Giving geological knowledge back to human society is an important part of geology, and engineering geology is one of the major branches of this discipline to play such a role. However, its own perspectives and methods required to achieve significant societal contributions have not yet been established. As a consequence, a lack of clarity exists surrounding both the nature of engineering geology and its position within the broader geological sciences. If the fundamental aim of contributing to society is to be achieved, the following missions are necessary: (i) improving our understanding of the relationship between society and geology; (ii) transforming and converting geological information at a variety of scales in both time and space; and (iii) conducting supplementary studies to eliminate gaps in existing geological studies. Balanced progress is needed in these areas. Furthermore, considering that the geological sciences are subdivided into many fields, it is essential for engineering geologists to be able to integrate information and knowledge from each field. Engineering geology includes both scientific and engineering disciplines, and it is the combination of both skillsets that contributes academic value. This value will be further enhanced by clarifying the framework required to advance the field of engineering geology.

Given that rock weathering influences the processes and rates of landform development, an understanding of the processes and rates of rock weathering is important in engineering geology. The study of weathering has been classified into three types: (1) the process (mechanism) of weathering, (2) weathering products and changes in rock properties, and (3) rates of weathering. Analyses of the physical, mechanical, and chemical properties of weathering products are also important because these rock properties are closely related to each other. However, works on weathering products have generally not been undertaken with the intention of estimating long-term weathering rates, because of difficulties in the estimation of time.

This review suggests that experimental studies have significantly progressed using new analytical methods on rock weathering in Japan. In particular, many studies on salt weathering and its influence of rock properties have recently been published. Rates of long-term weathering are estimated based on the assumption that the weathering period is equal to the period between the emergence age of river terraces or the formation age of lava domes, and the present. Accumulated data on weathering rates and changes in rock properties are needed to enable progress in studies of rock weathering.

Deep-seated gravitational slope deformation (DSGSD) creates characteristic geomorphological features, such as double (or multiple) ridges, uphill-facing scarps, downhill-facing scarps, and ridge-top depressions, which had been considered periglacial landforms until the 1970s. Research on such topographical features is important for landslide disaster mitigation, because they might develop into deep-seated, large-scale, and catastrophic landslides. This paper reviews the terminology, research history and perspective, as well as formation factors of DSGSD and related geomorphic features in Japan, mainly from the viewpoint of engineering geology.

The first paper to clearly propose that geomorphological features such as linear depressions were formed by DSGSD was published in 1980 in a study of the Hida Mountains. Many subsequent examples of DSGSD-related topographies have been reported, not only in alpine zones above the timberline, but also under forest canopy on low mountains. Some authors have successfully estimated the formation ages of these topographical features using radiocarbon dating and tephrochronology. Recent development of LiDAR (Light Detection and Ranging or Laser Imaging Detection and Ranging) surveying has revealed that uncountable DSGSD topographic features are present under forest canopy in low-altitude, high-relief mountainous areas that are difficult to access. The distribution of DSGSD topographic features is not homogeneous: their development is closely related to geomorphological and geological factors such as the relief of mountains, the amount of Quaternary uplift, and the orientation of foliation planes in basement rocks. The formation of some DSGSD topographic features might be triggered by earthquakes. In the future, we need clear criteria to differentiate and classify DSGSD-related topographic features when assessing the risk of landslide disasters.

Nontectonic geological structures are formed near the Earth's surface under the field where gravitational force dominates tectonic stress. This paper reviews studies on nontectonic structures that are related mainly to landslides, active faults, and geomorphic processes in Japan, published over the last two decades. Nontectonic faults are generated by the gravitational movement of rock masses, seismic shaking, and volcanic activity. Landslides cause nontectonic folds, such as buckling and bending folds, which can form gravitationally. Similarly, valley bulging makes anticlines along river channel. Studies on joint have progressed markedly, especially regarding sub-surface sheeting joints including closely developed micro-sheeting or lamination sheeting. It is difficult to discriminate nontectonic structures from tectonic ones in most cases, because both structures coexist in the same environment and, furthermore, polygenic or complex structures of both nontectonic and tectonic origins can exist in the same locality. Also from the standpoint of engineering geology, which applies geological knowledge to human society, it is important to comprehensively clarify the formative mechanism and history of geological structures, including tectonic and nontectonic processes.

A Permian brachiopod species, Leptodus nobilis, is identified for the first time in argillaceous limestone boulders within the basal conglomerate of the Pliocene Kume Formation, Hitachi area, central Japan, and added to the Ishinazaka fauna. This fauna, consisting of 18 species in 17 genera, is assigned to the Wordian stage (middle Permian). In terms of palaeobiogeography, the Ishinazaka fauna has a close affinity with the middle Permian brachiopod faunas of northeastern Japan (South Kitakami Belt), eastern Russia (South Primorye), and northern China (Inner Mongolia). The fossil-bearing boulders were probably derived from the Ayukawa Formation within the Hitachi Palaeozoic rocks. Therefore, the Hitachi area was probably part of a continental shelf situated along the eastern margin of North China (Sino-Korea) during the Wordian, and the Ayukawa Formation belongs to the South Kitakami Belt, northeastern Japan.

We present new biostratigraphic data from an exposed Miocene sedimentary section of the upper part of the Ichishi Group in Mie Prefecture, central Honshu. Mudstone samples were collected from outcrop exposures, mainly found along a river, where we mapped lithologies and structures. Planktonic foraminiferal assemblages consisting mainly of warm water species were obtained from 21 samples above and below the lithostratigraphic boundary between the Mitsugano Member (upper part of the Oi Formation) and the overlying Chaya Member (lower part of the Katada Formation). The sedimentary sequence is correlated to zones N.7 and N.8 of the planktonic foraminiferal zonal scheme. Importantly, our results from high-resolution sampling show that the N.7/N.8 zonal boundary is located within a horizon ~19 m below the Oi/Katada formation boundary. Diatom fossils of the Crucidenticula sawamurae Zone (NPD2B; 18.1-17.0 Ma) were found in calcareous concretions within the Mitsugano Member below the N.7/N.8 zonal boundary. Our results suggest that the section is a suitable candidate for assessing the validity of early-middle Miocene planktonic foraminiferal biochronology.

Back-arc basin basalts from the Shikoku Basin were recovered at DSDP Leg 58 Sites 442-444 and ODP Leg 131 Site 808. The geochemistry of these volcanic rocks was initially reported soon after their recovery (from the 1980s to the early 1990s), and therefore many of these data suffered from limits of accuracy inherent in data at the time. We reanalyzed archived samples of Sites 442-444 and 808 using recent analytical techniques of XRF and ICP-MS and reported these highly accurate results herein.

Boulders of biotite-phenocryst-rich, high-K basaltic rock were discovered in the upper stream of the Kuzuryu River in Katsuyama City, Fukui Prefecture. The biotite phenocrysts are zoned, with pale brown cores and dark brown margins. Relics of mafic minerals, replaced by carbonate minerals, contain chromian spinel. Although the primary chemical composition is affected by the formation of secondary minerals such as carbonate, the SiO₂ and K₂O contents of the studied rock are 48-49 wt% and 3.6 wt%, respectively, which are within the chemical range of absarokite. Chondrite-normalized rare earth element and primitive-mantle-normalized trace element patterns of the studied volcanic rocks are characterized by high LREEs/HREEs, high concentrations of LILEs, and negative anomalies of HFSEs (Nb, Ti). These petrological and geochemical characteristics represent a primary composition that has never before been reported in the Hokuriku district.