An intraplate tectonic fault evolves with repeated seismic cycles that may exhibit multi‐mode slip behaviors (continuous aseismic sliding, slow slip with silent earthquakes, and earthquakes resulting ...from stick‐slip frictional instability). Here, we show long‐term (geological time scale) fault zone weakening processes and short‐term (seismic cycle scale) fault behavior of the Yangsan Fault, SE Korea, based on structural and mineralogical observations of an across‐strike fault zone sequence retrieved by inclined borehole drilling. Since the Late Cretaceous, physical and chemical weakening processes have formed a wide and complex fault zone characterized by interconnected clay‐rich fault core strands and fractured lenses. The deformation is more concentrated in the eastern block (Cretaceous sedimentary rock with felsic dikes) of the fault zone than in the western block (Paleogene granite) of the fault zone. The asymmetrical deformation pattern is controlled by the distinct properties of the different host rocks and differential fluid‐assisted reaction softening involving hydrothermal processes. Of the five main strands and numerous subsidiary strands in the wide fault zone, strand S1 between the sedimentary rock and granite has accommodated the largest displacements. In particular, the smectite‐rich, <2‐cm‐wide principal slip zone within S1 has acted as the major pathway for past seismic slip. Our findings consider that slow deformation in the sedimentary rocks formed the asymmetrical wide fault zone over long geological time, whereas that the preferential propagation of repeated seismic slip events propagated preferentially along the narrow principal slip zone of S1.
Plain Language Summary
The Yangsan Fault Zone in SE Korea is an ideal case for understanding how faults evolve and produce earthquakes in continental interior. We conducted low‐angle borehole drilling across the fault zone and analyzed its internal structure and mineral compositions using the recovered drillcore samples. Our findings reveal that the ∼230‐m‐wide fault zone comprises of a 30‐m‐wide western damage zone (granite) and a ∼200‐m‐wide eastern damage zone (mainly sedimentary rock with felsic dikes), expressed as an asymmetrical architecture due to the different hardness between two main wall rocks. Five main fault core strands (S1–S5) are observed in the fault zone, representing multiple fault cores, together with a number of interjacent subsidiary strands. Most of the displacements (<30 km) were accommodated by the ∼2‐m‐wide main strand S1, which is located between the two wall rocks. The S1 includes a smectite‐rich narrow (<2‐cm‐wide) slip localization zone, a pathway for past earthquake slip. We consider that physico‐chemical slow deformation in the sedimentary rocks has played an important role in fault zone widening during long geological time periods, whereas that repeated earthquake slips have been restricted to one specific narrow zone within the wide fault zone during the Quaternary period.
Key Points
The ∼230‐m‐wide Yangsan Fault Zone is characterized by asymmetrical across‐zone architecture and multiple fault core strands
The fault zone has undergone physical and chemical weakening processes and shows slip displacements concentrated along the main core strand
Cyclical seismic ruptures appear to have propagated mainly along the ∼2‐cm‐wide smectite‐rich principal slip zone within the main core strand
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The purpose of this article is to discuss the inter-urban linkage between the non-capital cities in Korea and Japan, focusing on the relationships between Fukuoka and Busan, as part of an empirical ...research on the internationalization of non-capital cities in East Asia. We attempt to subdivide international trade activities of firms and analyze foreign destinations based on cities. The linkage between Busan and Fukuoka mainly sits at the apex of the international urban system, from the perspective of the gateway of 'Physical Distribution' and 'Business Trip'; however, links to Tokyo and Osaka mostly act as 'Transaction' and functional cores such as sales channels. Fukuoka airport and Shimonoseki port have been utilized as a gateway. Fukuoka Airport has a promising evaluation concerning accessibility and convenience. Shimonoseki port has certain advantages due to the short time required for customs formalities, brevity of the shipping time and convenient daily shipping schedules.
The overconsolidation ratio (OCR) was determined through three different series of consolidation tests on the samples, which were retrieved using an oil-operated fixed-piston sampler at two sites in ...a deltaic deposit. The constant rate of strain (CRS) consolidation test and the end-of-primary (ILEOP) consolidation tests proved to be superior tests with higher quality of samples and produced close OCR values. The CRS and ILEOP tests provided OCR values close to those of the field measurements, whereas the conventional 1D consolidation (IL24) test underestimates the values. The OCR values obtained from the CRS and ILEOP tests lie between the upper and lower bounds of existing empirical formulas, whereas those from the IL24 test belong to the lower bound. Empirical formulas that were suited for both sites were newly developed through the correlations between the results of the two consolidation tests and three field tests. The empirical formulas, which have been developed based on the correlation coefficients, are appropriate for predicting the OCR values for a site where the great majority of data are given. This trend is more pronounced in the predictions obtained from the piezocone and the field vane tests than the predictions from the flat dilatometer test.
•Overconsolidation ratio (OCR) varies depending on sample quality as well as consolidation testing methods.•Correlations between the OCR and in-situ test results lie within the limits of existing empirical formulas.•The correlations are appropriate for a site where a great majority of data is given.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
This report examines land-use trends, policies and practices in Korea, in particular in the city of Busan, through the lens of urban regeneration and citizen participation. Land-use planning is ...critical for the efficient and inclusive management of cities, pursuing sustainable and balanced development and improving quality of life and regional competitiveness.
In this study, a qualitative evaluation of the morphological changes in the seabed surrounding Jinwoo-Island due to the construction of the new Busan port were determined through a numerical ...simulation. Various scenarios for the discharge of the Nakdong river estuary dam and construction stage of the new Busan port were established and utilized for an indirect and qualitative investigation through simulation using the numerical model implemented in this study. It was concluded through a qualitative study that the morphological changes in the seabed surrounding Jinwoo-Island were typical estuary seabed changes due to the discharge of the Nakdong river estuary dam and waves from the open sea. The effects from the construction of the new Busan port were relatively small.
In this study, the chemical components of aerosols observed at ground level and in upper layers during the Korea–United States Air Quality (KORUS-AQ) campaign were analyzed in two representative ...metropolitan areas of Korea: the Seoul metropolitan area (SMA) and the Busan-containing southeastern metropolitan area (BMA). First, we characterized emissions using the Clean Air Policy Support System (CAPSS) emission statistics, and compared them with both ground- and aircraft-based measurements obtained during the KORUS-AQ campaign. The emission statistics showed that the SMA had higher NOx levels, whereas BMA had significantly higher SO2 levels. Ground-level observations averaged for the summer season also showed SMA–nitrate and BMA–sulfate relationships, reflecting the CAPSS emission characteristics of both areas. However, organic carbon (OC) was higher in BMA than SMA by a factor of 1.7, despite comparable volatile organic compound (VOC) emissions in the two areas. DC-8 aircraft-based measurements showed that, in most cases, nitrogen-rich localities were found in the SMA, reflecting the emission characteristics of precursors in the two sampling areas, whereas sulfur-rich localities in the BMA were not apparent from either ground-based or aircraft observations. KORUS-AQ measurements were classified according to two synoptic conditions, stagnant (STG) and long-range transport (LRT), and the nitrate-to-sulfate (N/S) ratio in both ground and upper layers was higher in the SMA for both cases. Meanwhile, organic aerosols reflected local emissions characteristics in only the STG case, indicating that this stagnant synoptic condition reflect local aerosol characteristics. The LRT case showed elevated peaks of all species at altitudes of 1.0–3.5 km, indicating the importance of LRT processes for predicting and diagnosing aerosol vertical distributions over Northeast Asia. Other chemical characteristics of aerosols in the two metropolitan areas were also compared.
Cities have exhibited spatial patterns of expansion or compacting in the process of economic and population growth. South Korea is a well-known example of a country that has experienced rapid ...economic growth and urbanization. This study’s target area, Busan Metropolitan City (BMC), experienced urban growth but, over the past 20 years, underwent economic and population stagnation. How will urban growth patterns change if economic and population growth stagnates? This study aimed to identify changes in urban growth patterns using population and urbanized areas in BMC, South Korea, from 1980 to 2020. It uses Exploratory Spatial Data Analysis, Bachi’s Index and the Standard Deviational Ellipse, and Social Network Analysis to identify population concentration, changes in centrality, inland expansion of urbanized land, and centrality of migration. The results showed that (1) BMC’s urban growth pattern extended outward, despite population and economic stagnation since 2000; (2) population and economic stagnation over the next 20 years expanded population polarization in the city’s urban center and outskirts; (3) the built-up area expanded in all directions for 40 years—the centrality of the urbanized area was seen in and around the urban center in 1980 but moved northeast in 2020; and (4) since 2000, when population stagnation first emerged, the centrality of the population in migration has been more evident in the outskirts. These results suggest that if there is no sustainable urban planning and development strategy when growth is stagnant, expansionary urban growth will continue, and cities will reach the growth limit.
Long-term settlement data of a thick soft clay deposit improved by vertical drains frequently shows different field settlement behaviors from laboratory-driven predictions by conventional theories ...due to the variability and uncertainty of the soil properties, modeling simplifications, and types of prediction methods. This paper presents the field application of a back-analysis method based on a genetic algorithm (GA) to evaluate the performance of a new settlement prediction method compared with conventional graphical settlement prediction methods, such as the hyperbolic method and the Asaoka method. The GA back-analysis method shows better flexibility in modifying surcharging plans and adaptability to multi-layered thick soft soil deposits at the early stages of post-construction settlement. Thus, this new settlement prediction method enables geotechnical engineers to subsequently modify the heights of surcharge fills in accordance with field settlement data monitored in the interim for rapid and cost-effective construction. The comparative results show that the GA back-analysis method is capable of superior field performance in settlement predictions compared with two conventional graphical methods, within a margin of less than 200mm in a thick soft clay deposit with multiple layers under complex loading conditions.
•We assessed the field performance of the GA method in settlement prediction.•The GA method shows a higher performance in a multi-layered thick soft soil deposit.•The GA method predicts the final settlement at the early stage of construction.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Soil liquefaction which is a disastrous phenomenon induced by the earthquake, is widely investigated in many researches in geotechnical engineering. In this study, a SPT-N based investigation is ...carried out to assess the susceptibility of liquefaction in Eco-Delta city, located in the southwestern part of Busan city in South Korea. Data from 229 sites are analyzed for the earthquake of 7.5 magnitude with a peak horizontal acceleration of 0.2 g to carry out the liquefaction potential index (LPI) through two deterministic methods which have different factors of safety (FS). The liquefaction probability is investigated by the deterministic and reliability methods and the liquefaction hazard maps are generated. To observe the effect of fines content and plasticity index on the liquefaction susceptibility, three different cases are considered. It is found that among the four approaches used, Overseas Coastal Area Development Institute of Japan (OCDI) method showed more sensitivity to changes of fines content and plasticity index. The Eco-Delta city is found to be highly vulnerable to liquefaction having 91% of sites with LPI values greater than 15.
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