A Framework to Include Time Dependency Earthquake Probability Model and Long-Period Characterization of Basin Topography in Seismic-Hazard Assessment

• Main Authors: Yu-Wen Chang, 張毓文
• Other Authors: Chin-Hsiung Loh
• Format: Others
• Language: en_US
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/ca5s48

博士 === 國立臺灣大學 === 土木工程學研究所 === 105 === The objective of a seismic design of building, power plant components and structures is to ensure safety of the plant and the people around in the event of an earthquake. The design basis ground motion is generally specified by a response spectra for various values of damping. Both probabilistic and deterministic methods have a role in seismic design performed for decision-making purposes in over 30 years. Prior to the acceptance and incorporation of probabilistic approach into standard hazard assessment methodologies, most seismic-hazard assessments were completed using scenario-based, “deterministic” analyses. They are proposed to provide design earthquakes for site-specific studies such as the designing of critical structures. The deterministic approach considers the scenarios that have the small occurrence number. Relatively, the all of the possible scenarios will have considered in the probabilistic approach. PSHA provides a key element for engineering seismic design. It is concerned with evaluating the various natural effects of earthquakes at specific levels, which may cause safety or design consequences to critical structures at particular sites such as dams, public structures, and nuclear power plants. Most of the developments in the PSHA have been primarily concerned with introducing different probabilistic models to describe randomness, such as earthquake magnitude, and recurrence rate, in order to achieve more realistic descriptions for a specific site. The analysis requires characterization of all known earthquake sources that could affect the site, including faults and areal sources. For a particular site, the hazard contributions are integrated over all magnitudes and distances for all source zones, according to the calculation of total probability theory. Extensive advances in seismic knowledge in recent years by a large and active community of researchers around the world, the gaps in the understanding of the mechanisms that cause earthquakes and the recurrence behavior of earthquake are reduced. These gaps in understanding mean that, when a PSHA is performed, the significant uncertainties in the numerical results will be decreased due to the correct models used. Up-to-date knowledge of the source data along with accurate models can provide valuable information in reducing such uncertainties and in facilitating a correct understanding of PSHA. For the earthquake recurrence model, the seismic data fitting well will promote the reliabilities for the hazard calculation. The subjective judgment and interpretation of the limited data affect the result of PSHA. The earthquake recurrence model that is used to describe the earthquake recurrence rate commonly is defined in epistemic uncertainty due to our lack of knowledge which will be reduced in time. The objectives of this study, one is to discuss the aspects of current model setting that need improvement in the recurrence rate model in the PSHA. The Gutenberg–Richter (1994) exponential frequency–magnitude relation uses to describe the earthquake recurrence rate for a regional source. It is a reference for developing a composite procedure modelled the occurrence rate for the large earthquake of a fault when the activity information is shortage. Given the probability distribution function relating to the recurrence interval and the occurrence time of the previous occurrence of a fault, a time-dependent probability model of a particular fault for seismic hazard assessment was developed that takes into account the active fault rupture cyclic characteristics during a particular lifetime up to the present time. The time-dependent model was used to describe the fault characteristic behavior. The effects of time-dependent and time-independent models of fault (e.g., Brownian passage time (BPT) and Poisson, respectively) in hazard calculations are also discussed. The proposed fault model result shows that the seismic demands of near fault areas are lower than the current hazard estimation where the time-dependent model was used on those faults, particularly, the elapsed time since the last event of the faults (such as the Chelungpu fault) are short. One of the aims of this study is to understand the effect of seismic source recurrence probability models on the hazard results by quantifying the differences in the design ground motions. Additionally, the difference of hazard contribution between the ranges of source models in the hazard analysis provide to contemplate for source or fault setting in the PSHA. The analysis also considers the attenuation of seismic energy as it emanates from the earthquake hypocenter to the site of interest, which is evaluated through the use of empirical GMPE. In Addaction, the effects of earthquake-induced basin amplification are caused by the interaction of wave-fields with a basin boundary, which depend on complex source to site distances, basin geometry (topography), and sediment distribution within the basin. In this study the identification of long-period waves induced by strong earthquake motions through basin topography together with local site effects of the basin is investigated. Through multivariate singular spectrum analysis (MSSA), a unique analysis tool for extracting tendencies and harmonic components in geophysical time series is used to extract the long-period wave of basin response caused by the seismic events. Seismic response data of Taipei Basin were used to examine the existing of the lowest dominant frequency of the basin caused by basin topography. Finally, the seismic-induced ground motion data can be separated to the basin motion caused by the effect of topography. A framework to include time dependency earthquake probability model and long-period characterization of basin topography in seismic-hazard assessment will be discussed in this study