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The tectonic stress field was investigated in and around the aftershock area of the Hokkaido Eastern Iburi earthquake (MJMA = 6.7) occurred on 6 September 2018. We deployed 26 temporary seismic stations in the aftershock area for approximately 2 months and located 1785 aftershocks precisely. Among these aftershocks 894 focal mechanism solutions were determined using the first motion polarity of P wave from the temporary observation and the permanent seismic networks of Hokkaido University, Japan Meteorological Agency (JMA), and High Sensitivity Seismograph Network Japan (Hi-net). We found that (1) the reverse faulting and the strike-slip faulting are dominant in the aftershock area, (2) the average trend of P- and T-axes are 78° ± 33° and 352° ± 51°, respectively, and (3) the average plunge of P- and T-axes are 25° ± 16° and 44° ± 20°, respectively: the P-axis is close to be horizontal and the T-axis is more vertical than the average of the P-axes. We applied a stress inversion method to the focal mechanism solutions to estimate a stress field in the aftershock area. As a result, we found that the reverse fault type stress field is dominant in the aftershock area. An axis of the maximum principal stress (σ1) has the trend of 72° ± 7° and the dipping eastward of 19° ± 4° and an axis of the intermediate principal stress (σ2) has the trend of 131° ± 73° and the dipping southward of 10° ± 9°, indicating that both of σ1- and σ2-axes are close to be horizontal. An axis of the minimum principal stress (σ3) has the dipping westward of 67° ± 6° that is close to be vertical. The results strongly suggest that the reverse-fault-type stress field is predominant as an average over the aftershock area which is in the western boundary of the Hidaka Collision Zone. The average of the stress ratio R = (σ1 - σ2) / (σ1 - σ3) is 0.61 ± 0.13 in the whole aftershock area. Although not statistically significant, we suggested that R decreases systematically as the depth is getting deep, which is modeled by a quadratic polynomial of depth.
Keywords
the Hokkaido Eastern Iburi earthquake, reverse fault, aftershock distribution, focal mechanism solution, temporary seismic network, stress inversion
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This is a list of supplementary files associated with this preprint. Click to download.
- fig00.jpg
- fig00.jpg
- 1StationList.csv
Additional file 1. Temporary seismic stations
- 1StationList.csv
Additional file 1. Temporary seismic stations
- 2MecanismsList.csv
Additional file 2. Focal mechanism solutions determined in this study
- 2MecanismsList.csv
Additional file 2. Focal mechanism solutions determined in this study
- 3StressList.csv
Additional file 3. Stress parameters at each node
- 3StressList.csv
Additional file 3. Stress parameters at each node
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View the published article at Earth, Planets and Space.
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Editorial decision: Minor Revision
On 01 Sep, 2020
Review #2 received
Received 31 Aug, 2020
Review #1 received
Received 10 Aug, 2020
Reviewer #2 agreed
On 21 Jul, 2020
Reviewer #1 agreed
On 19 Jul, 2020
Reviewers invited
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See the published version of this preprint at Earth, Planets and Space.
This is a preprint, a preliminary version of a manuscript that has not completed peer review at a journal. Research Square does not conduct peer review prior to posting preprints. The posting of a preprint on this server should not be interpreted as an endorsement of its validity or suitability for dissemination as established information or for guiding clinical practice.
Learn more about In Review
Full paper
Badges
Prescreen
This manuscript passed our Prescreen assessment
Complete author information
Appropriate declaration statements
Potential risks to human health
Prescreen
Peer Review Timeline
CURRENT STATUS: Published
View the published article at Earth, Planets and Space.
Version 4
Posted 24 Nov, 2020
No community comments so far
Editor assigned
On 18 Nov, 2020
Editorial decision: Accept
On 18 Nov, 2020
Submission checks complete
On 18 Nov, 2020
Editor invited
On 18 Nov, 2020
No comments provided
Review #1 received
Received 12 Nov, 2020
Reviewer #1 agreed
On 31 Oct, 2020
Editor assigned
On 29 Oct, 2020
Reviewers invited
Invitations sent on 29 Oct, 2020
Submission checks complete
On 29 Oct, 2020
Editor invited
On 29 Oct, 2020
No comments provided
Editorial decision: Minor Revision
On 11 Oct, 2020
Review #1 received
Received 07 Oct, 2020
Review #2 received
Received 05 Oct, 2020
Reviewer #2 agreed
On 23 Sep, 2020
Reviewer #1 agreed
On 22 Sep, 2020
Reviewers invited
Invitations sent on 21 Sep, 2020
Editor assigned
On 20 Sep, 2020
Submission checks complete
On 19 Sep, 2020
Editor invited
On 19 Sep, 2020
No comments provided
Editorial decision: Minor Revision
On 01 Sep, 2020
Review #2 received
Received 31 Aug, 2020
Review #1 received
Received 10 Aug, 2020
Reviewer #2 agreed
On 21 Jul, 2020
Reviewer #1 agreed
On 19 Jul, 2020
Reviewers invited
Invitations sent on 19 Jul, 2020
Editor assigned
On 15 Jul, 2020
Editor invited
On 14 Jul, 2020
Submission checks complete
On 10 Jul, 2020
First submitted
On 08 Jul, 2020
Metrics
Comments: 0
PDF Downloads: ...
HTML Views: ...
License:
This work is licensed under a CC BY 4.0 License. Read Full License
View the published article at Earth, Planets and Space.
The tectonic stress field was investigated in and around the aftershock area of the Hokkaido Eastern Iburi earthquake (MJMA = 6.7) occurred on 6 September 2018. We deployed 26 temporary seismic stations in the aftershock area for approximately 2 months and located 1785 aftershocks precisely. Among these aftershocks 894 focal mechanism solutions were determined using the first motion polarity of P wave from the temporary observation and the permanent seismic networks of Hokkaido University, Japan Meteorological Agency (JMA), and High Sensitivity Seismograph Network Japan (Hi-net). We found that (1) the reverse faulting and the strike-slip faulting are dominant in the aftershock area, (2) the average trend of P- and T-axes are 78° ± 33° and 352° ± 51°, respectively, and (3) the average plunge of P- and T-axes are 25° ± 16° and 44° ± 20°, respectively: the P-axis is close to be horizontal and the T-axis is more vertical than the average of the P-axes. We applied a stress inversion method to the focal mechanism solutions to estimate a stress field in the aftershock area. As a result, we found that the reverse fault type stress field is dominant in the aftershock area. An axis of the maximum principal stress (σ1) has the trend of 72° ± 7° and the dipping eastward of 19° ± 4° and an axis of the intermediate principal stress (σ2) has the trend of 131° ± 73° and the dipping southward of 10° ± 9°, indicating that both of σ1- and σ2-axes are close to be horizontal. An axis of the minimum principal stress (σ3) has the dipping westward of 67° ± 6° that is close to be vertical. The results strongly suggest that the reverse-fault-type stress field is predominant as an average over the aftershock area which is in the western boundary of the Hidaka Collision Zone. The average of the stress ratio R = (σ1 - σ2) / (σ1 - σ3) is 0.61 ± 0.13 in the whole aftershock area. Although not statistically significant, we suggested that R decreases systematically as the depth is getting deep, which is modeled by a quadratic polynomial of depth.
Figure 1
Figure 1
Figure 2
Figure 2
Figure 3
Figure 3
Figure 4
Figure 4
Figure 5
Figure 5
Figure 6
Figure 6
Figure 7
Figure 7
Figure 8
Figure 8
Figure 9
Figure 9
Figure 10
Figure 10
This is a list of supplementary files associated with this preprint. Click to download.
- fig00.jpg
- fig00.jpg
- 1StationList.csv
Additional file 1. Temporary seismic stations
- 1StationList.csv
Additional file 1. Temporary seismic stations
- 2MecanismsList.csv
Additional file 2. Focal mechanism solutions determined in this study
- 2MecanismsList.csv
Additional file 2. Focal mechanism solutions determined in this study
- 3StressList.csv
Additional file 3. Stress parameters at each node
- 3StressList.csv
Additional file 3. Stress parameters at each node
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