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Research about Japan

Source-linked reports with geographic coverage including Japan.

At least 37 records · Page 2Linked to original sources
USGS2019

Seismological, geological, and geotechnical engineering aspects of the 2018 MW 6.6 Hokkaido Eastern Iburi earthquake

The 2018 Hokkaido Eastern Iburi MW6.6 earthquake struck the southern coast of the north island of Japan in the early morning (3:08 AM JST) on September 6, 2018. The event had a hypocentral depth of 35 km, centered beneath the port city of Tomakomai. Extremely strong shaking with peak ground acceleration in excess of 0.5 g was felt in the communities directly north of Tomakomai, in the districts of Abira and Atsuma. There, a very high density of landslides occurred in pumices soil that affected the majority of slopes in the region above the floodplain. These landslides were typically a thin veneer of 1 to 3 m of recent (<9000 ybp) volcanic pumice mantling older Kawabata marine sedimentary rocks. The source of the pumice layers are recent eruptions from Mt. Tarumae, south of Shikotsu-ko Caldera lake. Several block megaslides were observed in the Kawabata marine unit. A flow failure resulting from soil collapse or liquefaction was observed in fill deposits placed in a residential community district of Kiyota ward in Sapporo. The community, Satozuka-1 is situated on a natural steep ravine that was filled with pumice soil to level construction area to a gently sloping landscape for housing construction. The flow failure consisted of lateral migration of soil from the upper slope regions of the community onto the surface of the lower community. The upper community topographically deflated as large quantities of fluidized soil flooded the lower streets.

Hokkaido↗
USGS2019

A leg-hold noose capture method for Brent Geese Branta bernicla at staging or wintering sites

Effective and efficient capture methods are needed for marking and monitoring individuals in studies of demography, migration and habitat use. We describe a novel use of leg-hold nooses aligned on lines and mats to capture non-breeding Brent Geese Branta bernicla in water at a staging and wintering site in Japan. A total of 24 Brent Geese were caught in autumn 2017 and 2018. The traps, which were easy to set up and transport, were effective at catching small numbers of Brent Goose at intertidal roosting and gritting sites. Leg-hold noose lines and mats may be a suitable alternative to other standard catching techniques, such as cannon-netting and flat net traps, in locations where it is not practicable to use these other methods.

Wildfowl↗
USGS2018

Consequences of abrading bed load on vertical and lateral bedrock erosion in a curved experimental channel

In this study, we conducted multiple physical experiments to estimate the efficacy and spatial pattern of erosion by abrading sediment moving through a simple U‐shaped channel bend with erodible bed and banks. The experiments showed that in the bend, lateral abrasion followed a monotonically increasing linear relationship with sediment feed rate. However, vertical incision had a more complex relation with the sediment feed rate, with an initial increase in abrasion as the feed rate increased followed by a decrease in abrasion of the bed as cover effects became dominant at higher feed rates. Bank erosion was large in places where the width and the lateral slope of the point bar were relatively large. On the other hand, in places where the width of the point bar was smaller, the bedrock bed was eroded primarily along the boundary of the point bar, resulting in a bedrock bench near the outer bank.

Shimanto River↗
USGS2018

A preliminary study of variation of Trapa in Japan

Summary Frequent occurrence of intermediate forms and poor knowledge on the variability of characters have caused some difficulties in the taxonomy of Trapa in Japan. Thus I made a preliminary analysis on the variation of nuts collected from 21 populations in Southwestern Japan. Attention was paid to some morphometrical characters of the nut and development of lower spines or “pseudohorns.” Each population usually contained different forms of nuts. Among them, however, several entities could be recognized based on the shape of nut as follows. 1) Two-spined form: This included nuts of middle size (width 30–50 mm) and ones of big size (width over 45 mm). In case of the former ones, the nuts with pseudohorns of varying degree of development usually occurred together within one population and even on a single plant. I propose to treat them as one taxon, Trapa japonica , sensu OHWI (1965), without inventing varieties. But at the same time, it was remarkable that the tendency of development of pseudohorns was apparently different from population to population. The bigger ones included two types, that is, one without pseudohorns and the other with pseudohorns. The former one may be identified as T. bispinosa ROXB., but the latter one has not been described in literature. 2) Four-spined form: The nuts of small size (width of about 20 mm) were well definable and thought to be T. incisa SIEB. et ZUCC. The nuts of bigger size showed some variations with respect to their size and/or stoutness of lower spines. The big ones (width over 45 mm) may be treated as one taxon, T. natans or its variety. The nuts of middle size have been named T. natans var. pumila NAKANO. But so far as present materials were concerned, its entity seemed dubious. They might be immature nuts of bigger ones. The different patterns of variation among populations were ascribed to genetic differentiation. Predominance of self-pollination and isolation of habitats were thought to promote genetic isolation and preservation of genetic variations which occurred in each population. But the possibility of hybridization cannot be excluded.

Open-File Report↗
USGS2018

Investigating the origin of continual radio frequency impulses during explosive volcanic eruptions

Volcanic lightning studies have revealed that there is a relatively long‐lasting source of very high frequency radiation associated with the onset of explosive volcanic eruptions that is distinct from radiation produced by lightning. This very high frequency signal is referred to as “continual radio frequency (CRF)” due to its long‐lasting nature. The discharge mechanism producing this signal was previously hypothesized to be caused by numerous, small (10–100 m) leader‐forming discharges near the vent of the volcano. To test this hypothesis, a multiparametric data set of electrical and volcanic activity occurring during explosive eruptions of Sakurajima Volcano in Japan was collected from May to June 2015. Our observations show that a single CRF impulse has a duration on the order of 160 ns (giving an upper limit on discharge length of 10 m) and is distinct from near‐vent lightning discharges that were on the order of 30 m in length. CRF impulses did not produce discernible electric field changes and occurred in the absence of a net static electric field. Lightning mapping data and infrared video observations of the eruption column showed that CRF impulses originated from the gas thrust region of the column. These observations indicate that CRF impulses are not produced by small, leader‐forming discharges but rather are more similar to a streamer discharge, likely on the order of a few meters in length.

Sakurajima Volcano↗
USGS2018

Temporal stress changes caused by earthquakes: A review

Earthquakes can change the stress field in the Earth’s lithosphere as they relieve and redistribute stress. Earthquake-induced stress changes have been observed as temporal rotations of the principal stress axes following major earthquakes in a variety of tectonic settings. The stress changes due to the 2011 Mw9.0 Tohoku-Oki, Japan, earthquake were particularly well documented. Earthquake stress rotations can inform our understanding of earthquake physics, most notably addressing the long-standing problem of whether the Earth’s crust at plate boundaries is “strong” or “weak.” Many of the observed stress rotations, including that due to the Tohoku-Oki earthquake, indicate near-complete stress drop in the mainshock. This implies low background differential stress, on the order of earthquake stress drop, supporting the weak crust model. Earthquake stress rotations can also be used to address other important geophysical questions, such as the level of crustal stress heterogeneity and the mechanisms of postseismic stress reloading. The quantitative interpretation of stress rotations is evolving from those based on simple analytical methods to those based on more sophisticated numerical modeling that can capture the spatial-temporal complexity of the earthquake stress changes.

Journal of Geophysical Research B: Solid Earth↗
USGS2018

Euler-vector clustering of GPS velocities defines microplate geometry in southwest Japan

I have used Euler-vector clustering to assign 469 GEONET stations in southwest Japan to k clusters ( k = 2, 3,..., 9) so that, for any k , the velocities of stations within each cluster are most consistent with rigid-block motion on a sphere. That is, I attempt to explain the raw (i.e., uncorrected for strain accumulation), 1996–2006 velocities of those 469 Global Positioning System stations by rigid motion of k clusters on the surface of a spherical Earth. Because block geometry is maintained as strain accumulates, Euler-vector clustering may better approximate the block geometry than the values of the associated Euler vectors. The microplate solution for each k is constructed by merging contiguous clusters that have closely similar Euler vectors. The best solution consists of three microplates arranged along the Nankaido Trough-Ryukyu Trench between the Amurian and Philippine Sea Plates. One of these microplates, the South Kyushu Microplate (an extension of the Ryukyu forearc into the southeast corner of Kyushu), had previously been identified from paleomagnetic rotations. Relative to ITRF2000 the three microplates rotate at different rates about neighboring poles located close to the northwest corner of Shikoku. The microplate model is identical to that proposed in the block model of Wallace et al. (2009, https://doi.org/10.1130/G2522A.1) except in southernmost Kyushu. On Shikoku and Honshu, but not Kyushu, the microplate model is consistent with that proposed in the block models of Nishimura and Hashimoto (2006, https://doi.org/10.1016/j.tecto.2006.04.017) and Loveless and Meade (2010, https://doi.org/10.1029/2008JB006248) without the low-slip-rate boundaries proposed in the latter.

southwest Japan↗
USGS2018

Mainshock-aftershock clustering in volcanic regions

Earthquakes break their general Poissonean behavior through two types of seismic bursts: swarms and mainshock-aftershock sequences. The former is commonly thought to dominate in volcanic and geothermal regions, but aftershock production, including within swarms, is not well studied in volcanic regions. Here we compare mainshock-aftershock clustering in active volcanic regions in Japan to nearby nonvolcanic regions. We find that aftershock production is similar in both areas by two separate metrics: (1) Both volcanic and nonvolcanic regions have similar proportions of areas that cluster into mainshock-aftershock sequences. (2) Volcanic areas with mainshock-aftershock sequences have aftershock productivity at least as high as nonvolcanic regions. We also find that volcano-tectonic events that are precursors to an eruption are more common at volcanoes without mainshock-aftershock clusters than at volcanoes with well-defined mainshock-aftershock clusters. This last finding hints at a strategy to identify volcanic systems where cataloged earthquakes are good predictors of behavior.

Geophysical Research Letters↗
USGS2017

Before and after retrofit behavior and performance of a 55-story tall building inferred from distant earthquake and ambient vibration data

A sparsely instrumented 55-story building in Osaka, Japan had recorded unprecedented, severe and long-duration long-period resonating responses during the March 11, 2011 M9.0 Tohoku earthquake that occurred at 767 km distance. Thereafter, studies of the records resulted in implementation of a significant retrofit design, comprising dampers and buckling restrained braces (BRBs). The responses of the retrofitted building were also recorded during the April 24, 2016 M7.3 Kumamoto earthquake that occurred at 478 km. The earthquake and on-demand acquired ambient response data are analyzed in this study to assess the impact of this rare, retrofitted and instrumented tall building subjected to long period strong shaking from events originating at far distances. As expected, the fundamental frequency and critical damping ratio of the building increased, albeit small, after the retrofit as compared to before the retrofit. Increase of damping percentage is a positive finding and indicates that even larger percentages may be attained under shaking stronger than the 2016 event. The records indicate that the building still experiences significant resonance, torsion, as well as a beating effect.

Osaka↗
USGS2017

Viscoelastic lower crust and mantle relaxation following the 14–16 April 2016 Kumamoto, Japan, earthquake sequence

The 2016 Kumamoto, Japan, earthquake sequence, culminating in the M w =7.0 16 April 2016 main shock, occurred within an active tectonic belt of central Kyushu. GPS data from GEONET reveal transient crustal motions from several millimeters per year up to ∼3 cm/yr during the first 8.5 months following the sequence. The spatial pattern of horizontal postseismic motions is shaped by both shallow afterslip and viscoelastic relaxation of the lower crust and upper mantle. We construct a suite of 2-D regional viscoelastic structures in order to derive an optimal joint afterslip and viscoelastic relaxation model using forward modeling of the viscoelastic relaxation. We find that afterslip dominates the postseismic relaxation in the near field (within 30 km of the main shock epicenter), while viscoelastic relaxation dominates at greater distance. The viscoelastic modeling strongly favors a very weak lower crust below a ∼65 km wide zone coinciding with the Beppu-Shimabara graben and the locus of central Kyushu volcanism. Inferred uppermost mantle viscosity is relatively low beneath southern Kyushu, consistent with independent inferences of a hydrated mantle wedge within the Nankai trough fore -arc.

Kumamoto↗
USGS2017

Evaluating a kinematic method for generating broadband ground motions for great subduction zone earthquakes: Application to the 2003 Mw 8.3 Tokachi‐Oki earthquake

We compare broadband synthetic seismograms with recordings of the 2003 M w "> M w Mw 8.3 Tokachi‐Oki earthquake to evaluate a compound rupture model, in which slip on the fault consists of multiple high‐stress‐drop asperities superimposed on a background slip distribution with longer rise times. Low‐frequency synthetics ( &lt; 1 &#x2009;&#x2009; Hz "> < 1 Hz <1 Hz ) are calculated using deterministic, 3D finite‐difference simulations and are combined with high‐frequency ( &gt; 1 &#x2009;&#x2009; Hz "> > 1 Hz >1 Hz ) stochastic synthetics using a matched filter at 1 Hz. We show that this compound rupture model and overall approach accurately reproduces waveform envelopes and observed response spectral accelerations (SAs) from the Tokachi‐Oki event. We find that sufficiently short subfault rise times (i.e., &lt; &#x223C; 1 &#x2013; 2 &#x2009;&#x2009; s "> < ∼ 1 – 2 s <∼1–2 s ) are necessary to reproduce energy &#x223C; 1 &#x2009;&#x2009; Hz "> ∼ 1 Hz ∼1 Hz . This is achieved by either (1) including distinct subevents with short rise times, as may be suggested by the Tokachi‐Oki data, or (2) imposing a fast‐slip velocity over the entire rupture area. We also include a systematic study on the effects of varying several kinematic rupture parameters. We find that simulated strong ground motions are sensitive to the average rupture velocity and coherence of the rupture front, with more coherent ruptures yielding higher response SAs. We also assess the effects of varying the average slip velocity and the character (i.e., area, magnitude, and location) of high‐stress‐drop subevents. Even in the absence of precise constraints on these kinematic rupture parameters, our simulations still reproduce major features in the Tokachi‐Oki earthquake data, supporting its accuracy in modeling future large earthquakes.

Bulletin of the Seismological Society of America↗
USGS2017

Geotechnical aspects of the 2016 MW 6.2, MW 6.0, and MW 7.0 Kumamoto earthquakes

The 2016 Kumamoto earthquakes are a series of events that began with an earthquake of moment magnitude 6.2 on the Hinagu Fault on April 14, 2016, followed by another foreshock of moment magnitude 6.0 on the Hinagu Fault on April 15, 2016, and a larger moment magnitude 7.0 event on the Futagawa Fault on April 16, 2016 beneath Kumamoto City, Kumamoto Prefecture on Kyushu, Japan. These events are the strongest earthquakes recorded in Kyushu during the modern instrumental era. The earthquakes resulted in substantial damage to infrastructure, buildings, cultural heritage of Kumamoto Castle, roads and highways, slopes, and river embankments due to earthquake-induced landsliding and debris flows. Surface fault rupture produced offset and damage to roads, buildings, river levees, and an agricultural dam. Surprisingly, given the extremely intense earthquake motions, liquefaction occurred only in a few districts of Kumamoto City and in the port areas indicating that the volcanic soils were less susceptible to liquefying than expected given the intensity of earthquake shaking, a significant finding from this event.

Report↗
USGS2016

Responses of a tall building with U.S. code-type instrumentation in Tokyo, Japan, to events before, during and after the Tohoku earthquake of 11 March 2011

The 11 March 2011 M 9.0 Tohoku earthquake generated long-duration shaking that propagated hundreds of kilometers from the epicenter and affected tall buildings in urban areas several hundred kilometers from the epicenter of the main shock. Recorded responses show that tall buildings were affected by long-period motions. This study presents the behavior and performance of a 37-story building in the Tsukuda area of Tokyo, Japan, as inferred from modal analyses of records retrieved for a time interval covering a few days before, during, and for several months after the main shock. The U.S. “code-type” array comprises three triaxial accelerometers deployed at three levels in the superstructure. Such a sparse array in a tall structure limits a reliable assessment, because its performance must be based on only the average drift ratios. Based on the inferred values of this parameter, the subject building was not structurally damaged.

Toyko↗
USGS2016

Responses of two tall buildings in Tokyo, Japan, before, during, and after the M9.0 Tohoku earthquake of 11 March 2011

The 11 March 2011 M 9.0 Tohoku earthquake generated significant long duration shaking that propagated hundreds of kilometers from the epicenter and affected urban areas throughout much of Honshu. Recorded responses of tall buildings at several hundred km from the epicenter of the main shock and other events show tall buildings were affected by long-period motions of events at distant sources. This study presents behavioral aspects of 29-story and 30-story neighboring buildings in the Shinjuku area of Tokyo, Japan, as inferred from records retrieved from a sparse array of accelerometers deployed in the superstructures, at ground and 100 m below the ground level over a time interval covering before, during, and after the main shock. Such long-period effects are common in several regions of Japan as well as in the United States and in other seismically active countries. Permanent shifts in fundamental frequencies are observed. Drift ratios indicate possible structural nonlinear behavior occurred during the main shock. The need to consider risks to built environments from distant sources, including those in neighboring countries, is emphasized.

Tokyo↗
USGS2016

An overview of the geotechnical damage brought by the 2016 Kumamoto Earthquake, Japan

The 2016 Kumamoto earthquake with a moment magnitude of 7.0 (Japanese intensity = 7) that struck on April 16 brought devastation in many areas of Kumamoto Prefecture and partly in Oita Prefecture in Kyushu Region, Japan. The earthquake succeeds a foreshock of magnitude 6.5 (Japanese intensity = 7) on April 14. The authors conducted two surveys on the devastated areas: one during April 16-17, and the other during May 11-14. This report summarizes the damage brought to geotechnical structures by the two consecutive earthquakes within a span of twenty-eight hours. This report highlights some of the observed damage and identifies reasons for such damage. The geotechnical challenges towards mitigation of losses from such earthquakes are also suggested.

Report↗
USGS2015

Observatory geoelectric fields induced in a two-layer lithosphere during magnetic storms

We report on the development and validation of an algorithm for estimating geoelectric fields induced in the lithosphere beneath an observatory during a magnetic storm. To accommodate induction in three-dimensional lithospheric electrical conductivity, we analyze a simple nine-parameter model: two horizontal layers, each with uniform electrical conductivity properties given by independent distortion tensors. With Laplace transformation of the induction equations into the complex frequency domain, we obtain a transfer function describing induction of observatory geoelectric fields having frequency-dependent polarization. Upon inverse transformation back to the time domain, the convolution of the corresponding impulse-response function with a geomagnetic time series yields an estimated geoelectric time series. We obtain an optimized set of conductivity parameters using 1-s resolution geomagnetic and geoelectric field data collected at the Kakioka, Japan, observatory for five different intense magnetic storms, including the October 2003 Halloween storm; our estimated geoelectric field accounts for 93% of that measured during the Halloween storm. This work demonstrates the need for detailed modeling of the Earth&rsquo;s lithospheric conductivity structure and the utility of co-located geomagnetic and geoelectric monitoring.

Kakioka↗
USGS2014

The tsunami source area of the 2003 Tokachi-oki earthquake estimated from tsunami travel times and its relationship to the 1952 Tokachi-oki earthquake

We estimate the tsunami source area of the 2003 Tokachi-oki earthquake (Mw 8.0) from observed tsunami travel times at 17 Japanese tide gauge stations. The estimated tsunami source area ( ∼ 1.4 × 10 4 km 2 ) coincides with the western-half of the ocean-bottom deformation area ( ∼ 2.52 × 10 4 km 2 ) of the 1952 Tokachi-oki earthquake (Mw 8.1), previously inferred from tsunami waveform inversion. This suggests that the 2003 event ruptured only the western-half of the 1952 rupture extent. Geographical distribution of the maximum tsunami heights in 2003 differs significantly from that of the 1952 tsunami, supporting this hypothesis. Analysis of first-peak tsunami travel times indicates that a major uplift of the ocean-bottom occurred approximately 30 km to the NNW of the mainshock epicenter, just above a major asperity inferred from seismic waveform inversion.

Earth, Planets and Space↗