Natural hazards continue to be an increasing challenge to societies around the world, with many societies being impacted by multiple types of hazard events. To reduce the impact of these hazards, we ...must not only quantify the hazard and risk associated with multi-hazard events but also understand the uncertainty associated with these events. Resilience can only be improved by considering all these factors. Multi-hazard and risk-modeling approaches are receiving increasing attention globally; however, the challenges of assessing uncertainty in both single- and multi-hazard risks are considerable. Without a clear understanding of the risks and their uncertainties, measures to mitigate these risks and to increase resilience face difficult decisions. In the present Special Issue, we have five papers and one report on the Tokyo Metropolitan Resilience Project:
Interdisciplinary and Industry-Academia Collaboration Research for Enhancing Social Resilience to Natural Disasters in the Tokyo Metropolitan Area –DEKATSU Activity–
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Multi-Data Integration System to Capture Detailed Strong Ground Motion in the Tokyo Metropolitan Area
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Development of the Training Tool “KUG” for Temporary Lodging Facilities and Companies for Stranded Commuters
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Development of Matching Modeling for Human Resource Allocation of Shelter Management by the Set Theory
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Time-Cost Estimation for Early Disaster Damage Assessment Methods, Depending on Affected Area
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A Report of the Questionnaire Survey on Awareness of COVID-19 and Shelters
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It has been about 20 years since the Headquarters for Earthquake Research Promotion (HERP) was established following the Great Hanshin-Awaji Earthquake Disaster. Now the time has come to examine its ...contributions to disaster resilience. On April 14 and 17, 2016, a series of large earthquakes, including M6.5 and M7.3 events, occurred in Kumamoto Prefecture in Kyushu, Japan. More than 200 fatalities and 8,600 totally collapsed houses were reported. The earthquakes occurred on known active faults, which were assessed by the Earthquake Research Committee (ERC) before the events. The regional disaster management plan by Kumamoto Prefecture had predicted the events reported by the ERC and estimated damages at about the same level as what was actually seen. However, even though the estimate was accurate, the countermeasures were insufficient: the local people still did not seriously expect a large earthquake to strike in their local area, and their efforts to enhance the disaster resilience of the Kumamoto area were insufficient. This suggests that the efforts by the HERP were not sufficient to make the local community resilient enough to withstand a large earthquake.
Seismic wave resonance in sedimentary basins is a well-recognized seismic hazard; however, concentrated areas of earthquake damage have been observed near basin edges, where wave propagation is ...particularly complex and difficult to understand with sparse observations. The Tokyo metropolitan area is densely populated, subject to strong shaking from a diversity of earthquake sources, and sits atop the deep Kanto sedimentary basin. It is also instrumented with two seismic arrays: the dense MEtropolitan Seismic Observation network (MeSO-net) within the basin, and the High sensitivity seismograph network (Hi-net) surrounding it. In this study, we explore the 3-D seismic wavefield within and throughout the Kanto basin, including near and across basin boundaries, using cross-correlations of all components of ambient seismic field between the stations of these two arrays. Dense observations allow us to observe clearly the propagation of three modes of both Rayleigh and Love waves. They also show how the wavefield behaves in the vicinity of sharp basin edges with reflected/converted waves and excitation of higher modes.
In 2007, we initiated a 5-year-research project named the “Tokyo Metropolitan Resilience Project.” This project is intended to improve the resilience to natural disasters, particularly earthquakes, ...in the Tokyo metropolitan area. For this purpose, we have organized multi-disciplinary research including social sciences, natural sciences such as seismology, and civil engineering, with a focus on earthquake engineering. In addition, we facilitate mutual communication between industry and academia. We established the “Data Use and Application Council for Resilience” (Japanese abbreviation: DEKATSU) to organize private and public stakeholders. The DEKATSU council consists of four sectors: industry, government, NPO/NGOs, and academia. The policy promoted to the participating organizations is “When we make organizations resilient, the Tokyo metropolitan area also becomes resilient.” To date, 67 organizational members and 13 personal members have joined, and the targeted idea is becoming accepted but not fully implemented in society.
We propose an extended 3D space (longitude, latitude, and depth) epidemic-type aftershock sequence (ETAS) model for seismicity forecasts beneath the greater Tokyo area (the Kanto region), which also ...takes into account the effects induced by the M9 Tohoku-Oki earthquake of 2011. The model is characterized by a number of 3D location-dependent parameters, such as the background seismicity rates, and the productivity rate induced by the Tohoku earthquake. These allow production of high-resolution predictive mappings in zones where hypocenters are densely populated. The optimally inverted 3D spatial images of the characterizing parameters effectively discriminate seismicity features in the crust and near the plate boundaries. The success of the model is demonstrated using short-, intermediate- and long-term probability forecasts of intermediate and large earthquake occurrences beneath the Kanto region.
An M6.1 earthquake occurred in the northern part of Ōsaka-fu (Osaka Prefecture) on June 18, 2018, with many areas in the Kinki region experiencing intense shaking. In Ōsaka City and Takatsuki City ...seismic intensity 6 lower was observed, resulting in 4 deaths, 15 people sustaining serious injuries, 419 people sustaining minor injuries, 10 completely destroyed residence, 181 partially destroyed residences, and 32,989 residences partially damaged (as of July 17, 2018). There were 339 cases of people being trapped in elevators. At most, approximately 1700 people were evacuated. While there were no derailment incidents on the Shinkansen or local train lines, service was suspended on most railways. Following this earthquake, Ōsaka-fu took the decision to apply The Disaster Relief Act. Response was then enacted by the government local public bodies, and the private sector.
SUMMARY
Uncovering the distribution of magnitudes and arrival times of aftershocks is a key to comprehending the characteristics of earthquake sequences, which enables us to predict seismic ...activities and conduct hazard assessments. However, identifying the number of aftershocks immediately after the main shock is practically difficult due to contaminations of arriving seismic waves. To overcome this difficulty, we construct a likelihood based on the detected data, incorporating a detection function to which Gaussian process regression (GPR) is applied. The GPR is capable of estimating not only the parameters of the distribution of aftershocks together with the detection function, but also credible intervals for both the parameters and the detection function. The property that the distributions of both the Gaussian process and aftershocks are exponential functions leads to an efficient Bayesian computational algorithm to estimate hyperparameters. After its validation through numerical tests, the proposed method is retrospectively applied to the catalogue data related to the 2004 Chuetsu earthquake for the early forecasting of the aftershocks. The results show that the proposed method stably and simultaneously estimates distribution parameters and credible intervals, even within t ≤ 3 hr after the main shock.
We show fine‐scale variations of seismic velocities and converted teleseismic waves that reveal the presence of zones of high‐pressure fluids released by progressive metamorphic dehydration reactions ...in the subducting Philippine Sea plate in Tokai district, Japan. These zones have a strong correlation with the distribution of slow earthquakes, including long‐term slow slip (LTSS) and low‐frequency earthquakes (LFEs). Overpressured fluids in the LTSS region appear to be trapped within the oceanic crust by an impermeable cap rock in the fore‐arc, and impede intraslab earthquakes therein. In contrast, fluid pressures are reduced in the LFE zone, which is deeper than the centroid of the LTSS, because there fluids are able to infiltrate into the narrow corner of the mantle wedge, leading to mantle serpentinization. The combination of fluids released from the subducting oceanic crust with heterogeneous fluid transport properties in the hanging wall generates variations of fluid pressures along the downgoing plate boundary, which in turn control the occurrence of slow earthquakes.
Tokyo, like many seismically threatened cities, is situated atop a sedimentary basin that has the potential to trap and amplify seismic waves from earthquakes. We study amplification in the Kanto ...Basin by exploiting the information carried by the ambient seismic field. We use 375 seismic stations from the high sensitivity seismograph network across central Honshu as virtual sources and 296 seismic stations of the Metropolitan Seismic Observation network shallow borehole seismometers within the basin as receivers to map the basin response. We find a linear relationship between ground motion and basin depth at periods of 2–10 s that could be used to represent 3‐D basin effects in ground motion prediction equations. We also find that the strength of basin seismic amplification depends strongly on the direction of illumination by seismic waves.
Key Points
Combine dense networks to construct ambient seismic field Green's functions
The ambient seismic field contains sedimentary basin wave propagation effects
Seismic amplification strongly depends on earthquake source location
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