TAILIEUCHUNG - Basic Geotechnical Earthquake Phần 5

Năng lực của động đất được trải dài trong một diện tích lớn, và trong các trận động đất lớn có thể trải hết toàn cầu. Các nhà khoa học thường có thể định được điểm mà các sóng địa chấn được bắt đầu. Điểm này được gọi là chấn tiêu. Hình chiếu của điểm này lên mặt đất được gọi là chấn tâm. | 54 Basic Geotechnical Earthquake Engineering Selection of Design Earthquake The selection of a design earthquake may be based on a Known design-level and maximum credible earthquake magnitudes. These are associated with a fault whose seismicity has been estimated. b Specification of probability of occurrence of the earthquake for a given life of the structure such as having a 10 percent chance of being exceeded in 50 years . c Specification of a required level of ground motion. This specification is available in the code provision. d Fault length empirical relationships. The original magnitude scale proposed by Gutenburg and Richter is calculated from a standard earthquake. The standard earthquake is the one which provides a maximum trace amplitude of 1 mm on a standard Wood Anderson torsion seismograph at a distance of 100 km. Magnitude is the log10 of the ratio of the amplitude of any earthquake at the standard distance to that of the standard earthquake. Each full integer step in the scale two to three for example represents an energy increase of about 32 times. Because of the history of seismology there are actually several magnitude scales. Modern earthquakes are described by the moment magnitude Mw. Earlier earthquake events may be described by any of a number of other scales. Fortunately the numerical values are usually within to magnitude units for magnitudes up to about . For larger events the values deviate significantly. Intensity In areas where instrumental records are not available the strength of an earthquake has usually been estimated on the basis of the modified Mercalli MM intensity scale. The MM scale is a number based mostly on subjective description of the effects of earthquakes on structures and people. Intensity is a very qualitative measure of local effects of an earthquake. Magnitude is a quantitative measure of the size of the earthquake at its source. The MM intensity scale has been correlated with peak horizontal ground

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