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
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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)
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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)
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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
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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
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Calculated tsunami propagation
Maximum water level
min
Bathymetric data:
GEBCO
Calculated by
using linear
shallow water
equations with a
finite-difference
method
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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
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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%
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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)
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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)
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Past tsunami events in Sulawesi
The northern part of the island has been more frequently
inundated by tsunamis
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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
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2018 Sulawesi Tsunami Survey Team
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Measured tsunami inundation & run-up heights
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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
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South area
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South area
Multistory shopping mall and parking garage
These served as a vertical evacuation
destination for many people during the event
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South area
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South area – building at IAIN Palu campus
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Aerial photographic survey using UAV
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Aerial image & digital elevation model (DEM)
(South area)
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East area – damage in Mamboro
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East area – grounded ship in Wani2
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West area – damage in Buluri
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West area – damage in Loli
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West area – gravel quarries
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West area – reclaimed land
Unstable coastal areas (river mouths and
reclaimed land using gravel and sand) along
the western shore of Palu Bay → landslides???
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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
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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
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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