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Axford Lecture

Axford Lecture 2

Philip Li-Fan LIU
National University of Singapore

Mon- 29 Jul, 4:45-5:15pm
Nicoll Room, Level 3

"2018 Sulawesi Earthquake and Palu Tsunami"

On September 28, 2018 a shallow (20 km) earthquake of Mw = 7.5 struck in the neck of Minahassa Peninsula, Sulawesi. Roughly 20 to 30 min after the main shock, a tsunami hit city of Palu and many settlements along the shore of Palu Bay. The shaking of earthquake not only damaged many buildings, but also caused severe liquefaction in areas in and around Palu, which let to mudflows. The combined effects of earthquake and tsunami led to the death of at least 2,256 people.

The focal mechanism of the earthquake showed that it was caused by strike-slip faulting on the Palu-Koro fault, trending North-South. Geodetic evidence (Pixel tracking and InSAR images) clearly showed rupture (including surface rupture through the city of Palu) over a length of 150 km. It is noted that at Palu there are several parallel fault strands defining the margins of a pullapart basin.

The tide gage (an acoustic sensor), located inside the port of Pantoloan, recorded clear tsunami signals. They indicated that the leading tsunami wave arrived at Pantoloan about 6 min after the earthquake and was a depression wave. The leading wave height was about 4 m with a wave period about 4 min. Several videos showed the arrival of tsunamis at Palu city roughly 20 ~ 30 min after the earthquake. Other videos indicated that many local (smaller scale) landslides generated tsunamis inside the bay.

Several post-tsunami field surveys were conducted. Runup heights and inundation depths along the coast of Palu bay as well as along the northern coast outside the bay were reported. It was evident that there was very little evidence of the tsunami damage along the coast outside of the Palu bay. This suggests that the sources for tsunami generation must be within the bay.

Tsunami simulations were performed using the geodetic constrained slip models. Simulated tsunami waves significantly under-estimated the measured wave heights at Pantoloan as well as those reported in Palu city area. This further suggests possible mechanisms such as submarine landslides or a pull-apart occurred in the bay area that had triggered the localized tsunami waves inside the bay.

To confirm or refute the hypotheses, two submarine bathymetry surveys were conducted. Multi- Beam and Single-Beam echo sounders were used. The horizontal resolution in the deeper water (> 300 m) is about 10 m, while in the shallower water the resolution is about 80 cm. The new survey data are compared with the pre-earthquake bathymetry data (2014). The results strongly indicate the occurrence of several local landslides and a large area of subsidence in the deepwater region north of Pantoloan port. Further analysis is being carried out and results will be reported in the lecture.

Philip L.-F. Liu is the Vice President for Research and Technology and also a Distinguished Professor in the Department of Civil and Environmental Engineering at NUS.

After graduating with a B.S. degree in Civil Engineering from National Taiwan University in 1968, Liu received a S.M. degree in Civil Engineering in 1971 and a ScD degree in 1974 from Massachusetts Institute of Technology. He joined Cornell faculty as an Assistant Professor in the School of CEE in 1974 and was promoted to Full Professor in 1983. He served as the Associate Director of the School in 1985-1986 and as the Associate Dean for Undergraduate Studies of Engineering College in 1986-1987. Liu was the Director of the School of CEE from July 1, 2009 to June 30, 2015. Liu is currently the Class of 1912 Professor in Engineering, Emeritus in Cornell University, Honorary Professor in Tsinghua University, China, and Li Kwoh-Ting Chair Professor in National Central University, Taiwan.

Liu is a member of the National Academy of Engineering, an Academician of Academia Sinica (Taiwan), a Fellow of the American Geophysical Union, and a distinguished member of the American Society of Civil Engineers. He also received the ASCE Walter L. Huber Civil Engineering Research Prize (1978), the J. S. Guggenheim Fellowship (1980), the ASCE John G. Maffatt & Frank N. Nichol Harbor and Coastal Engineering Award (1997), the International Coastal Engineering Award ASCE (2004), the Alexander von Humboldt Research Award (2009), and the International Award for Enhancement of Tsunami/Coastal Disaster Resilience (2017).