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The Kumamoto area includes 11 municipalities and a population of about one million. The area represents the largest total use of groundwater in Japan. The main recharging area for this groundwater used to be paddy fields for rice production located along the mid-stream section of the Shirakawa River. In the past few decades, the area of paddy fields has rapidly decreased due to the Japanese government's rice production adjustment policy and urbanization. In consequence, the groundwater recharge decreased from 656.2 million m3 in 1992 to 606.9 million m3 in 2006. Thus, groundwater recharge from paddy fields only might not be sufficient for groundwater demand in the future. For this reason, an artificial recharge system was established to increase groundwater recharge. In this study, we review the history of groundwater management and results of 14 years' operation of a large-scale artificial groundwater recharge project in the Kumamoto area. We visualize the resilience of the groundwater management and recharge project by influence of the 2016 Kumamoto Earthquake. It is shown that through an integrated approach of all societal groundwater stakeholders, a sustainable groundwater management can be achieved. The hydrological methods in this integrated approach quantify recharging groundwater volumes for different types of recharge fields by use of 170 local experimental observations. Results and experiences outlined in this paper can be used by planners and managers of dwindling groundwater resources to build resilient systems for groundwater recharge by involving all societal stakeholders through an integrated approach. [ABSTRACT FROM AUTHOR]

This analysis is an extension of the studies based on the space–time–magnitude domain nearest-neighborhood distances (ƞ) obtained from two successive earthquakes. We included epicentral depth as a parameter, and established a new analytical solution for seismicity clustering in the space–time–depth–magnitude domain. The proposed technique was applied to SW Japan seismic observation data for 2011–2018, and revealed that the temporal, spatial, and epicentral (T, R, E) components of the joint distribution for ƞ were prominently bimodal, indicating the presence of two, statistically distinct, earthquake populations. We used the Lomb–Scargle periodogram (LSP) to generate a power spectrum preceding the Kumamoto earthquake, and detected the periodic component of unequally spaced points for log10ƞ (logarithmic scale of ƞ). The LSP showed a dominant peak corresponding to the time period between foreshocks and aftershocks, due to the highest number of recorded ƞ observations. The technique presented in this paper can be applied globally for any time period and any seismotectonic zone preceding large earthquakes of interest. [ABSTRACT FROM AUTHOR]

The 2016 Kumamoto earthquake first occurred on April 14, 2016 with magnitude 6.5 in Kumamoto, Japan as a foreshock. Subsequently, after 28 h, an even larger earthquake occurred with magnitude 7.3 as the main shock on April 16, 2016. These earthquakes were caused by two active faults: the Futagawa and Hinagu faults. This paper proposes a landslide susceptibility calculation method that considers the geomaterial strength reduction from peak to residual state and ground motion directivity. Although there is a lack of information regarding the strength parameters of geomaterials in the slopes, a parametric analysis with various strength parameters of friction angle and cohesion was carried out. To simulate the actual landslides triggered by the 2016 Kumamoto earthquake, the best combination of friction angle and cohesion in each lithology was optimized by a proposed weighted prediction rate. Based on the calculated permanent seismic displacement, a landslide susceptibility map was produced to show the degree of susceptibility over a wide area comprising 100 km2. The proposed regional landslide susceptibility map will be valuable for estimating the locations of possible slope failures and the extent of damage, as well as for planning field reconnaissance and preventing secondary disasters immediately after earthquakes. [ABSTRACT FROM AUTHOR]

An amendment to this paper has been published and can be accessed via the original article. [ABSTRACT FROM AUTHOR]

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Electromagnetic emissions (EMEs) associated with earthquake (EQ) epicenters are found to be one of the most reliable phenomena for the short-term pre-seismic mechanism of earthquakes. The detection mechanism of such emissions can have both direct and indirect techniques. In this manuscript, we attempted to present the signature of such emissions before two strong EQs, one in Fukushima on November 21, 2016, and another in Kumamoto on April 15, 2016, in Japan. We use the lithospheric emission in the range of ultra-low frequency (ULF) waves as observed from the Kakioka observatory in Japan for direct measurement. For the indirect investigation, we use the concept of energetic particle precipitation in the inner radiation belt due to wave–particle interaction through the pitch angle scattering processes. We use the particle enhancement (electron and proton) observed from the space-based National Oceanic and Atmospheric Administration (NOAA) satellites. The ULF results found an abnormal increase in lithospheric radiation for Kumamoto and Fukushima EQs on three days and ten days before the EQs, respectively, and an ionospheric depression on six days before both the cases. The satellite observations related to the EMEs from these EQs exhibit electron particle bursts (PB) on the day of the Fukushima EQ. We observe particle bursts 4–5 and 10 days before the mainshock for the Kumamoto EQ. We are not found any proton precipitation for the Fukushima EQ where signatures of proton count number are observed for the Kumamoto EQ. This type of simultaneous observation from the ground and satellite-based instruments establishes that EMEs are observed before the EQs and can be a potential candidate for short-term precursory studies. [ABSTRACT FROM AUTHOR]

Is it possible to predict location, time and magnitude of earthquakes through identifying their precursors based on remotely sensed data? Earthquakes are usually preceded by unusual natural incidents that are considered as earthquake precursors. With the recent advances in remote sensing techniques which have made it possible monitoring the earth's surface with different sensors, scientists are now able to better study earthquake precursors. Thus, the present study aims at developing the algorithm of classic PS-InSAR processing for obtaining crustal deformation values at the epicenter of earthquakes with magnitude larger than 5.0 on the Richter scale and with oblique thrust faulting and then after calculating temperature values using remotely sensed thermal imagery at the epicenter of same earthquakes; thermal and crustal deformation anomalies were calculated using data mining techniques before earthquake occurrence. In the next stage, taking the correlation between thermal anomalies and crustal deformation anomalies at the epicenter of the study earthquakes into account, an integrated technique was proposed to predict probable magnitude and time of oblique thrust earthquakes occurrence over the earthquake-prone areas. Eventually, the validity of the proposed algorithm was evaluated for an earthquake with a different focal mechanism. The analysis results of the thermal anomalies and crustal deformation anomalies at the epicenter of April 16, 2016, Japan-Kumamoto earthquake of magnitude 7.0 with strike-slip faulting, showed completely different trends than the suggested patterns by the proposed algorithm. [ABSTRACT FROM AUTHOR]

The M 7.3 Kumamoto earthquake that occurred at 1:25 JST on April 16, 2016, not only triggered aftershocks in the vicinity of the epicenter, but also triggered earthquakes that were 50-100 km away from the epicenter of the main shock. The active seismicity can be divided into three regions: (1) the vicinity of the main faults, (2) the northern region of Aso volcano (50 km northeast of the mainshock epicenter), and (3) the regions around three volcanoes, Yufu, Tsurumi, and Garan (100 km northeast of the mainshock epicenter). Notably, the zones between these regions are distinctively seismically inactive. The electric resistivity structure estimated from one-dimensional analysis of the 247 broadband (0.005-3000 s) magnetotelluric and telluric observation sites clearly shows that the earthquakes occurred in resistive regions adjacent to conductive zones or resistive-conductive transition zones. In contrast, seismicity is quite low in electrically conductive zones, which are interpreted as regions of connected fluids. We suggest that the series of the earthquakes was induced by a local accumulated stress and/or fluid supply from conductive zones. Because the relationship between the earthquakes and the resistivity structure is consistent with previous studies, seismic hazard assessment generally can be improved by taking into account the resistivity structure. Following on from the 2016 Kumamoto earthquake series, we suggest that there are two zones that have a relatively high potential of earthquake generation along the western extension of the MTL. [ABSTRACT FROM AUTHOR]

To understand the cause of heavy structural damage during the mainshock (on April 16, 2016) of the 2016 Kumamoto earthquake sequence, we carried out a field survey from April 29 through May 1, 2016, in Mashiki where heavy damage concentration was observed. The heavy damage concentration in downtown Mashiki could be understood based on the observed strong motions with the Japan Meteorological Agency instrumental seismic intensity of VII and information collected by the field investigation. First, the fundamental features of the structural damage in downtown Mashiki were summarized. Then, a distribution map of peak frequencies was derived from horizontal-to-vertical spectral ratios of microtremors. We could not see any systematic correlation between the peak frequencies and spatial distribution of damage ratios. We also analyzed observed strong motion data at two sites to obtain fling-step-like motions in the displacement time histories through the double integration of unfiltered accelerograms. It turned out that at both strong motion observation sites in Mashiki, only the east-west (EW) components had very strong velocity pulses westward before the emergence of the fling-step-like motion eastward, which would be the primary cause of heavy structural damage in downtown Mashiki, not site effects nor the fling-step-like motion itself. [ABSTRACT FROM AUTHOR]