Seismic History

Seismie analysis is carried out for all important engineering structures such as dams, bridges and nuclear power plants. For regions where these are to be located the likely expectations of an earthquake as well as the extent of its magnitude must be assessed on the basis of the seismic history and the earthquake records of the region (Figures 14.12 to Figure 14.16). Based on these and other factors such as soil stratification, site dependent response spectra are determined. These are the RRS for equipment mounted... 

Qu, H. 2011. Selections of ground motions in seismic history analysis for bridges with high piers. Dalian Dalian Maritime University. 

Details about the occurrence, magnitude and effects of earthquakes through time can be obtained by carrying out long-term seismic monitoring. In the absence of suitable instrumental data, the seismic history of an area may be established by interpretation of historical, archaeological and geological evidence. 

The number of occurrences over a given time interval are independent of the number of earthquakes that occur in any other time interval (i.e., the system has no memory from past seismic history, while there are other time-dependent models that keep track of occurred events). 

Paleoseismic trenching plays an important role in the reconstruction of a seismic history and makes an invaluable contribution to seismic risk assessments of a region (Giirpmar 2005). However, paleoseismology has advantages and limits like any other applied techniques. It is important to know all these aspects of paleoseismic studies to construct a sound project and solve a scientific problem. 

The reconstruction of the seismic history from well-chosen trench sites provides reliable information for seismic risk assessments. 

In regions with seismic history, accelerometers shall be used to detect any seismic activity, and shutdown the reactor when necessary. 

Now that it is possible to establish test facilities in a laboratory to simulate the time history of an earthquake seismic tests are conducted by creating the ground movements in the test object. Other methods, such as by analysis or by combined analysis and testing, are also available. Refer to IEEE 344 and lEC 60980 for more details. For this purpose a shake table, able to simulate the required seismic conditions (RRS) is developed on which the test object is mounted and its performance observed under the required shock conditions. Since it is not easy to create such conditions in a laboratory, there are only a few of these facilities available. The better equipped laboratories are in Japan, the USA, the UK, Greece, Germany, India and China. In India the Earthquake Engineering Department (EQD) of the University of Roorkee (UoR) is equipped with these facilities. 

This is the duration sufficient to simulate seismic conditions. It depends upon the algorithm used to find time history from the reqtiired response spectrum (RRS). The minimum duration of a strong movement, as recommended by IEEE 344, is 15 seconds as illustrated in Figure 14.24(b). This will require a total duration of the order of 20 seconds, including the movement s times of rise and time of decay. A duration of 20.48 seconds, as noted in the figure, is typical of a test conducted at University of Rorkee. The following tests may be conducted ... 

The Seismic Safety Margins Research Program developed a computer code called SMACS (Seismic Methodology Analysis Chain with Statistics) for calculating the seismic responses of structures, systems, and components. This code links the seismic input as ensembles of acceleration time histories with the calculations of the soil-structure interactions, the responses of major structures, and the responses of subsystems. Since uses a multi-support approach to perform the time-history response calculations for piping subsystems, the correlations between component responses can be handled explicitly. SMACS is an example of the codes that are available for calculating seismic response for PSA purposes. 

The potential for natural disaster, based on die history and knowledge of the region and eaitli structure, should be indicated in die plan. Items such as seismic fault zones and flood plains, and potentials for hurricanes and winter storms should be noted. 

Raw data gathered from seismic surveys must be processed to compensate for and to remove a variety of distortions unwanted noises created by weathered near-surface rocks, normal time delays, and echoing by rebounding acoustic waves—to provide the clearest possible image of the strata below. Computers can restore these distortions in a fraction of the time that was formerly required to adjust the data painstakingly by hand. Advanced techniques not only permit presentations in three dimensions, but also in color, and to create contour maps and models of subterranean features. However, even with the use of sophisticated tools, there remains a large measure of uncertainty. History has shown repeatedly that a prospective area rejected by one petroleum firm has been accepted by another and proved to be successful. 

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