Palu – Day 4

This morning, representatives of the team met with engineers from the Irrigation Unit from Public Works Department. Some productive discussions were had, with Irrigation Unit sharing information very generously, and EEFIT/TDMRC discussing our preliminary thoughts in return. Some members then met with BMKG (Institute of Geophysics, Meteorology and Climatology), who presented some of the useful maps they had prepared.

In the afternoon, the Geo team traced the fault rupture south from its emergence at Palu Bay, where the left lateral strike slip fault had displaced by approximately 4m at the coast, clearly visible across a major road, now partly submerged. Back from the coast, the fault was visible across road crossings heading southwards. About 600m back from the shore and crossing the fault, a field of liquefaction sand ejecta was seen, with clear displacements of 300 mm relative to nearby intact ground. The fault then led the team to further liquefaction sites in Lasoso area, with housing and Majid Iqra Mosque affected, the latter exhibiting spectacular tilting of minarets and extensive sand ejecta. The team then followed the fault rupture as far south as daylight permitted, measuring reducing slip displacements down to 2.5m in increasingly rural environments.

Another part of the EEFIT-TDMRC was joined by Indra from Save the Children to conduct structural surveys of representative school complexes affected by the earthquake ground shaking. Overall, 4 schools compounds with more than thirty school buildings were surveyed. These structures were mainly confined masonry and reinforced concrete brick-infilled frame buildings and showed a variety of damage levels and mechanisms. The latter included damage from ground settlement and out of plane collapse of confined masonry walls.

In addition, a small team left to survey inundation and tsunami damage starting at Mamboro on the east coast, working around to end at the mouth of the Palu river in Palu Bay. The team interviewed several residents along the way who lived in houses close to the coastline. One interview was particularly remarkable as the man recounted that he had been swimming in the sea at the time of the earthquake. He left the water after the earthquake and persuaded his family to run up the nearby hill, but he remained to watch the wave. Waiting near his house, he noticed a child by the shoreline who was in the path of the oncoming wave. He dashed forward, grabbed the child but could not run back to safety quickly enough and both were engulfed by the wave. Thankfully, both survived though the child couldn’t walk for 2 weeks due to injuries he sustained.

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Palu – Day 3

The team travelled north from Palu today, along the west side of the bay through the Donggala regency. First stop was the tourist site Tanjung Karang at the most northerly point of the promontory. There was very little evidence of tsunami inundation, except for a line of debris on the beach close to what looked like an earlier failure of an old seawall. Eye witnesses reported seeing three successive waves travelling south to the bay, though the inundation in the car park next to the beach was only ankle deep.

Returning southwards towards Palu, the Team observed very little damage due to ground shaking in non-engineered structures. The ground shaking damage started to become more noticeable only south of Lolidondo, where the Team stopped to investigate damage to two schools. These schools, constructed of confined masonry, had been closed due to extensive cracks in walls and one due to differential displacement of its foundation.

Evidence of coastal area liquefaction was also seen by the team. A significant example included the “sunken city” at Donggala port, where buildings sited on reclaimed land experienced settlement and tilting, and large portions of the port area were missing entirely. The latter likely due to flow liquefaction failure of the reclaimed land fill material with subsequent sliding into the sea.

Along the coast, further symptoms of liquefaction were seen, most significantly around the sea walls at Donggala Kota Wisata, where significant seawards displacements had occurred, possibly in the gravelly sand beneath the walls.

Further down the coast, at Loli Tasiburi eyewitnesses reported seeing soil bubbling and water spouting from the ground before a large area of land detached from the coastline. The behaviour of the water following the largest earthquake on 28 September provided the motivation for residents to flee inland, up the steep slope behind the beach. “Tasiburi” means “black sand” in the Kaili dialect, and this describes the soil seen here very well.

Tsunami damage was evident along most of the coastline, with increasing severity southwards towards Palu. This damage did not extend greatly inland (< 100 m), with indicative inundation heights up to 2.5 m. Low lying non-engineered structures suffered worst, many of these being washed away from their foundations.  Most of the structures were non-engineered (either confined masonry or timber frame 1 storey buildings) and in low-lying areas suffered the collapse of external walls or were washed away from their foundations.

Finally, at Watusanpu Naval Base several boats were left high and dry by the tsunami, though didn’t travel very far inland due to the fairly steep topography.IMG_1921IMG_1886IMG_1999image_ship

Palu – Day 2

In contrast to the first day, we focused on geotechnical hazards rather than the structures. Structures were damaged, but principally due to mass movement, with levels of destruction similar to those due to the tsunami in the Palu Bay area.

In the morning we visited Potobo in the south-east of Palu where had significant mass movement had been observed on pre-mission aerial photography. We parked at the landslide toe, walking upwards, initially across the zone of deposition, which had been levelled to remove surface detail except for a few structures. One remaining structure sitting at the bottom of the gully indicated the thickness of material that had been deposited, up to 4-5 m. We continued to traverse up the landslide, noting another uncleared mosque amidst the bull-dozed areas. It was unclear whether the mosques are being left for structural reasons or because of religious sensitivities. The exposure and intense heat then forced us to retreat for an early lunch. It transpired that some areas that had appeared unaffected by the landslide, after checking against the aerial photos had actually moved as a mass over a considerable a distance, up to a kilometer.

After lunch the team visited Balaroa district in the south-west of Palu and observed a similarly destructive landslide. This time we started reconnaissance at the top, observing the failure scarp, which at its highest was 8-9 m. Walking down the landslide it was noted that many of the destroyed buildings had not yet been cleared, painting an even clearer picture of the destructive power of the landslide.

At various locations in the Balaroa area, evidence of significant fault displacement was observed in the form of previously straight roads being offset by up to 4 m.

At the end of the day the team visited the town of Sigi where signs of liquefaction was observed. Contrasting to Petobo and Balaroa, the town of Sigi was largely still in-situ however there was significant ground movement and differential settlement along with tension cracking.  Comparing the aerial photography from Sigi to the other landslide locations suggests there was a different failure mechanism in this area.

Palu – Day 1

The team arrived at 06:30 to Palu and got straight to work as signs of structural damage were immediately evident on the exterior and interior of the airport terminal building.

After dropping kit bags at the local digs, the team headed out in convoy to have an initial scope-out of the damaged areas and recorded some preliminary findings. On arrival at the Palu bay-front area the tsunami damage was stunningly clear with the total destruction of all but a few structures. Most notably the Masjid APUNG Arqam Baburahman Palu Mosque, now affectionately ‘the floating mosque’, sits stranded offshore but with the structure mostly still intact.

In the afternoon the team visited the local Tadulako University and were welcomed by representatives of the university. After a delicious local lunch, the team sat down to discuss how we could collaborate and conduct an effective field mission supported by representatives of the university.

See below for a few general photos of the damage in Palu…

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The Team

See the list of team members for the joint EEFIT-TDMRC mission below:

EEFIT Team

Professor Tiziana Rossetto, (EEFIT Team Lead), Professor in Earthquake and Tsunami Engineering, University College London.

Professor Alison Raby, Professor of Environmental Fluid Mechanics, Plymouth University

Dr Andrew Brennan, Senior Lecturer in Geotechnical Engineering, University of Dundee

Dr David Robinson, Research Associate in Tsunami Modelling, University College London

Rohit Kumar Adhikari, PhD Student on seismic assessment of schools, University College London

Muhammad Rezki-Hr, PhD student on transport infrastructure resilience, Newcastle University

Richard Lagesse, Engineering Geologist, Arup Singapore

TDMRC Team

Dr Ella Meilianda, (TDMRC Team Leader) Assistant Professor in Coastal Morphology at TDMRC Syiah Kuala University

Dr Yunita Idris, Researcher in Structural Engineering at TDMRC Syiah Kuala University

Ibnu Rusydy, Researcher in Geological Engineering at TDMRC Syiah Kuala University

Intan Dewi Kumala, Psychologist at TDMRC Syiah Kuala University

The participation of Prof. Rossetto and of Dr Robinson in the mission is supported by the European Research Coincil (ERC) Starting Grant URBANWAVES. The participation of Prof. Raby, Dr Brennan, Mr Rezki and Mr Adhikari is supported by the UK Engineering and Physical Sciences Research Council.