Naoshi Hirata

The University of Tokyo | Todai · Earthquake Research Institute

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. Resili...

We present a deep‐learning approach for earthquake detection using waveforms from a seismic array consisting of multiple seismographs. Although automated, deep‐learning earthquake detection techniques have recently been developed at the single‐station level, they have potential difficulty in reducing false detections owing to the presence of local...

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 contamination...

The Tokyo metropolitan area, in the Kanto region of Japan, lies on the Okhotsk plate. Historically, the city has suffered severe damage as a result of megathrust ruptures and intra‐plate earthquakes (M ≥ 7) caused by the dual subduction of the Philippine Sea (PHS) slab and the Pacific slab. To understand the unique seismotectonics of the region, we...

We propose an optimization method for applying the seismic-wave gradiometry (SWG) method to a dense seismic station network consisting of nonuniformly distributed seismographs. As a nonuniformly distributed station array, we consider the station layout of the Metropolitan Seismic Observation Network (MeSO-net) operated in and around the Tokyo metro...

The magnitude 6.2 foreshock on the 14th of April and the magnitude 7.3 main shock on the 16th of April occurred in the 2016 Kumamoto Earthquakes. The main shock over than the magnitude 6.2 was not anticipated because the foreshock was considered to be the main shock. The successive two large shocks increased physical damage but also affected the Ja...

Uncovering the distribution of magnitudes and arrival times of aftershocks is a key to comprehend the characteristics of the sequence of earthquakes, which enables us to predict seismic activities and hazard assessments. However, identifying the number of aftershocks is very difficult due to contaminations of arriving seismic waves immediately afte...

It is our great pleasure to present the fifth JDR Award to Dr. Yuichiro Usuda. Dr. Usuda has made outstanding contributions to the Journal of Disaster Research (JDR) as the guest editor and the author of the JDR’s “Special Issue on NIED Frontier Researches on Science and Technology for Disaster Risk Reduction and Resilience 2017” in Vol.12 No.5, wh...

In the Kanto district, Metropolitan Seismic Observation network (MeSO-net) of highly dense seismic network has accumulated continuous waveform data since 2008. It is expected that higher resolution of three-dimensional attenuation structures can be obtained by using these high-density observation records. However, seismometers of MeSO-net is instal...

Abstract 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-dependen...

Plain Language Summary On 25 April 2015, the Gorkha earthquake (Mw 7.8) struck central Nepal and resulted in nearly 9,000 fatalities. Destructive earthquakes have occurred repeatedly in the Himalayan region. The Himalayan seismogenic zone is located in the India‐Eurasia plate collision zone where the Indian plate underthrusts the Eurasian plate alo...

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...

This study analyses the seismicity in the Kanto region by fitting the 2-D-epicentre and 3- D-hypocentre ETAS models to the JMA catalogue for events above magnitude M4.0. In the 3-D ETAS model, the focal depth is assumed to follow the beta distribution. Compared with results from the 2-D-epicentre ETAS model, the 3-D ETAS model greatly improves the...

The Collaboratory for the Study of Earthquake Predictability (CSEP) is a global cyberinfrastructure for prospective evaluations of earthquake forecast models and prediction algorithms. CSEP’s goals are to improve our understanding of earthquake predictability, advance forecasting model development, test key scientific hypotheses and their predictiv...

Almost all forecasting of the magnitude of the next earthquake has assumed the same independent probability distribution, such as the Gutenberg-Richter (G-R) law, with the same b-value (b = 0:9 in Japan region standard), throughout an earthquake sequence. Identifying a broadened forecasting procedure for general models of space-time magnitude seque...

Strong ground motion can induce dynamic strains large enough for the Earth's subsurface to respond non-linearly and to cause permanent, or plastic, damage. The 2011 M w 9.0 Tohoku-Oki earthquake, Japan, generated exceptional and well recorded ground motions in the greater Tokyo area. We use continuous records from 234 stations of the dense MeSO-net...

The Itoigawa-Shizuoka Tectonic Line (ISTL) is a major oblique left-lateral crustal fault that is expected to host M7+ events in the near future. Its proximity to the Kanto sedimentary basin poses a threat to the population of Metropolitan Tokyo. This study constructs ground motion predictions for scenario earthquakes on the ISTL using virtual earth...

We present a complete history of earthquake detection probabilities and detection completeness levels for the Japanese seismic network from 1923 to, and including, 2014 in high resolution over space and time. In our study, we employ the probability-based magnitude of completeness method developed by Schorlemmer and Woessner (2008). Using this metho...

Hazard and risk researchers are using their research results to target several vastly different stakeholders: the scientific community, governmental institutions, engineers and the larger technical community, companies, and finally the local residents. Each of these groups has a different focus on the results and is drawing different conclusions fr...

The 2016 Kumamoto earthquake consisted of a magnitude 6.2 foreshock that occurred on the 14th of April, and a magnitude 7.3 main shock that occurred on the 16th of April. The main shock occurring over the magnitude 6.2 foreshock was not anticipated because the foreshock was originally considered to be the main shock. After the earthquakes occurred,...

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 Pre...

In order to reveal the current status and issues of the victims of the 2016 Kumamoto Earthquake eight months after its occurrence, we conducted large-scale random sample questionnaire surveys with victims aged 18 and over in the most affected municipalities from November to December 2016. We decided to sample a total of 7,000 victims (1,600 from Ku...

Long-period ground motions due to large earthquakes can cause devastating disasters, especially in urbanized areas located on sedimentary basins. To assess and mitigate such damage, it is essential to rapidly evaluate seismic hazards for infrastructures, which can be simulated by seismic response analyses that use waveforms at the base of each infr...

The epidemic type aftershock sequence (ETAS) model is widely used to describe and analyze the clustering behavior of seismicity. Instead of regarding large earthquakes as point sources, the finite-source ETAS model treats them as ruptures that extend in space. Each earthquake rupture consists of many patches, and each patch triggers its own aftersh...

Earthquakes sometimes cause serious disasters not only directly by ground motion itself but also secondarily by infrastructure damage, particularly in densely populated urban areas that have capital functions. To reduce the number and severity of secondary disasters, it is important to evaluate seismic hazards rapidly by analysing the seismic respo...

After the occurrence of the 2011 magnitude 9 Tohoku earthquake, seismicity in the overriding plate changed. This chapter considers some possible evidence of the influence of crustal fluid/water on the occurrence of the triggered seismicity after the 2011 Tohoku-Oki earthquake. It estimates the permeability from the observed hypocenter diffusion. Sh...

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 wavepropagation is particularly complex and difficult to understand with sparse observations. TheTokyo metropolitan area is densely populated, subject to strong shaking from a d...

A destructive M 6.7 earthquake struck Northern Nagano prefecture on November 22, 2014. The main shock occurred on the Kamishiro fault segment of the northern Itoigawa–Shizuoka Tectonic Line (ISTL). We used data recorded at 41 stations of the local seismographic network in order to locate 2118 earthquakes that occurred between November 18 and Novemb...

The dense seismic array “MeSO-net” (Metropolitan Seismic Observation network), in which 296 accelerometers, at this moment, are installed with several kilometer intervals, was established in 2007 for the purpose of the disaster mitigation for forthcoming large earthquakes. Whether the actual azimuths of MeSO-net seismometers newly installed after 2...

The Lishan fault has been characterized alternately as a major discontinuity in stratigraphy, structures and metamorphism, a ductile shear zone, a tectonic suture or non-existent. In addition to being a geological boundary, it also marks transitions in subsurface structures. Thus, the seismicity to the west of the fault permeates through the upper...

Modern seismological analyses are difficult for earthquakes which occurred in the early period of instrumental observation (between 1870’s to 1920’s) because of sparse station distributions and low quality of data particularly in clock errors. Source parameters of such old earthquakes can be estimated through comparisons with recent seismological d...

We studied the seismicity rate increase in the Kanto region around Tokyo following the 2011 Tohoku-Oki earthquake (Mw 9.0) to examine whether this increase was correlated with the static increases in the Coulomb failure function (ΔCFF) of the Tohoku-Oki earthquake sequence. Because earthquakes in the Kanto region exhibit various focal mechanisms, t...

We determine the hypocenters and focal mechanisms for earthquakes occurred in Kanto region, Japan between 1885 and 1923. In this period, available seismological data are limited because of sparse station distributions and low quality of data particularly in absolute timing. The number of reported phase arrival times and first-motion polarities of e...

After the occurrence of the 2011 magnitude 9 Tohoku earthquake, the seismicity in the overriding plate changed. The seismicity appears to form distinct belts. From the spatiotemporal distribution of hypocenters, we can quantify the evolution of seismicity after the 2011 Tohoku earthquake. In some earthquake swarms near Sendai (Nagamachi-Rifu fault)...

We show contrasting subduction structures within the Philippine Sea plate inferred from active-source wide-angle reflection data. Previous studies showed that large-amplitude reflections from the slab are observed in southwest Japan and indicated that a thin low-velocity layer with a high fluid content is formed along the top of the subducting ocea...

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...

We report the surface roughness analysis of the lunar highlands for the baseline range 0.15–100 km. We use the Median Differential Slope αm to investigate the scale dependency of the roughness and derive the global αm distribution from SELENE Laser Altimeter and Terrain Camera data. While αm(l) versus baseline l (km) plots vary among different high...

The Earthʼs surface is influenced continuously by natural forces such as tides, air pressure, and precipitation, as well as human-induced sources. To separate the geodetic strain of trend components from these induced responses, state-space modeling is applied to volumetric strain data recorded with borehole Sacks-Evertson strainmeters, which have...

[1] The Izu-Bonin arc (IBA) has been colliding with the more northerly Honshu arc since the middle Miocene, forming a globally unique active Izu arc-arc collision zone (ICZ) in central Japan. To determine crustal structure of the ICZ, we constrain P and S wave velocities from active source refraction data. The velocity structures reveal that the st...

Abrupt increases in seismicity rate have been observed in the Kanto region, where the Tokyo Metropolitan area is located, after the 2011 off the Pacific coast of Tohoku earthquake (M9.0) on March 11, 2011. They are well explained by the static increases in the Coulomb Failure Function (ΔCFF) imparted by the gigantic thrusting while some other possi...

The 2011 off the Pacific coast of Tohoku earthquake occurred in the plate boundary of the Pacific Plate subducting beneath Tohoku-Japan (Yokota et al., 2011) was extremely large with the scale of Mw 9.0. However, long-period ground motions for several periods observed in the Kanto basin were not extremely large against the scale of the magnitude, f...

[1] Active and passive seismic experiments in the Kii Peninsula, southwest Japan, revealed prominent structural features around the segment boundary of a megathrust earthquake associated with the subduction of the Philippine Sea Plate (PHS). A distinct reflection band in the uppermost part of the PHS shows significant lateral variation along its st...

The largest aftershock (M w 7.8) of the giant M 9.0 Tohoku-oki earthquake occurred near the coast of Ibaraki Prefecture about thirty minutes after the main shock. We have imaged the rupture process of the M w 7.8 earthquake by back-projection of waveform data from the Metropolitan Seismic Observation network (MeSO-net). Original acceleration seismo...

Seismicity in southern Kanto activated with the 2011 March 11 Tohoku earthquake of magnitude M9.0, but does this cause a significant difference in the probability of more earthquakes at the present or in the To? future answer this question, we examine the effect of a change in the seismicity rate on the probability of earthquakes. Our data set is f...

The Hidaka region in the central part of Hokkaido Island, Japan is known as an arc-arc collision zone where the Kuril Arc (southern part of eastern Hokkaido) has been collided against the NE Japan Arc (western Hokkaido) since the middle Miocene. This collision is a controlling factor for the formation of the Hidaka Mountains, the westward obduction...

One major focus of the current Japanese earthquake prediction research program (2009-2013) is to move toward creating testable earthquake forecast models. For this purpose we started an experiment of forecasting earthquake activity in Japan under the framework of the Collaboratory for the Study of Earthquake Predictability (CSEP) through an interna...

The Central Disaster Management Council of Japan estimates the next great M7+ earthquake in the Tokyo metropolitan region will cause 11,000 fatalities and 112 trillion yen (1 trillion US) economic loss at worst case if it occur beneath northern Tokyo bay with M7.3. However, the estimate is based on a source fault model by conventional studies about...

is an important feature of elastic wave propagation in the Earth and can arise from a variety of ordered architectures such as fractures with preferential alignments or preferred crystal orientations. We studied the regional variations in shear wave anisotropy around a deep Low-Frequency Earthquake (LFE) zone beneath the Kii Peninsula, SW Japan, us...

We conducted aftershock observations of 20 September, 1999 Chi-Chi, Taiwan Earthquake beginning 15 days after the main shock. We deployed 20 seismographs twice in a 100km by 100 km area around the focal area of the main shock. Each observation period lasted one month. Two months of observations yielded about 80GB of continuously recorded aftershock...

Intense swarm-like seismicity associated with shallow normal faulting was induced in Ibaraki and Fukushima prefectures, Japan, following the 2011 Tohoku-Oki earthquake. This seismicity shows a systematic spatiotemporal evolution, but little is known of the heterogeneity in crustal structure in this region, or its influence on the evolution of the s...

The Itoigwa-Shizuoka-Tectonic Line (ISTL) fault system is considered to have one of the highest probabilities for a major inland earthquake occurrence in the whole of Japan. It is a complex fault system with the dip directions of the local fault segments changing from north to south between an east dipping low angle thrust fault, a strike slip faul...

抄録 Long term slow slip (LTSS) and non-volcanic low frequency earthquakes (LFEs) were reported in the central part of the Tokai district, central Japan. Such LTSS and LFE events are considered to take place at a transition zone of frictional property from stick-slip to stable sliding on the top of subducting Philippine Sea plate. To clarify the spat...

We have investigated the material properties and the tectonic processes that govern the Pacific plate just before it is subducted in the Japan Trench Subduction zone. We reprocessed the 500 km long data retrieved by the summer 1991 seismic survey offshore of the Boso peninsula and Tohoku regions and produced a high resolution image of the Pacific p...

We examined a relationship between the Coulomb Failure Function (ΔCFF) due to the Tohoku earthquake (March 11, 2011; MJMA 9.0) and the seismicity rate change in Tokyo Metropolitan area following March 2011. Because of large variation in focal mechanism in the Kanto region, the receiver faults for the ΔCFF were assumed to be two nodal planes of smal...

The Gutenberg-Richter frequency-magnitude distribution of earthquakes has become well established in seismology. The slope of the relation between frequency and magnitude (b value) is typically 1, but it often shows variations around 1. Based on an analysis of seismicity prior to the 2011 Tohoku and 2004 Sumatra earthquakes (both in magnitude (M) 9...

Although no deterministic and reliable earthquake precursor is known to date, we are steadily gaining insight into probabilistic forecasting that draws on space–time characteristics of earthquake clustering. Clustering-based models aiming to forecast earthquakes within the next 24 hours are under test in the global project ‘Collaboratory for the St...

The 2007 Niigata-ken Chuetsu-oki earthquake occurred on July 16, 2007 with a magnitude of 6.8. Immediately after the mainshock, a dense network of ocean-bottom seismometers and temporary land seismic stations were deployed to obtain the accurate aftershock location. A seismic survey using ocean-bottom seismometers, land stations and controlled sour...

Major objectives of the Japanese earthquake prediction research program for the period 2009-2013 are to create earthquake forecasting models and begin the prospective testing of these models against recorded seismicity. For this purpose, the Earthquake Research Institute of the University of Tokyo has joined an international partnership to create a...

One major focus of the current Japanese earthquake prediction research program (2009-2013), which is now integrated with the research program for prediction of volcanic eruptions, is to move toward creating testable earthquake forecast models. For this purpose we started an experiment of forecasting earthquake activity in Japan under the framework...

Many large earthquakes are preceded by one or more foreshocks, but it is unclear how these foreshocks relate to the nucleation process of the mainshock. On the basis of an earthquake catalog created using a waveform correlation technique, we identified two distinct sequences of foreshocks migrating at rates of 2 to 10 kilometers per day along the t...

The earth's surface is under the continuous influence of a variety of natural forces such as earthquakes, wave, wind, tide, air pressure, precipitation and a variety of human induced sources, which create noise when monitoring geodetic strain. Eliminating these noise inputs from the raw strain data requires proper statistical modeling, for automati...

In Tokai region, central part of Japan, the Philippine Sea plate is descending to the NW direction. The configuration of the subducting slab has been revealed by the seismic tomography and refraction/reflection studies. Those studies suggested that the top of the slab was not smooth. A clear image of the subducting ridges was figured out. The chara...

Collaboratory for the Study of Earthquake Predictability (CSEP) is a global project of earthquake predictability research. The final goal of this project is to have a look for the intrinsic predictability of the earthquake rupture process through forecast testing experiments. The Earthquake Research Institute, the University of Tokyo joined the CSE...

The deep geometry of active faults and the mid-crustal detachment at the base of seismogenic layer is important for understanding active tectonic process and accessing the risk of destructive earthquakes. The detailed image of source fault and subducting slab have been delineated by the controlled-source reflection profiling with the dense array of...

Strong ground motions from the 2011 off the Paci[|#2#|]c coast of Tohoku Earthquake, the most powerful earthquake in and around Japan after the installation of modern seismic network were recorded for more than 300 seconds by a dense and wide-span seismic network, the Metropolitan Seismic Observation Network (MeSO-net) installed around the Tokyo me...

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