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Environmental Health Emergencies, Disasters, and Terrorism
Published in Herman Koren, Best Practices for Environmental Health, 2017
An earthquake occurs when two sides of a fault slip suddenly against each other and produce vibrations. A fault is a fracture in the rock or the crust of the Earth where the two sides are displaced against each other in a minor or major way. The slippage causes a shaking or vibration because of a sudden release of stored elastic energy from within the Earth and seismic waves (waves of energy) may be produced. Seismic shaking is not uniform. As the waves approach the ground surface and potentially travel through areas of loose soil, the amplitude of the waves will increase producing larger waves that may be far more damaging to structures than the original waves. Other earthquake hazards include ground failure and/or rupturing of the fault resulting in the creation of cracks, settlement of the soil, vertical shifting of the ground after large earthquakes, soil liquefaction, where the soil, in an area of sand and silt as well landfill areas, takes on the characteristics of a liquid during the shaking of an earthquake and flows like a liquid; this can cause enormous damage to any structures that are within this area. Aftershocks, which may occur for periods of time after the initial major shock, can be extremely damaging to structures and can cause additional injuries and deaths. (See endnotes 6, 8, 10.) Thousands of faults are currently present in California, the United States, and the rest of the world. There are thousands of earthquakes each year throughout the world.
Earthquake activity
Published in F.G. Bell, Geological Hazards, 1999
Initial movement may occur over a small area of a fault plane, subsequently being followed by slippage over a much larger surface. Such initial movements, which represent preliminary shattering of small obstructions along a fault zone, account for the foreshocks that precede an earthquake. When these have been overcome the main movement occurs, but complete stability is not restored immediately. The shift of strata involved in faulting relieves the main stress but develops new stresses in adjacent areas. Because stress is not relieved evenly everywhere, minor adjustments may arise along the fault plane and thereby generate aftershocks. The decrease in the strength of the aftershocks is irregular, and occasionally they may continue for a year or more after the principal shocks.
Microseismic monitoring technologies for deep mining
Published in Xia-Ting Feng, Rock Mechanics and Engineering, 2017
Short-term seismic hazard assessment (SHA) refers to a time scale of minutes to a day. Short-term SHA can be broken down into several steps: Determine the required sensitivity and location accuracy.Delimit datasets in space and time.Select the seismic parameters to be analyzed. Many parameters may be used, such as the seismic activity, b-value, Energy Index and Cumulative Apparent Volume. Since the removal of rock at depth is the driving force of mine seismicity, seismic activity is closely correlated with mining activity and thus should be taken into account when analyzing the seismicity data.Select the non-seismic parameters to be analyzed. These are similar to those used for medium-term SHA.Identify signals that might indicate a change in seismic hazard. An example is shown in Figure 7.React to a warning. Usually an audit is conducted to ensure that support and escape ways meet standards. In some cases, part or all the mine may be evacuated or re-entry delayed until the hazard subsidesQuantify the SHA success rate. The “success” of an SHA method can only be determined if the objective of the exercise is clearly stated. Earthquake and mine seismologists have made strenuous efforts to develop methods to predict the location, time and magnitude of a seismic event. While some success has been achieved in predicting instabilities and the duration of aftershock sequences, the reliable prediction of earthquakes remains an elusive and perhaps impossible goal. Hence the objective of short-term SHA is often defined in broad terms, e.g. “to raise awareness”, “to check on ground conditions and ensure compliance with support standards”, or “to select areas for visits by safety, production or rock engineering personnel”.
A new methodology for estimating seismic resilience of buildings under successive damage-retrofit processes during the recovery time
Published in Structure and Infrastructure Engineering, 2022
Rayehe Khaghanpour-Shahrezaee, Mohammad Khanmohammadi
Figure 1 illustrates the building functionality curve after an earthquake occurrence (t0) until the desired performance level is reached (tfinal). This duration can be divided into two timespans: critical timespan after mainshock occurrence and recovery time. After the critical timespan, the recovery process starts to improve the building functionality during the time. The occurrence of aftershocks is likely in both timespans and may affect the functionality of buildings, cause new damage and lead to further losses. During the recovery timespan, the structure is subjected to both recovery and degradation phenomena (aftershocks). At any point in this timespan, two cases are possible: (a) no aftershock occurs and the recovery progresses; (b) an aftershock occurs; thus, the system can recover or go to a worse state because of both phenomena. The methodology presented in this paper proposes a new probabilistic framework for calculating the functionality of structures affected by earthquakes and successive aftershocks during recovery operations.
Seismic Damage of Submerged Intake Tower under the Sequence of Mainshocks and Aftershocks
Published in Journal of Earthquake Engineering, 2022
Morteza Aghaeipoor, Mohammad Alembagheri
Reinforced concrete intake-outlet towers can be vulnerable due to their slender shape in the case of seismic events. If tower structure is damaged by a mainshock, even weak aftershocks may cause cumulative damage and increase the probability of collapse. For this reason, the seismic sequence of main shock-aftershocks should be considered for realistic modelling of these structures(Wang et al. 2017). In the performance-based design of intake towers, they are designed to meet the normal operating requirements when subjected to frequent earthquakes, to undergo repairable damage during a design basis earthquake, and to prevent uncontrollable failure during a calibrated earthquake(Manual 2007; Vidot et al. 2004). However, earthquakes, in general, do not occur as a single event but as a series of shocks. A large mainshock usually triggers numerous aftershocks in a short period of time(Zhai et al. 2013). The mainshock–aftershock seismic sequences represent a realistic situation that requires special treatment in the seismic design(Wang et al. 2017). Aftershocks are earthquakes that occur following a large shock, and are usually smaller than the mainshock. The aftershock can be more severe than the mainshock, because the intensity component depends on various parameters, including peak ground acceleration, which can have a larger quantity than the mainshock (Bormann and German 2011; Yeo 2005; Zhang, Wang, and Sa 2013).
Stochastic Model for Simulation of Ground-Motion Sequences Using Kernel-Based Smoothed Wavelet Transform and Gaussian Mixture Distribution
Published in Journal of Earthquake Engineering, 2021
R. Sharbati, H. R. Ramazi, F. Khoshnoudian, H. R. Amindavar, H. Rabbani
In recent studies, the focus has been on the impact of aftershocks on the structural response and damage. In such studies, various nonlinear structural models, including single degree of freedom systems [e.g., Luco et al., 2004; Hatzigeorgiou and Beskos, 2009; Hatzigeorgiou, 2010] and multi-degree-of-freedom systems [e.g., Fragiacomo et al., 2004; Li and Ellingwood, 2007; Hatzigeorgiou and Liolios, 2010; Erochko et al., 2011] with different hysteretic models [e.g., Li and Ellingwood, 2007; Moustafa and Takewaki, 2010; Goda, 2012; Zhai et al., 2013], have been used. It was concluded that, regardless of structural system, buildings can be progressively damaged by aftershocks, so the probability of structural failure will be higher than when considering the main shock only [Kumar et al., 2009, 2015; Kumar and Gardoni, 2014b; Priestley, 1988]. Sufficient recorded or synthetic ground motion sequences are essential to accurately evaluate the combined seismic demand of mainshocks and their aftershocks [Kumar and Gardoni, 2014a; Huang et al., 2009]. However, there are not sufficient real mainshock ground motions and aftershock ground motions for many seismic hazard scenarios. To overcome this shortcoming, it was proposed to select ground motions from other scenarios and then modify them by scaling or spectrum matching [Naeim and Lew, 1995; Luco and Bazzurro, 2007].