SD-Lecture02-Seismology

SD-Lecture02-Seismology - CEG CEG-5065C Soil Dynamics 5065C...

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Unformatted text preview: CEG CEG-5065C Soil Dynamics 5065C Soil Dynamics Lecture #02 Lecture #02 Geophysics: Elementary Seismology o Seismic waves o The internal structure of the Earth o Continental drift o Plate tectonics o Plate boundaries o Faults o Elastic rebound theory o Earthquake recurrence Luis Prieto-Portar 2009 Understanding earthquakes requires understanding the media in which they take place: the Earths crust and the upper mantle. This study commences with the science of Seismology (Greek seismos means earthquake and logos means science). Seismology currently provides a basic understanding of the mechanics of earthquakes and the rates of their occurrences around the world. Richard Oldham of Great Britain was the first physicist to study seismology in 1902. A few years later in 1909, the Croatian physicist Andrija Mohorovicic use it to map the boundary between the mantle and the crust (now known as the Moho discontinuity). Basic Geophysical facts about the Earth. The Earth is not exactly spherical: its equatorial diameter is 12,740 km versus the polar diameter of 12,700 km. The difference is due to the higher velocities due to the earths rotation. The earth weighs 5.4 x 10 21 tons, so that the average specific gravity is about 5.5. The specific gravity of surface rocks range from 2.7 to 3. Therefore, the deeper mass must have much higher specific gravities. Seismology has studied the internal structure of the earth using large earthquakes that produce enough energy to shake most parts of the earth surface. Seismic Waves. Earthquakes produce body waves and surface waves . Body waves travel though the interior of the earth as p-waves and s-waves . P-waves are also known as primary , compressional or longitudinal waves . These waves involve successive compression and rarefication of the material through which the waves pass. Sound waves are similar to P-waves, and the material particles travel in the same direction as the wave. Also like sound waves, p-waves travel through both solids and fluids. P-waves. S-waves are also known as secondary , shear or transverse waves . They move through materials causing transverse deformations. The direction of movement of particles is transverse to the direction of travel of the wave. S-waves have two orthogonal components: the SV (vertical) and the SH (horizontal). The speed of S-waves varies with the stiffness of the material. Since fluids do not have shear strength, S-waves can not travel through them. Earth solids are stiffest in compression, therefore the p-waves travel faster than other waves, and are the first to arrive at a recording station. S-waves. Surface-waves are the type that ensue when the body waves emerge at the surface....
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SD-Lecture02-Seismology - CEG CEG-5065C Soil Dynamics 5065C...

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