Abstract
Events characterized by widespread landslides provide rare but valuable opportunities to investigate the spatial and size distributions of landslides in relation to seismic, climatic, geological and morphological factors. This study presents a unique event inventory for the co-seismic landslides induced by the February 25, 2018 Mw 7.5 Papua New Guinea earthquake. The mainshock rupture was dominated by reverse fault motion, and this was also the case for the aftershocks. The latter also triggered widespread landslides in combination with rainfall during the period between February 26 and March 19. We mapped approximately 11,600 landslides of which, more than 10,000 were triggered by the mainshock, with a total failed planimetric area of about 145 km2. Such a large area makes this inventory the world's second-largest recorded landslide event after the 2008 Mw 7.9 Wenchuan earthquake, where the motion changed from predominantly thrust to strike-slip. Large landslides are abundant throughout the study area located within the remote Papua New Guinea Highlands. Specifically, more than half of the landslide population is larger than 50,000 m2 and overall, post-seismic landslides are even larger than their co-seismic counterparts. To understand the factors controlling the distribution of landslides' occurrence and size, we combine descriptive statistics as well as more rigorous bivariate and multivariate analyses. We statistically show that the 15-day antecedent precipitation plays a role in explaining the spatial distribution of co-seismic landslides. Also, we examine four strong aftershocks (Mw ≥ 6.0) within 9 days after the mainshock and statistically demonstrate that the cumulative effect of aftershocks is the main factor disturbing steep hillslopes and causing the initiation of very large landslides, up to ~5 km2. Overall, the dataset and the findings presented in this paper represent a step towards a holistic understanding of the seismic landslide hazard assessment of the entire Papua New Guinea mainland.
Highlights
The island of New Guinea lies along the northern margin of the Australian continent and is part of the ‘Ring of Fire’ around the Pacific Ocean (Figure 1a)
Our analyses show that 10,403 landslides with a total area of 145 km2 were triggered by the mainshock, whereas the remainder (1,138 landslides with a total area of 40 km2) were induced by either aftershocks or succeeding rainfall events between February, 26 and March, 19
We differentiated the landslides triggered by the mainshock and the ones induced by the aftershocks or succeeding rainfall events as much as possible based on the availability of cloud free satellite images
Summary
The island of New Guinea lies along the northern margin of the Australian continent and is part of the ‘Ring of Fire’ around the Pacific Ocean (Figure 1a). The U.S Geological Survey (USGS) Ground Failure tool provides estimates regarding the distribution of co-seismic landslides in near-real-time (Allstadt et al, 2016) Through this scientific progress, earthquake-induced landslide (EQIL) inventories have provided valuable information helping us to better understand the factors controlling the spatial and size distribution of landslides. Strong earthquakes triggering tens of thousands of landslides receive a lot of attention from the worldwide scientific community (e.g., Harp and Jibson, 1995; Gorum et al, 2011; Roback et al, 2018) and due to the increasing availability of high-resolution imagery, multiple landslide inventories have been recently mapped (Tanyaş et al, 2017) Despite this strong interest in large EQIL-events, as of July 2021, no EQIL inventory or detailed landslide study regarding the 2018 Papua New Guinea (PNG) earthquake (Mw 7.5) has been published
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