Liquefaction in Palu: the cause of massive mudflows

Abstract

The 7.5 Mw tectonic earthquake that hit Palu City on 28 September 2018 was followed by tsunami and liquefaction, triggered massive mudflows in Balaroa, Petobo, and Jono Oge areas. This study focuses on the generating factors of liquefaction such as the condition of soil lithology, depth of water table, the distance to the focal mechanism, and the thickness of soft sediment. Microtremor data, including the Horizontal Vertical Spectral Ratio (HVSR), geological condition, and borehole data, were examined to conduct the liquefaction analysis. The analysis results based on the microtremor data showed that the distribution of ground shear strain values in Palu City ranged from 0.75 × 10–4 to 2.56 × 10–4. The distribution of the locations of the liquefaction was correlated to the distribution of ground shear strain values. High ground shear strain values and a shallow groundwater level were discovered in Palu City valley, which indicates that liquefaction in Palu City will undoubtedly occur. The semi-empirical method confirmed that Balaroa, Petobo, and Jono Oge had undergone large-scale liquefaction at a maximum depth of 16 m below the ground level. The average peak of water runoff that generated the mudflow was estimated to be at 11.31 cm3/s. Since the soil has loose soil grain with high water content, the soil will turn into a massive amount of mud during the liquefaction.

Mitigation plan against liquefaction potential on Gumbasa Irrigation Canal around Jono Oge area after 2018 Central Sulawesi Earthquake

“…The earth lining irrigation canal in the Jono Oge area experienced a large deformation and lateral spreading when the earthquake hit on September 28, 2018. Other studies concluded that water flow on the Gumbasa Irrigation Canal also accelerated the emergence of mudflows through the ground fractures [17]. In addition to understanding the geotechnical conditions of the soil around the irrigation canal is needed.…”

Integrated mapping of the earthquake-induced liquefaction in Wates Groundwater Basin, Kulon Progo for land use planning consideration: A preliminary study

“…Historically, as of 2019, there are minimally 37 liquefaction disasters already happened in Indonesia [1]. One of the latest and biggest damages of liquefaction, in Indonesia, was the massive mudflows in Balaroa, Petobo, and Jono Oge, Central Sulawesi which happened in early October 2018 [2]. The 7.5 Mw tectonic earthquake that happened on 28 September 2018 was the major triggering factor responsible for the flow slides [3].…”

Cascading disasters triggered by earthquake hazards: An infrastructure resilience approach

“…Roughly 63 percent of the victims of the 2011 Japan tsunami in Ishinomaki occurred in their houses [1]. In addition, the settlement in the Balaroa, Petobo, and Jono Oge regions had sunk because of the tremendous liquefaction caused by the Palu earthquake disaster [2]. Examples of cascading chains of geological events include: earthquake rupture creating tsunami; intense earthquake shaking prompting large-scale landslide and liquefaction, and mainshock causing a series of destructive aftershocks [3].…”