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Understanding the location of risk to natural hazards, namely the areas of high exposure and vulnerability is a major priority that was identified by the Sendai framework for Disaster Reduction 2015-2030 in order to reach substantial reduction of disaster risk. It is also a necessary decision-making tool for disaster mitigation policy-makers in Japan and around the world. This paper successfully develops a simple methodology using only open data to build the first large-scale (whole country), fine resolution (sub-municipal level) social vulnerability analysis in the context of five different types of natural hazards (earthquake, tsunami, storm surge, flooding and landslide). The result is then compared to an indicator of exposure of population to these hazards in Japan in order to propose a representation of disaster risk. Results show that vulnerability in Japan is highly heterogeneous with urban/rural and north/south fractures. Combining the social vulnerability index with exposure analysis, results show a wide variety of spatial patterns of risk areas in Japan., (© 2023. The Author(s).)

In recent times increasing numbers of high-rate GPS stations have been installed around the world and set-up to provide data in real-time. These networks provide a great opportunity to quickly capture surface displacements, which makes them important as potential constituents of earthquake/tsunami monitoring and warning systems. The appropriate GPS real-time data analysis with sufficient accuracy for this purpose is a main focus of the current GPS research. In this paper we propose an augmented point positioning method for GPS based hazard monitoring, which can achieve fast or even instantaneous precise positioning without relying on data of a specific reference station. The proposed method overcomes the limitations of the currently mostly used GPS processing approaches of relative positioning and global precise point positioning. The advantages of the proposed approach are demonstrated by using GPS data, which was recorded during the 2011 Tohoku-Oki earthquake in Japan.

Since November 30, 2020, an intense seismic swarm and transient deformation have been continuously observed in the Noto Peninsula, central Japan, which is a non-volcanic/geothermal area far from major plate boundaries. We modeled transient deformation based on a combined analysis of multiple Global Navigation Satellite System (GNSS) observation networks, including one operated by a private sector company (SoftBank Corp.), relocated earthquake hypocenters, and tectonic settings. Our analysis showed a total displacement pattern over 2 years shows horizontal inflation and uplift of up to ~ 70 mm around the source of the earthquake swarm. In the first 3 months, the opening of the shallow-dipping tensile crack had an estimated volumetric increase of ~ 1.4 × 107 m3 at a depth of ~ 16 km. Over the next 15 months, the observed deformation was well reproduced by shear-tensile sources, which represent an aseismic reverse-type slip and the opening of a southeast-dipping fault zone at a depth of 14–16 km. We suggest that the upwelling fluid spread at a depth of ~ 16 km through an existing shallow-dipping permeable fault zone and then diffused into the fault zone, triggering a long-lasting sub-meter aseismic slip below the seismogenic depth. The aseismic slip further triggered intense earthquake swarms at the updip. [ABSTRACT FROM AUTHOR]

This study aims at increasing earthquake preparedness knowledge perception and practice among Nepalese immigrants residing in Japan through an educational intervention. A single arm quasi experimental study was conducted among Nepalese immigrants residing in Japan. An educational intervention was prepared along with a 52 itemed questionnaire. In total, 165 participants responded to our questionnaire. Majority of them were male (67.88%), and the mean age was 32.78 years. Generalized equation model showed that the knowledge score of earthquake preparedness was 4.01 points higher immediately after the intervention [95% CI (2.78–5.24), p-value < 0.001] compared to baseline with a further increase by 7.02 points [95% CI (5.96–8.09), p-value < 0.001] at two weeks follow up. However, the practice score increased only by 2.83 points [95% CI (2.51–3.14), p-value < 0.001] immediately after the intervention with a similar increase at two weeks and 12 weeks follow up period [OR: 2.62, 95% CI (2.29–2.96), p-value < 0.001]. The educational intervention, when conducted in native language, can increase both the knowledge and practice score of earthquake preparedness hence, information related to earthquake preparedness in Nepali languages in the government websites of Japan could potentially increase information seeking behavior of people. [ABSTRACT FROM AUTHOR]

This study investigates the instability of prosociality in the real world by looking at the age-specific non-linear relationship between disaster exposure and prosocial behavior. We employed unique microdata from two communities in Japan that were hit by the Great East Japan Earthquake and Tsunami disaster in 2011. Exploiting exogenous variations in disaster exposure, we find age-specific heterogeneous effects of disaster exposure on prosocial behavior captured by the behavior of sending New Year's cards as well as attitudinal survey questions. Among the older groups, disaster damages undermine prosociality, whereas the younger groups show reinforced prosocial behaviors. These findings can be explained consistently by combining two possible determinants of prosocial behavior: pure or impure altruism and self-enforcements in repeated interactions at workplaces. Age information can help disentangle these two elements at least partially. [ABSTRACT FROM AUTHOR]

We investigated the spatiotemporal changes in strain associated with the occurrence of slow slip events (SSEs) in the subduction zones of the Japanese Islands and compared the spatial distribution of both the amount of strain accumulated for the period before and during the SSEs release using time series data from the Global Navigation Satellite System (GNSS). In this study, four SSEs were analysed: the Tokai long-term SSE (2000–2005), the Boso-Oki short-term SSE (2007), and the Bungo Channel long-term SSEs (2009–2011 and 2018–2019). As a result, we found strong negative correlations for all four dilatations before and during SSE occurrence. For these dilatations, we estimated the amount of strain released at the time of occurrence of the SSE relative to that accumulated during the period prior to the SSE. The result indicates that not all the accumulated strain before the SSEs was released when the SSEs occurred. Moreover, it is highly likely that the strain released by SSE is not only due to the strain accumulation just below the SSE occurrence region, but also due to the strain accumulation on the shallower plate boundary, which is a seismogenic zone for a future megathrust earthquake. [ABSTRACT FROM AUTHOR]

The 2011 Tohoku-Oki earthquake (M 9.0) rupture propagated along a shallow plate boundary thrust fault (i.e. decollement) to the trench, displaced the seafloor, and triggered a devastating tsunami. Physical properties of the underthrust sediments which control the rupture propagation are yet poorly known. We use a 2D seismic dataset to build velocity model for imaging and apply reverse time migration. We then calculate pore-fluid pressure along the decollement as the top boundary of underthrust sediments, and along the backstop interface as the boundary between undeformed structures in the continental plate and the severely deformed sediments in the accretionary prism. The results show that within horizontal distance of 40–22 km toward the trench, pore-fluid pressure is 82–60% higher than the hydrostatic pressure for both decollement and backstop interface. It then reduces to hydrostatic level for the backstop interface but remains 60–40% higher than hydrostatic level for the decollement, causing frictional instability in favor of fault rupture along the decollement. We report for the first time, by our knowledge, detailed seismic images of fluid-rich trapped bucket sediments, quantitative stress states, and fluid drainage conditions at shallow tsunamigenic portion of the Japan Trench, which are consistent with the seafloor and borehole observations. [ABSTRACT FROM AUTHOR]

Abnormal increases in radon (222Rn, half-life = 3.82 days) activity have occasionally been observed in underground environments before major earthquakes. However, 222Rn alone could not be used to forecast earthquakes since it can also be increased due to diffusive inputs over its lifetime. Here, we show that a very short-lived isotope, thoron (220Rn, half-life = 55.6 s; mean life = 80 s), in a cave can record earthquake signals without interference from other environmental effects. We monitored 220Rn together with 222Rn in air of a limestone-cave in Korea for one year. Unusually large 220Rn peaks were observed only in February 2011, preceding the 2011 M9.0 Tohoku-Oki Earthquake, Japan, while large 222Rn peaks were observed in both February 2011 and the summer. Based on our analyses, we suggest that the anomalous peaks of 222Rn and 220Rn activities observed in February were precursory signals related to the Tohoku-Oki Earthquake. Thus, the 220Rn-222Rn combined isotope pair method can present new opportunities for earthquake forecasting if the technique is extensively employed in earthquake monitoring networks around the world. [ABSTRACT FROM AUTHOR]