Sub-theme
4.1 The 1940 Shakotan-Oki Earthquake
4.2.5 Validity of the fault model
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3. 4.2.4 Calculation conditions of the tsunami propagation analysis
Table 4-7 shows the calculation conditions of tsunami propagation analysis．
126
model was set to 70° based on reflection seismic data of 0–5 km. In the deepest parts, the tilt of the fault area was set to 30°.
Fig. 4-13 shows the comparison of the two plates of the tilt angle model. There is a tendency that tsunami height fluctuates widely in the area of the opposite shore of the region of the main two faults (Nakadomari and Fukaura) excluding the northern end (enclosed in a red dotted line in Fig. 4-13). This study compared this tendency with tsunami trace heights in the coastal area (Fig.
4-14). Maximum tsunami heights were used to select reliability level A, B; these data were obtained from the Japan Tsunami Trace database [7]. The tsunami trace points in the inland area correspond to the 150-m mesh of the surrounding coast. The blue line in the figure is the calculation result of the fault model of Chubu - 11, and the gray line shows the maximum value of all calculation results at each evaluation point.
In the Matsumae region, by setting the large slip region of the northern fault to the south of the two main faults, the tsunami heights decreased and tended to approach the trace heights. Even in the Kojima region, similar to the Matsumae region, when the large slip regions of the northern fault plate was set to the southern end, tsunami tended to approach the trace heights. In the Nishi-Tsugaru region, setting the large slip region of the northern fault plate to set to the southern end made the tsunami higher than the trace heights. Setting the large slip region of the northern fault plate to set to the northern end made closer to the trace heights. In the Noshiro region, the tsunami trace heights were locally high, and it was impossible to reproduce the tsunami trace heights in all fault models. In addition, in the Oga Peninsula region, the estimated tsunami heights tended to be higher than the tsunami trace heights in all fault models.
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Fig. 4-10 Wave source fault models for the Nihonkai–Chubu earthquake.
Chubu-11（L/R） Chubu-12（L/L） Chubu-21（R/R） Chubu-33
Fig. 4-11 Combination pattern of the examined large slip regions.
Chubu-32（C/L） Chubu-23 (R/C) Chubu-31（C/R） Chubu-13(L/C)
128
Fig. 4-12 Example of a survey line cross-section with a change in the tilt angle model.
(a) P-wave velocities are used to identify the marine reflection seismic prospecting image collar
(b) Fault modeling of a change tilt angle (image).
Seabed c.a. 5 km
Conrad discontinuity
30 deg.
apparent dips:
70 deg.
a
b
129 .
Fig. 4-14 Comparison of maximum tsunami heights and tsunami trace heights in the two tilt angles model.
Simulated maximum tsunami heights along the eastern part of the Sea of Japan (blue lines) with tsunami traces (level A: red circles; level B: orange circles) and tsunami heights of combined the maximum cases (gray lines) for each model.
Fig. 4-13 Comparison of the one/two plats of the tilt angle model.
Tsunami trace
● Level A
● Level BC
Matsumae
Koima
Kitatsugaru NIshitsugar
u Noshiro
Oga
130 (2) Second stage inspection
Based on the first stage inspection, this study reduced the tsunami heights in the northern region and examined how to set a high fault model in the Noshiro region. If large slip regions were not set in the fault on the north side, the fault shape from JAMSTEC, the maximum tsunami heights in the coast, and the tsunami trace heights were compared when the large slip region’s position, area, aspect ratio were changed (4 cases: Fig. 4-15). Using Chubu - 11 as a comparative model, the amount of moment released by large slip regions is the basic model. The study case is as follows.
· Chubu - 11 W–S: The fault width was set to about half, and it was set only on the south side of the fault, to not change the area of large slip regions.
· Chubu - 11 W: The fault width was set to about half, and it was set on the south and north sides, to not change the area of large slip regions.
· Chubu - 11h - S: Half the area of large slip regions was set only on the south side of the fault.
In the Matsumae region, in all cases the maximum tsunami heights (gray lines) surmount tsunami traces (level A: red circles; level B: orange circles). The maximum tsunami heights (blue lines) of the selected four cases reproduce tsunami traces. In the Kojima region, approaching the trace heights was the large slip region of the northern fault plate to shorten in the southern end (Chubu-11W (L/R), 11(L/R)). However, the average slip value of the whole fault when the large slip regions were not set was larger than the slip amount of the background area when large slip regions were set. Thus, the slip amount of the fault in the area closest to Kojima was getting larger, and the analyzed tsunami heights got higher. The simulated value tended to exceed the tsunami trace heights in the Nishitsugaru region. This study approached the tsunami trace heights by not setting large slip regions in the fault on the north plate (Chubu-11h-S (/R), 11W-S (/R)). In this case, however, it was difficult to satisfy the conditions of trace heights in the Kojima and Nishitsugaru regions at the same time because the trace heights were higher in the Kojima region. In the Noshiro region, trace heights could not be reproduced. In the Oga Peninsula region, the trace heights reproduced in case of the
131
length of the large slip regions on the south plate were shorter (Chubu-11W (L/R), 11W-S (/R)).
Thus, the tsunami in Matsumae region explained the trace heights largely by the large slip regions of the north fault not being set (Chubu-11h-S (/R), 11W-S (/R)). In addition, in the Nishitsugaru region, the analyzed tsunami heights tended to be somewhat higher than the trace heights, and in the Noshiro region. The results that reproduced the trace heights obtained in this area were obtained by setting large slip regions, and the fault was not so significant even changed fault shape.
132
Fig. 4-15 Comparison of maximum tsunami heights and tsunami trace heights in large slip regions Simulated maximum tsunami heights along the eastern part of the Sea of Japan (blue lines) with tsunami traces (level A: red circles; level B: orange circles) and tsunami heights of combined the maximum cases (gray lines) for each model.
Max Chubu4 Level A Level B
Max Chubu4 Level A Level B
Max Chubu4 Level A Level B
Max Chubu4 Level A Level B
Nishitsugaru
Noshiro
Oga peninsula Matsumae
Kojima
Tsunami Hight (m)
Tsunami Hight (m)
Tsunami Hight
(m) Tsunami Hight
(m)
Tsunami trace
● Level A
● Level BC
Tsunami trace
● Level A
● Level BC
Tsunami trace
● Level A
● Level BC
Tsunami trace
● Level A
● Level BC
133 (3) Third stage inspection
This model had longer faults than the Aida (1984) [8] model and the research organization meeting about large-scale earthquakes in the Sea of Japan (MLIT (2014)) [17] model, which was organized by the Japan Ministry of Land, Infrastructure, Transport and Tourism (MLIT). The moment magnitudes of the fault models set in the MLIT study is Mw 7.91 for two fault models and Mw 7.97 for three fault models. However, the size of the fault model of the study for the Aida model was Mw 7.7. The Sato (1985) [21] model used Mw 7.9, which corresponded with the previous study of the two fault models covered in this study. The length of the fault of this study is much longer than that of the previous study. In the previous study, the fault plane of the Nihonkai–Chubu earthquake was set to a low angle, so the fault width was larger. Compared with the fault shape used in this study and the aftershock distribution, the southern tip of the fault model by the JAMSTEC trace reached the southern part of the Oga Peninsula region. However, the aftershock distribution was within the northern part of the Oga Peninsula region. The northern end of the fault model reached the Matsumae Peninsula in Hokkaido. The area where there were frequent aftershocks was off the coast of the southern part of Aomori Prefecture. Fig. 4-16 shows the fault model.
134
The fault length was set by considering the combination of aftershock faults. As a result, the length to be set was about 10 km longer than the fault length of the Aida (1984) [5] study, which was close to the previous study (about 110 km) by Aida (1984) [8]. The fault angle in the previous study, at 30°, was considered to be low, according to the Recipe [1] developed by the Headquarters for Earthquake Research Promotion.
The angle of inclination was changed so that the fault angle was the high angle in the shallow parts of the fault as high and the low angle in deep parts. The magnitude was Mw 7.61 and the scale became slightly smaller than that in the previous study.
The model setting of the fault showing with a change in the tilt angle model the result in Fig. 4-17 is shown below.
Fig. 4-16 Comparison of the proposed model, the Aida (1984) [5] model and the MLIT (2014) [17]
model.
Proposed model Aida（1984）
MLIT（2014）
135
· Chubu - 30 deg - BLR: Fault angles were set at 30°. The large slip region was set to the lower part of the fault on the north plate and the south plate.
· Chubu - 30 deg - BR: Fault angles were set at 30°. Only the fault on the south plate and large slip region on the lower part were set.
Chubu - 30 deg - BR - 2 pt: The fault angles with shallow parts and deep parts were changed to make an average of 30°. Only the fault on the south plate set the large slip region on the lower parts.
Chubu - 45 deg - BR - 2 pt: The fault angles with shallow parts and deep parts were changed, making an average of 45°. Only the fault on the south side set the large slip region on the lower parts.
The calculations of the four simulated maximum tsunami heights shown in Fig. 4-17 were almost the same as the tsunami trace heights in the Matsumae and Kojima regions, and the same as the tsunami trace heights in the Nishitsugaru region. A high degree of maximum tsunami height was calculated. In the Noshiro region, the maximum tsunami heights were lower than the tsunami trace heights. However, in the Oga Peninsula region, the same result as maximum tsunami height and the tsunami trace heights were obtained in Chubu - 30 deg – BR case. From these results, this study could explain the tsunamis from the Nihonkai–Chubu earthquake by considering the combination of faults based on aftershock distributions. The above discussion is an outline calculation using a topography model with a minimum mesh size of 150 m. In this study, a fault model was chosen for detailed calculation using a topological model of a 50-m mesh for a tsunami propagation analysis
136 4.2.6 Comparison with Previous Studies
The fault model that contributes to the detailed calculation of the model of 50-m mesh selected as the result of preliminary calculation of the tsunami propagation analysis using the 150-m mesh model. The calculated area of the tsunami prediction analysis is shown in Fig. 4-18. The calculation area was subdivided at a ratio of 3:1 from the open ocean to the coast. The mesh size of each calculation area was 1350 m, 450 m, 150 m, and 50 m from the open ocean toward the coast. The topological model from FY2005 was used in this project [1,2]. For the calculation conditions, the mesh size and the calculation time under the conditions shown in Table 4-8 were changed to 6 hours.
The results of the tsunami prediction analysis are shown in Fig. 4-19. Fig. 4-20 shows the maximum tsunami heights and trace heights. To validate the fault model in the present study, we compared the coastal maximum tsunami heights and trace heights of tsunami propagation analysis.
The maximum tsunami heights were used to calculate the values of K and κ [5] to select the fault model; these data were obtained from the Japan Tsunami Trace database [7] as shown Table 4-8.
The maximum tsunami heights were compared the values of K and κ based on the Aida (1984) [8] fault model. The K values were in the 1.35 range and the κ values were below 1.58. For the fault model set in this study, high relative K–κ was obtained with the following two patterns. The first model of case 3 was set to a low angle (30°) on the south side large slip region model, which had K values in the 1.01 and κ values below 1.56. In the fault model of Aida (1984) [5] and the fault model set in this study, the value of K had a large range of fitness from 0.89 to 1.51. However, the value of κ varied greatly from 1.53 to 1.62 (Table 4-8). According to the Nuclear Civil Engineering Committee [7], these values are recommended for use under the following conditions: K values in the 0.95–1.05 range and κ values below 1.45. Results in this range were not obtained in these cases.
However, the value of K obtained multiple calculation results falling within the range 0.95 <K <1.05.
Regarding the reproducibility of the tsunami heights, this study demonstrated a fault model that reproduced the tsunami heights caused by the Nihonkai–Chubu earthquake.
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Table 4-8 Fault models by using reliability of tsunami trace with K-κ value.
Model name Fault area Angle Large slip K κ
① Chubu-AIDA Aida
(1984) 40°, 25° － 1.35 1.58
② Chubu-3f_30deg Aftershock 30° － 1.45 1.53
③ Chubu-3f-R Aftershock 30° Upper end of the
South Fault 0.97 1.53
④ Chubu-30deg-BLR Aftershock 30°
Lower end of the North and South
Fault
0.92 1.58
⑤ Chubu-30deg-BR Aftershock 30° Lower end of the
South Fault 1.01 1.56
⑥ Chubu-30deg-2pt Aftershock 69°, 22.6° － 0.98 1.60
⑦ Chubu-30deg-BR-2pt Aftershock 69°, 22.6° Lower end of the
South Fault 0.89 1.62
⑧ Chubu-3f-2pt_45deg Aftershock 69°, 37.4° － 1.51 1.59
⑨ Chubu-3f-R-2pt Aftershock 69°, 37.4° Upper end of the
South Fault 1.32 1.56
⑩ Chubu-45deg-BR-2pt Aftershock 69°, 37.4° Lower end of the
South Fault 1.38 1.60
138
Fig. 4-18 Calculation area of the tsunami prediction analysis for each mesh size.
Red 50 m mesh Blue 150 m mesh Green 450 m mesh Whole area 1350 m mesh
139
Fig. 4-20 Tsunami traces (red) and tsunami propagation analysis results at the eastern part of the Sea of Japan in the Nihonkai–Chubu earthquake (Recommended model within the red dotted frame).
Fig. 4-19 Maximum tsunami propagation analysis results (T.P. 0 m).
① ② ③ ➃ ⑤ ⑥ ⑦ ⑧ ⑨ ⑩
140 4.2.7 Conclusions
This study validated the fault model in the source area of the 1983 Nihonkai–Chubu earthquake.
Validity verification was conducted using tsunami propagation analysis with the comparison of the project [4] fault models and previous models [5, 17-21]. Observation records of maximum tsunami heights, trace heights and geodetic data on the coastline of K–κ were obtained from the tsunamis, and the scale of the tsunamis was quantified and evaluated.
In the selection of the fault model were detailed for the calculations by parametric studies. This study examined the modeling method of fault data obtained in the JAMSTIC project. The following results were obtained.
1) For the fault model two cases were prepared: a constant fault angle and a case where the fault angle was high in the shallow part and the low in the deep part. In addition, a parametric study was conducted with eight patterns of large slip region positions. As a result, there was a difference in the fault parameter setting in the area near the opposite shore, which was the boundary between the north and the south faults. These areas increased the variation in coastal tsunami height rise. By setting the large slip region of the fault on the north side from the south, the maximum tsunami heights in the Matsumae region approached the trace heights. In the Noshiro region, trace heights were locally high, so this study could not reproduce them.
2) Based on the first stage inspection, this study performed multiple patterns and parameter studies of fault models with different large slip region setting methods. This study considered a fault model that sustained tsunami heights in the northern part of the calculation area low and gathered high waves in the Noshiro region. As a result, the trace heights in the Matsumae region could be explained largely by not setting a large slip region at the north fault. Regarding Noshiro's surroundings, it was impossible to achieve a tsunami height that could reproduce. In the Noshiro region, it was reported that a soliton wave was observed by the previous study, which may have possibly resulted in local high tsunami heights.
141
3) Based on the first stage to third stage inspections of this study, the difference between the fault model in the previous study and the aftershock distribution of the Nihonkai–Chubu earthquake were compared. As a result, a fault model referencing the aftershock distribution was set up. Tsunami propagation analysis was carried out and compared where the fault angle was set low (30°) and where it was normal (45°). The fault angle was changed in the tilt angle model.
This study examined how to set the large slip region. As a result, by setting the fault model by considering the aftershock distribution, we generally explained the tsunami trace heights caused by the Nihonkai–Chubu earthquake. This study selected the fault model for verification by quantitatively judging the fitness of the model using the result of K–κ parameter study.
In the tsunami propagation analysis of the Nihonkai–Chubu earthquake, this study used the 50-m mesh topographic model based on the fault model selected by the above parameter study. The reproducibility of the tsunamis created by Nihonkai–Chubu earthquake were investigated.
4) The maximum tsunami heights were compared the values of K and κ based on the Aida (1984) [8] fault model. The K values were in the 1.35 range and the κ values were below 1.58.
・K–κ was obtained with the following two patterns among fault models set in this study.
a) The slope angle was set low (30°) and a large slip region was set only on the south fault plate in the north end portion.
b) In the slope angle was low, the large slip region was set from the north end of the south fault plane.
For a), K–κ obtained was K = 0.97, κ = 1.53. For b), K = 1.01, κ = 1.56.
5) In the fault model of Aida (1984) [5] and the fault model set in this study, the value of K had a large range of fitness from 0.89 to 1.51. However, the value of κ was 1.53 to 1.62, which was a large difference. As a criterion of conformity in the Civil Engineering Society Nuclear Power Civil Engineering Committee, κ <1.45 was set. However, results falling within this range were not obtained in this study. For K, several calculation results falling within the range of 0.95 <K
<1.05 were obtained.
142
6) Based on the fault data obtained by referring to geological, topological and seismological data, such as aftershock distribution, it is possible to estimate tsunami height past earthquakes.
The possibility of explaining the tsunami trace heights caused by an earthquake was demonstrated.
143 Reference
[1] Strong ground motion prediction method ("Recipe") for earthquakes with specified source faults (2009), Headquarters for Earthquake Research Promotion [in Japanese].
[2] Irikura K. and Miyake H. (2001), Prediction of Strong Ground Motions for Scenario Earthquakes, J., of Geography, 110(6), 849-875.
[3] Satake K (1986), Re-examination of the 1940 Shakotan-oki earthquake and the fault parameters of the earthquakes along the eastern margin of the Japan Sea, Phys. Earth and Planetary Int, 137-147, 1986.
[4] Project for the Comprehensive Analysis and Evaluation of Offshore Fault Informatics (2015), The Headquarters for Earthquake Research Promotion, [in Japanese].
[5] Aida, I. (1978), Reliability of a tsunami source model derived from fault parameters, Journal of Physics of Earth, Vol.26, pp. 57–73.
[6] Tsunami Assessment Method for Nuclear Power Plants in Japan (2006), The Tsunami Evaluation Subcommittee, The Nuclear Civil Engineering Committee, JSCE (Japan Society of Civil Engineers), 321p.
[7] Japan Tsunami Trace database, Tsunami trace height information, International Research Institute of Disaster Science (IRIDeS), Tohoku University,
[8] Tanioka, Y. and Satake, K. (1996), Tsunami generation by horizontal displacement of ocean bottom, Geophys. Res. Letters 23, 861-864.
[9] Okada, Y. (1992): Internal Deformation due to Shear and Tensile in a half-space, Bull. Seismol.
Soc. Am., 85, 1018–1040.
[10] Geospatial Information Authority of Japan, Measurement of the sea level at a tide station, [in Japanese]
[11] Miyabe N (1941), Tunami associated with the Earthquake of August 2, Bull. Earthq. Res. Inst., Univ. Tokyo, 104–114 [in Japanese].
[12] Kaneda, Y., Takahashi, N., Oikawa, N.,Ohsumi, T. and Fjiwara, H. (2014), Comprehensive Analysis and Evaluation of Offshore Fault Informatics，Seismological Society of Japan, autumn meeting in 2014.[in Japanese with English abstract]
[13] Ohsumi, T., Norimatsu, K.,, Matsuyama, H. and Fujiwara, H. (2015), Consideration of Fault Modelling for the Japan Sea Area based on the “Off Shore Faults Research Project”, Seismological Society of Japan, autumn meeting in 2015. [in Japanese with English abstract]
[14] No, T., Hiramatsu, T, Sato, T., Miura1, S., Chiba, T., Kamiyama, S., Iki, S. and Kodaira, S.
(2016)，Red relief image map and integration of topographic data in and around the Japan Sea.
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JAMSTEC Report of Research and Development, 22, p. 13-29, doi: 10.5918/jamstecr.22.13. V [in Japanese with English abstract]
[15] No, T., Hiramatsu, T, Sato, T., Kodaira, S. and Kaneda, Y. (2012), Seismic Reflection Survey in the eastern margin of the Japan Sea, Ultrasonic Technology, 24, 6, 15-20. [in Japanese]
[16] Takagi, A. Hasegawa, A., Saijyo, T., Yamamoto, A. and Misada, M., et al. (1984), General study of the disaster by the 1983 Nihonkai–Chubu earthquake, 2.2 Seismic activity before and after the main shock， Ministry of Education’s Res. Grant Program (No.58022002) , Catastrophic failure disaster results of research of Research in Natural Disaster Report, pp. 24-30. [in Japanese]
[17] Tada, T. (1984), Nihonkai–Chubu earthquake and crustal movements, The Earth Monthly, Vol.
6, pp.18-21. [in Japanese]
[18] Tanaka, K., Sato, T., Kosuga, M. and Sato, H. (1984), General study of the disaster by the 1983 Nihonkai–Chubu earthquake, 2.4 Characteristic of Nihonkai–Chubu earthquake， Ministry of Education’s Res. Grant Program (No.58022002) , Catastrophic failure disaster results of research of Research in Natural Disaster Report，pp. 39-45. [in Japanese]
[19] Satake, K. (1985), The mechanism of the 1983 Japan Sea earthquake as inferred from long-period surface eaves and tsunamis, Physics of the Earth and Planetary Interiors, 37:249-260.
[20] Kanamori, H. and Astiz, L. (1985), The 1983 Akita-Oki Earthquake (Mw = 7. 8) and Its Implications for Systematics of Subduction Earthquakes, Terra Scientific Publishing Company (Terrapub), Tokyo, Japan. Earthq. Predict. Res. 3 (1985) 305 317.
[21] Sato, T. (1985), Rupture Characteristics of the 1983 Nihonkai Chubu (Japan Sea) Earthquake as Inferred from Strong Motion Accelerograms, J. Phys. Earth, 33:525-557.
[22] Kosuga, M., Ikeda, H., Kamazuka, Y. and Sato, H. (1986), Static Fault Model of the 1983 Nihonkai-Chubu (Japan Sea), Earthquake as Inferred from Aftershock Distributions, Crustal Deformation, and Tsunami Data，Journal of the Geodetic Society of Japan，Vol.32, No.4, 290-302.
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145
Chapter 4
Development of a Real-Time Damage Estimation System for Embankment Using Earthquake Early Warning Information
1. Motivation
In cases where river embankments are damaged by an earthquake, any damage could be exacerbated by subsequent tsunami run-up. Following the occurrence of an earthquake, it takes time to detect damage done to linear structures such as river embankments. Moreover, because of the characteristics of seismic waves, it is difficult to identify in advance those areas likely to be affected most. Based on both the seismic intensity distribution identified immediately following an earthquake early warning and the seismic intensity measured by seismographs, the application proposed herein could be used to identify potential disaster sites. Therefore, the application could be a valuable asset in the coordination of initial disaster response in regions where tsunamis occur frequently.
Specifically, the application has two primary elements: (1) issue an emergency earthquake bulletin for affected basins and (2) estimate the magnitude of embankment subsidence using relational expressions between seismic intensity and subsidence. Based on assumed disaster areas, the proposed application could be used to select areas of priority for surveying and to identify evacuation routes immediately following an earthquake. By assuming arbitrary hypocentres and estimating the potential damage by virtual earthquakes, river administrators could consider necessary emergency measures in advance.
Keywords— 2011 off the Pacific Coast of Tohoku Earthquake, Earthquake Early Warning (EEW), embankment, settlement
146 2. Introduction
Certain limitations of the Earthquake Early Warning (EEW) system in Japan became apparent during and after the 2011 off the Pacific Coast of Tohoku earthquake. To overcome these problems, this study propose a method that uses “Earthquake Damage Estimation Tables” for automatic analysis and correction of detection errors evident when embankment settlement occurs. Thus, embankment damage attributable to large earthquakes could be evaluated.
The proposed application offers a solution to the problems of underestimation of the magnitude and seismic intensities of major earthquakes, and the fact that alarms were announced to areas within a certain definite range of the epicentre without consideration of the seismic intensities estimated using empirical equations. Our method could be used by licensed operators in the event of major earthquakes. For example, it has been applied to a prototype of a decision-making support system for an expressway company. This study have also considered the possibility of false alarms in cases when two earthquakes might occur close to one another. The probability of false alarms has been quantified and a decision-making support system developed to improve the operational characteristics of the proposed disaster prevention system.