Physics
Earthquake Shock Waves
Earthquake shock waves are seismic waves that travel through the Earth's crust following an earthquake. These waves can be classified into two main types: primary (P-waves) and secondary (S-waves). P-waves are faster and can travel through solids, liquids, and gases, while S-waves are slower and can only travel through solids. The study of these waves provides valuable insights into the Earth's interior and helps in understanding earthquake behavior.
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8 Key excerpts on "Earthquake Shock Waves"
eBook - PDFGeology
Earth in Perspective
- Reed Wicander, James Monroe, Reed Wicander(Authors)
- 2019(Publication Date)
- Cengage Learning EMEA(Publisher)
Key Concepts Review • Earthquakes are vibrations caused by the sudden release of energy, usually along a fault. • The elastic rebound theory is an explanation for how energy is released during earthquakes. As rocks on opposite sides of a fault are subjected to force, they accumulate energy and slowly deform until their inter- nal strength is exceeded. At that time, a sudden move- ment occurs along the fault, releasing the accumulated energy, and the rocks snap back to their original, unde- formed shape. • Seismology is the study of earthquakes. Earthquakes are recorded on seismographs, and the record of an earth- quake is a seismogram. • An earthquake’s focus is the location where rupture within Earth’s lithosphere occurs and energy is released. The epicenter is the point on Earth’s surface directly above the focus. • Approximately 80% of all earthquakes occur in the circum-Pacific belt, 15% within the Mediterranean– Asiatic belt, and the remaining 5% mostly in the inte- rior of the plates and along oceanic spreading ridges. • The two types of body waves are P-waves (primary waves), which are compressional (expanding and compressing) and the fastest seismic waves, traveling through all material, and S-waves (secondary waves), which are shear (moving material perpendicular to the direction of travel) and slower than P-waves and can travel only through solids. • There are several types of surface waves, but the two most important are Rayleigh waves (R-waves) and geothermal gradient Earth’s temperature increase with depth; it averages 25°C/km near the surface but varies from area to area. Copyright 2021 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience.
eBook - PDF- Dentcho Ivanov(Author)
- 2015(Publication Date)
- CRC Press(Publisher)
1 Origin of Earthquakes and Seismic Waves During a disturbance deep in the Earth’s crust or mantle such as faults, tectonic plate shifts, volcano eruptions or underground explosions, a large amount of energy is released as a result of which seismic longitudinal (P-waves), shear (S-waves), and surface waves propagate, causing an earthquake. This cause-and-effect process seems simple and easy to understand. However for describing step by step the generation and propagation of various types of seismic waves, many factors should be taken into consideration. Deep seismic disturbances cannot be directly studied, but observations of man-caused explosions causing tremors point to the generation of short, powerful, pressure pulses reaching Mega or even Giga Pascal ranges in the focus of the earthquake. However, a pressure pulse is not a wave. A wave is a periodic transient motion in a medium of propagation that requires a continuous driving force. The question is how a pressure pulse becomes the origin of a seismic wave? Of course, in an earthquake’s focus not one, but a raw of pressure pulses can occur. They follow each other at random intervals of time and the question of the origin of seismic waves is still relevant. In this chapter we will discuss the mechanism of the generation of various kinds of transient seismic waves from a high energy pressure pulse that are able to travel long distances in a heterogeneous, dispersive, and dissipative media causing what we call an earthquake. 1.1 Statement of the problem Seismic waves are usually assumed to be elastic waves that propagate in the Earth’s body. When an elastic wave propagates in some material it applies 8 Seismic Resistant Design and Technology periodic mechanical force per unit of surface F 1 (stress) resulting in a periodic deformation (strain). The material reacts to the deformation with a restoring force – F 2 trying to bring the material’s initial shape back to its equilibrium state.
eBook - PDFPhysical Geology
The Science of Earth
- Charles Fletcher(Author)
- 2017(Publication Date)
- Wiley(Publisher)
Earthquake magnitude is a way to measure the amount of destruction it causes. Earthquake intensity is a measure of the physical effects of shaking and how much damage it caused. Expand Your Thinking 24. What method is typically used by the media to characterize an earthquake? Why? LO 11.9 Describe how seismic wave characteristics result in P-wave and S-wave shadow zones. One of the great discoveries in the science of geophysics was that seismic waves from earthquakes can be used to improve our understanding of Earth’s interior. Seismology Is the Study of Seismic Waves to Improve Our Understanding of Earth’s Interior 341 FIGURE 11.25 Seismic waves both reflect and refract when they encounter the boundary between two materials of differing density. Earthquake focus Earthquake focus Reflected wave Less dense rock More dense rock Refracted wave bent up Reflected wave More dense rock Less dense rock Refracted wave bent down Sunlight refracts when it passes from the air into water. Which way does a light ray refract: upward or downward? Within Earth’s interior, seismic wave velocities generally increase with depth because rock density usually increases with depth and waves travel faster in denser material. As a result, waves are continually refracted along curved paths (called ray paths) that arc gently back toward Earth’s sur- face (Figure 11.26a). However, should there be a sudden change in rock density, the wave velocity will change sud- denly in response; such an interface is called a discontinuity. Discontinuities found at well-mapped depths in the interior of the planet help us mark boundaries between various layers, such as core, mantle, and crust. P waves change the volume of material that they encounter. Hence, any material that resists changing volume, including most liquids and solids, will transmit P waves rather than absorb them.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Academic Studio(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter 5 Seismic Wave Body waves and surface waves ________________________ WORLD TECHNOLOGIES ________________________ p-wave and s-wave from seismograph Seismic waves are waves of energy that travel through the earth or other elastic bodies, for example as a result of an earthquake, explosion, or some other process that imparts low-frequency acoustic energy. Seismic waves are studied by seismologists and geophy-sicists. Seismic wavefields are measured by a seismograph, geophone, hydrophone (in water), or accelerometer. The propagation velocity of the waves depends on density and elasticity of the medium. Velocity tends to increase with depth, and ranges from approximately 2 to 8 km/s in the Earth's crust up to 13 km/s in the deep mantle. Earthquakes create various types of waves with different velocities; when reaching seismic observatories, their different travel time enables the scientists to locate the epicenter. In geophysics the refraction or reflection of seismic waves is used for research of the Earth's interior, and artificial vibrations to investigate subsurface structures. Types of seismic waves There are two types of seismic waves, body waves and surface waves . Other modes of wave propagation exist than those described in this article, but they are of comparatively minor importance for earth-borne waves, although they are important in the case of asteroseismology, especially helioseismology. ________________________ WORLD TECHNOLOGIES ________________________ Body waves Body waves travel through the interior of the Earth. They follow raypaths refracted by the varying density and modulus (stiffness) of the Earth's interior. The density and modulus, in turn, vary according to temperature, composition, and phase. This effect is similar to the refraction of light waves.
eBook - PDFThe Solid Earth
An Introduction to Global Geophysics
- C. M. R. Fowler(Author)
- 2004(Publication Date)
- Cambridge University Press(Publisher)
Chapter 4 Seismology Measuring the interior 4.1 Waves through the Earth 4.1.1 Introduction Seismology is the study of the passage of elastic waves through the Earth. It is arguably the most powerful method available for studying the structure of the interior of the Earth, especially the crust and mantle. There are various other geo-physical techniques, including the study of gravity, magnetism and the electrical properties of the Earth, which can be applied on scales ranging from the planet as a whole to large regions or small areas or even individual rock samples (Telford et al . 1990; Dobrin and Savit 1988); but seismology is probably the most widely used and the most informative. This chapter discusses the methods by which we obtain information about the interior of the planet from the study of elastic waves passing through the Earth. Earthquake seismology is perhaps the best technique for investigating the Earth’s interior. The study of earthquakes was of major significance in giving us our understanding of plate tectonics: earthquake foci have delineated the bound-aries of the tectonic plates very accurately. It has also helped us to map the internal structure of our planet. The distribution of earthquakes shows us where the Earth is active (mostly near the surface), and the passage of seismic waves through the Earth allows us, as it were, to CAT-scan its interior. When an earthquake or an explosion occurs within the Earth, part of the energy released takes the form of elastic waves that are transmitted through the Earth. These waves can be detected by an instrument called a seismograph , 1 consisting of a seismometer , which measures and amplifies the motion of the ground on which is rests, and a recorder, which transfers the data onto paper, magnetic tape or disc. The speed with which these elastic waves travel depends on the density and elastic moduli of the rocks through which the waves pass.
- Tanjina Nur(Author)
- 2019(Publication Date)
- Arcler Press(Publisher)
Waves undergo diffraction, in addition to the refraction and reflection. Similarly as sound bends around the corner of a building, letting us to hear the things we cannot see, seismic waves bend around “obstacles” such as the earth’s core (Figure 1.6). Introduction: Seismology, Earthquakes, and Structural Engineering 7 Figure 1.6. Modern weather predictions. Source: https://en.wikipedia.org/wiki/Weather_forecasting#/media/File: 2005– 09–22–10PM_CDT_Hurricane_Rita_3_day_path.png The basic data for these studies are seismograms, records of the motion of the ground resulting from the arrival of refracted, reflected, and diffracted seismic waves. In order to determine the travel time, seismograms integrate precise timing. The response of the seismometer is known, therefore the seismogram can be linked to the real ground motion. Three different components (east-west, north-south, and up–down) are typically recorded as the ground motion is a vector. Seismograms contain beneficial and interesting information, hence, even though initially they appear to be simply wiggly lines. To exemplify the usage of seismology in the analysis of earth structure, consider an example of the time when a seismogram in Colorado recorded a magnitude 6 earthquake in Colombia approximately some 4900 kilometers away. Phases are defined as several seismic wave arrivals and they are recognized using a simple terminology which explains the path each followed from the base to the receiver (Figure 1.7). Seismology, Earthquake Engineering and Structural Engineering 8 Figure 1.7. Seismic waves. Source: https://upload.wikimedia.org/wikipedia/commons/c/c8/Earthquake_ wave_paths.svg Seismic waves are divided into two type’s, i.e., compressional waves or P where material moves to and fro in the direction in which the wave propagates and the other one is S or shear waves, where material moves at right angles to the propagation direction.
eBook - PDF- Zeeya Merali, Brian J. Skinner(Authors)
- 2012(Publication Date)
- Wiley(Publisher)
S wave The second kind of body wave to be detected by a seismograph. shear wave A seis- mic body wave in which rock is sub- jected to side-to-side or up-and-down forces, perpendicular to the direction of travel; S wave or sec- ondary wave. 248 CHAPTER 8 Earthquakes and Earth’s Interior detected by a seismograph. Figure 8.12A shows a typical seismogram, in which the P waves’ arrival is first, followed by the arrival of the S waves, and finally by that of the surface waves. There are two kinds of surface waves, and both are named for the English mathemati- cians who first predicted their existence. Rayleigh waves, named for Lord Rayleigh, cause Earth’s surface to move up and down, like a wave on the ocean. Love waves, named for A. E. H. Love, cause the surface to shake in a sideways motion, but do not cause any vertical motion. Surface waves are responsible for much ground shaking and structural damage during major earthquakes. LOCATING EARTHQUAKES The epicenter, or surface location, of an earthquake can be determined through simple calculations using travel-time curves from at least three seismographs that have recorded the quake. The first step is to find out how far each seismograph is from the source of the earthquake. The greater the distance traveled by the seismic waves, the more the S waves will lag behind the P waves. Thus, the lag time between the P and S waves on a seismo- gram (see Figure 8.12B) provides seismologists with the necessary distance information. After determining the distance from each seismo- graph to the source of the earthquake, the seismologist draws a circle on a map, with the seismic station at the center of the circle. The radius of the circle is the dis- tance from the seismograph to the focus. It is a circle be- cause the seismologist knows only the distance, not the direction.
eBook - PDFThe Seismic Cycle
From Observation to Modeling
- Frederique Rolandone(Author)
- 2022(Publication Date)
- Wiley-ISTE(Publisher)
This characteristic is due to the fact that the majority of the path traveled by the direct teleseismic waves is in the Earth’s lower mantle (see Figure 1.3), which is relatively homogeneous. On the contrary, body waves that undergo multiple reflections, and even more surface waves, strongly interact with the Earth’s superficial structure. This superficial structure, where there are strong gradients of seismic velocity, causes complexities in the wave field (especially “triplications”, see section 4.3 in [SHE 19]). Furthermore, the most superficial layers have high lateral variability in their elastic parameters, and modeling of surface waves, even at low frequencies (down to 0.01Hz), therefore requires a three-dimensional computation of the wave field. We now consider a horizontal rupture propagation, starting from the hypocentral point ξ h (this rupture direction hypothesis is not required for a deep earthquake, as the direct P wave can be analyzed alone, without any interference from depth phases). The case of a point source, with no explicit propagation of the rupture, is also included in this configuration. This horizontal propagation model may appear restrictive, however it makes it possible to represent a subduction earthquake, whose plane has a shallow dip, by an extended fault [1.12], or a large strike-slip earthquake by a line source Determining the Main Characteristics of Earthquakes from Seismological Data 17 [1.13]. The travel times then do not depend on the vertical slowness (different for the P , pP and sP waves) and are written in an approximation of plane waves: T (k) (x, ξ) = T (k) (x, ξ h ) − s P H .(ξ − ξ h ) [1.16] At this stage, it is useful to express the following relations in the Cartesian basis (e 1 , e 2 , e 3 ) with e 1 , e 2 , e 3 , respectively, in the directions north, east and vertical downward.
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