• Journal of the Korean earth science society
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• v.35 no.5
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• pp.354-361
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• 2014

Fault plane solutions in North Korea and the northern part of the Yellow Sea ($37.5^{\circ}N-40.5^{\circ}N$, $124.5^{\circ}E-128.5^{\circ}E$) was studied for the earthquakes that occurred from November, 2008 to May, 2013. The analysis was based on the data collected from seismic networks in Korea and China. Fault plane solutions were obtained from P and SH wave polarities and SH/P amplitude ratioes. Most earthquakes exhibited predominantly strike-slip fault characteristics with NNE-SSW or WNW-ESE nodal planes. The P-axes trends are mainly NE-SW or ENE-WSW direction in the northern part of the Yellow Sea and inland area of North Korea except some areas in the Hwanghae province. Fault plane solutions and main axis of stress field in the study region were similar to those observed in the southern part of the Korean Peninsula.

• Journal of the Korean earth science society
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• v.29 no.5
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• pp.437-445
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• 2008

We analyzed fault plane solutions of the recent twenty-two earthquakes which occurred from 2004 to 2006 in the central part of the Korean Peninsula by using P- and S-wave polarities along with SH/P amplitude ratios. The fault plane solution shows that strike-slip fault is dominant here, especially for the events with local magnitude equal to or greater than 3.0. However, some events with local magnitude less than 3.0 show normal fault or strike-slip fault with normal components. In the case of strike-slip fault, its orientation is almost in the direction of NNE-SSW to NE-SW almost parallel to the general trend of faults, while the compressional axis of the stress field trends ENE to E-W. The result is almost consistent with the stress field in and around the Korean peninsula, as reported previously. We cannot give any appropriate explanations to the normal faulting events along the western offshore and inland areas whether it is related to the local stress changes or tectonically unidentified extensional structures. Thus, an extension of investigations is desirable to clarify the cause of such phenomena.

• Journal of the Korean Geophysical Society
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• v.3 no.4
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• pp.245-250
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• 2000

By using amplitude ratios (SV/P, SH/P, SV/SH) and P and S wave polarities, we obtained fault plane solutions of the June 26, 1997 Kyong-ju earthquake. The solutions show $150{\pm}4^{\circ}$ in strike, $63{\pm}6^{\circ}$ in dip and $65{\pm}7^{\circ}$ in rake, or $18{\pm}12^{\circ}$ in strike, $26{\pm}3^{\circ}$ in dip and $120{\pm}5^{\circ}$ in rake. This result implies the stress field trending ENE-WSW, which is remarkably consistent with the previous results obtained from the moment tensor inversion, and from the composite fault plane solution for the events occurred around the Yangsan fault area.

• Journal of the Korean Geophysical Society
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• v.1 no.1
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• pp.23-30
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• 1998

Fault-plane solutions of the December 13, 1996 Yeongweol earthquake with magnitude 4.5 is obtained using the grid test technique. Thirty polarities of P waves recorded at KMA, KIGAM, KSRS and JAPAN stations are used for the event. The obtained fault plane solution shows strike-slip motion with significant amount of thrust component. The orientation of the fault is 180±20° in strike, 50±5° in dip and 150±5° in rake, or 292±3° in strike, 65±5° in dip and 30±10° in rake. These solutions are similar to those of earthquakes occurred at Sagju (Jan. 7, 1980), Pohang (Apr. 15, 1981) and offshore Gunsan (Oct. 6, 1976). The compressional axis of the stress field is trending from ENE to WSW, which is consistent with the previously defined typical regional tectonic stress orientation in and around Korean Peninsula.

• Journal of the Korean earth science society
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• v.28 no.2
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• pp.202-213
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• 2007

The Odaesan earthquake $(M_L=4.8)$ occurred near Mt. Odae, Jinbu-Myon, Pyongchang-Gun, Kangwon Province on January 20, 2007. It has a shallow focal depth about 10 km. Its felt area covers most of the southern peninsula except some southern and western inland area. The maximum MM intensity was VI in the areas including Jinbu, Doam, Kangreung, Jumunjin, and Pyongchang. In these areas, there was a very strong shaking that caused several cracks on the walls of buildings and houses, slates falling off the roof, tiles being off the wall, things falling off the desk, and rock falling from the mountains. In order to get fault plane solutions, grid searches were performed by fitting distributions of P-wave first-motion polarities and SH/P amplitude ratios for each event. The results showed that the main shock represented right-lateral strike-slip sense and two aftershocks, reverse sense. It seems that the seismogenic fault may be the NNE-SSW trending Weoljeongsa fault near the epicenter based on the distribution of epicenters (foreshock, main shock, and aftershocks), damage area, and fault plane solution. The distribution of the epicenters indicates that the length of the subsurface rupture is estimated to be about 2 km.

• Journal of the Korean earth science society
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• v.22 no.4
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• pp.292-300
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• 2001

By using two methods we obtained plane solutions for 5 groups of earthquakes including 13 events, which occurred in the central region of South Korea after December 1997. The first method is the composite fault plane solution by P wave polarity, and the second the solution by amplitude ratio (SV/P, SH/P, SV/SH) and P and S wave polarities. The two method results show similar results. The strike of fault is in the direction of NNE-SSW and WNW-ESE with the movement of strike-slip or strike-slip including thrust component. The compressional axis of the stress field dominantly trends ENE-WSW or NE-SW. The results are almost consistent with the other main events occurred in and around the Korean Peninsula.

• Journal of the Korean earth science society
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• v.38 no.7
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• pp.561-569
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• 2017

Fault plane solutions of the Iksan earthquake ($M_L=3.85$) and two aftershocks were obtained using the FOCMEC (FOCal MEChanism determination) program. The main event showed the characteristic of strike slip faulting with reverse component. It has the fault planes with NE-SW or NW-SE direction. This is similar to the fault characteristics of earthquake pattern in the inland area of the Korean Peninsula. In order to detect micro-earthquake events, continuous seismic waveform data of the thirteen seismic stations within a radius of 100km from epicenter were analyzed by PQLII program (PASSCAL, 2017) for the period from December 15, 2015 to January 22, 2016. The epicenters of nineteen micro-events were newly determined by Hypoinverse-2000 program. They are not concentrated along some lineaments or fault lines. The intensity of the Iksan earthquake was obtained by estimating the telephone inquiries, the degree of ground shaking or damage all around the southern peninsula. The instrumental intensity was also obtained using PGA (Peak Ground Acceleration) records. As a result, the maximum MM intensity was estimated to be V near the epicenter.

• Journal of the Korean earth science society
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• v.34 no.1
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• pp.59-68
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• 2013

Focal mechanism solutions in the southwestern region of the Korean Peninsula ($34^{\circ}N-36^{\circ}N$, $126^{\circ}E-128^{\circ}E$) were obtained from the analysis of the recent 22 earthquakes ($M{\geq}2.0$) occurred from January, 2005 to March, 2011. The spatial differences between the epicenters recalculated by this study and those by KMA (Korea Meteorological Administration) and KIGAM (Korea Institute of Geoscience and Mineral Resources) are less than $0.05^{\circ}$, indicating a small deviation. However, they become a little bit larger in the coastal area due to a biased arrangement of seismic stations. Redetermined depths of hypocenters show a difference less than 12.7 km by comparison with the depth data announced by KIGAM. Most epicenters in inland area are located closely to the lineaments. Fault plane solutions were obtained from the analysis of P and SH wave polarities, and SH/P amplitude ratios. They show strike-slip faulting or strike-slip faulting with reverse components dominantly. The P-axes trends are mainly ENE-WSW or E-W directions. The direction of fault plane and auxiliary plane with 'NNE-SSW and WNW-ESE' or 'NE-SW and NW-SE' are dominant and almost parallel to the general trends of lineaments in the study area.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2003.03a
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• pp.16-22
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• 2003

The focal mechanisms of the earthquakes occurred in 2001 and 2002 are analyzed to understand the regional stress and tectonics in and around Korean Peninsula. The forty -three fault plane solutions are derived using the polarities of first arrival P-waves recorded at KIGAM, Bmh and KEPRI stations. The result suggest that thrust motion with significant amount of strike slip component is dominant mode of faulting. The larger population of mechanism is characterized by WNW-ESE striking nodal planes. NE-SW direction is interpreted as dominant compressional axis orientation of stress field. These solutions are similar to those of medium size earthquakes studied previously, which is known as typical regional tectonic stress orientation in and around Korean Peninsula.

• Journal of the Korean earth science society
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• v.32 no.2
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• pp.161-169
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• 2011

Focal mechanism solutions in the central and western areas of the Korean Peninsula (36-37.8$^{\circ}N$, 126-128$^{\circ}E$) were obtained from the analysis of the recent seventeen earthquakes (M${\geq}$2.2) which occurred from January, 2005 to May, 2010. The spatial differences between the epicenters recalculated by this study and those announced by the Korea Meteorological Administration are less than $0.03^{\circ}$, indicating a small deviation. Focal mechanism solutions were obtained from the analysis of P wave polarities, SH wave polarities and SH/P amplitude ratios. The focal mechanism solutions show dominant strike-slip faulting or oblique slip faulting with strike-slip components. The P-axes trends are mainly ENE-WSW or E-W directions. The direction of fault plane and auxillary fault plane with NNE-SSW and WNW-ESE are almost parallel to the general trends of lineaments in the study area. The results also show that focal mechanism solutions and the main axis of stress field in the Kyonggi massif and Okchon belt are almost same.