TSUNAMI

Presented by

SAURAV SHEKHAR

ENTRY NO 2014CEU2921

Case Study - 2011 Tohuku Tsunami, Japan

Caused by 9.0 magnitude EarthquakeDate- 11 March 2011The quake was centered 130 kilometers to

the east of the prefecture’s capital, Sendai.The oceanic Pacific Plate subducts (sinks

under) the Eurasian Plate.Japan was largely prepared for the

earthquake and many buildings remained standing afterwards, but it was not prepared for the subsequent Tsunami.

Contd.

200000 people killed500km2 coastal plains hit, destroying farmland, settlements and

communications.Ruptured gas pipes led to fires.Explosions at the Fukushima nuclear power plant- this led to nuclear

contamination and the possibility of meltdown as the cooling systems failed.Electricity lost in 6 million homes, 1 million had no running water.

PAPER-Erosion, deposition and landscape change on the Sendai coastal plain, Japan

INTRODUCTION

Case studies of recent tsunami impacts have proven to be extremely useful in understanding the geologic processes involved during inundation and return flow, and refining the criteria used to identify paleotsunami deposits in the geologic record.

Field observations focused on measurements of tsunami flow characteristics (height and direction), mapping of erosion features and assessing sediment deposition based on shallow trenches at 50–100 m spacing.

In this paper the survey results for the surficial deposits, flow heights and directions, and landscape change with an emphasis on erosion and deposition along a 4.5 km shore-perpendicular transect based on field observations and measurements were described. This study documents the geologic characteristics of the 2011 Tohoku-oki tsunami on the Sendai coast, and provide a background for related studies including sedimentology, geochemistry, micropaleontology, mineralogy and modeling that are reported in this special issue.

METHOD A shore-normal transect line (T3) was established along the Sendai coastal plain just north of

Sendai Airport with measurement locations at 50 m intervals from the shoreline to 4500 m inland.

The tsunami deposits were described and sampled at 50–100 m intervals along with observations of erosion and landscape change. At many localities the deposit thickness was measured at the center line and at 5 and 10 m spacing away from the center to document local variability.

Tsunami inundation heights (elevation above Tokyo Peil, TP, which corresponds to the mean sea level determined in Tokyo Bay) and topographic profiles were measured using high resolution survey equipment (Promark 3, Ashtech), hand-held laser rangefinders and GPS units.

One of the advantages of studying a transect adjacent to Sendai Airport was the comprehensive video coverage of the area taken during inundation, thus allowing comparison of local flow variations with deposit characteristics and landscape changes.

RESULTS: TRANSECT MORPHOLOGY AND OBSERVATIONS

Beach face and back beach (T3 1– 4; 0– 150 m)

• The active beach was composed of unconsolidated sand with little or no vegetation in a ~ 150 m wide zone. The beach face slope at the time of the survey was 12 degrees. This was the site of extensive erosion during the passage of the tsunami wave(s) and the source area for much of the sand deposited further inland.

• Flow acceleration in the lee of the dune ridge is the probable erosional mechanism forming the elongate depression.

• Funnel shaped incisions in thebeach face, with the widest portion facing seaward, were partially infilled at the time of our survey.

• The tsunami eroded into the poorly-developed soil and sparse back beach vegetation, which was preserved between the incisions.

Coastal Dune Forest (T3 4– 9; 150– 400 m)• A 300 m wide coastal forest of predominately

Japanese Black Pine was planted to stabilize and enhance the coastal dunes reaching about 3 m above TP.

• Most of the trees were bent or broken by the tsunami giving a clear indication of the primary WNW flow direction

• A sharp basal contact was overlain by multiple layered and laminated tsunami sand capped at some sites by post-tsunami, eolian rippled sand.

• An infilled scour-depression and associated depositional fan that contained a thick (~60 cm) tsunami sand deposit characterized by at least five distinct laminated layers

• The sedimentary sequence was generally fining upward although the coarsest sediment occurred near the middle of the section and included some pebbles and rip-up clasts .

• Multiple laminations highlighted by dark mineral concentrations were also present in each unit

Low-lying wetland and Teizan Canal (T3 10– 17; 400 800 m)

• The landward margin of the dune field was marked by abundant scour depressions around obstacles such as trees and man-made objects

• The overall deposit can be characterized as a locally varying sand sheet with occasional coarser material (granules and pebbles) typically occurring near the base of the tsunami deposit

• Exposed locations with abundant sand were often reworked by post tsunami winds forming dry eolian sand deposits overlying the wetter tsunami sediments

• The canal acted as a trap for material transported by the tsunami including sediment, vegetation, and man-made debris. However, the canal acted not only as a sink but also a source for tsunami material.

Elevated terrace (T3 18– 21; 850– 1000 m)

The tsunami deposits in this area were thin and patchy in distribution, especially when compared to adjacent sites. Artificial hills within the park were scoured and eroded with patches of sand and debris accumulating in topographic lows

Rice fields (T3 22– 42; 1050– 2050 m)• Rice paddies extend for about 1 km west of the

elevated terrace and occupy generally low-lying and low-relief agricultural land

• The dominant topographic features are a reticulated network of low earthen dykes a few dm high and up to about 1 mwide separating individual rice paddies of about 20 × 50 m in size.

• The paddies are generally elongated in a NE–SW orientation, quasiparallel to the coast. Groups of paddies are further separated by a network of unpaved roads that are slightly higher and wider than the paddy dykes.

• The overall landscape is therefore one of the relatively flat and low-relief terrain interrupted by a reticulated network of elevated barriers that can interact with and obstruct tsunami flow throughout the area

Mixed agriculture, commercial, and housing (T3 43 58; 2100– 2850 m)

Sedimentary deposits were thin and combined with extensive rafted debris mostly of man-made material and vegetation. Where present, the tsunami sand deposits were still recognizable but had a patchy distribution. The thicker (up to ~8 cm) deposits in this section of the transect were typically limited to topographic depressions more conducive to sediment deposition.

Rice paddies with predominantly mud deposition (T3 58– 88; 2950– 4450 m)

The remaining ~1500 m of the transect was mostly across rice paddies adjacent to an elevated paved road and through one slightly elevated housing subdivision. The deposit here consisted mainly of mud and rafted debris

Summary diagram showing the variation in major deposit characteristics along the transect. Sorting assessment was confirmed by grain size analyses. Moderate erosion means that there was evidence of soil erosion (uprooted plants, clear erosional contact with tsunami deposits). Strong erosion was related to sites where up to several meters wide erosional niches or depressions were formed. The tsunami deposit thickness variation as determined by a series of transect trenches every 50–100 m, with additional side trenches spaced 5 m apart perpendicular to the main transect is shown (total maximum and minimum thickness as well as mud thickness)

CONCLUSIONS Erosion of the land surface was widespread and severe for at least the first 2 km inland from the

coast. Much of the eroded soil re-deposited farther inland was most likely a major component ofthe mud cap.

Erosion on the foreshore was also significant although natural coastal processes rapidly restored the active beach to near pre-tsunami conditions.

An irregular sheet-like deposit of sand was deposited over a distance of approximately 2700–2900 m inland from the coast.

Considering the relatively flat and low-lying nature of the Sendai plain, it was remarkable to find such a large variability in deposit thickness over short distances.

This has important implications for the study of paleotsunami deposits where discontinuous sediment layers may be present.

SAFETY PRECAUTIONS BEFORE TSUNAMI

Learn about the potential for danger in advanceBe aware if tsunamis have struck your coastal region in the pastPrepare essential materials in an easy-to-obtain locationDevelop an evacuation plan

SAFETY PRECAUTIONS DURING TSUNAMI

Abandon the belongingsMove inland, and to high groundReact quickly if you are caught up in the waterClimb a sturdy tree

SURVIVING AFTER TSUNAMI

Brace for aftershocks and additional wavesTry to get reliable informationWait for local authorities to issue an “All Clear”Rally the community behind a rehabilitation planKnow that survival continues after the tsunami has passed

REFERENCES BRUCE RICHMOND, WITOLD SZCZUCI ŃSKI, CATHERINE CHAGUÉ-GOFF, KAZUHISA

GOTO E, DAISUKE SUGAWARA F, ROB WITTER, DAVID R. TAPPIN , BRUCE JAFFE, SHIGEHIRO FUJINO, YUICHI NISHIMURA:EROSION, DEPOSITION AND LANDSCAPE CHANGE ON THE SENDAI COASTAL PLAIN, JAPAN, RESULTING FROM THE MARCH 11, 2011 TOHOKU-OKI TSUNAMI

CATHERINE CHAGUÉ-GOFF PRZEMYSLAW NIEDZIELSKI , HENRI K.Y. WONG , WITOLD SZCZUCIŃSKI:ENVIRONMENTAL IMPACT ASSESSMENT OF THE 2011 TOHOKU-OKI TSUNAMI ON THE SENDAI PLAIN

NOBUHITO MORI,1 TOMOYUKI TAKAHASHI:SURVEY OF 2011 TOHOKU EARTHQUAKE TSUNAMI INUNDATION AND RUN‐UP

ALASTAIR G. DAWSON AND SHAOZHONG SHI: TSUNAMI DEPOSITS

INTERNET SITES

HTTP://CHATWITHSAFETY.BLOGSPOT.IN/P/TSUNAMI.HTML

HTTPS://WWW.DOSOMETHING.ORG/TIPSANDTOOLS/HOW-BE-PREPARE-AND-BE-SAFE-DURING-A-TSUNAMI

HTTP://WWW.WIKIHOW.COM/SURVIVE-A-TSUNAMI

THANK YOU