SD-Lecture12-Strong-Ground-Motions

SD-Lecture12-Strong-Ground-Motions - CEG CEG-5065C Soil...

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Unformatted text preview: CEG CEG-5065C Soil Dynamics 5065C Soil Dynamics Lecture Lecture 12 12 Strong Ground Motions Luis A. Prieto-Portar 2009 The first seismograph was invented in 132 A.D. by the Chinese astronomer and mathematician Chang Heng. He called it an "earthquake weathercock. Each of the eight dragons had a bronze ball in its mouth. Whenever there was even a slight earth tremor, a mechanism inside the seismograph would open the mouth of one dragon. The bronze ball would fall into the open mouth of one of the toads, making enough noise to alert someone that an earthquake had just happened. Imperial watchman could tell which direction the earthquake came from by seeing which dragon's mouth was empty. In 136 A.D. a Chinese scientist named Choke updated this meter and called it a "seismoscope." Columns of a viscous liquid were used in place of metal balls. The height to which the liquid was washed up the side of the vessel indicated the intensity and a line joining the points of maximum motion also denoted the direction of the tremor. As it moves, the instrument records displacements of case relative to the mass as they change with time. The record is known as a seismogram. Seismographs are the principal instruments of the researchers who study earthquakes and those who map the Earth's inside. The Earth's motion during an earthquake is measured in terms of its movement relative to some object that remains independent of the ground motion. In a seismograph, this object is a seismometer which consists of a mass suspended on springs within a case. During an earthquake the mass remains still while the case around it moves with the ground. Nanometrics Trillium Compact. Standing at just 128 mm (5.04) tall with a diameter of only 90 mm (3.54), Trillium Comp act combines the superior performance of a broadband seismometer with the installation convenience of a rugged geophone. The instrument incorporates a symmetric triaxial force feedback sensor with a response flat to velocity from 120 seconds to 100 Hz. Scientists no longer need to compromise on performance in applications demanding small, highly portable seismometers. Bandwidth -3 dB points at 120 s and 100 Hz. Clip level 26 mm/s from 0.1 Hz to 10 Hz. Extremely low power consumption of just 160 mW. No mass lock, no mass centering required. The Nanometrics Titan is a force balance accelerometer providing exceptional performance over a wide frequency range from DC to 225 Hz. The Titan is aimed at higher precision strong motion and structural monitoring applications, where scientists and engineers require exceptional dynamic range combined with ultra-low self-noise performance comparable to that of some broadband seismometers....
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SD-Lecture12-Strong-Ground-Motions - CEG CEG-5065C Soil...

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