Characteristics of tuff breccia-andesite in diverse mechanisms of landslides in Oita Prefecture, Kyushu, Japan

Heavy rainfall frequently occurred in Kyushu and triggers the landslides every year. This study observes the landslides which occurred in Oita Prefecture, Kyushu, Japan. The landslides in this study, consisting of the same soil materials, tuff breccia and andesite materials; however, the landslide mechanisms were different. Two landslides occurred caused by heavy rainfall in the different timing of the landslide occurrence, and another landslide occurred without the heavy rainfall or an earthquake occurs. Therefore, this study aims to analyse the physical and mechanical properties of tuff breccia and andesite materials with diverse landslide mechanisms. This study performed soil stratigraphic analysis and soil hardness measurements in the field, and performed physical properties, saturated permeability, mechanical properties, and XRD tests in the laboratory. This study found that characteristics of tuff breccia and andesite in diverse mechanisms of landslides were not very different, especially on the landslides caused by heavy rainfall. Furthermore, the landslide in the andesite and tuff breccia areas could be divided into three types based on the timing of the landslide occurrence, scale of the landslide, and landslide mechanisms.

Towards A Geo-Hydro-Mechanical Characterization of Landslide Classes: Preliminary Results

Nowadays, landslides still cause both deaths and heavy economic losses around the world, despite the development of risk mitigation measures, which are often not effective; this is mainly due to the lack of proper analyses of landslide mechanisms. As such, in order to achieve a decisive advancement for sustainable landslide risk management, our knowledge of the processes that generate landslide phenomena has to be broadened. This is possible only through a multidisciplinary analysis that covers the complexity of landslide mechanisms that is a fundamental part of the design of the mitigation measure. As such, this contribution applies the “stage-wise” methodology, which allows for geo-hydro-mechanical (GHM) interpretations of landslide processes, highlighting the importance of the synergy between geological-geomorphological analysis and hydro-mechanical modeling of the slope processes for successful interpretations of slope instability, the identification of the causes and the prediction of the evolution of the process over time. Two case studies are reported, showing how to apply GHM analyses of landslide mechanisms. After presenting the background methodology, this contribution proposes a research project aimed at the GHM characterization of landslides, soliciting the support of engineers in the selection of the most sustainable and effective mitigation strategies for different classes of landslides. This proposal is made on the assumption that only GHM classification of landslides can provide engineers with guidelines about instability processes which would be useful for the implementation of sustainable and effective landslide risk mitigation strategies.

Submarine Landslides and Their Tsunami Hazard

Most tsunamis are generated by earthquakes, but in 1998, a seabed slump offshore of northern Papua New Guinea (PNG) generated a tsunami up to 15 m high that killed more than 2,200 people. The event changed our understanding of tsunami mechanisms and was forerunner to two decades of major tsunamis that included those in Turkey, the Indian Ocean, Japan, and Sulawesi and Anak Krakatau in Indonesia. PNG provided a context to better understand these tsunamis as well as older submarine landslide events, such as Storegga (8150 BP); Alika 2 in Hawaii (120,000 BP), and Grand Banks, Canada (1929), together with those from dual earthquake/landslide mechanisms, such as Messina (1908), Puerto Rico (1928), and Japan (2011). PNG proved that submarine landslides generate devastating tsunamis from failure mechanisms that can be very different, whether singly or in combination with earthquakes. It demonstrated the critical importance of seabed mapping to identify these mechanisms as well as stimulated the development of new numerical tsunami modeling methodologies. In combination with other recent tsunamis, PNG demonstrated the critical importance of these events in advancing our understanding of tsunami hazard and risk. This review recounts how, since 1998, understanding of the tsunami hazard from submarine landslides has progressed far beyond anything considered possible at that time. ▪ For submarine landslide tsunamis, advances in understanding take place incrementally, usually in response to major, sometimes catastrophic, events. ▪ The Papua New Guinea tsunami in 1998, when more than 2,200 people perished, was a turning point in first recognizing the significant tsunami hazard from submarine landslides. ▪ Over the past 2 to 3 years advances have also been made mainly because of improvements in numerical modeling based on older tsunamis such as Grand Banks in 1929, Messina in 1908, and Storegga at 8150 BP. ▪ Two recent tsunamis in late 2018, in Sulawesi and Anak Krakatau, Indonesia, where several hundred people died, were from very unusual landslide mechanisms—dual (strike-slip and landslide) and volcanic collapse—and provide new motivations for understanding these tsunami mechanisms. ▪ This is a timely, state of the art review of landslide tsunamis based on recent well-studied events and new research on older ones, which provide an important context for the recent tsunamis in Indonesia in 2018. Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 49 is May 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.