SD-Lecture03-Earthquakes

SD-Lecture03-Earthquakes - CEG CEG-5065C Soil Dynamics...

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Unformatted text preview: CEG CEG-5065C Soil Dynamics 5065C Soil Dynamics Lecture #03 Lecture #03 Earthquakes efinitions o Definitions o Distance to the epicenter o Intensity of an earthquake o Magnitude of an earthquake o Duration of an earthquake o Amplitude of the acceleration Luis Prieto-Portar 2009 Definitions. ocus or Hypocenter Focal depth 1. Shallow-focus : 0 to 70 km deep; (constitute about 75% of all earthquakes); 2. Intermediate-focus : 70 to 300 km deep; (constitute about 22% of all earthquakes); Epicenter Focal or Hypocentric distance Focus or Hypocenter point of rupture of a fault 3. Deep-focus : 300 to 700 km deep; (constitute about 3% of all earthquakes). Epicentric distance L The effective distance to the causative fault. This distance is the epicentric distance should be to the midpoint of the fault length. Length L of the fault rupture. epicentric distance Length L of the fault rupture. epicentric distance The primary cause of seismic waves (vibrations) are, (1) the sudden dislocations or rupture and changes within the earth’s crust plates due to their movements against each other, (2) volcanic eruptions, and (3) deep artificially induced explosions. In bedrock, the p-wave velocity range from 3 to 8 km/sec, whereas the s-wave velocity ranges from 2 to 5 km/sec. During an earthquake, the sudden changes in the sea floor at depth (large rising and dropping) set a massive wave in the water in motion. As the wave approaches a land mass, the deep sea floor transitions gradually to a shallower floor. Since the wave has a constant mass, this change causes the wave height to increase. Also, its velocity decreases due to the increased friction with the shallower floor. Sea waves are called tsunami (which means “sea wave” in Japanese). Other synonymous terms are tidal wave and surface-water wave . Locating the Epicenter of the Earthquake. Seismic waves are measured with a seismometer . The seismometer measures the actual displacement of the ground with respect to a fixed reference point. At least three seismographs are needed to clearly define the position of the earthquake’s epicenter. The distance d from the seismometer and the focus of the earthquake, 1 1 p s t d v- Δ =- where & t p-s is the time difference between the first p-wave and the first s-wave received at the seismometer. s p v v Using three seismographs to determine the location of the earthquake’s epicenter. Intensity. The oldest measure of earthquake size is intensity . In the USA we use the Modified Mercalli Scale , developed by the Italian seismologist Mercalli in 1931. It divides the intensity into an arbitrary scale of 12 levels of intensity. The comparison between the Richter magnitude scale and the Modified Mercalli intensity scale is approximately as follows, A brief list of some recent major earthquakes is, 28 March 2005 Northern Sumatra (Indonesia) 8.7 26 December 2004 West coast of northern Sumatra 9.0 23 December 2004 Macquarie Island, Pacific Ocean 8.1 17 November 2003...
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SD-Lecture03-Earthquakes - CEG CEG-5065C Soil Dynamics...

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