Seismic waves

The magnitude of shocks and vibrations caused by an earthquake is the measure of energy released (E) at the focal point in the form of seismic waves. It is measured on a Richter scale. An American seismologist called... 

This defines the focus, i.e, the point of source within the earth s body, from where the stored energy is released. It causes an earthquake and travels outwards in the form of seismic waves to the earth s surface. 

Small or moderate thickness of soil Where there is some soil, ground displacement will be greater and seismic waves will pass through the soil. There may be some settlement of the structure due to soil compaction. While the structure will now be less subject to seismic forces, this may prove to be a worse case, as in addition to the structure being subject to almost the full intensity of the earthquake, there may also be settlement of the soil, which may result in settlement of the structure and cause it to collapse or develop cracks. 

More complicated numerical methods, such as the Runge-Kutta method, yield more accurate solutions, and for precisely formulated problems requiring accurate solutions these methods are helpful. Examples of such problems are the evolution of planetary orbits or the propagation of seismic waves. But the more accurate numerical methods are much harder to understand and to implement than is the reverse Euler method. In the following chapters, therefore, I shall show the wide range of interesting environmental simulations that are possible with simple numerical methods. 

Addnl Refs A) Collective, "Air Burst in Blast Bombs . A Compilation of Papers Presented at NDRC Div 2 Symposium, OSRD 4923 (1945) B) Collective, "Underground Explosion Test Program , Final Rept, Vol II, "Rock , Engineering Research Associates, Division of Remington Rand Inc, 30 April 1953 (Conf) (Not used as a source of information) C) G.R. Pickett, "Seismic Wave Propagation and Pressure Measurements Near Explosions , Quarterly of the Colorado School of Mines 50(4) (Oct 1955) D) W.E. Deal, "Shock Hugoniot in Air , JApplPhys 28, 782-84(1957) E) Dunkle s Syllabus, Session 26, 23 Apr 1958, pp 313-18 F) Dunkle s Syllabus, Suppl to Section 26 (1961) G) Dunkle, private communication,... 

The velocities deduced for seismic waves emanating from the core revealed that it must consist of very dense material, but its composition remained a mystery. However, cosmochemical reasoning provided important constraints. The core comprises approximately... 

Blasters can use this equation to estimate the peak particle velocity of a seismic wave or they can use the graph shown in Fig 2. For example Determine the typical peak particle velocity from a normally confined blast with a maximum charge-weight-per-delay-period of 400 lbs at a distance of 1000 ft from the receiving site. The scaled distance, R/W 4 = 1000/40044 = 50 corresponds to a peak particle velocity of 0.31 ips on the graph in Fig 2... 

It should be emphasized that the expression given in the above equation relating the peak particle velocity, charge-weight-per-delay-period, and distance provides typical values only for planning blasting projects in the absence of seismic data. For further detailed information on blasting situations where the above equation is not applicable, the measurement and interpretation of seismic waves, and techniques necessary to reduce blast vibration, the reader is referred to Refs 1,3 4 Effects of Seismic Waves on Structures. 

The intensity of seismic motion that can be tolerated by various kinds of structures must be established before acceptable charge weights at various distances can be determined. Obviously, the level of motion required to damage a structure depends upon its construction. For example, a steel-framed warehouse can tolerate a more. intense seismic wave than a residential structure with plaster walls. Because plaster is the weakest of the most commonly used materials of construction, and because of the prevalence of such structures, most damage criteria are based oh this type of structure... 

Seismic Waves from a Shot-Generated Cavity , Suppl Note, Geological Survey, Menlo Park, Ca (1967) 50) L. Rudlin et al, The Early... 

Elastic constants of minerals are the key to understanding geophysical properties of the Earth s interior. Bulk modulus and rigidity parameters, for example, influence the velocities of seismic waves through the Earth. Numerous experi-... 

Tanks in the Whittier area suffered great damage from the seismic wave (Fig.2.2). A witness who tried to escape by car crossed the tank yard about one minute after the start of the earthquake when the top of a 53,500bbl capacity gasoline tank broke and the contents blew out. Fearful that the car would catch fire, he left the car and ran to the exit. Just as he left the tank yard, the seismic wave came and the explosion occurred 4 3. ... 

The rupture of the top of the gasoline tank caused the contents to be blown out and explode, and four tanks (2 for gasoline, 1 for kerosene, and 1 for diesel oil) caught fire. Eleven tanks were moved by the seismic wave, most irreparably damaged 4 21. ... 

The very high apparent seismic wave velocities of about 9 km/sec obtained for the layer below the crust imply that the lunar mantle is differentiated and its composition varies with depth. 

Kuster, G. T. and Toksoz, M. N., "Velocity and Attenuation of Seismic Waves in Two-Phase Media Part 1. Theoretical Formulations and Part 2. Experimental Results," Geophysics. 1974,... 

Most seismological constraints on mantle composition are derived by comparison of values of seismic wave velocities inferred for particular regions within the Earth to the values measured in the laboratory for particular minerals or mineral assemblages, with such comparisons being made under comparable regimes of pressure (P) and temperature (T). The primary parameters of interest, then, are the compressional (or P-) wave velocities (Vp) and the shear (or S-) wave velocities (Ej). These wave velocities are simply related to the density (p) and to the two isotropic elastic moduli, the adiabatic bulk modulus (Ks)... 

This isothermal bulk modulus (Kj) measured by static compression differs slightly from the aforementioned adiabatic bulk modulus (X5) defining seismic velocities in that the former (Kj) describes resistance to compression at constant temperature, such as is the case in a laboratory device in which a sample is slowly compressed in contact with a large thermal reservoir such as the atmosphere. The latter (X5), alternatively describes resistance to compression under adiabatic conditions, such as those pertaining when passage of a seismic wave causes compression (and relaxation) on a time-scale that is short compared to that of thermal conduction. Thus, the adiabatic bulk modulus generally exceeds the isothermal value (usually by a few percent), because it is more difihcult to compress a material whose temperature rises upon compression than one which is allowed to conduct away any such excess heat, as described by a simple multiplicative factor Kg = Kp(l + Tay), where a is the volumetric coefficient of thermal expansion and y is the thermodynamic Griineisen parameter. 

Experimentally, the bulk modulus is the simplest parameter to measure, but the seismological parameters of primary interest, Vp and Vg, both involve the shear modulus as well. It is convenient, therefore, to define a new parameter, the bulk sound velocity (V ), which eliminates all dependence upon the shear modulus (G) through a judicious linear combination of the squares of the two seismic wave velocities =... 

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