Effects of finite source rupture on landslide triggering: the 2016 <i>M</i><sub>w</sub> 7.1 Kumamoto earthquake

Abstract

Abstract. The propagation of a seismic rupture on a fault introduces spatial variations in the seismic wave field surrounding the fault. This directivity effect results in larger shaking amplitudes in the rupture propagation direction. Its seismic radiation pattern also causes amplitude variations between the strike-normal and strike-parallel components of horizontal ground motion. We investigated the landslide response to these effects during the 2016 Kumamoto earthquake (Mw 7.1) in central Kyushu (Japan). Although the distribution of some 1500 earthquake-triggered landslides as a function of rupture distance is consistent with the observed Arias intensity, the landslides were more concentrated to the northeast of the southwest–northeast striking rupture. We examined several landslide susceptibility factors: hillslope inclination, the median amplification factor (MAF) of ground shaking, lithology, land cover, and topographic wetness. None of these factors sufficiently explains the landslide distribution or orientation (aspect), although the landslide head scarps have an elevated hillslope inclination and MAF. We propose a new physics-based ground-motion model (GMM) that accounts for the seismic rupture effects, and we demonstrate that the low-frequency seismic radiation pattern is consistent with the overall landslide distribution. Its spatial pattern is influenced by the rupture directivity effect, whereas landslide aspect is influenced by amplitude variations between the fault-normal and fault-parallel motion at frequencies <2 Hz. This azimuth dependence implies that comparable landslide concentrations can occur at different distances from the rupture. This quantitative link between the prevalent landslide aspect and the low-frequency seismic radiation pattern can improve coseismic landslide hazard assessment.

Landslide Geometry Reveals its Trigger

“…A possible reason for the emergence of this universality could be that both rainfall-induced and coseismic landslides in our databases consist of a mostly shallow landslide, e.g., debris flows (Kasai & Yamada, 2019;von Specht et al, 2019;Watakabe & Matsushi, 2019). Although coseismic rockslides tend to cut the mountain ridge and slide through concave slopes likely on a lithological failure plain with relatively short accumulation zones (Havenith, 2002), the number of such failures is limited in our databases.…”

“…More contemporary mapping includes repeated satellite monitoring of landslide‐prone regions to create complete landslide databases (Behling et al., 2014; Tanyas et al., 2017). Although event‐based inventories include clear traces of the triggering mechanisms of landslides (von Specht et al., 2019), many other inventories, such as satellite‐based, lack crucial information linking a given landslide to a specific triggering mechanism (Behling et al., 2014). The missing information about triggering mechanisms decreases the efficacy of these inventories in landslide hazard analyses, as this could introduce biases, for instance, inadvertently using earthquake‐triggered landslides to assess landslide hazard for extreme rainfall (Ozturk et al., 2020).…”

Can global rainfall estimates (satellite and reanalysis) aid landslide hindcasting?

“…Our analysis relied on the ALOS World 3D digital elevation model (DEM), which is provided by the Japan Aerospace Exploration Agency (JAXA) and its advanced land observing satellite (ALOS) project with a horizontal resolution of 1″ (≈30 m) (Tadono et al 2015). The DEM forms the basis for computing hillslope inclination and visualization using TopoToolbox (Schwanghart and Scherler 2014), as well as the total curvature according to (von Specht et al 2019). Data on major geological units are obtained from the Seamless Digital Geological Map of Japan (scale of 1:200,000) by the Geological Survey of Japan (Yamada et al 1986;Kubo et al 1993), Fig.…”

Earthquake-induced debris flows at Popocatépetl Volcano, Mexico

“…Volcanoes store or drain water in and through aquifers that can grow and empty as impermeable barriers develop or as they are breached by deformation, respectively (Delcamp et al, 2016). Even if not completely saturated, ground vibrations induced positive pore pressure and triggered liquefaction and slope failure (Kameda et al, 2019;Wang et al, 2019). It is important to note that on 10 August a rainfall of 35 mm, similar to the 4 October event that triggered the sediment-laden flow observed at San Juan Tehuixtitlán town, did not induce any channel response, indicating the stability of the slopes of this sector of the volcano prior to the earthquake.…”