IMPLICATION OF RECENT CASE HISTORIES OF
EARTHQUAKE-INFLICTED MASS MOVEMENT; A
CASE STUDIES AT OJIYA CITY AFTERMATHS THE
2004 MID NIIGATA PREFECTURE EARTHQUAKEAND AT IWAKI CITY AFTERMATHS THE 2011
FUKUSHIMA PREFECTURE HAMADORIEARTHQUAKE
Cigdem Tetik∗
MEE10510

Supervisor:

Kazuo KONAGAI∗∗ABSTRACT
Large strains built up in soils and rocks along a dislocated seismic fault can trigger post-earthquake
disasters such as landslides and debris flows, which can cause long-lasting serious problems forrehabilitations and land conservations. Therefore one of what required of us is to deduce as muchhidden signs as possible from observable change of landforms for rational rehabilitation strategies.
Recent development of remote sensing technologies has enabled us to detect precise landform changes
in the Eulerian space. However the description in the Eulerian coordinate system is to be converted toLagrangian description of displacements to cope with post-earthquake geo-hazards. In this individual
study, two examples are highlighted. One is in Uragara Hamlet, Ojiya City, Niigata prefecture in anactive folding zone of low-rise mountain terrain, which was affected by the 2004 Mid-Niigata
Prefecture Earthquake. An attempt was made to extract Lagrangian components of displacements fromavailable set of elevation data for Uragara Hamlet. The second case study is from the 2011 Fukushima
Prefecture Hamadori Earthquake. This normal-fault type earthquake triggered some landslides androck falls in Iwaki City, Fukushima Prefecture, and there is a concern that they will grow into a serious
problem given frequent aftershocks and heavy rains in summer. Much of effort is thus devoted tocompile the current exact landforms as the reference for possible future soil/rock mass movements.
Keywords: Hidden Landslides, Lagrangian Displacements, Hamadori Earthquake.

1. INTRODUCTION
Generally, landslides triggered by an earthquake are one of the most damaging natural disasters. We
have to recognize that not only shaking but also ground deformations can be equally or often more
responsible for big devastation. A big earthquake can cause large strains to be localized near theactivated seismic fault, where large scale mass movements such as landslides, rock falls and debris
flows would occur. By taking a look at historical cases, it is found that these mass movements can lastlong and cause serious problems for rehabilitations and land conservations. Such cases include theMay 8th, 1847 Zenkoji Earthquake (M7.4), October 23rd, 2004 Mid Niigata Prefecture Earthquake(M6.8) and May 12th, 2008 Wengchuan Earthquake (M7.9).
∗Republic of Turkey, Prime Ministry Disaster and Emergency Management Presidency, Recovery Department,Turkey.
∗∗Professor, Institute of Industrial Science, The University of Tokyo, Tokyo, Japan.

12. CASE HISTORIES OF EARTHQUAKE-INFLICTED MASS MOVEMENTS
Earthquake-inflicted landslides and breaching failures of landslide dams frequently occurredworldwide. A large scale landslide is a rare event, to be sure, but once it takes place, it can cause long
lasting serious problems. Two case histories of Japan, the 1707 Hōei Earthquake and the 1858 Hietsu
Earthquake which triggered big mass movements, will follow hereafter.
2.1 Oya-Kuzure and Tateyama Mass Movement
Oya-Kuzure debris flow was caused by the 1707 Hōei Earthquake (M8.6), which occurred at 14:00
local time on October 28, 1707. At least one major slope failure was triggered by the earthquake, theOhya slide in Shizuoka. This slope failure, one of the three largest in Japan, involved an area of
1.8 km2, with an estimated volume of 120 million m3. Another historical case is Tateyama(Tobiyama-kuzure) debris flow. The Hietsu Earthquake (M7.1) on April 9, 1858 caused numerous
sediment disasters along the Atotsugawa Fault system. These debris flows completely transformed theJoganji River into one of the most devastated rivers in Japan and had generated serious sediment
runoff causing ongoing problems despite numerous sabo facilities in the past century (Inoue et. al.
2010). A total of 400 million m3 debris mass reportedly flowed down the mountain side. There is 200
million m3 unstable debris mass still remaining there.
Earthquakes in active folding zones often trigger long lasting landform changes.
Examining old documents, some past earthquakes have shown that earthquakes in such active foldingzones can trigger long-lasting geological rehabilitation issues; they include the 1847 Zenkoji
Earthquake, the 1914 Akita-Senboku Earthquake and the 2004 Mid-Niigata Prefecture Earthquake(Konagai and Kazmi 2011).

3. DETECTION OF HIDDEN LANDSLIDES
3.1 Method
The development of technologies such as Laser Imaging Detection and Ranging Technology (LIDAR),Interferometric Synthetic Aperture Radar (InSAR) and Differential-InSAR enabled us to acquire theimages of landforms and the changes in elevation with high precision. On the other hand, the methods
allow us to detect displacements only in the Eulerian description, in which the description of motion ismade in terms of the spatial coordinates which does not follow the motion of soil particles.
Discussions of earthquake-inflicted geotechnical issues require more direct description of soil particle
movements because soils are typically history-dependent materials. Rather than the Euleriandisplacements, we need to extract Lagrangian displacements of soils, whose behaviors are typicallyhistory dependent. Konagai et al. (2009) obtained Lagrangian components of tectonic displacement byassuming that tectonic displacements varies gently in space, and therefore three adjacent nodes ofDigital Elevation Model (DEM) would have Lagrangian displacements. The method was later
improved by Zhao (2010) and Konagai and Kazmi (2011) for more rational and robust scheme whichallowed coherent and rotational mass movement to be extracted.
3.2 Target Area
A sequence of powerful earthquakes jolted Mid Niigata Prefecture, central Japan. The main shock
occurred at 5:56 PM JST on October 23, 2004 with its hypocenter at 37.3 N; 138.8E, its focal depth of
13km and magnitude of 6.8 determined by the Japan Meteorological Agency (JMA). The 2004 MidNiigata Prefecture Earthquake triggered and/or reactivated thousands of landslides, and the economic
loss due to these landslides was initially estimated to be about 8 billion US dollars, making this one of
the costliest landslide events in history (Kieffer et al., 2006).

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Lagrangian displacements were extracted from DEMs for the area before and after theearthquake using the method proposed by Konagai and Kazmi (2011). The extracted displacements
include both tectonic deformations caused by deep seated tectonic forces and shallow soil
displacements. Moving average method was utilized to extract deeper soil deformations, which wasexpected to show more gentle variation in space than that of shallow soils. 1.4km x 1.4km squarewindow was used for extracting lateral and vertical components of surface tectonic displacement.
Figure 1, showing lateral components of the extracted Lagrangian displacements, highlights two majorclusters of large lateral movements. One is the NNE-SSW trending 1 to 2 km wide belt of eastward
movement to the west of and along the Kajigane syncline and the other is north-westward movement
near Uragara Hamlet. Uragara Hamlet is near the projection on the ground surface of the hidden fault
rupture plane for the first largest aftershock of M6.3, which took place at 18:03 JST, about 7 minutes
after the main shock. Zoom in right on the Uragara area, Figures 2 and 3 show respectively lateral andvertical components of the extracted tectonic displacements. To obtain shallower soil displacements, asmaller square window of 200m x 200m was used, and the tectonic displacements were subtracted
from the extracted displacements through the 200m x 200m window. Then a coherent downslope mass
movement of about 1m was seen on the valley slope immediately north of Uragara. This information isreally suggestive that there are still many shear planes hidden in the interior of soils (Figure 4). Carefuland continuous eyes are to be kept on any suspicious movements of these hidden landslides.

Figure 1. Horizontal component of tectonic
displacement superimposed with landslides.

Figure 2. Lateral components of surface tectonic
displacement of the target zone on superimposedwith landslide distribution.

Figure 3. Horizontal components of surface
tectonic displacement of the target zone onsuperimposed with landslide distribution..

Figure 4. Shallow soil displacements of the targetzone, Japanese National Grid System on Zone,
VIII which are superimposed with landslides.

3Our findings about the Uragara Hamlet study are summarized as follows;
I. A strong earthquake can cause soils and rocks in its epicentral areas to be largely deformed, andtriggers long lasting geotechnical problems.
II. If there exists a hidden landslide, a hasty rehabilitation would cause too much to lose. The sourcearea of the 2004 Mid Niigata Prefecture Earthquake, we need to remember that many hidden
landslides can be reactivated especially in snow-melting times. An attempt is made herein todetect hidden coherent mass movements by reducing the smoothing window size to 200m x200m.
III. Figure 4 shows the lateral components of the detected coherent mass movements in Uragara area.
It is noted that there is a cluster of 0.5 to 1.5 meters soil displacements.

4. LANDSLIDES ALONG NORMAL FAULT TRACE
The earthquake and tsunami of March 11th, 2011 revealed vulnerabilities of disaster prevention
schemes/systems along the several hundred kilometers stretch of the Pacific Coast of east Japan, given
the tsunami heights exceeding the determined design heights. However, shaking damage to slopes wassignificantly less than what would be expected based on measured accelerations, indicating that it wasa huge but far earthquake. More seriously some inland earthquakes that followed the March 11th
Earthquake caused damage to slopes. They included the March 12th earthquake of M6.7 that took placenear the border between Nagano and Niigata prefectures and the 2011 Fukushima Prefecture
Hamadori Earthquake of M7.0 that took place in the mountainous outskirts of Iwaki City, southernpart of Fukushima Prefecture. Though they are considered to have some physical cause-and-effectlinks with the March 11th earthquake, each earthquake is quite large enough to cause serious slope
failures. All the more there is a concern that more intense aftershocks will follow these events, weneed to keep a careful eye on these landslide masses which may exhibit some more continual
movements.
4.1 The 2011 Fukushima Prefecture Hamadori Earthquake
One month after the great M9.0 the 2011 off the Pacific coast of Tohoku Earthquake of March 11th
2011 the Iwaki region of Fukushima Prefecture, was jolted by a series of moderate to large aftershocks(JMA, 2011). The largest one of them was the 2011 Fukushima Prefecture Hamadori Earthquake ofJMA Magnitude Mj7.0 or USGS magnitude Mw6.6 that occurred at 17:16 JST (08:16 UTC) on
Monday, 11 April 2011. The 2011 Fukushima Prefecture Hamadori Earthquake was followed by eightaftershocks above magnitude 4.5 in the first 24 hours, including three with magnitude greater than 5.5
and hypocenters shallower than or equal to 20 km deep (Table 1).
Table 1. According to NIED records; main shock of the 2011 Fukushima
Prefecture Hamadori Earthquake and following aftershocks above M4.5 in
the first 24 hours (from 11 to 12 April 2011)
DateApril 11th
April 12thTime
17:56
20:42
22:05
00:43
00:57
02:21
05:03
07:03
14:07

Magnitude
7.0
5.9
4.7
4.5
5.0
4.5
4.5
4.5
6.4

4

Depth (km)
6.4
10.5
11.2
10.8
10.5
20
1020
15.0

The focal mechanism of this earthquake was normal-fault type with tensional axis toward WSW-ENE,
and that was a shallow crustal earthquake. This area had been seismically inactive until the March 11th
massive earthquake occurred but frequent seismic events of the normal fault type have been reported
since then. In the 2011 Fukushima Prefecture Hamadori Earthquake, surface fault ruptures appearedalong the recognized traces of Idosawa and Yunotake Faults. Idosawa Fault is the NNW-SSE trending
right lateral strike slip fault while Yunotake fault is a NW-SE trending southwest dipping normal fault.
Figure 5 shows epicenters of the 2011 Fukushima Prefecture Hamadori Earthquake and its aftershocks
and location of both Idosawa and Yunotake Faults.
On 23rd and 24th July 2011, we made a site investigation trip around Idosawa and Yunotake
Fault areas. In this survey, five geotechnical hazards were found near the southeastern end ofYunotake Fault as shown in Figure 15. One of major concerns was that they would move again inupcoming June, the rainy season in Japan, and in possible aftershocks that might occur in rapid
succession. Therefore, much of time of our survey was devoted to gather every small sign of continualmass movements. As was explained above, there are two coherent mass movements (No. 1 and 2), tworock falls (No. 3 and 4) and one lateral spread (No. 5) in Figure 6 near the southeastern end ofYunotake Fault. It is also noted there was a conjugate fault of Yunotake appeared near No. 1 and 2.

YUNOTAKE
FAULT
IDOSAWA
FAULT

Figure 5. The 2011 Fukushima Prefecture
Hamadori Earthquake location andaftershocks distribution between
07.04.2011-14.04.2011. White star refers the2011 Fukushima Prefecture Hamadori
Earthquake and white circles aftershocks.

Figure 6. Iwaki city mass movement locations.
1-Gosaisho Highway Landslide Area, 2- Landslide
Area Near The High School, 3- Rock Fall Area Near
The House,, 4- Rock Fall Area Outside Of The
Settlement Area, 5- Iwasaki Lateral Spreading Area.

Among the above mentioned five locations of geo-hazards, Landslide No. 1 is seemingly themost serious. The coherent soil mass moved down the slope, burying the road which was constructedby cutting the toe of the slope (Figure 16). One person, whose vehicle happened to pass by, was founddead in the landslide mass. Knowing the importance of that road, a new temporary road is planned tobe constructed over the landslide mass to restate the route. It was, therefore, important to monitor thegradual movement of the landslide mass given the current landform as reference. Seismic activity is
still high at Iwaki city and its vicinity. Moreover rains are expected in June, July and August.
Therefore one of the most serious concerns in the affected areas is if these landslides will move again
they frustrate all attempts for rehabilitation Our findings through the site investigation are summarized
as follows:
I. The 2011 Fukushima Prefecture Hamadori Earthquake, in which Idosawa and Yunotake faults
appeared as vertical offsets, triggered landslides and rock falls in Iwaki.
II. Mountains along Idosawa Fault were generally higher than those along Yunotake Fault.
III. Major geo-hazards including two cohesive mass movements, two rock falls and one lateral spread
were found near the southeastern end of Yunotake Fault, though.
IV. The hypocenters of the 2011 Fukushima Prefecture Hamadori Earthquake and its aftershocks
lined up not Yunotake Fault but Idosawa Fault.
V. Vertical offsets observed along Idosawa Fault were in general larger than those along Yunotake

5Fault.
VI. There appeared a conjugate fault near the southeastern end of Yunotake Fault. The largest mass
movement was found at around where the conjugate fault dies out. Although no clear evidence
was observed, it is possible that the conjugate fault might have skimmed the landslide area and isresponsible for triggering the landslide.
VII. Along Idosawa Fault, Abukuma metamorphic rocks are found while along Yunotake Fault, soft
sedimentary deposits are clearly observed. This geological difference may have been the cause of
geo-hazards distribution.

5. CONCLUSIONS
Earthquake induced landslides often cause serious destruction, which is often more serious
than the immediate aftermath of the earthquakes. Historical data shows that both visible and hidden
landslides can cause long lasting geotechnical problems for rehabilitations. In this individual study two
examples were highlighted. One is in Uragara Hamlet in an active folding zone of low-rise mountainterrain, which was affected by the 2004 Mid Niigata Prefecture Earthquake. Though no distinct signof a cohesive mass movement was reported on the valley slope of the Asahi River immediately northbehind Uragara Hamlet, pavement of the National Route #291 was buckled up in this hamlet
indicating the presence of a hidden landslide. A coherent downslope mass movement of about 1m wasseen on the valley slope immediately north of Uragara. This information is really suggestive that there
are still many shear planes hidden in the interior of soils. Careful and continuous eyes are to be kept on
any suspicious movements of these hidden landslides.
The 2011 Fukushima Prefecture Hamadori Earthquake was considered to have somephysical cause-and-effect link with the March 11th earthquake, and this earthquake was quite large
enough to cause serious slope failures. Seismic activity is still high at Iwaki city and its vicinity.
Moreover rains were expected in June, July and August. Therefore one of the most serious concerns in
the affected areas was if these landslides would move again frustrating all attempts for rehabilitation,and it was necessary to keep a careful eye on these landslide masses.
On the basis that the method for extracting Lagrangian components of mass movements
would be used in future, it was proven to be useful for coherent mass movements in mountain terrains.
However, the obtained images are a mere indicator of hidden mass movements without clear-cut
information of depths. Therefore it is necessary for this method to be combined with the otherinvestigations so that causes of landform changes will be rationally discussed in a comprehensive
manner. More case-histories are to be analyzed for more advanced use of the method for disasterpreventions and land conservations.
AKNOWLEDGEMENT
I would like to express my heartiest gratitude to my advisor Dr. T. Yokoi (IISEE, BRI) for giving mevery useful pieces of advice and suggestion during my individual study.

REFERENCES
Inoue, K., Mizuyama, T. and Sakatani, Y., 2010, Journal of Disaster Research, 5, 245-256.
Kieffer, D.S., Jibson, R., Rathje, E.M. and Kelson, K., 2006, Earthquake Spectra, 22, S47-S73.
Konagai, K. and Kazmi, Z. A., 2011, Book Chapter, Earthquake Research and Analysis / Book 2,
ISBN 979-953-307-273-8 (accepted for publication).
Konagai, K, Fujita T, Ikeda T, and Takatsu S., 2009, Soil Dynamics and Earthquake Engineering,
29:261-267.
Zhao, Y., 2010, Institute of Industrial Science, University of Tokyo, Phd Thesis.

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