Kitamura et al. Progress in Earth and Planetary Science
https://doi.org/10.1186/s40645-019-0305-y(2019) 6:57

RESEARCH ARTICLE

Progress in Earth andPlanetary Science

Open AccessGeologic evidence for coseismic uplift at ~AD 400 in coastal lowland deposits on the
Shimizu Plain, central Japan
Akihisa Kitamura1,2* , Tomoya Ina3, Daisuke Suzuki3, Keito Tsutahara3, Daisuke Sugawara4, Kazuyoshi Yamada4 andAkira Aoshima3

Abstract
Megathrust earthquakes of magnitude ~ 8 and ensuing large tsunamis occur along the Nankai and Suruga troughs,
central Japan, with a recurrence interval of 90–270 years since an AD 684 Hakuho earthquake. Historical records
show that the AD 1854 Ansei-Tokai earthquake caused coseismic uplift of ~ 1 m in coastal areas west of Suruga Bay,
including the Shimizu Plain, east Shizuoka Prefecture. The 1361 Shohei Tokai earthquake was accompanied bycoseismic uplift, but no evidence has been found to indicate uplift before the earthquake. This study examined
sediment cores recovered from the coastal beach ridge in the Shimizu Plain using sedimentological andpaleontological analyses and radiocarbon dating. We infer from the results that a relative sea-level fall of 1.6 m took
place at AD 398–428. This coincides with archeological evidence suggesting the occurrence of a large earthquake
in west Shizuoka Prefecture in AD 400. This combination of evidence indicates that the drop in sea level wascaused by coseismic uplift associated with a megathrust rupture along the Suruga Trough, with a recurrence
interval of ~ 500–1000 years. The results also indicate that a megathrust rupture occurred in the region from theEastern Nankai Trough to the Suruga Trough at ca. AD 400.
Keywords: Sediment core, Coseismic uplift, Facies analysis, Late Holocene, Nankai and Suruga troughs,
Paleoseismology, Shimizu Plain

Introduction
The 2011 off the Pacific coast of Tohoku earthquake
was the largest earthquake recorded (Mw 9.0) in Japan,
and it generated a mega-tsunami that severely damaged
the coastal areas (CDMC, 2011). Following this event,the Japanese Government re-assessed the earthquakes
and tsunamis expected in the future in the Suruga andNankai troughs, close to central and western Japan (Fig. 1).
Many studies have examined the earthquakes and tsunami
events along subduction zones (e.g., Atwater 1987;
Minoura et al. 2001; Nanayama et al. 2003; Monecke et al.
2008; Shishikura et al. 2010; Ishimura and Miyauchi 2015;
Kitamura 2016; Inoue et al. 2017; Ando et al. 2018;* Correspondence: kitamura.akihisa@shizuoka.ac.jp
1
Faculty of Science, Shizuoka University, 836 Ohya, Suruga-ku, Shizuoka
422-8529, Japan
2
Center for Integrated Research and Education of Natural hazards, Shizuoka
University, 836 Ohya, Suruga-ku, Shizuoka 422-8529, Japan
Full list of author information is available at the end of the article

Kitamura et al., 2018a, b; Goto et al. 2018). The Philippine
Sea Plate is subducting beneath the Eurasian Plate at thesetroughs, and megathrust earthquakes of magnitude ~ 8and ensuing large tsunamis have occurred since an AD
684 Hakuho earthquake, with a recurrence interval of
90–270 years (Ando 1975b; Ishibashi 2004).
Historical documents show that the Suruga and Nankai
troughs are divided into six segments based on patternsof seismicity, labeled A–E and Z (Ando 1975b;
Ishibashi 1976; Furumura et al. 2011). The 1854 AnseiTokai, 1854 Ansei-Nankai, 1944 Tōnankai Earthquakeand 1946 Nankai Earthquake were caused by rupturesof segments C–E, A–B, C–D and A–B, respectively(Ishibashi 1976). Segment E (Suruga Trough) has not
ruptured since the 1854 Ansei-Tokai earthquake, andthis section shows remarkable interseismic crustal
movement. In this context, Ishibashi (1976) predictedthat a M-8 earthquake (Tokai earthquake) will occur
sooner or later upon this segment. A geodetic precursor© The Author(s). 2019 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0
International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, andreproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to
the Creative Commons license, and indicate if changes were made.

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Fig. 1 Spatiotemporal distribution of great earthquakes along the Nankai and Suruga troughs, from Ando (1975b), Ishibashi and Satake (1998),
Ishibashi (2014) and Kitamura et al. (2018a, b). Photographs are used with permission from the Geospatial Information Authority of Japan (https://
maps.gsi.go.jp/development/ichiran.html). 1 Akatsuchiyama mound tomb (data source: Sangawa (2013)); 2 Sakajiri (data source: Sangawa (2001));
3 Tsurumatsu (data source: Sangawa (2001)); 4 Harakawa (data source: Sangawa (2001)); 5 Kawai (data source: Sangawa (2001)); 6 this study

was reported for the 1944 Tōnankai Earthquake (Fig. 1).
The data, taken far from the epicentral region, were interpreted as suggesting uplift of a few centimeters due topre-slip that occurred one or two days before the main
shock (Ando 1975a; Sato 1977; Mogi 1984/1985). Consequently, the Japanese government enacted the Large-Scale
Earthquake Countermeasures Act (1978) for preparedness

and short-term prediction of the Tokai Earthquake,
although the earthquake has yet to occur.
During the past 40 years, many studies have investigated the occurrence of the Tokai Earthquake and thefeasibility of short-term predictions of this event. For
example, both historical and geological records indicate
the 1854 Ansei-Tokai earthquake resulted in 1.5–1.8 m

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of coseismic uplift to the west of the Suruga Trough(Ishibashi 1984; Kitamura and Kobayashi 2014) (Fig. 2),
although uplift in the western part of Suruga Bay was
not detected during the 1707 Hoei and 1498 Meio earthquakes (Hatori 1975, 1977). On the other hand,
Kitamura et al. (2018a, b) recently found emerged fossilsof boring bivalves at Cape Omaezaki, which faces seismic segments D and E, indicating at least 2.5 m of totalcoseismic uplift resulting from the Tokai earthquake andthe AD 1361 Shohei (Koan)–Nankai earthquake. Thesefindings imply that ruptures of segments C, D, and E
were simultaneous, and the estimated recurrence interval of ~ 500 years is consistent with the interval of
450–500 years reported by Kuroki et al.’s (2004) basedon a numerical simulation. However, since the recurrence intervals and sizes of great earthquakes in many
subduction zones worldwide are highly variable (e.g.,
Satake and Atwater 2007; Shimazaki et al. 2011;

Kitamura et al. Progress in Earth and Planetary Science

a

b

c

d

e

Fig. 2 Locality map of the study area. a Estimated coseismic vertical crustal displacement (m) resulting from the AD 1854 Ansei-Tokai earthquake
along the coast of Suruga Bay (after Ishibashi (1984) and Kitamura and Kobayashi (2014)). b Locations of Shimizu Plain, Orido Bay, and Miho
Peninsula, showing isobaths are based on Tsuchi (1955). c Location of the study area. The figure is modified from a map issued by the Geospatial
Information Authority of Japan (http://maps.gsi.go.jp/). d Aerial photograph of the study area, used with permission from the Geospatial
Information Authority of Japan (https://maps.gsi.go.jp/development/ichiran.html). e Topographic map of the Shizuoka and Komagoe districts(1:25,000 scale, compiled in 1932), showing the location of the study area

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Rubin et al. 2017), we must examine the temporal
distribution of earthquake prior to the 1361 Shohei
Tokai earthquake.
Coseismic uplift events have been identified from geological and geomorphological records such as uplifted marine terraces (e.g., Fujiwara et al. 2010; Komori et al. 2017),
emerged marine sessile assemblages (e.g., Shishikura et al.
2008; Iryu et al. 2009; Kitamura et al. 2014, 2015, 2017,
Kitamura et al. 2018a, b), and changes in sedimentary facies
and microfossil fauna in coastal lowland strata (e.g., Atwater
1987; Nelson et al. 1996a, b; Hayward et al. 2004;
Sawai et al. 2004; Shimazaki et al. 2011; Kitamura andKobayashi, 2014; Mannen et al. 2018). However, geomorphological records can be strongly influenced by humandisturbances. Examining the sedimentary features ofcoastal lowland deposits is a promising approach in reconstructing ancient coseismic uplift events.
This study examines geological evidence for late Holocene megathrust earthquakes based on observations of
sedimentary features in cored deposits collected from thearea around the Kaicho-ji Temple on the Shimizu Plain,
Shizuoka Prefecture, which faces seismic segment E(Fig. 2). The temple was built in AD 1011 on a beach ridge(Fig. 2) with an elevation of about 4 m. This timing provides reliable constraints on the age determination of theemergence of the study area. We identified an abruptchange in sedimentary facies that could have been causedby coseismic uplift during the early fourth century.

uplifts of 1.5–2.0 m and 3 m, respectively. Kitamura andKobayashi (2014) reported geological and paleontologicalevidence indicating a maximum coseismic uplift of 1.2 m
caused by the 1854 Ansei-Tokai earthquake, on the areaof the intertidal flat that emerged during the earthquake,and a total post-earthquake subsidence of ~ 0.6 m. Although historical documents show that the 1707 Hoei and
1498 Meio earthquakes caused damage on the Shimizu
Plain, there were no coseismic uplifts (Hatori 1975, 1977).
There are no historical records of earthquakes in theregion prior to the 1361 Shohei Tokai earthquake. Nevertheless, archeological sites near segments D and E show
sand boils and other liquefaction features that indicate
intense shaking during certain time periods, including
during the mid seventh to early eighth centuries AD, thesecond and early fourth centuries AD, and in the second
century BC (Sangawa 2001, 2013) (Fig. 1). It is possiblethat these intense shaking events were caused by rupturesof segments D and E.
Historical reports also show that the coastal area of the
Shimizu Plain was struck by tsunamis associated with the1854 Ansei-Tokai and 1707 Hoei earthquakes. The wave
heights of the tsunami caused by the 1854 Ansei-Tokai
earthquake along the northeast-facing coast of the Miho
Peninsula and the coastal area of the northern Shimizu
Plain are estimated to have been 6 m and 3 m, respectively(Hatori 1977). No tsunamis have been documented in the
inner part of Orido Bay (Hatori 1977). The tsunami related to the 1707 Hoei earthquake along the northeastfacing coast of Miho Peninsula and the coastal area of thenorthern Shimizu Plain had estimated wave heights of 5 m
and 4 m, respectively (Hatori 1977).

Kitamura et al. Progress in Earth and Planetary Science

Study area

The Shimizu Plain is a fluvial-coastal lowland adjacentto Orido Bay, which is protected from the open ocean
by Miho Peninsula (Fig. 2), a sand and gravel spit with
an elevation of up to 10 m that formed at 5000 years BP(Matsubara, 1989). The Kaicho Temple is located on thebeach ridge in the coastal area of the innermost part of
Orido Bay. The Miho Peninsula is composed of sediment carried by the Abe River and derived from the
Udo Hills to the west of the peninsula (Matsubara, 1989;
Ishihara and Mizuno, 2016). The coastline is under amicrotidal regime, with a mean tide range of 1.6 m at
Shimizu Port. Tidal gauge data during 1955–2016 showthat the Shimizu area has subsided at a rate of c. 6.3mm/year (Coordinating Committee for Earthquake
Prediction, 2018). According to Tsuchi (1956), mollusk
remains collected at 5 m water depth provide evidenceof euxinic and stagnant conditions throughout most of
Orido Bay.
The coseismic uplift of the Shimizu Plain resulting fromthe 1854 Ansei-Tokai earthquake is documented on historical maps compiled immediately after the earthquake
and mentioned in interviews conducted 38 years after theearthquake (Hatori 1976, 1977). Based on these accounts,
Hatori (1977) and Ishibashi (1984) estimated coseismic

Methods
We conducted ground-penetrating radar (GPR) surveys
along three lines using an SIR-4000 unit (GSSI Co. Ltd.,
Nashua, NH, USA) with a 400 MHz antenna, with a vertical resolution of ~ 15 cm (Fig. 3). After acquisition, theGPR data was processed using the GSSI’s software
RADAN version 7.4.15. During the processing, the finite
impulse response (FIR) filter was used to reduce thenoise and the gain correction was used to improve thevisibility of the data.
Sediment cores (7 m long and 6 cm in diameter) recovered at two sites in the study area (Fig. 2) were split longitudinally and logged according to lithology, sedimentary
structures, and the presence of mollusks. X-ray radiographs were taken of slab samples (6 cm wide × 20 cm
long × 1 cm thick) from the split cores.
Grain size was measured using the wet-sieving method
at 1-phi intervals in the range of − 3 phi (8 mm) and 5phi (32 μm). A portion of the remaining subsamples wasdried and ground following the removal of sandy grains.
A 1 N HCI solution was added to 10 mg of sample in a

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Fig. 3 Profiles obtained from a ground-penetrating radar survey. The right-hand vertical axis shows two-way travel time (ns) and the left-handvertical axis shows estimated depth (m) for a given specific inductive capacity (ν; 14.0, 9.0, and 6.0 for profiles A−B, C−D, and E−F, respectively)

silver container to remove inorganic carbon, and theremaining sample was heated on a hot plate for 2 h.
Dried samples were placed in a tin container. The total
sulfur content (TS) and the ratio of total organic carbon
to TS (the C/S ratio) were determined using a CHNS
material analyzer (Flash 2000, Thermo Fisher Scientific).
The accuracy of the procedure was controlled using
the BBOT standard (2,5-Bis-(5-tert.-butyl-benzoxazol2-yl)-thiophen). As the C/S ratio of muddy sediments
is higher in freshwater than in marine (Berner andRaiswell 1984) and euxinic and brackish coastal waters (Leventhal 1983), C/S ratios have been used to distinguish between ancient marine and freshwater sedimentarydeposits (Berner and Raiswell 1984; Kamei et al. 1997;
Kitamura et al. 2019) (Fig. 4).
Foraminiferal tests were picked from the > 0.063 mm
size fraction of core sediment samples. Taxonomic identification was based on Takata et al. (2006, 2016) andCharrieau et al. (2018). We calculated the number of
specimens of the dominant taxa per gram of sediment.
Transfer functions are commonly applied to coastal deposits for sea-level reconstruction (Horton et al. 1999);
however, the very low abundance of foraminifera precluded the use of this technique in the present study.

Seventeen samples of well-preserved leaves and woody
material were subjected to radiocarbon dating at Beta
Analytic, using accelerator mass spectrometry (Table 1).
The results were translated into the 2σ calendar-year range
using the program OxCal4.1 (Bronk Ramsey 2009), basedon a comparison with IntCal13 data (Reimer et al. 2013).

Results
GPR profile

The GPR profile along the line A–B showed seaward
dipping reflections between 1 and 2 m in depth (Fig. 3).
It suggests that the depositional setting near site 1 corresponds to the seaward slope of the beach ridge. The reflection pattern indicates continuous progradation of thecoastline to the northeast. Note that reflections below 2
m were not successfully resolved due to the presence of
the water table, and burial of artificial objects is visible
in the systematic reflection patterns near the surface.
The GPR profile along the lines C–D and E–F,
which is shore-normal and shore-parallel directions,
respectively, showed horizontal to sub-horizontal reflections below 1 m in depth (Fig. 3). It suggests a
different sedimentary environment near site 2

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Fig. 4 Scatter plots of TS versus TOC for the cored sediments, and marine and freshwater sediments

Table 1 14C ages of samples from the study area
Sample no.

Site

Depth (m)Altitude(m above m.s.l.)Materials

δ13C (‰)

Conventional 14C
age (year BP)

Calibrated age(2σ; cal. year BP; 95.4%)

Beta ID

1

1

4.05

0.45

Wood

− 27.022050 ± 30

166 cal BC to 20 cal AD

496227

2

1

4.20

0.30

Wood

− 29.131650 ± 30

264–532 cal AD

496228

3

1

4.21

0.29

Leaf

− 30.08

1600 ± 30

398–539 cal AD

502135

4

1

4.21

0.29

Leaf

− 29.89

1740 ± 30

236–386 cal AD

5021365

1

4.53− 0.03Wood− 26.34

2080 ± 30

191–38 cal BC

49622961

6.47− 1.97

Plant material− 26.212380 ± 30

726–392 cal BC

517951

8

2

2.10

1.70

Leaf

− 29.521670 ± 30

258–428 cal AD

502137

9

2

2.10

1.70

Leaf

− 29.46

1740 ± 30

236–386 cal AD

502138

10

2

3.66

0.14

Plant material− 28.80

2120 ± 30

345–50 cal BC

508311

11

2

3.67

0.13

Wood

–

3430 ± 40

1877–1636 cal BC

503648

12

2

4.64

− 0.84

Plant material− 22.423110 ± 30

1437–1288 cal BC

508312

13

2

4.87

− 1.07

Plant material− 24.63

2530 ± 30

797–543 cal BC

508313

14

2

4.98

− 1.18Plant material− 28.503040 ± 30

1397–1216 cal BC

508314

15

2

5.20

− 1.40

Plant material− 27.72420 ± 30

748–402 cal BC

517953

16

2

5.34

− 1.54

Plant material− 24.62680 ± 30

897–802 cal BC

517954

17

2

5.51

− 1.71

Plant material− 27.12940 ± 30

1257–1043 cal BC

517955

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comparing with that near site 1. Note that reflections above 1 m in depth was chaotic, which may
correspond to landfills.

The relative abundance of P. japonicum shows an upward
decrease and increase in sites 1 and 2, respectively (Fig. 8).
Facies B consists of laminated clay and graded sandbeds (<10 cm thick) (Fig. 5), and overlies Facies A. The
facies contains plant materials, but no mollusks or foraminifera (Fig. 8). The TS content and C/S ratio in theclay are 1–2% and ~ 0.7, respectively (Fig. 8). Clay (<32 μm) contents are 70–80% (Figs. 6 and 7). The youngest 14C age from the clay is AD 398 to 539, obtained
from a sample of a leaf (Fig. 5, Table 1).
Facies C consists of alternating sand and clastsupported gravel beds and occupies the uppermost partof the borehole sediments. The base comprises a layer(10 cm thick) of massive to weakly laminated finegrained sand, and it overlies Facies B across a sharpboundary. This facies contains mud clasts and woody
material, but no mollusks or foraminifera. At site 2, awoody debris bed was identified at a depth of 2.04–2.10 m

Kitamura et al. Progress in Earth and Planetary Science

Sedimentary facies

We classified the borehole sediments into three facies
on the basis of lithology, grain size, color, sedimentary
structures, and fossil (Fig. 5; Appendixes 1 and 2).
Facies A is composed of massive, bluish-gray mediumgrained sand and shows a fining-upward trend (Figs. 4, 5, 6
and 7). The lowest part of the borehole sediments contains
plant materials and shells of the mollusks Umbonium
moniliferum and Batillaria cumingii (Fig. 8). The relative
abundance of mollusk shells shows an upward decrease
within the facies. A few individuals of benthic foraminifera
were found, which were Ammonia spp., Elphidium
advenum, and Pseudononion japonicum (Fig. 8, Table 2).

Fig. 5 Columnar sections of two sediment cores collected at the study area, showing two specimens of leaf materials (specimens 3 and 8).
Details of radiocarbon dating reported are provided in Table 1

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Fig. 6 Grain-size distribution of cored sediments at site 1. See Fig. 5 for legend(Figs. 5 and 7). Leaf material in this bed yielded 14C agesof AD 258 to 428 (Fig. 4, Table 1). GPR reflections show
parallel to seaward dipping layers that indicate progradation of the beach ridge and shoreline (Fig. 3).
Table 2 List of foraminifera from cored sediment samples
Site

1

2

Depth (m)

5.505

5.955

6.105

Ammonia spp.

6

3

2

3.955

4.555

7

3

Bolivina sp.

6.205
2
2

2

Elphidium advenum

6

15

2

6

4

9

8

4

9.0

10.1

8.1

7.9

Elphidium somaense
Pseudononion japonicum
Pseudononion sp. A
Unidentified

1

Sediment (g)

6.7

6.0

Discussion
Facies A contains shells of the mollusks U. moniliferumand B. cumingii, which inhabit the intertidal to shallow subtidal zones in tidal flats (Okutani 2000) (Fig. 8). A few individuals of benthic foraminifera Ammonia spp., Elphidium
advenum, and Pseudononion japonicum were found inFacies A (Fig. 5). Ammonia spp. are generally found in the
innermost bay regions and brackish water (e.g., Matsubara,
1989; Kosugi et al. 1991; Kitamura et al. 2019), andElphidium advenum and Pseudononion japonicum inhabit
the sublittoral zone (Akimoto and Hasegawa, 1989; Oki,1989). As such, we interpret Facies A to have been

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Fig. 7 Grain-size distribution of cored sediments at site 2. See Fig. 5 for legend

deposited in a sandy marine environment, representative of
the intertidal to shallow subtidal zones. According to
Nomura and Seto (1992), Pseudononion japonicum prefers
salinities of > 25‰. The difference in the relative
abundance of P. japonicum at sites 1 and 2 might indicate movement of the river mouth over time.
The preservation of laminations and absence of mollusks and foraminifer shells in Facies B indicate deposition in euxinic bottom water. The C/S value of the clay(~ 0.7) is consistent with that of deposits in euxinic andbrackish coastal water, such as the Black Sea (Leventhal
1983), and is much lower than those of intertidal mudflat deposits (4.9–11.4) (Kitamura et al. 2019). This indicates that Facies B was deposited under euxinic andstagnant conditions below the intertidal zone. As themean tide range at Shimizu Port is 1.6 m, the water
depth of Facies B was estimated to be greater than − 0.8
m. The very low TS content (0.1%) and high C/S ratio(6.3) in the uppermost part of Facies B at site 1 mightreflect alteration resulting from the seepage of groundwater from the overlying Facies C.
Facies C is characterized by alternating sand and clastsupported gravel beds and the occurrence of mud clasts.
These features indicate a sedimentary environment characterized by high-energy hydrodynamic conditions.
According to Kennedy and Woods (2012), wood debris
beds on gravel-dominated beaches can be deposited
during high wave events and are located at the top of
the storm berm. It is therefore likely that Facies C wasdeposited in a backshore or beach ridge environment at
an elevation of > 0.8 m, which corresponds to the sea
level at high tide.
The vertical facies succession suggests the sedimentary environment changed from intertidal to shallow
subtidal zones (Facies A), through a euxinic subtidal
zone (Facies B), and then to a beach area (Facies C),

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Fig. 8 Stratigraphic distributions of the dominant species of mollusk fossils, total sulfur content (TS), ratio of total organic carbon to TS (i.e., the C/
S ratio), and foraminifera in cored deposits at sites 1 and 2. See Fig. 5 for legend

indicating a sea-level rise followed by a drop. Radiocarbon dating shows that the sea-level rise took place between 1257 cal BC and 400 cal AD. Tanabe et al. (2016)
estimated about 2 m of relative sea-level rise during
1000–0 cal BC based on the analysis of sedimentary
records around Kanto Plain, central Japan. However,eustatic sea level was likely stable during that time
(Sloss et al. 2007; Woodroffe et al. 2012). As noted
above, the mean subsidence rate is 6.3 mm/year in the
Shimizu area. With the duration of the depositional
event assumed to be 1660 years (i.e., between 1257 cal
BC and 400 cal AD), the mean sedimentation rate is estimated to be about 1.2 mm/year. We therefore interpretthat the sea-level rise during the deposition of Facies A–B
was caused mainly by local subsidence (Fig. 9).
Of note, the abrupt change from the subtidal zone
(below − 0.8 m) to beach conditions (above 0.8 m) is

indicated by lithofacies changes from Facies B to C, with
an absence of intertidal Facies A. The fall in relative sea
level is estimated to have been up to 1.6 m (Fig. 9). The
youngest 14C age within Facies B is AD 398–539, derived
from leaf material (specimens 3), while the oldest 14C
age within Facies C is AD 258–428, also derived fromleaf material (specimen 8) (Fig. 5). As these specimens
are thin and delicate leaves, their very well-preserved
condition (Fig. 5) indicates that they have not beenreworked from older deposits. As such, based on the 14C
ages of these specimens, we estimate that sea level fellduring the period AD 398–428.
There are no reports of eustatic sea-level decreases at thistime; however, Sangawa (2001, 2013) (Fig. 1) reported evidence for intense shaking in west Shizuoka Prefecture during the early fourth century (segment D). The present study
area experienced 1.2 m of coseismic uplift during the 1854

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Fig. 9 Reconstruction of water-depth changes and depositional environments in the study area (Shimizu, central Japan) for the periods before
and after the AD 400 earthquake

Ansei-Tokai earthquake (Kitamura and Kobayashi 2014).
We therefore propose that the fall in relative sea level wascaused by coseismic uplift associated with the rupture ofsegment E, possibly during the AD 400 earthquake (Fig. 9).
As the base of Facies C is located at mean sea level, the total
subsidence was at least 0.8 m greater than the uplift causedby the coseismic uplift events after the AD 400 earthquake.
This study did not identify a tsunami deposit associatedwith the AD 400 event, for which there are two potential explanations. The first is that Miho Peninsular reduced the tsunami’s energy. Indeed, no tsunami associated with the 1854
Ansei-Tokai earthquake has been documented in the innerpart of Orido Bay, even though the wave height of the tsunami along the coastal area of the northern Shimizu Plain is
estimated to have been 3 m (Hatori 1977). The second
explanation is that an earthquake nucleating in segment Emight induce significant uplift but does not cause a large tsunami because the segment is located too close to the shore.
Sangawa (2001, 2013) postulated that a large earthquake occurred around AD 400 within segment B, asinferred from slope failure at Akatsuchiyama moundtomb (Fig. 1). Therefore, it is thought that megathrust
ruptures of segments B–E occurred simultaneously or
within a few years of each other at ~ AD 400. The interval between the AD 400 and 684 Hakuho earthquakes isabout 280 years, slightly longer than the average intervalof 220–230 years between events that occurred between
the AD 684 and 1361 earthquakes. The data from thisstudy show that segment E ruptured during the 1854
Ansei-Tokai, 1361 Shohei Tokai, and AD 400 earthquakes, and that the recurrence interval varies fromabout 500–1000 years.

Conclusion
To clarify the history of megathrust earthquakes along the
Suruga Trough, central Japan, we studied the sediment,
fossil contents, and the C/S ratio of two sediment cores collected at Kaichoji Temple, which was built in AD 1011 on abeach ridge in the coastal area of the Shimizu Plain, which isprotected from the open sea by the Miho Peninsula. The results can be summarized as follows:
1. We identified three sedimentary facies: Facies 1(intertidal to shallow subtidal zones), Facies 2(stagnant conditions below the intertidal zone), andFacies 3 (backshore and beach ridge). A sharpboundary between Facies 2 and the overlying Facies
3 at 0.20–0.25 m above sea level indicates a rapid
fall in relative sea level of 1.6 m at AD 398–428.
2. The age of the boundary between Facies 2 andFacies 3 corresponds to the timing of a large
earthquake in west Shizuoka Prefecture aroundAD 400. The abrupt change in the sedimentary
environment was possibly related to coseismic
uplift caused by a megathrust rupture along the
Suruga Trough.

Kitamura et al. Progress in Earth and Planetary Science

Appendix 1

Fig. 10 Photograph of the core from site 1(2019) 6:57

Page 12 of 15

Kitamura et al. Progress in Earth and Planetary Science(2019) 6:57

Page 13 of 15

Appendix 2

Fig. 11 Photograph of the core from site 2

Acknowledgements
We thank two anonymous reviewers whose constructive comments
significantly helped to improve this paper. We thank landowner in the study
area for allowing us access to the land for our research activities.
Authors’ contributions
AK conceived the study designed, collected samples, and identified
specimens of foraminiferal samples. TI, DSuz, TK, and AA analyzed coredsediments, conducted grain-size analysis, and identified mollusk samples. KY
analyzed total sulfur contents and the ratio of total organic carbon to TS.
DSug conducted ground-penetrating radar (GPR) surveys. All authors readand approved the final manuscript.

Competing interests
The authors declare that they have no competing interests.
Author details
1
Faculty of Science, Shizuoka University, 836 Ohya, Suruga-ku, Shizuoka
422-8529, Japan. 2Center for Integrated Research and Education of Natural
hazards, Shizuoka University, 836 Ohya, Suruga-ku, Shizuoka 422-8529, Japan.
3
Iwata Minami High School, 3084 Mitsuke, Iwata City, Shizuoka Prefecture
438-8686, Japan. 4Museum of Natural and Environmental History, Shizuoka,
5762 Ohya, Suruga-ku, Shizuoka City, Shizuoka Prefecture 422-8017, Japan.
Received: 8 April 2019 Accepted: 1 August 2019

Funding
This study was funded by “Future Scientists’ School in Shizuoka University”, aspecial program supported by JST, the Japan Science and Technology
Agency, a Grant-in-Aid (17H02074) from the Japan Society for the Promotionof Science, and the Center for Integrated Research and Education of Natural
Hazards, Shizuoka University.
Availability of data and materials
Please contact the corresponding author for data requests.

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