• Tunnel and Underground Space
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• v.23 no.6
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• pp.581-592
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• 2013

This article provides an overview on the geothermal energy research in Europe and one of the EU funded projects 'GEISER (Geothermal Engineering Integrating Mitigation of Induced Seismicity in Reservoirs)' in which the authors were involved. More details are given for description of GEISER, in particular, about aims and discussions and how the project was managed. Emphasis is given to one of the work packages 'Induced Seismicity and Large Magnitude Events (LME)' and results of this work package are summarized. This article intends to summarize the lessons learned in the GEISER project and give recommendations to future geothermal projects by creating Enhanced Geothermal Systems hydraulic stimulation where induced seismicity issues are expected to be a major issue and obstacle.

• Journal of Korean Association for Spatial Structures
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• v.12 no.4
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• pp.71-80
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• 2012

Because a smart isolation system cannot be used as a base isolation system for tall buildings, top-story or mid-story isolation systems are required. In this study, adaptability of a smart top-story isolation system for reduction of seismic responses of tall buildings in regions of low-to-moderate seismicity has been investigated. To this end, 20-story example building structure was selected and an MR damper and low damping elastomeric bearings were used to compose a smart base isolation system. Artificial earthquakes generated based on design spectrum of low-to-moderate seismicity regions are used for structural analyses. Based on numerical simulation results, it has been shown that a smart top-story isolation system can effectively reduce both structural responses and isolation story drifts of the building structure in low-to-moderate seismicity regions in comparison with a passive top-story isolation system.

• Earthquakes and Structures
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• v.4 no.6
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• pp.629-647
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• 2013

Loading protocols have been developed for quasi-static cyclic testing of structures and components. However, it is uncertain if protocols developed for conditions of intense ground shaking in regions of high seismicity would also be applicable to regions of low-moderate seismicity that are remote from the tectonic plate boundaries. This study presents a methodology for developing a quasi-static cyclic displacement loading protocol for experimental bracing evaluation of cold-formed steel stud shear walls. Simulations presented in the paper were based on conditions of moderate ground shaking (in Australia). The methodologies presented are generic in nature and can be applied to other regions of similar seismicity conditions (which include many parts of China, Korea, India and Malaysia). Numerous response time histories including both linear and nonlinear analyses have been generated for selected earthquake scenarios and site classes. Rain-flow cycle counting method has been used for determining the number of cycles at various ranges of normalized displacement amplitude. It is found that the number of displacement cycles of the loading protocol increases with increasing intensity of ground shaking (associated with a longer return period).

• Tunnel and Underground Space
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• v.19 no.3
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• pp.174-180
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• 2009

This paper gives a brief review of seismicity and seismic monitoring in surface mines. A summary of various researches related to seismicity is presented. Our research focuses on the understanding of seismicity and the application of analytical techniques to seismicity. Seismic monitoring plays an important role in the identification of potential failure planes and thereby predict potential failures. Much of the instrumentation used in our research is derived from earthquake monitoring systems. The major aspects in seismic monitoring are an instrumentation used, size of the network and data acquisition systems. Seismic monitoring in surface mines could be successfully applied to the improvement of safety standards in slope stability.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2006.04a
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• pp.741-748
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• 2006

Seismic performance evaluation was conducted for four wind-designed concentrically braced steel highrise buildings in order to check the feasibility of designing steel highrise buildings per elastic seismic design criterion (or strength and stiffness solution) in the regions of strong wind and moderate seismicity. The pushover analysis results revealed that the wind-designed highrise buildings possess significantly increased elastic seismic capacity due to the overstrength resulting from the wind serviceability criterion. The strength demand-to-capacity study showed that, due to the wind-induced overstrength, highrise buildings with a slenderness ratio of larger than four or five can withstand elastically even the maximum considered earthquake at the performance level of immediate occupancy. Based on the analytical results of this study, practical elastic seismic design procedure for steel highrise buildings in the regions of moderate seismicity is proposed.

• Nuclear Engineering and Technology
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• v.41 no.10
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• pp.1255-1262
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• 2009

This paper introduces the status of and issues related to the PSHA (Probabilistic Seismic Hazard Analysis) of Korean Nuclear Power Plant sites. PSHA was first introduced to the nuclear industry in the mid-1980s. The Korean PSHA is based on Cornell and accommodates the modem approach for eliciting expertise and statistical treatment. Due to the low seismicity in Korea, large uncertainties exist in the PSHA database including seismic source maps, seismicity parameters of seismic sources, and attenuation formulae. Though research in seismology, geology, and earthquake engineering since the mid-1990s has significantly reduced uncertainties, a considerable amount still exists. Considering the low seismicity of the Korean Peninsula, especially the lack of strong motion data, further reduction will take several decades.

• Journal of Korean Society of Steel Construction
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• v.24 no.3
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• pp.325-336
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• 2012

Smart base isolation systems developed for structures in high seismic regions cannot be directly applied to structures in regions of low-to-moderate seismicity, such as Korea. Therefore, the problems that occur by applying the smart base isolation system for high seismic regions to the structures in regions of low-to-moderate seismicity have been investigated in this study. To this end, a five-story building is used as an example, and an MR damper and low damping elastomeric bearings were used to compose a smart base isolation system. Artificial earthquakes are simulated for ground motions in regions of high and low-to-moderate seismicity. Based on numerical simulation results, the MR damper capacity that can provide good control is quite different among regions of high and low-to-moderate seismicity. Moreover, it is noted that the properties of a smart base isolation system for the regions of low-to-moderate seismicity should be carefully designed because the base isolation effects of the smart base isolation system for high seismic regions deteriorate when it is applied to the structures in regions of low-to-moderate seismicity.

• Tunnel and Underground Space
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• v.23 no.6
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• pp.493-505
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• 2013

This numerical study investigates seismicity and fault slip induced by fluid injection in deep geothermal reservoir with pre-existing fractures and fault. Particle Flow Code 2D is used with additionally implemented hydro-mechanical coupled fluid flow algorithm and acoustic emission moment tensor inversion algorithm. The output of the model includes spatio-temporal evolution of induced seismicity (hypocenter locations and magnitudes) and fault deformation (failure and slip) in relation to fluid pressure distribution. The model is applied to a case of fluid injection with constant rates changing in three steps using different fluid characters, i.e. the viscosity, and different injection locations. In fractured reservoir, spatio-temporal distribution of the induced seismicity differs significantly depending on the viscosity of the fracturing fluid. In a fractured reservoir, injection of low viscosity fluid results in larger volume of induced seismicity cloud as the fluid can migrate easily to the reservoir and cause large number and magnitude of induced seismicity in the post-shut-in period. In a faulted reservoir, fault deformation (co-seismic failure and aseismic slip) can occur by a small perturbation of fracturing fluid (<0.1 MPa) can be induced when the injection location is set close to the fault. The presented numerical model technique can practically be used in geothermal industry to predict the induced seismicity pattern and magnitude distribution resulting from hydraulic stimulation of geothermal reservoirs prior to actual injection operation.

• Earthquakes and Structures
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• v.11 no.4
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• pp.539-561
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• 2016

The rate of occurrence of intraplate earthquake events has been surveyed around the globe to ascertain the average level of intraplate seismic activities on land. Elastic response spectra corresponding to various levels of averaged (uniform) seismicity for a return period of 2475 years have then been derived along with modifying factors that can be used to infer ground motion and spectral response parameters for other return period values. Estimates derived from the assumption of uniform seismicity are intended to identify the minimum level of design seismic hazard in intraplate regions. The probabilistic seismic hazard assessment presented in the paper involved the use of ground motion models that have been developed for regions of different tectonic and crustal classifications. The proposed minimum earthquake loading model is illustrated by the case study of Peninsular Malaysia which has been identified with a minimum effective peak ground acceleration (EPGA) of 0.1 g for a return period of 2475 years, or 0.07 g for a notional return period of 475 years.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1998.04a
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• pp.23-30
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• 1998

An estimation of seismic risk parameters by seismic zones of the Korea Peninsula in order to calculate the seismic hazard values using these was erformed. Seven seismic source zones were selected in consideration of seismicity and geology of Korean Peninsula. The seismicity parameters that should be estimated are maximum intensity, activity rate and b value in the Gutenberg - Richter relation. For computation of these parameters, least square method or maximum likelihood method is applied to the earthquake data in two ways; the one for the data without maximum intensity and the other with maximum intensity. Earthquake data since Choseon Dynasty is regarded as complete and estimation of parameters was made for these data using above two ways. And recently, a new method is published that estimate the seismicity parameters using mixed data containing large historical events and recent complete observations. Therefore, this method is applied to the whole earthquake data of the Korean Peninsula. It turns out that the b value computed considering maximum intensity is slightly lower than that computed considering without maximum intensity, and it becomes still lower when the incomplete data prior to Choseon Dynasty is used. In the case of the activity rates, the values obtained without maximum intensity and that with maximum intensity are similar, though they are lower when the incomplete data is used. The values of maximum intensities are usually lower when considering incomplete data. In the seismic source zone including the Yangsan Fault zone, however, the values are higher when considering the incomplete data.