• The Journal of Engineering Geology
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• v.2 no.2
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• pp.155-165
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• 1992

The purpose of this study is to evaluate compatability of seismic source characteristics of the Kern County earthquake to those of Korean Peninsula seismotectonics. The compatability could be used to make Korean type response spectrum from the strong ground motions observed from the assingned earthquake. The July 21, 1952, Kern County, California, earthquake is the largest earthquake to occur in the western U.S. since 1906, and the repeat of this event poses a significant seismic hazard. The Kern County event was a complex thrusting event, with a surface rupture pattern that varied from pure leftlateral strike-slip to pure dip-slip. A time dependent moment tensor inversion was applied to ten observed teleseismic long-period body waves to investigate the source complexity. Since a conventional moment tensor inversion(constant geometry through time) returns a non-double-couple source when the seismic source changes(fault orientation and direction of slip) with time, we are required to use the time dependent moment tensor which allows a first-order mapping of the geometric and temporal complexity. From the moment tensor inversion, a two-point seismic source model with significant overlap for the White Wolf fault, which propagates upward(20 km to 5 km) from SW to NE, fits most of the observed seismic waveforms in the least squares sense. Comparison of P, T and B axes of focal mechanisms and focal depths suggests that seismic source characteristics of the Kern County earthquake is consistant with those of Korean Peninsula Seismotectonics.

• Journal of the Korean Society of Hazard Mitigation
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• v.1 no.3 s.3
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• pp.123-136
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• 2001

The purpose of application of moment tensor inversion method is to determine source parameters, such as, focal mechanism, seismic moment and source depth. This paper presents results of focal mechanism solutions of 14 recent events with magnitudes ranging from M3.3 to M4.8 by using moment tensor inversion method called TDMT_INV. The strike of faults is in the direction of NE-SW and NW-SE with the movement of strike-slip or strike-slip of minor reverse component. The compressional axis of the stress field is predominantly E-W or ENE-WSW except for some faults, which are distributed at Ryongnam Massif and Wonsan, they have a compressional axis of N-S or NNW-SSE.

• Geophysics and Geophysical Exploration
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• v.17 no.2
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• pp.58-65
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• 2014

We studied the source mechanisms of very-long-period event recorded at seismic station WIZ near White Island Volcano, New Zealand on August 4, 2012. Since seismic data at only one station were available, we conducted moment tensor inversion using three simplified models (explosion, crack, and pipe models). To constrain the moment tensor solution of seismic event, we computed synthetic data for each model to compare with observed data. Type and orientation for the best model is a crack at a depth of 1600 m with a dip of $80^{\circ}NE$ and a strike of $N80^{\circ}W$. We interpret that a deep explosion may have opened a crack for gases to escape, and the upward gas flow triggered the surface explosions four hours later as confirmed by a webcam. The interpretation based on moment tensor inversion is consistent with previous studies of geochemical data of the volcanic island.

• The Journal of Engineering Geology
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• v.17 no.4
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• pp.673-680
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• 2007

The seismic source parameters of the Odaesan earthquake on 20 January 2007, including focal depth, focal mechanism, magnitude, and source characteristics, are analysed using seismic moment tensor inversion. The Green's function for different 3 crust models representing the southern Korean Peninsula are used. Final results show that the event, considering 6 seismic moment tensor elements, is caused by the typical strike slip fault with nearly NNE strike. The focal depth is estimated to be about 11km and 6 seismic moment tensor elements with 7.2% CLVD value shows typical double couple seismic source. The consistent characteristics of the strike and epicenter of the event with Odaesan fault imply that Odaesan earthquake is mainly caused by movement of the Odaesan fault.

• The Journal of Engineering Geology
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• v.5 no.2
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• pp.215-231
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• 1995

The key concepts of seismic moment tensor are introduced in a 'physicist - oriented' style. The theory and application of seismic moment tensor which have been developed since the 1970s have become one of the most important branches in modern seismology. The description of earthquake sources in the modern seismology have led to much deeper understanding of the physics of indigenous earthquakes as well as various kinds of artificial seismic events, such as underground explosions, mining rockbursts, and reservoir induced tremors. Furthermore, with the development of digital seismological observation, some concepts, which were not included in 'classical' seismology, or not so important in 'classical' seismology, has become more and more important. It seems that it has been the time to have a new look at the fundamentals of seismology as a branch of applied physics, especially the part dealing with the physics of earthquake sources. Also in this field it may be important to clarify some fundamental concepts which, unexpectedly, have caused confusions even among professionals.

• Geophysics and Geophysical Exploration
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• v.12 no.1
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• pp.114-120
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• 2009

Rupture directivity is the important parameter in estimating damage due to earthquakes. However, the traditional moment tensor inversion technique cannot resolve the real fault plane or the rupture directivity. To overcome these limitations, we have developed a new inversion algorithm to determine the moment tensor solution and the rupture directivity for moderate earthquakes, using the waveform inversion technique in the frequency domain. Numerical experiments for unilateral and bilateral rupture models with various rupture velocities confirm that the method can resolve the ambiguity of the fault planes and the rupture directivity successfully. To verify the feasibility of the technique, we tested the sensitivity to velocity models, which must be the most critical factor in practice. The results of the sensitivity tests show that the method can be applied even though the velocity model is not perfect. If this method is applied in regions where the velocity model is well verified, we can estimate the rupture directivity of a moderate earthquake. This method makes a significant contribution to understanding the characteristics of earthquakes in those regions.

• Journal of the Earthquake Engineering Society of Korea
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• v.11 no.6
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• pp.33-39
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• 2007

The seismic source parameters of the Uljin earthquake on 29 May 2004, including focal depth, focal mechanism, magnitude, and moment tensor elements for source characteristics, are analysed using moment tensor seismic source inversion. The Green‘s function for 3 crust models representing the southern Korean Peninsula are used. Also 3 kinds of epicenters are used to find optimum solution for seismic source parameters. Results show that seismic source parameters have a little dependency of azimuthal distribution and epicentral distances of seismic stations. Final results show that the event, considering 6 moment tensor elements, is caused by the typical reverse fault with nearly NS strike. The focal mechanism implies that the tectonic force around epicenter area currently has compressive environment, with nearly EW principal axis. The focal depth is estimated to be about 12km. The resultant focal mechanism show fairly good agreement to those of other studies. However, focal depth is much different from that of other studies.

• Geomechanics and Engineering
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• v.19 no.5
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• pp.369-381
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• 2019

The objective of this paper is to study the two dimensional deformation in transversely isotropic thermoelastic medium without energy dissipation due to time harmonic sources using new modified couple stress theory, a continuum theory capable to predict the size effects at micro/nano scale. The couple stress constitutive relationships have been introduced for transversely isotropic thermoelastic medium, in which the curvature tensor is asymmetric and the couple stress moment tensor is symmetric. Fourier transform technique is applied to obtain the solutions of the governing equations. Assuming the deformation to be harmonically time-dependent, the transformed solution is obtained in the frequency domain. The application of a time harmonic concentrated and distributed sources have been considered to show the utility of the solution obtained. The displacement components, stress components, temperature change and couple stress are obtained in the transformed domain. A numerical inversion technique has been used to obtain the solutions in the physical domain. The effects of angular frequency are depicted graphically on the resulted quantities.

• Structural Engineering and Mechanics
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• v.76 no.1
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• pp.17-26
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• 2020

The objective of this paper is to study the deformation in transversely isotropic thermoelastic solid using new modified couple stress theory subjected to ramp-type thermal source and without energy dissipation. This theory contains three material length scale parameters which can determine the size effects. The couple stress constitutive relationships are introduced for transversely isotropic thermoelastic solid, in which the curvature (rotation gradient) tensor is asymmetric and the couple stress moment tensor is symmetric. Laplace and Fourier transform technique is applied to obtain the solutions of the governing equations. The displacement components, stress components, temperature change and couple stress are obtained in the transformed domain. A numerical inversion technique has been used to obtain the solutions in the physical domain. The effects of length scale parameters are depicted graphically on the resulted quantities. Numerical results show that the proposed model can capture the scale effects of microstructures.

• 한국지구물리탐사학회:학술대회논문집
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• 2007.06a
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• pp.69-74
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• 2007

The source mechanism parameters of the Ulgin earthquake on 29 May 2004 are analyser using moment tensor inversion technique. The Green's function are calculated for the Kim's(1985) crust model of southern Korean Peninsula. Results derived from the Ulgin earthquake show the dependence of azimuthal station distribution and epicentral distances. final results show fairly good agreement to those of other authors. the focal mechanism for the Ulgin earthquake is found to be oblique reverse motion with NNE strike. The focal depth is estimated to be 10-12km.