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1、6.1 Earthquake-Induced Vibration of Structures,Topics,Seismicity and Ground Motions Influence of Local Site Conditions Response of Structures to Ground Motions,Seismicity and Ground Motions,The earth is made up of four layers, the crust, the mantle, the outer core, and the inner core.,Lithosphere is
2、 broken into a number of tectonic plates. Tectonic plates are rigid, relatively cool slabs about 100 km thick consist of the earths crust and lithosphere.,Tectonic plates 构造板块float on the molten mantle （asthenosphere软流圈）of the Earth and move relative to one another at the rate of 10 to 100 mm/year.,
3、The 6,000-km-plus journey of the India landmass (Indian Plate) before its collision with Asia (Eurasian juE5reiViEn欧亚大陆Plate) about 40 to 50 million years ago. India was once situated well south of the Equatori5kweitE, near the continent of Australia.,If the plates are pushing together, one plate te
4、nds to dive under the other and, depending on the density of the material, it may resurface in the form of mountains and valleys.,*In some cases, the plate margins are moving away from one another. In those cases, molten rock appears from deep in the Earth to fill the gap, often manifesting itself a
5、s volcanoes.,*Another possibility is that the plate boundaries will slide sideways past each other, essentially retaining the local surface area of the plate.,pull apart,平滑断层 ，横向断层,*The basic mechanism causing earthquakes in the plate boundary regions appears to be that the continuing deformation of
6、 the crustal structure eventually leads to stresses/strains which exceed the material strength. Rocks fracture. These fractures are called faults. *A rupture will then initiate at some critical point along the fault line and will propagate rapidly through the highly stressed material at the plate bo
7、undary,It is believed that approximately three quarters of the worlds earthquakes are accounted for by this rubbingstrikingslipping mechanism, with ruptures occurring on faults on boundaries between tectonic plates. Such earthquakes are referred to as interplate earthquakes 边缘地震.,Intraplate earthqua
8、kes板内地震,*Earthquakes also occur at locations away from the plate boundaries. Such events are known as intraplate earthquakes板内地震 and they are much less frequent than interplate earthquakes.,*Earthquake-occurrence maps usually indicate the location of various epicenters of past earthquakes *these epi
9、centers are located (确定 ，找出) by seismological 7saizmE5lCdVikEl adj. 地震学上的 analysis of the effect of earthquake waves on strategically located receiving instruments called seismometerssaiz5mCmitE n. 测震仪 .,Energy spreads out through the earth in different wave types P-Waves S-Waves Surface Waves,*When
10、 an earthquake occurs, several types of seismic wave are radiated from自.发出the rupture. The most important of these are the body waves (primary (P) and secondary (S) waves).,Magnitude of the earthquake,*The total strain energy released during an earthquake is known as the magnitude of the earthquake
11、震级 and it is measured on the Richter scale,*Richter scale is defined quite simply as the amplitude 振幅 of the recorded vibrations on a particular kind of seismometer located at a particular distance from the epicenter.,Modern seismometers (or seismographs) provide digitized 5didVitaiz将资料数字化or graphic
12、al records of earthquake-induced accelerations加速度 in both the horizontal and vertical directions at a particular site.,Accelerometers provide records of earthquake accelerations and the records may be appropriately integrated to provide velocity records and displacement records. Peak accelerations,
13、velocities, and displacements are all in turn significant for structures of differing stiffness.,The recording of the acceleration of the ground during an earthquake.,Acceleration, Velocity, Displacement,Intensity,A measure of the effect, or the strength, of an earthquake hazard at a specific locati
14、on based on observed human behavior and structural damage. *The local intensity of a particular earthquake is measured on the subjective Modified Mercalli scale which ranges from 1 to 12,唐山7.8级地震等震线图,唐山7.8级地震等震线图,Modified Mercalli scale,A means by which damage may be assessed after an earthquake. al
15、beitC:l5bi:It虽然 subjective and qualitative, regions of varying seismic risk may be identified. used to assist in the delineation dI9lInIeIFEn 描绘 of these regions.,Influence of Local Site Conditions,Local geological 地质的 and soil conditions may have a significant influence on the amplitude and frequen
16、cy content of ground motions. Interaction between the bedrock earthquake motion and the soil column will modify the actual ground accelerations input to the structure The soil properties in the proximityprCk5simiti 邻近of the structure contribute significantly to the effective stiffness of the structural foundation. strength (and response) of the local soil under earthquake shaking may be critical to the overall stability of the structure.,Response of Structures to Ground Mo
