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![Regional variations in seismic and geophysical estimates in the Korean Peninsula: a crustal thicknesses (Hong et al. 2008), b crustal P amplification (Hong and Lee 2012), c crustally-guided shear-wave attenuations (Lg Q0-1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$Q_{0}^{-1}$$\end{document}) (Hong 2010), d seismicity densities, C, of earthquakes with magnitudes equal to or larger than 2.5 during 1978–2013 (Houng and Hong 2013), e surface heat flows (Lee et al. 2010), f Bouguer gravity anomalies (Cho et al. 1997), g variation in Moho P (Pn) velocities relative to 7.95 km s-1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^{-1}$$\end{document} (Hong and Kang 2009), h shear-wave velocities at a depth of 6.75 km (Choi et al. 2009), and i upper-crustal VP/VS\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$V_{\text {P}}/V_{\text {S}}$$\end{document} ratios (Jo and Hong 2013)](publication/318133826/figure/fig5/AS:959997563400214@1605892663560/Regional-variations-in-seismic-and-geophysical-estimates-in-the-Korean-Peninsula-a.gif)
Regional variations in seismic and geophysical estimates in the Korean Peninsula: a crustal thicknesses (Hong et al. 2008), b crustal P amplification (Hong and Lee 2012), c crustally-guided shear-wave attenuations (Lg Q0-1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$Q_{0}^{-1}$$\end{document}) (Hong 2010), d seismicity densities, C, of earthquakes with magnitudes equal to or larger than 2.5 during 1978–2013 (Houng and Hong 2013), e surface heat flows (Lee et al. 2010), f Bouguer gravity anomalies (Cho et al. 1997), g variation in Moho P (Pn) velocities relative to 7.95 km s-1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^{-1}$$\end{document} (Hong and Kang 2009), h shear-wave velocities at a depth of 6.75 km (Choi et al. 2009), and i upper-crustal VP/VS\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$V_{\text {P}}/V_{\text {S}}$$\end{document} ratios (Jo and Hong 2013)
Source publication
The strength of seismic ground motion is a consequence of seismic source strength and medium response. The dependence of seismic amplitudes and seismic intensity on regional geological structures and crustal properties in the stable intraplate region around the Korean Peninsula is investigated. An instrumental seismic intensity scale based on spect...
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Citations
... where N is the number of sites with reported damages, I j max is the upper bound of seismic intensity at site j, I j min is the lower bound of seismic intensity at site j, I j t (x, m) is the theoretical seismicity intensity at site j for a case when the event with a magnitude of m occurs at a location x, and σ is the standard deviation of observed seismicity intensities from the reference (theoretical) seismic intensities. We set σ to be 0.65 in MMI unit (Park and Hong, 2017). ...
The occurrence mechanism and key factors to induce the 15 November 2017 MW5.5 Pohang earthquake are investigated through combined interpretation of active fault zone, stress field evolution, earthquake source properties, fault structure, and spatiotemporal seismicity change. Analysis of historical earthquakes suggests the presence of active faults spawning moderate-size earthquakes around the Pohang Enhanced Geothermal System. The instrumental seismicity suggests that the faults were kept loaded until the occurrence of the Pohang earthquake. The Coulomb stress changes induced by the 2016 ML 5.8 (MW5.4) Gyeongju earthquake and the 2011 MW9.0 Tohoku-Oki earthquake suggest additional stress loading on the faults. The spatial distribution and focal mechanism solutions of mainshock and aftershocks illuminate a complex segmented fault structure. The fault geometry suggests that the fluid injection was made at the northeastern fault-segment conjunction. Numerical modeling of stress transfer and rupture dimension suggests that a ML3.1 (MW3.3) earthquake 7 months before the mainshock loaded the stress of tens of kilopascals around the hypocenter of mainshock. A series of the seismic activities including the Tohoku-Oki earthquake and local moderate-size earthquakes as well as high-pressure fluid injection contributed to the occurrence of the Pohang earthquake.
... Also, it is noteworthy that the crustal structure may serve an additional role in seismic amplification. For instance, seismic waves are highly amplified in the crust of the southern Korean Peninsula (Hong and Lee, 2012;Park and Hong, 2017). ...
The Korean Peninsula is located in a stable intraplate region with low-seismicity rates and long recurrence intervals of major earthquakes. Recent moderate-size earthquakes demonstrate possible occurrence of seismic damages in the Korean Peninsula. A probabilistic seismic hazard analysis based on instrumental and historical seismicity is applied for the Korean Peninsula. Three seismotectonic province models are used for area sources. Seven ground-motion prediction equations calibrated for bedrock condition are considered. Fault source models are not applied due to poor identification of active faults. A 500 yr long historical record of earthquakes includes moderate and large earthquakes of long recurrence intervals. The influences of model parameters are reflected through a logic-tree scheme. The process and results are verified by Monte Carlo ground-motion level simulation and benchmark tests. Relatively high-seismic hazards are modeled in the northwestern, south-central, and southeastern Korean Peninsula. The horizontal peak ground accelerations reach ∼0.06, 0.09, 0.13, 0.21, and 0.28g for periods of 25, 50, 100, 250, and 500 yr, respectively, with exceedance probability of 10%. Successive moderate-size earthquakes since the 11 March 2011 Tohoku–Oki megathrust earthquake have temporarily increased the seismic hazards in the southeastern peninsula.
... where r is the hypocentral distance in km. The seismic intensity attenuation equation for the Korean Peninsula is given by (Park and Hong 2017) IðM L ; rÞ ¼ À0:998ðAE0:222Þ þ 1:72ðAE0:04ÞM L À 0:644ðAE0:027Þ lnðrÞ À 0:00608ðAE0:00049Þ r; ...
The earthquakes in the western East Sea (Sea of Japan) mostly occur in the continental margin off the east coast of the Korean Peninsula. The seismic hazard potentials in and around the western Ease Sea are studied based on analyses of tectonic structures, seismicity features, earthquake source properties, Coulomb stress changes, and strong ground motions. The earthquake source mechanisms suggest that paleo-rifting structures in the western East Sea were activated by the current stress field. A low stress cumulation rate results in the occurrence of earthquakes with long recurrence intervals. The background seismicity suggests that earthquakes with magnitudes \(M_w\) 5.0, 6.0, and 7.0 may occur within every \(\sim \) 44, \(\sim \) 336, and \(\sim \) 2550 years at 95 % confidence level. The spatial distribution of earthquakes changes with time. Most earthquakes are clustered within \(\sim \) 60 km from the coast. The seismicity analysis indicates an apparent increase of moderate-size (\(M_w\) 3–5) earthquakes since the 2011 \(M_w\) 9.0 Tohoku-Oki megathrust earthquake. Static stress changes by moderate-size inland earthquakes induce offshore events. The seismicity and Coulomb stress changes suggest high seismic potentials around the western margin of the Ulleung basin. Earthquakes with magnitudes \(M_w\) 6.0–7.0 in the western East Sea may produce peak ground accelerations of 0.2 g within the distance of \(\sim \) 40–80 km, which includes the coastal regions.
... We can infer the levels of ground motions by seismic waves in local and regional distances. We measured the peak ground accelerations (PGAs) as a function of distance 1,22 (see Supplementary Materials). The PGA decay rate is low in the Korean Peninsula compared to other tectonic regions 22 . ...
... We measured the peak ground accelerations (PGAs) as a function of distance 1,22 (see Supplementary Materials). The PGA decay rate is low in the Korean Peninsula compared to other tectonic regions 22 . We determine the PGA attenuation curve by calibrating the level of the reference PGA curve for the observed PGAs in regional distances. ...
The North Korean nuclear explosion test site in Punggye-ri is located in a seismically quiescent region on a stable Precambrian basement. The 3 September 2017 MW5.6 North Korean underground nuclear explosion (UNE) test produced unprecedented strong ground motions. The peak ground accelerations might reach tens to hundreds m/s2 on the surface of the UNE test site, decaying exponentially with distance. Ten shallow events with magnitudes greater than or equal to ML2.5 and source depths less than 3 km followed the 2017 UNE for 5 months in an area with a radius of 15 km from the UNE where strong ground shaking was experienced. The largest event with MW3.7 occurred 20 days after the 2017 UNE test at shallow depths less than 3 km. Its moment tensor solution indicates a combined source behavior with comparable strengths of double-couple and compensated linear vector dipole (CLVD) components, suggesting an unusual event different from typical natural earthquakes in the Korean Peninsula. The clustered shallow seismic events appeared to have occurred in damaged media that were effectively perturbed by the strong ground motions of the UNE.
... The spatial distribution of the peak ground accelerations (PGAs) of the 2017 M L 5.4 earthquake was similar to that of the 2016 M L 5.8 earthquake (Fig. 2). The PGA decays gradually with distance on the Korean Peninsula 29 . The characteristic slow distance-dependent decay of PGAs suggests a high potential for seismic damage over wide regions when a large event occurs in the stable intraplate region. ...
The distance-dependent coseismic and postseismic displacements produced by the 2011 MW9.0 Tohoku-Oki megathrust earthquake caused medium weakening and stress perturbation in the crust around the Korean Peninsula, increasing the seismicity with successive ML5-level earthquakes at the outskirts of high seismicity regions. The average ML5-level occurrence rate prior to the megathrust earthquake was 0.15 yr-1 (0.05-0.35 yr-1 at a 95% confidence level), and the rate has increased to 0.71 yr-1 (0.23-1.67 yr-1 at a 95% confidence level) since the megathrust earthquake. The 2016 ML5-level midcrustal earthquakes additionally changed the stress field in adjacent regions, inducing the 15 November 2017 ML5.4 earthquake. The successive 2016 and 2017 moderate-size earthquakes built complex stress fields in the southeastern Korean Peninsula, increasing the seismic hazard risks in the regions of long-term stress accumulation. The increased seismic risks may continue until the medium properties and stress field are recovered.
A significant amount of energy is released from sub-surface during an earthquake which is caused by seismotectonic activity. The occurrences of earthquake and its distribution pattern are necessary to correlate with concentrated and deviated energy in the sub-surface for better understanding the seismotectonic activity. Hence, the main aim of the present research is to develop hierarchical sub-surface energy anomaly index and its significant on seismotectonic activity by geospatial analysis of the seismic cluster zone and active tectonic signature through geoinformatics for Lower Tista sub-basin, India. In the present research, sub-surface energy has been quantified and threshold energy has been computed to estimate sub-surface energy anomaly in various hierarchical order. Also, the hierarchical sub-surface energy anomaly index has been computed and compared with the seismic cluster zone, seismotectonic activity, and geological formation. The analysis shows that the north and central part of the study region along Rathong chhu, Kalet Khola and Great rangit micro basin denotes as HSEAI Class V which represents low intensity earthquake with clustered concentration and includes in least to weak shaking anomaly zone. This zone is located in the fringe of greater and lesser Himalayan sequence along Main central thrust and inside Ramgarh thrust of lesser Himalayan sequence. It suggests higher energy concentrated and released through micro earthquakes along the active thrust with less energy anomaly. The southern part of the study region in quaternary surface adjacent to Himalayan foothills along Lish, Gish, Chel, and Dharala micro basin denotes as HSEAI Class II which are not resemble with any recent earthquakes and lies on least intensity sub-surface energy anomaly zone. This region intersects the frontal thrust and adjoins with Gish fault and Tista lineament which is presently not in active even though higher energy is concentrated in the sub surface. It suggests the energy anomaly is less even though energy accumulated in the sub-surface which signifies the energy concentrated in the sub-surface but not yet released. It predicts the energy may release with the displacement of thrust in future with higher magnitudes.
A series of moderate-size (Mw 4.0–6.0) earthquakes occurred in South Korea after the 2011 Mw 9.0 Tohoku–Oki megathrust earthquake, incurring public concern about possible occurrence of devastating earthquakes in Seoul—the capital city of South Korea, where historical seismic damage was reported. The seismicity is distributed in Seoul, being dominated by strike-slip earthquakes. The fault planes are oriented in north-northeast–south-southwest, which is a favorable direction to respond to the ambient stress field. Higher rates of seismicity are observed in the northwestern Seoul at depths of <10 km. Micro-to-small earthquakes occur episodically in the central Seoul along the Chugaryeong fault system that traverses Seoul in north–south. Seismic, geophysical, and geological properties illuminate the fault structures. Stochastic modeling of ground motions reproduces the seismic damages of historical earthquakes reasonably, supporting the occurrence of devastating historical earthquakes in Seoul. The seismicity distribution, focal mechanism solutions, geological features, and seismic and geophysical properties suggest the possible presence of earthquake-spawning blind faults in Seoul. The peak ground motions are assessed for moderate-size scenario earthquakes (Mw 5.4 with focal depth of 7 km) at six representative subregions in Seoul. The upper bounds of peak ground accelerations reach ∼11 m/s2. The seismic damage potentials for moderate-size earthquakes are high in most areas of Seoul, particularly around river sides covered by alluvium.
Earthquakes in the Korean Peninsula often occur in subsurface hidden faults that are hardly identified before the seismic activity. We investigate a midcrustal subsurface hidden fault in a seismically quiescent region of the central Korean Peninsula that produced the 28 October 2022 ML 4.1 earthquake. A combined analysis of seismicity, geophysical properties and geological features constrain the subsurface fault geometry. The midcrustal fault may extend to the lineament on the surface that presents low gravity anomalies. The focal mechanism solutions and seismicity distribution suggest that the lineament may correspond to the surface trace of the fault. Further, the responsible fault is a left-lateral strike-slip fault with dip of 88○ and bilateral rupture at depths of ∼12-14 km. The lateral extent of the fault may reach >25 km. A series of foreshocks formed the source zone to induce the mainshock. The mainshock nucleated at a location of lateral contrasts of heat fluxes and magnetic anomalies in the fault. The strong ground motions by the mainshock are amplified by the sedimentary layers in the event site, inducing aftershocks to spread along the fault with time. The fault orientation is laid to respond to the ambient stress field. The Coulomb stress changes induced by the mainshock load stress the fault, increasing the possibility of another earthquake occurrence. The study suggests that a combined analysis of seismicity, geophysical properties and geological features may provide constraints on seismogenic subsurface hidden faults.
