JSCE Journal of Disaster FactSheets, FS2022-E-0002, 2022

Geotechnical Preliminary Report of The Mj 7.3 Fukushima Earthquake on March 16, 2022
Masataka SHIGA1, Kwok-Kwan LAU2, Pei-chen HSIEH3, and Takashi KIYOTA4
1Member of JSCE, Assistant Professor, Institute of Industrial Science, The University of Tokyo

(4-6-1, Komaba, Meguro, Tokyo 153-8505, Japan)
E-mail: shiga815@iis.u-tokyo.ac.jp
2 Ph.D. student, Dept. of Civil Eng., Graduate School of Eng., The University of Tokyo
(4-6-1, Komaba, Meguro, Tokyo 153-8505, Japan)
E-mail: jklau@iis.u-tokyo.ac.jp
3 Member of JSCE, Ph.D. student, Dept. of Civil Eng., Graduate School of Eng., The University of Tokyo
(4-6-1, Komaba, Meguro, Tokyo 153-8505, Japan)
E-mail: hsieh@iis.u-tokyo.ac.jp
4 Member of JSCE, Associate Professor, Institute of Industrial Science, The University of Tokyo
(4-6-1, Komaba, Meguro, Tokyo 153-8505, Japan)
E-mail: kiyota@iis.u-tokyo.ac.jp

Key Facts
・ Hazard Type: Earthquake
・ Date of the disaster: March 16th, 2022
・ Location of the survey: Fukushima Prefecture and Miyagi Prefecture
・ Date of the field survey: March 21st and 22nd, 2022
・ Survey tools: Photos, videos, UAV, and LiDAR・ Key findings(1) Cracking, ground settlement, and ground deformation were observed in the roads, bridge approaches, and embankments in Fukushima Prefecture and Miyagi Prefecture(2) The landslides in Date Dam, Unoomisaki Tunnel portal area, and Tarumizu Dam could be
associated with the strong ground motion of this earthquake event.
(3) Liquefaction was also identified in Soma Port of Fukushima Prefecture.
Key Word: The 2022 Earthquake off the coast of Fukushima Prefecture, Ground Damage, Slope Failure,
Liquefaction

However, the 2022 earthquake ruptured the fault
plane in a northeast direction, which is different fromthe behavior of the two previous earthquakes.
The most significant peak ground acceleration
PGA was 1232.7 gal at Kawasaki Seismic Station in
Miyagi Prefecture (MYGH07) of the KiK-net strongmotion seismograph network3). In addition, someother seismic stations in the surrounding area recorded an intense acceleration, such as Shinchi Town
of Fukushima Prefecture and Yamamoto Town of
Miyagi Prefecture. Furthermore, level 4 of the longperiod ground motion scale of JMA was alerted inseveral cities in Miyagi Prefecture4).
This paper aims to summarize ground damage induced by the 2022 earthquake. The survey was conducted on March 21st and 22nd, 2022. The

1. INTRODUCTION
An intense earthquake of Mj 7.3 or Mw 7.4 (JMA,2022) occurred on March 16th, 2022, off the coast of
Fukushima Prefecture. The epicenter (37.697N,
141.621E) was about 60km deep. The maximum intensity observed was 6+ on the JMA intensity scale inTome City and Zao Town of Miyagi Prefecture, andKunimi Town, Soma City, and Minami-Soma City ofFukushima Prefecture1).
The earthquake fault was located within the subduction zone of the Pacific Plate and subjected to acompressive field oriented in the east-southeast direction2). Several earthquakes have similar fault rupture mechanisms, such as the earthquake on February
13th, 2021 (Mj 7.3) and April 7th, 2011 (Mj 7.2).
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slope along the Dake Walking Trail on the southernpart of Dake Dam, as shown in Fig.3. The slope angle
was about 60 degrees. The shotcrete facing the slope
fell onto the path exposing the partially weatheredmudstone behind. The geological map of AIST5)
shows that the local surficial geology of the adjacentarea is classified as granite formed during the Cretaceous Period. Granite can lose its stiffness due toweathering because it contains compositional minerals with different coefficients of thermal expansion5).
Therefore, the shear resistance of the weathered mudstone was possibly exceeded by the sliding force during the earthquake event, causing shallow failure on
the slope.

investigation locations are within the affected area inFukushima Prefecture and the southern part of
Miyagi Prefecture, as shown in Fig.1. Photos, videos,
UAV, and LiDAR implemented on a mobile phone
were used for the documentation.

2.
DAMAGE
PREFECTURE

IN

FUKUSHIMA(1) Minami-machi, Yabuki Town
Fig.2 shows the damage on the shoulder of a local
road next to a hotel facility, which stands over the
Kumato River. Cracks or a cavity had developed overan area of 2m by 4m and were covered with blue
sheets. Upslope of the ground settlement, there weretraces of repaired works in the parking lot’s pavementof the hotel. In addition, fresh soil could be seen in ahollow area on the downslope side. These suggestthat the earthquake may have induced loosening of
the cavity in the ground. Nevertheless, the UAV survey identified no significant deformation in the
nearby bridge abutment or concrete revetment along
the river.

(3) Tohoku Shinkansen viaduct, Kunimi Town
One Tohoku Shinkansen viaduct pier at 15km
northeast of Fukushima Station suffered from tilting
after the earthquake. The pier inclined towards the direction of the Shiroishizao Station. The lower part ofthe viaduct showed a typical shear failure; the failureof the cover concrete and buckling of the axial reinforcement bars, based on the preliminary report fromthe East Japan Railway Company7). The direct causeof the shear failure can be attributed to the insufficient(2) Dake Dam, Nihonmatsu City
A small-scale slope failure occurred on the steep

Fig.1 Survey route, investigation sites, the epicenter of the earthquakes on March 16th, 2022, February 13th, 2021 and April 7th, 2011,
and the seismic stations that recorded 6+ on the JMA intensity scale
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shear strength of the pier because no land subsidence
was observed around the pier. As shown in Fig.4, restoration works have been in progress to realign theharmed pier when our team arrived
The Active Fault Map from the Geospatial Information Authority of Japan (GSI)8) shows the damaged pier locates on the alluvial plain of the Takigawa
River, neighboring a higher terrace in the southeast(Fig.5). The higher terrace on the downstream of the
Takigawa River has been lifted up because of two reversal faults called Fujita East Fault and Fujita West
Fault. These liftings could change the flow directionof the Takigawa River and might result in depositinga loose and soft sedimentary layer around the affectedsite.
Fig.6 shows the absolute inclination angle of thecatenary poles near the site, based on a 3D model created from the sequential images of the UAV9). The
pole above the inclined pier was named CP_8. The
suffix number decreases as the pole is located westsouthward. CP_5 is almost above the boundary between a lower terrace and the alluvial plain of the
Takigawa River. Fig.6 indicates that the angle of thepoles near the boundary is larger than one in otherareas. Although other factors such as pier length or
steel lining may affect the pole behavior, the difference in the inclination angle implies the local topography changing the damage characteristics.

Fig.2 Cracked and subsided area in Yabuki Town of Fukushima
Prefecture (a) Whole view, (b) Subsided area of 2m by 4m,(c) Backfilled area in the parking lot(4) Soma Port Quay No. 2 and No. 5
At Soma Port, ground settlement of approximately
0.5 m to 1 m was recorded at Quay No. 2, as shownin Fig.7. The 5m-thick quay wall concrete block has
moved towards the sea by about 20 cm to 30 cm. A
small amount of boiled sand was observed in the gap
between the quay wall and the settled ground in thesoutheastern corner, in which liquefaction also happened in the 2021 Fukushima Earthquake. A simple
sieve analysis was carried out with the sand ejecta toobtain the particle gradation curve. Fig.8 indicatedthat D50 of the sample is 0.15 mm, and the curve waswithin the range particularly prone to liquefaction
based on the guideline from MLIT10). A similar deformation pattern was observed at Matsukawaura
New Fishing Port, located southeast of Soma Port. In
addition, extensive cracks with a length of 85m-100m
and an opening size of about 30cm, parallel to thequay wall, occurred at about 14m from the quay wall.
The resulting damage was similar to that caused by
the 2021 Fukushima Earthquake11).
At Quay No .5, a 130m-long crack was recorded on
the carriageway (Fig.9(a)). There were small steps on
the cracked road due to settlement. A slight displacement between seawall panels was also identified. Another implication of the earthquake was the destruction of two of the four coal unloading machines

Fig.3 Small slope failure on the steep slope along the Dake Walking Trail

Fig.4 Inclined pier of Tohoku Shinkansen viaduct in Kunimi
Town

installed at Quay No. 5, as shown in Fig.9(b). This
destruction has halted the operation of the Shinchi
Thermal Power Station, severely affecting the electricity supply in the service area of Tokyo ElectricPower Company (TEPCO) on March 22nd, 2022.

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8)

Fig.5 Local topography map around the damaged viaduct in Kunimi Town based on the Active Fault Map

Fig.6 Absolute inclination of the catenary poles in the adjacent area. The decimated 3D model is available9)
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Fig.7 Cracks between the quay wall blocks

Fig.8 (a) Sand ejecta taken from a quay wall block, (b) Particle distribution curve and the diameter range of sand prone to liquefaction

Fig.9 (a) a 130m-long crack on the carriageway in Quay No. 5, (b) Coal unloading machine with ruptured transverse beam

sandstone layers, the bedding plane orientation in thisarea is almost horizontal. The slope is prone to rockfall failure because it is divided by multiple verticaljoint sets. Rockfalls could have taken place following
the vertical joints that are orange-brown and show
significant signs of chemical weathering brought by
seepage. The rock boulders were as large as 5 m wide.
Collapsed electricity poles, rock and surface soil debris, and pine trees on top of the cliff blocked a smallpart of the carriageway (Fig.10 (a)). The extent of therockfall was estimated to be about 15 m in breadth.

(5) The tunnel portal of Unoomisaki Tunnel near
the Matsukawa-ura Bridge
Rock slope failure was triggered by the earthquakeat the northern side of the tunnel portal of Unoomisaki Tunnel along the 2-lane carriageway of Matsukawaura Bridge, as demonstrated in Fig.10. From the
1:50,000 Geological Map of the Soma-Nakamura
District, this region is composed of greenish-graymudstone (D2) of the Pliocene Dainenji Formation12).
With the observation of some several cm thickness
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Saito et al.13) reported a similar rockfall slope failure
occurred 300 m west of the 2021 earthquake. Osumi
et al.14) conducted a series of biochemical analyses
and pointed out chemical weathering by microorganisms as the predisposing cause of the collapse.

3. DAMAGE IN THE SOUTHERN PARTOF MIYAGI PREFECTURE(1) Tarumizu Dam, Natori City
A massive landslide was inspected along the roadleading from the top-left water dam and the dam office (Fig.11). The landslide debris of shotcrete, rock,mud, and trees entirely blocked the 4m-wide road.
The debris mass continued to run out downslope tothe top part of the spillway structure overlooking theMasuda River. The average slope inclination was between 50 degrees and 60 degrees. The crest of the
scarp area was located about 25 m high from the roadlevel. The width and depth of the landslide wereabout 20 m and 1 m, respectively. The failed section
was of the largest height compared to the adjacentslope reinforced by shotcrete. The collapsed soil
mass mainly comprises brown, slightly weathered
gravels.

Fig.10 Rock failure at the northern side of the tunnel portal of
Unnomisaki Tunnel (a) Whole view, (b) Fallen rockFig.11 Steep landslide at the downside of Tarumizu Dam (a)Whole view, (b) debris crossing the road, (c) partiallyweather rock in the debris

Fig.12 Cracks distribution appeared in the section from Kunimi to Shiraishi of Tohoku Expressway (a) Whole Map, (b) enlarged map,(c) captured cracks by NEXCO15) soon after the earthquake, (d) repaired pavement on April 23rd
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(2) Tohoku Expressway in Shiroishi CityThe Tohoku Expressway was affected by moderate ground cracking and settlement associated withthe 2022 Fukushima Earthquake (Fig.12). Manybumps were present during a brief survey driving
north on the Tohoku Expressway. An approximately
50 m long retaining wall seems to have been damaged
as it was under immediate recovery works.
By comparing the observations from the reconnaissance survey against Google Street View as ofAugust 2021, a preliminary analysis of the distribution of ground cracking was carried out. As presented
in Fig.12, cracks induced by this 2022 earthquake
were identified at localities marked by blue dots. Yellow dots indicate cracking locations that propagate
after the ground shaking, while glay dots are locations with existing cracks. The new cracks occurred
mainly in the vicinity of the boundary between thebox culvert and embankment regions. They are also
concentrated on the western side of Shiroishi City,
for instance, near Box Culvert Kunimi 65, 66, 67, 69,
71, and 75.

Fig.13 Cracks on the pavement of the parking lot ot a hotel(3) Arahama Fishing Port, Watari District
Slight ground surface damages were observed in
the vicinity of Arahama Fishing Port. For example, acrack was found at the bottom of an electric pole neara hotel (Fig.13). In addition, some cracks and ejecta
in the Torinoumi Park close to the sea wall have been
identified by a resident, as shown in Fig.14(a).
Wakamatsu15) found a similar pattern of sand ejecta
and ground fissure after the 2021 earthquake at thesame location (Fig.14(b)) and indicated that the liquefied area is located near a shoreline in the latest reclaimed area of the port.

Fig.14(a) Sand ejecta after the 2022 earthquake captured by Mr.
aito, a local resident, (b) sand ejecta after the 2021 earthquake at the same location15)

was being repaired; in a nearby petrol station, there
seems to be uplift in the surface drainage channel.
Our previous survey11) after the 2021 earthquake revealed building structures in the area that sufferedfrom damages were those constructed before the2011 earthquake, while the ground was damaged in
the areas reclaimed after the 2011 earthquake. A similar pattern was observed after the 2022 earthquake(Fig.16).

(4) Taiyo Newtown, Yamamoto Town, Watari
District
The damage conditions in the residential embankment area of Taiyo Newtown in Yamamoto Town
were examined as significant ground deformation in
the 2011 Tohoku Earthquake. While cracks of 10 cm
to 20 cm in width could be identified on a slope along
the road connecting to the National Route 6 (Fig.15),
less critical geotechnical damage was brought by the2022 earthquake than by the 2011 earthquake.

4. CONCLUSION
Different manifestations of geotechnical damage
due to the 2022 Fukushima earthquake have been investigated in this survey. Cracking, ground settlement and deformation were observed in the roads,
bridge approaches and embankments. The landslides
in Date Dam, Unoomisaki Tunnel portal area and Tarumizu Dam could be associated with the strong
ground motion of this earthquake event. Liquefaction
was also identified in Soma Port of Fukushima Prefecture.

(5) Sakamoto, Yamamoto Town, Watari District
The inspection was made around the Disaster Prevention and Communication Center of Yamamoto
Town. Cracks and ground settlement could be observed in the surrounding area of the Center (Fig.16).
On the National Route 6 in the Sakamoto area, theground settled mildly, and a crack of about 30 m long7

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Fig.15 Ground deformation of the slope of Taiyo Newtown (a) after the 2011 earthquake, (b) after the 2022 earthquake, (c) uneven
deformation, (d) cracks on the embankment

Fig.16 (a) Collapsed house (old residential area), (b) collapsed concrete-block wall (old residential area), (c) ground crack in thevicinity of the Center (newly landfilled area)
https://www.kyoshin.bosai.go.jp/kyoshin/topics/html20220316233630/main_20220316233630.html (Accessed April 13, 2022)
4) Japan Meteorological Agency: Observation information on
long-period seismic motions,
https://www.data.jma.go.jp/svd/eew/data/ltpgm_explain/data/past/20220316233646/index.html (Accessed April
13, 2022)
5) National Institute of Advanced Industrial Science and Technology: 1:50,000 scale geological map (Nihonmatsu),
https://www.gsj.jp/data/50KGM/JPG/GSJ_MAP_G050_07033_
1995_200dpi.jpg (Accessed April 13, 2022)
6) Goudie A. S., Allison R. J., and McLaren S. J.: The relations
between modulus of elasticity and temperature in the context ofthe experimental simulation of rock weathering by fire, Earth
Surface Processes and Landforms, Vol.17, No. 6, pp. 605-615,
1992.
7) Inoue, K. and Uemura K.: Report on the structural damage
investigation of the earthquake off the coast of Fukushima Prefecture on March 16, 2022,

ACKNOWLEDGMENT: The authors would like toacknowledge Prof. Wakamatsu from Kanto Gakuin
University for the provision of photographic recordsof liquefaction at Arahama Fishing Port.
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https://committees.jsce.or.jp/eec2/system/files/20220330_福島沖の地震被害調査報告(井上_植村）.pdf (Accessed April 13,
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