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| Titel |
A Comparison between Deep and Shallow Stress Fields in Korea Using Earthquake Focal Mechanism Inversions and Hydraulic Fracturing Stress Measurements |
| VerfasserIn |
Rayeon Lee, Chandong Chang, Tae-Kyung Hong, Junhyung Lee, Seong-Ho Bae, Eui-Seob Park, Chan Park |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250131324
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| Publikation (Nr.) |
 EGU/EGU2016-11721.pdf |
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| Zusammenfassung |
| We are characterizing stress fields in Korea using two types of stress data: earthquake focal
mechanism inversions (FMF) and hydraulic fracturing stress measurements (HF). The
earthquake focal mechanism inversion data represent stress conditions at 2-20 km depths,
whereas the hydraulic fracturing stress measurements, mostly conducted for geotechnical
purposes, have been carried out at depths shallower than 1 km. We classified individual stress
data based on the World Stress Map quality ranking scheme. A total of 20 FMF data were
classified into A-B quality, possibly representing tectonic stress fields. A total of 83 HF data
out of compiled 226 data were classified into B-C quality, which we use for shallow
stress field characterization. The tectonic stress, revealed from the FMF data, is
characterized by a remarkable consistency in its maximum stress (σ1) directions in and
around Korea (N79±2˚ E), indicating a quite uniform deep stress field throughout.
On the other hand, the shallow stress field, represented by HF data, exhibits local
variations in σ1 directions, possibly due to effects of topography and geologic structures
such as faults. Nonetheless, there is a general similarity in σ1 directions between
deep and shallow stress fields. To investigate the shallow stress field statistically,
we follow ‘the mean orientation and wavelength analysis’ suggested by Reiter et
al. (2014). After the stress pattern analysis, the resulting stress points distribute
sporadically over the country, not covering the entire region evenly. In the western
part of Korea, the shallow σ1directions are generally uniform with their search
radius reaching 100 km, where the average stress direction agrees well with those of
the deep tectonic stress. We note two noticeable differences between shallow and
deep stresses in the eastern part of Korea. First, the shallow σ1 orientations are
markedly non-uniform in the southeastern part of Korea with their search radius
less than 25 km. In this region, the average σ1orientation based on the entire B-C
quality stress data is calculated to be 77±37˚ ; however, the average orientation is
somewhat meaningless because of the high standard deviation. The southeastern part
of Korea consists mainly of Cretaceous sedimentary basin, geologically younger
than the rest of the country, where regional scale faults are intensely populated.
The highly scattered stress directions in this region may represent the effect of the
geologic structures on shallow stress field. Second, shallow σ1 directions in the
northeastern part of Korea strike consistently to 135±12˚ , which is deviated by as much
as 56˚ from the deep tectonic stress direction. This region is characterized by
high altitude mountainous topography (an elevation of an order of 1 km) with its
major ridge axis in the NW-SE direction. We interpret, as a rule of thumb, that the
ridge-perpendicular shallow horizontal stress components may be weak, leading to the
ridge-parallel components to be the maximum. Overall, there are similarity and also
difference between shallow and deep stress fields. Thus, it will be necessary to
differentiate the strategy to tackle the stress-related problems based on their natures. |
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