elastic.... Slower than P-waves, the path it takes depends on the elastic properties density! Go through each wave type individually to expound upon the differences efforts focused. Upon the differences on Earth 's surface and shallow structure and are traveling line ) edges of plates. That occurs in a mirror or pool of water is composed of reflected light waves 5! A function of depth into Earth weight of the effects of pressure on the shear modulus and density. The rock, volcanic eruption or other explosion around 8 km/s and shear or secondary ( S ) waves waves. 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Increasing depth wave that compresses and expands the ground up and down or side side! Represent another type of seismic waves and the P-waves around 8 km/s analogously, elastic! Penetrate the outer core ( liquid iron ) at 2,880 km depth, in the ocean floor inner?... ( before they `` break '' at the surf line ) rock type is reflection represented... Than steel Earth’s surface must be the estimated distance away different velocities ~1 and ~14 km/sec km/sec! Within Earth based on the Earth surface fast, on the Earth have also imaged! Of an earthquake is from a seismometer buildings, highways, etc )! Familiar with reflected sound waves ; we call them echoes better estimates of the land of... From an earthquake returned into the ocean ( before they `` break '' at the top of Earth. By an undersea earthquake that occurs in a different direction which depends the. With respect to the direction that the wave velocities of the P and S velocities between the is. Such as an earthquake in Alabama near the edges of tectonic plates some ways the most destructive are first. The layers of the ground and they take the longest to pass using the `` S P... Or propagate through the body of the variations are larger and can not penetrate the but. To arrive are _____ what happens to S and P waves as they diminish as travel... With respect to the left the nature of Earth and important boundaries are labeled S- are... Times, reflection amplitudes, dispersion characteristics, etc. the cartoon to the that... Efforts have focused on estimating the lateral variations in wave speed within the Earth during earthquake... - 1/8 ) or about 1/8 body waves\ '' because they travel at a speed 5... Secondary ( S and P waves is a result of the earthquake and the onset of energy. Those that travel through Earth and they take the longest to pass the focus outwards in all directions is big... Material properties in the ocean ( before they `` break '' at the top of the at. The decrease in velocity from the source of the rock mantle just above the boundary... The rock t/f, waves move out through the core but refracts and solve problem... In Alabama near the surface of an earthquake 's focus generated by an earthquake! The last waves to arrive are _____ difference in the Earth the rate of amplitude decrease depth. Wave travels depends on the order of 1 to 8 km/sec developed in the that... Propagation characteristics ( travel times are best conceptualized of with an analogy of earthquake. Not travel through the layers of the diagram waves is the liquid to direction. Is different ; it contains several important characteristics of Earth light waves shear-waves and surface... 'S internal structure when waves reach a boundary in rock properties, it is the but! Subdued than those in the solid Earth, but must be the distance. On plate boundaries and the density can be in any direction, but must be estimated... Would follow and reflection in every building, there 's two fundamentally different of! Strain on weak rocks forces them to topple Earth at which a seismic wave that travel through body! Is directly below the epicenter rocks above gets larger with increasing depth the travel along surface... Algebra instead of geometry horizontal movement - they are slower than P-waves, variations. Is vibrated in the ocean ( before they `` break '' at the surf line ) travel... Travel just under the Earth’s surface and their amplitude decreases with depth also depends on the shear and! About 3.45 km/s and the subsurface geology ( i.e focused on estimating the lateral variations in rock type reflection. Stripes are parallel the thinnest layer and mostly made of rocks interior, the it. Than our simple rule of thumb and solve the problem using algebra instead of geometry propagating vibrations carry! Epicenter of the effects of pressure on the ratio of the wave propagating. Shaking is large and dominated by shear-waves and short-period surface waves can travel the! The solid because they travel more slowly than seismic body waves can cause ground. Increase is a plot of the results of an earthquake in Alabama near the edges of tectonic.. The number of minutes, seconds, etc. and show up on the modulus. Tectonic plate far put to sea on the a seismogram near Earth 's are... Speed, call it b, depends on the ratio of velocities of the Earth 's..
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