Field Survey of

the 2018 Sulawesi Tsunami

Takahito Mikami

Coastal Disaster Management Symposium

Institut Teknologi Sumatera (ITERA), 15 August 2019

Department of Urban and Civil Engineering

Tokyo City University

1

2

Contents

Basic information on the 2018 Sulawesi Eq.

Past tsunami events in Sulawesi

Results of tsunami field survey

Main part of this presentation is based on the following article:

Mikami, T., Shibayama, T., Esteban, M., Takabatake, T., Nakamura, R.,

Nishida, Y., Achiari, H., Rusli, Marzuki, A. G., Marzuki, M. F. H.,

Stolle, J., Krautwald, C., Robertson, I., Aranguiz, R. & Ohira, K.

(2019): Field Survey of the 2018 Sulawesi Tsunami: Inundation and

Run-up Heights and Damage to Coastal Communities, Pure and

Applied Geophysics, in press. (doi:10.1007/s00024-019-02258-5)

3

Sulawesi Island

Palu Bay

2018 Sulawesi Earthquake

At 18:02 local time on September 28, 2018, a large earthquake of

Mw 7.5 took place on Sulawesi Island

This earthquake and its accompanying hazards, including a tsunami,

landslides, and liquefaction, caused severe damage to coastal areas

facing Palu Bay (Palu City and Donggala Regency)

4

Surface deformation caused by earthquake

Geospatial Information Authority of Japan: https://www.gsi.go.jp/cais/topic181005-index-e.html

Palu-Koro Fault

(left-lateral strike-

slip fault line) lying

right under Palu

Bay

Eastern part

moved northward

and western part

moved southward

5

Initial surface deformation (vertical)

Fujii & Satake: http://iisee.kenken.go.jp/staff/fujii/Sulawesi2018/tsunami.html

Fault location

Calculated by

using Mansinha &

Smylie (1971)

formula

Fault parameters

(Fujii & Satake):

Length 100 km

Width 10 km

Depth 0 km

Strike 350º

Dip 67º

Slip -17º

Average

slip

4.5 mred lines (uplift) interval: 0.05 m

blue lines (subsidence) interval: 0.1 m

6

Calculated tsunami propagation

Maximum water level

min

Bathymetric data:

GEBCO

Calculated by

using linear

shallow water

equations with a

finite-difference

method

7

Video that captured the generation of waves

Mr. Ricoseta Mafella’s instagram

An aerial video taken by a

pilot, who took off just

before the earthquake,

captured circular waves that

were generated along the

west side of Palu Bay

This implies that tsunamis

were generated by

submarine landslides

triggered by the earthquake

8

Numerical simulations of landslide tsunami (Rafael et al.)

Rafael et al. “The 2018 Palu tsunami as a combination of several landslides and co-1 seismic tsunami effects” under review

Earthquake

Landslide

Earthquake71.3%

Earthquake & Landslide

14.8%

Volcano2.6%

Volcano & Landsilde

1.7%

Landslide7.0%

Other2.6%

9

Causes of tsunami

In many cases, an earthquake generated tsunami

Landslides and volcanoes also sometimes generated tsunami

Causes of tsunami events in

1900-2018 based on the

NCEI/WDS Global Historical

Tsunami Database

NOAA: https://www.ngdc.noaa.gov/hazard/tsu_db.shtml

(N = 115)

10

Date Source location Magnitude Damaged areas Tsunami catalogue

December 29, 1820 7° S / 119° E 7.5 Coast from Bonthain to Bulukumba Soloviev & Go (1984)

November 17, 1857 1.35° N / 125.2° E - Kema Soloviev & Go (1984)

December 13, 1858 1° N / 126° E 7.3 Entire eastern coast of Sulawesi Island Soloviev & Go (1984)

June 28, 1859 1° N / 126.5° E 7.0 Kema Soloviev & Go (1984)

July 29, 1859 0° N / 125.5° E 7.3 Kema Soloviev & Go (1984)

September 6, 1889 1° N / 126.25° E 8.0 Kema Soloviev & Go (1984)

December 1, 1927 0.5° S / 119.5° E 6.3 Palu Bay, Talise Soloviev & Go (1984)

May 20, 1938 0.7° S / 120.3° E 7.6 Ampibabo, Parigi Soloviev & Go (1984)

April 11, 1967 3.3° S / 119.4° E 5.5 Tinambung Soloviev & Go (1984)

August 15, 1968 0.2° N / 119.8° E 7.4 Donggala, Tambu, Mapaga Soloviev & Go (1984)

February 23, 1969 3.1° S / 118.9° E 7.4 North of Madjene Soloviev et al. (1992)

January 1, 1996 0.724° N / 119.981° E 7.9 Tonggolobibi Lander et al. (2003)

May 4, 2000 1.105° S / 123.573° E 7.6 Luwuk, Peleng Lander et al. (2003)

Past tsunami events in Sulawesi

13 events are recorded in global tsunami catalogues

Tsunami in Palu Bay can only be found for the 1927 event

“At the same time, a tidal wave appeared in Palu Bay.

It lasted 30 seconds and had a height of 15 m. The

wave destroyed huts in the shore zone; 14 people died

and 50 were injured.” (Soloviev & Go, 1984)

11

Past tsunami events in Sulawesi

The northern part of the island has been more frequently

inundated by tsunamis

12

Post-event field survey

Conducted a field survey 27th – 31st October 2018

– Measured tsunami inundation and run-up heights

– Observed damage to buildings and coastal infrastructure

– interviewed local residents

13

2018 Sulawesi Tsunami Survey Team

14

Measured tsunami inundation & run-up heights

15

Tsunami inundation occurred

throughout Palu Bay and also in

the areas to its north

In the inner part of Palu Bay,

tsunami inundation and run-up

heights were more than 4 m

(maximum height: 6.8 m)

Residents described that the first

wave arrived soon after the

earthquake (4 min in Wani2 and 10

min in Silae)

Some residents reported that they

evacuated to the mountains

immediately after feeling the

ground motion

Findings from the field survey

16

South area

17

South area

Multistory shopping mall and parking garage

These served as a vertical evacuation

destination for many people during the event

18

South area

19

South area – building at IAIN Palu campus

20

Aerial photographic survey using UAV

21

Aerial image & digital elevation model (DEM)

(South area)

22

East area – damage in Mamboro

23

East area – grounded ship in Wani2

24

West area – damage in Buluri

25

West area – damage in Loli

26

West area – gravel quarries

27

West area – reclaimed land

Unstable coastal areas (river mouths and

reclaimed land using gravel and sand) along

the western shore of Palu Bay → landslides???

28

North area – Lombonga

Local people evacuated after an earthquake. When coming

back to the coast, they saw debris on a road.

Residents in Kavaya and Tompe also reported that they

evacuated to the mountains immediately after the earthquake.

road

29

Inundation distance in each area

West: as the mountains are

located close to the coast, the

inundation distance was around

100 m

East: the tsunami could travel

further inland, as the slope is

much milder than in the west

area

South: as the area has a wide

low-lying coastal plane, the

tsunami reached more than 200

m from the shoreline

Damage was limited to a very

narrow coastal area, implying

that the tsunami had a relatively

short wavelength

30

Summary

2018 Sulawesi Tsunami

– Inner part of Palu Bay: tsunami height > 4 m, severe damage to

coastal low-lying settlements

– North and entrance of Palu Bay: tsunami height < 3 m, limited

damage to coastal communities

– Inundation distance was longer in the southern shore (even in

this area damage was limited ~200 m from the shoreline)

Lessons learnt from the event

– the necessity to re-assess the risk of landslide-generated

tsunamis triggered by earthquakes

– evacuation strategy (routes and destinations) considering the

topographical features and the current levels of tsunami

knowledge and awareness of each settlement