• The Journal of the Korea Contents Association
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• v.21 no.1
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• pp.561-571
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• 2021

The 2017 Pohang earthquake left us with issues related to long-term repair and restoration from massive earthquake damage. The existing Earthquake response manual was insufficient to consider the flow of earthquake disaster work and the characteristics of long-lasting earthquake disaster. Accordingly, It is important to analyze and record how to earthquake response work was carried out during the Pohang earthquake. The functions that require the most work and manpower in the event of an earthquake disaster were emergency life stabilization support, facility emergency recovery, and energy functional restoration. As a result of analyzing the difficulties and problems of disaster response by function, it was found that the prevention and preparation for damage in advance was insufficient for each function. In conclusion, we subdivided the response step applied with the concept of time and presented the overall work flow process for thirteen collaboration functions. It is expected that this result will help disaster managers to work effectively in the event of a large scale earthquake.

• Economic and Environmental Geology
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• v.53 no.5
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• pp.585-596
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• 2020

The 2017 Pohang Earthquakes occurred near a drill site in the Pohang Enhanced Geothermal System. Water injected for well stimulation was believed to have reactivated the buried near-critically stressed Miocene faults by the accumulation of the Quaternary tectonic strain. However, surface expressions of the Quaternary tectonic activity had not been reported near the epicenter of the earthquakes before the site construction. Unusual, large-scale water-escaped structures were identified 4 km away from the epicenter during a post-seismic investigation. The water-escaped structures comprise Miocene mudstones injected into overlying Pleistocene coastal sediments that formed during Marine Isotope Stage 5. This indicates the vulnerable state of the mudstones long after deposition, resulted from the combined effects of rapid tectonic uplift (before significant diagenesis) and the development of an aquifer at their unconformable interface of the mudstone. Based on the detailed field analysis and consideration of all possible endogenic triggers, we interpreted the structures to have been formed by elevated pore pressures in the mudstones (thixotropy), triggered by cyclic ground motion during the earthquakes. This interpretation is strengthened by the presence of faults 400 m from the study area, which cut unconsolidated coastal sediment deposited after Marine Isotope Stage 5. Geological context, including high rates of tectonic uplift in SE Korea, paleo-seismological research on Quaternary faults near the study area, and historical records of paleoearthquakes in SE Korea, also support the interpretation. Thus, epicenter and surrounding areas of the 2017 Pohang Earthquake are considered as a paleoseismologically active area, and the causative fault of the 2017 Pohang Earthquakes was expected to be nearly critical state.

• Geophysics and Geophysical Exploration
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• v.21 no.2
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• pp.125-131
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• 2018

2017 Pohang earthquake (M 5.4) was more disastrous than 2016 Gyeongju earthquake (M 5.8), partly because of its shallow focal depth. However, precise focal depth of Pohang earthquake is still controversial. Close crustal model showed 6 ~ 11.5 km in relocation depth, whereas other models showed almost surface range. Geothermal study indicated temperature of $300^{\circ}C$ at depth of 7.5 km. Related with observations of seismogenic layer, the focal depth of Pohang earthquake seems to be 7 km depth as obtained by close model.

• Journal of Science and Technology Studies
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• v.19 no.3
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• pp.51-117
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• 2019

On 15th November 2017, the coastal city of Pohang, located in the Southeastern part of South Korea was shaken by a magnitude 5.4 earthquake. The earthquake displaced more than 1,700 residents and caused more than $ 300 million dollars of economic loss. It was the second most damaging earthquake in the history of Korea. Soon after the earthquake, a group of scientists raised a possible link between the first Enhanced Geothermal System (EGS) project and the earthquake. At the same time, another group of scientists put forward a different hypothesis of the causation of the earthquake claiming that it was caused by the geological movements that were initiated by the Great Tohoku Earthquake in 2011. Since then, there were scientific debates between the two different groups of scientists. The scientific debate on the causation of the earthquake has been concluded temporarily by the Research Investigatory Committee on the Pohang Earthquake in 2019. The research committee concluded that the earthquake was caused by the Pohang EGS system: this means that the earthquake can be defined not as a natural earthquake, but as an artificially triggered earthquake. This article is to examine the Pohang earthquake can be defined as an Anthropocenic event. The newly suggested concept, the Anthropocene is a relatively novel term to classify the earthly strata and their relationship to geological time. The current geological period should be defined by human activities and man-made earthly environment. Although the term is basically related to geological classification, the Anthropocene has been widely debated amongst humanist and social science scholars. The current disastrous situation of our planet also implies with the Anthropocene. This paper is to discuss how to understand anthropogenic events. In particular, the paper pays attention to two different scholarly positions on the Anthropocene: Isabelle Stenger's Gaia theory and Barbara Herrnstein Smith's relativist theory. The former focuses on the earthly inevitable catastrophe of Anthropocene while the latter suggests to situate and contextualise anthropogenic events. On the basis of the theoretical positions, the article is to analyse how the Pohang earthquake can be located and situated.

• The Journal of Engineering Geology
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• v.28 no.2
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• pp.217-246
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• 2018

During the selection and characterization of target formations in the Small-scale Offshore $CO_2$ Storage Demonstration Project in the Pohang Basin, we have carefully investigated the possibility of induced earthquakes and leakage of $CO_2$ during the injection, and have designed the storage processes to minimize these effects. However, people in Pohang city have a great concern on $CO_2$-injection-intrigued seismicity, since they have greatly suffered from the 5.4 magnitude earthquake on Nov. 15, 2017. The research team of the project performed an extensive self-investigation on the safety issues, especially on the possible $CO_2$ leakage from the target formation and induced earthquakes. The target formation is 10 km apart from the epicenter of the Pohang earthquake and the depth is also quite shallow, only 750 to 800 m from the sea bottom. The project performed a pilot injection in the target formation from Jan. 12 to Mar. 12, 2017, which implies that there are no direct correlation of the Pohang earthquake on Nov. 15, 2017. In addition, the $CO_2$ injection of the storage project does not fracture rock formations, instead, the supercritical $CO_2$ fluid replaces formation water in the pore space gradually. The self-investigation results show that there is almost no chance for the injection to induce significant earthquakes unless injection lasts for a very long time to build a very high pore pressure, which can be easily monitored. The amount of injected $CO_2$ in the project was around 100 metric-tonne that is irrelevant to the Pohang earthquake. The investigation result on long-term safety also shows that the induced earthquakes or the reactivation of existing faults can be prevented successfully when the injection pressure is controlled not to demage cap-rock formation nor exceed Coulomb stresses of existing faults. The project has been performing extensive studies on critical stress for fracturing neighboring formations, reactivation stress of existing faults, well-completion processes to minimize possible leakage, transport/leakage monitoring of injected $CO_2$, and operation procedures for ensuring the storage safety. These extensive studies showed that there will be little chance in $CO_2$ leakage that affects human life. In conclusion, the Small-scale Offshore $CO_2$ Storage Demonstration Project in the Pohang Basin would not cause any induced earthquakes nor signifiant $CO_2$ leakage that people can sense. The research team will give every effort to secure the safety of the storage site.

• Korean Journal of Mineralogy and Petrology
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• v.35 no.4
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• pp.485-505
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• 2022

On November 15, 2017, a Mw 5.4 Pohang Earthquake occurred at about 4 km hypocenter in the Heunghae area, and caused great damage to Pohang city, Korea. In the Heunghae area, which is the central part of the Pohang Basin, the Cretaceous Gyeongsang Supergroup and the Late Cretaceous to Early Paleogene Bulguksa igneous rocks as basement rocks and the Neogene Yeonil Group as the fillings of the Pohang Basin, are distributed. In this paper, structural and geological researches on the crustal deformations (folds, faults, joints) in the Pohang Basin and the coseismic ground deformations (sand volcanoes, ground cracks, pup-up structures) of Pohang Earthquake were carried out, and the deformation history of the Pohang Basin and characteristics of the coseismic ground deformations were considered. The crustal deformations were formed through at least five deformation stages before the Quaternary faulting: forming stages of the normal-slip (Gokgang fault) faults which strike (N)NE and dip at high angles, and the high-angle joints of E-W trend regionally recognized in Yeonil Group and the faults (sub)parallel to them, and the conjugate normal-slip faults (Heunghae fault and Hyeongsan fault) which strike E-W and dip at middle or low angles and the accompanying E-W folds, and the conjugate strike-slip faults dipped at high angles in which the (N)NW and E-W (NE) striking fault sets show the (reverse) sinistral and dextral strike-slips, respectively, and the conjugate reverse-slip faults in which the NNE and NNW striking fault sets dip at middle angles and the accompanying N-S folds. Sand volcanoes often exhibit linear arrangements (sub)parallel to ground cracks in the coseismic ground deformations. The N-S or (N)NE trending pop-up structures and ground cracks and E-W or (W)NW trending ground were formed by the reverse-slip movement of the earthquake source fault and the accompanying buckling folding of its hanging wall due to the maximum horizontal stress of the Pohang Earthquake source. These structural activities occurred extensively in the Heunghae area, which is at the hanging wall of the earthquake source fault, and caused enormous property damages here.

• Journal of the Korean Geotechnical Society
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• v.34 no.8
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• pp.51-64
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• 2018

Korean peninsula is known to be far from the plate boundary and not to generate large-scale earthquakes. However, earthquakes recently occurred in Gyeongju (2016/09/12, $M_L=5.8$) and Pohang (2017/11/15, $M_L=5.4$). The interest in earthquake engineering has increased, and various studies are actively underway by recently events. However, the seismic station network in Korea is less dense than that of the western U.S., resulting in the lack of data for detailed analyses of earthquakes. Therefore, KMA (Korea Meteorological Administration) set up temporary seismic stations and recorded ground motions from aftershocks. In this study, characteristics of Pohang seismic propagation and generation of bedrock motion are analyzed through the aftershock ground motion records at both permanent and temporary stations, as well as through the collected geological structure and site information. As a result, the response at Mangcheon-Li shows evidences of basin effects from both geology structures and measured aftershock motions.

• Journal of Korean Society of Disaster and Security
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• v.12 no.3
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• pp.25-34
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• 2019

Modern disasters prevent accidents in advance and recover after accidents are very important. Our government's current response to these accidents is not appropriate. As for disaster management so far, it has been the center of disaster response and recovery efforts, and has been led by the government against it. The reality is that most private organizations and agencies have only subsidized government disaster management agencies. Korea is no longer a safe zone for earthquakes. Now for the establishment of effective disaster management system for earthquakes in the diagnosis is very urgent and the problems of the operational disaster management, which the problems of the nation.Policies to improve academic efforts to seek alternative proposal is also at a time when volume can be said to be very big need to mine. This study from 2016 to 2019, about the earthquake that took place between National Statistical Office, based on analysis of data to. First of all, research 1: What was the government's plan on Pohang earthquake? The results showed that the residents' evacuation of Pohang was important in the Pohang earthquake, but for the sake of students' safety, they were directly assigned to the test site to cope with the emergency situation. Therefore, the research and analysis shows that the nation should continue to think about the causes and responses of the damage at the disaster site and strive to develop technologies and methods to minimize the damage.

• Journal of the Society of Disaster Information
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• v.15 no.4
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• pp.626-633
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• 2019

Purpose: The primery objecting of this paper is to explore the seismics fragility of curved bridge based on the change of girder section. Method: The cross section of the bridge structure was constructed with I, T, and Box shapes and then, in order to perform the seismic fragility 24 seismic ground motions were used, including Gyeongju Pohang Earthquake. Result: Fist, T-Shape of the bridge strucrue was much fragility in terms of the stress on girder section, in comparison to the other shapes. The seismic fragilies of the structures with respect to displacement(drift ratio), however, were shown simialr. Conclusion: In other to wvaluation the seismic fragility of curved structure using different girder shapes, analytical models of the structure were constructed and then, the probability failure of box-shape girder was shown lower probability. In further, Parametric studies of curved structures must be conducted.

• Korean Journal of Remote Sensing
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• v.37 no.3
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• pp.649-655
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• 2021

This study purposes to cross-validate its performance by applying the optimal seismic vulnerability assessment model based on previous studies conducted in Gyeongju to other regions. The test area was Pohang City, the occurrence site for the 2017 Pohang Earthquake, and the dataset was built the same influencing factors and earthquake-damaged buildings as in the previous studies. The validation dataset was built via random sampling, and the prediction accuracy was derived by applying it to a model based on a random forest (RF) of Gyeongju. The accuracy of the model success and prediction in Gyeongju was 100% and 94.9%, respectively, and as a result of confirming the prediction accuracy by applying the Pohang validation dataset, it appeared as 70.4%.