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Volume 45, Issue 1
Displaying 1-5 of 5 articles from this issue
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So Gu Kim, Zhongliang Wu1997 Volume 45 Issue 1 Pages 1-11
Published: 1997
Released on J-STAGE: April 30, 2009
JOURNAL FREE ACCESSAt present, most of the single-station location approaches are based on the Using a 3-Component Single Station estimation of azimuths and epicenter distances. In this paper, the uncertainty of such kind of single-station location for local and regional earthquakes is analyzed systematically. The uncertainty of the azimuth estimation is proportional to the average noise level of the seismogram taken for analysis. However, in the analysis, still a larger uncertainty comes from the fact that sometimes the selection of waveforms is subjective, and the results may depend on that selection. To evaluate this kind of uncertainty and possibly avoid the arbitrariness of the selection of waveforms, we proposed a timedirection stacking approach. The uncertainty of the estimation of distances comes from the travel time readings and the apparent velocity model. To reduce the uncertainties of distance estimation, we proposed an apparent velocity model which depends on the range of distances. As an application, we present the results of expected uncertainty for the Korean Peninsula and its vicinity.View full abstractDownload PDF (727K) -
So Gu Kim, Fuchun Gao1997 Volume 45 Issue 1 Pages 13-27
Published: 1997
Released on J-STAGE: April 30, 2009
JOURNAL FREE ACCESSIn this paper, a case study has been made on the characteristics of earthquakes and explosions, mainly through the polarization method, estimating the epicentral azimuths and incident angles in the case of shallow- and deep-focus earthquakes as well as explosions based on three-component signal-to-noise ratios. We have found that it is possible to determine the epicenter and incident angle of an earthquake or an explosion by three-component single-station polarization analysis, especially using body waves like Pn, and in some cases, stable and accurate results are obtained. We made a theoretical discussion on the polarization properties of shear waves, and found that multievents which take place occasionally within explosions can be discerned by azimuth and motion pattern monitoring.View full abstractDownload PDF (1155K) -
Nikko-Ashio and Teishi Knoll AreasGuillermo F. E. Rocco, Shigeki Horiuchi, Akira Hasegawa1997 Volume 45 Issue 1 Pages 29-40
Published: 1997
Released on J-STAGE: April 30, 2009
JOURNAL FREE ACCESSWe have estimated the stress tensor at two earthquake swarm areas in Japan, Nikko-Ashio, Tochigi Prefecture and off Ito, Izu Peninsula, by applying a technique that inverts P-wave polarity data for a large number of events under the following assumptions: 1) Stress field in a small region is uniform, 2) slips occur along pre-existing weak planes randomly distributed in the region, and 3) slip direction is parallel to the direction of the maximum shear stress. We inverted data collected by the 1993 Joint Seismic Observation in the Nikko-Ashio area. The estimated maximum principal stress in this area is nearly horizontal in the NW-SE direction and the minimum principal stress is sub-vertical. Moreover, the state of stress just beneath Nikko-Shirane Volcano is different from that in the surrounding areas. The orientation of the minimum principal stress is sub-horizontal and perpendicular to the strike direction of opening cracks found at the top of Mt. Nikko-Shirane, an active quaternary volcano. This local change is probably related to recent magmatic activity. We also analyzed data from the 1989 Teishi Knoll eruption area. The estimated direction of the minimum principal stress is parallel to that of the maximum extension of the crustal deformation measured during the submarine eruption at Teishi Knoll. Spatial variations in the state of stress off Ito were found to be small.View full abstractDownload PDF (1155K) -
Stuart Crampin, Sergei V. Zatsepin1997 Volume 45 Issue 1 Pages 41-66
Published: 1997
Released on J-STAGE: April 30, 2009
JOURNAL FREE ACCESSEarthquakes are extraordinarily complicated phenomena and deterministic prediction of the magnitude, time and place of large earthquakes is likely to be intrinsically impossible. A more simple phenomenon, the build up of deformation which leads to the earthquake, can be monitored by the behaviour of seismic shear waves, and this offers a way of forecasting the proximity of large earthquakes. Recent results, including field observations of shear waves before earthquakes, laboratory experiments with stress cells, and theoretical modelling of microscale deformation, demonstrate that long-term precursory build-up of deformation can be monitored for some years before a large earthquake. There may even be the possibility of identifying short-term precursors a few hours or days before the earthquake. This paper suggests that reliable routine earthquake forecasting would require controlled seismic experiments between a specific pattern of deep wells.View full abstractDownload PDF (2558K) -
Mamoru Kato1997 Volume 45 Issue 1 Pages 67-71
Published: 1997
Released on J-STAGE: April 30, 2009
JOURNAL FREE ACCESSDownload PDF (474K)
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