A5062320419- earthquake and tectonic studies
- Seismology and Earthquake Studies
- Seismic Waves and Analysis
- Geological and Geochemical Analysis
- High-pressure geophysics and materials
- Earthquake Detection and Analysis
- Seismic Imaging and Inversion Techniques
- Methane Hydrates and Related Phenomena
- Geological and Geophysical Studies
- Geophysics and Sensor Technology
- Cryospheric studies and observations
- Geophysics and Gravity Measurements
- Geology and Paleoclimatology Research
- Planetary Science and Exploration
- Landslides and related hazards
- Geological Modeling and Analysis
- Polar Research and Ecology
- Geological Studies and Exploration
- Image and Signal Denoising Methods
- Underwater Acoustics Research
- Geophysical and Geoelectrical Methods
- Cerebrospinal fluid and hydrocephalus
- Nuclear Issues and Defense
- Drilling and Well Engineering
- Bacillus and Francisella bacterial research
Kagoshima University
2010-2023
Graduate School USA
2020
Relay Graduate School of Education
2014-2015
Japan Meteorological Agency
2008
Hokkaido University
1984-2001
Kyushu University
1997-2001
Abstract We present a new whole mantle P wave tomographic model GAP_P4. used two data groups; short‐period of more than 10 million picked‐up onset times and long‐period 20 thousand differential travel measured by waveform cross correlation. Finite frequency kernels were calculated at the corresponding bands for both long‐ data. With respect to an earlier GAP_P2, we find important improvements especially in transition zone uppermost lower beneath South China Sea southern Philippine owing...
Detection of shallow slow earthquakes offers insight into the near-trench part subduction interface, an important region in development great earthquake ruptures and tsunami generation. Ocean-bottom monitoring offshore seismicity off southern Kyushu, Japan, recorded a complete episode low-frequency tremor, lasting for 1 month, that was associated with very-low-frequency (VLFE) activity plate interface. The tremor exhibited two migration modes reminiscent deep down-dip seismogenic zone some...
Abstract After the occurrence of 2011 magnitude 9 Tohoku earthquake, seismicity in overriding plate changed. The appears to form distinct belts. From spatiotemporal distribution hypocenters, we can quantify evolution after earthquake. In some earthquake swarms near Sendai (Nagamachi‐Rifu fault), Moriyoshi‐zan volcano, Senya fault, and Yamagata–Fukushima border (Aizu‐Kitakata area, west Azuma volcano), observe temporal expansion focal area. This is attributed fluid diffusion. Observed...
Abstract The tectonic stress field was investigated in and around the aftershock area of Hokkaido Eastern Iburi earthquake ( M JMA = 6.7) occurred on 6 September 2018. We deployed 26 temporary seismic stations for approximately 2 months located 1785 aftershocks precisely. Among these aftershocks, 894 focal mechanism solutions were determined using first-motion polarity P wave from observation permanent networks University, Japan Meteorological Agency (JMA), High Sensitivity Seismograph...
A recent extensive seismic wide‐angle experiment revealed a new image of crustal and uppermantle structure across Northern Honshu Arc, Japan. The western part the arc recorded deformation by Miocene back spreading Sea crust is composed highly deformed Tertiary sedimentary layers, relatively low velocity (5.75–5.9 km/s) crystalline basement 15‐km thick lower with 6.6–7.0 km/s. Clear westward thinning from 32 to 27 km represents extensional backarc spreading. attains maximum thickness...
Intense swarm‐like seismicity associated with shallow normal faulting was induced in Ibaraki and Fukushima prefectures, Japan, following the 2011 Tohoku‐Oki earthquake. This shows a systematic spatiotemporal evolution, but little is known of heterogeneity crustal structure this region, or its influence on evolution seismicity. Here, we elucidate high‐resolution model region determine precise hypocenter locations. Hypocenters Prefecture reveal planar earthquake alignment dipping SW at ~45°,...
One- and three-dimensional velocity structures down to 80 km beneath the Hidaka Mountains in Southern Hokkaido, Japan, were derived by a simultaneous inversion of P-arrival time data from local earthquakes. Arrival for derivation obtained observation earthquakes recorded at 27 seismic stations. In order obtain an appropriate starting P-wave structure hypocentral parameters be used inversions, one-dimensional inversions first carried out. The made with simplified algorithm calculation travel...
Abstract We investigate seismic wave velocity structure and spatial distribution of the seismicity in source region 2016 Kumamoto earthquake sequence. A one‐dimensional mean shows that seismogenic zone has a high‐velocity low‐Vp/Vs ratio relative to average Kyushu Island. This indicates crust is relatively strong, capable sustaining sufficiently high strain energy facilitate two large ( M j > 6.5) earthquakes close proximity one another rapid succession. Three‐dimensional tomography...
In 1981, the Research Group for Explosion Seismology recorded a seismic-refraction profile across northern and central Nagano Prefecture, Japan, to study velocity structure of upper crust. The 220-km-long profile, which consisted six shot points 82 temporary stations, extended northeastward from near Mt. Ontake southwestern part Niigata crossing Itoigawa-Shizuoka tectonic line. entire region is characterized by highly heterogeneous northeastern three thick folded surface layers with P-wave...
The 2011 off the Pacific coast of Tohoku Earthquake occurred offshore northeast Japan region on March 11th, 2011. In order to study aftershock activity this event, we started deployment seventy-two ocean bottom seismometers (OBSs) four days after mainshock. south source region, thirty-four longterm OBSs (LT-OBSs) had been deployed before occurrence mainshock, and recovered three LT-OBSs clarify depth distribution aftershocks. Using data OBSs, ninety-nine aftershocks were located. Most...
The three‐dimensional P ‐wave velocity structure of the Iwate volcano, northeastern Japan, is determined to depths 2 km through an active seismic survey conducted in October 2000. Seismic tomography applied approximately 2700 travel‐time data. most prominent discovery existing column‐like high‐velocity body (Vp > 5.4 km/s) that extends vertically for beneath caldera. While western part volcano extending from caldera characterized by a moderate‐velocity region (4.8 < Vp km/s), summit...
We have applied an inverse method to P and S wave arrival time data observed at 52 seismic stations for 349 local earthquakes in order estimate a three-dimensional (3-D) velocity structure beneath northern Japan. The is characterized by simultaneous determination of the two-dimensional depth distributions boundaries, 3-D distribution station corrections as well hypocenter parameters earthquakes. Moho discontinuity under eastern Hokkaido in-clined from 32 km Hidaka Mountains 20 Konsen...
We have elucidated depth variations in the stress field associated with 2007 Noto Hanto, Japan, earthquake by tensor inversion using high-quality aftershock data obtained a dense seismic network.Aftershocks that occurred above 4 km indicated strike-slip regime.By contrast, aftershocks deeper parts thrust faulting regime.This variation regime correlates well slip direction derived from finite source model geodetic data.Furthermore, maximum principal (s 1 ) axis was stably oriented...
Abstract Temporal variations of Green functions associated with the eruptive activity at Sakurajima Volcano, Japan, were estimated using an accurately controlled routinely operated signal system (ACROSS). We deconvolved 400 s waveforms ACROSS nearby stations by a known source time function and stacked results based on relative to individual eruptions eruption intervals; quantities obtained this procedure are corresponding various stages activity. found energy decrease in later phase active...
First testing of volcanic activity monitoring with a system continuously operatable seismic sources, named ACROSS, was started at Sakurajima Volcano, Japan. Two vibrators were deployed on the northwestern flank volcano, distance 3.6 km from main crater. We successfully completed continuous operation 12 June to 18 September 2012, single frequency 10.01 Hz and modulation 10 15 Hz. The signal detected even station that is 28 source, establishing amplitude decay relation as function in region...
On October 4, 1994, an earthquake with magnitude Mw8.3 occurred in the western part of Kurile Islands at 43.42°N, 146.81°E and 33 km depth. The hypocenter parameters were determined by Hokkaido University Japan. Aftershocks following this remarkable event located using data from a local seismic network operated University. We found that most aftershocks (1) on fault plane mainshock, (2) subducting plate around (3) focal area largest aftershock, which 9 Mw7.3. Both not active immediately...
In 1997, two earthquakes (M6.5 and M6.3) occurred in the northwestern part of Kagoshima Prefecture, Japan. We carried out temporary seismic observation to obtain detailed aftershock distribution. constructed a 3-D P wave velocity model by inverting travel times aftershocks observed at 14 stations around focal area relocated more than 14,000 with model. The general features distribution are as follows: (1) Aftershocks first main shock (M6.5) distributed strike nearly E-W (N100°E) vertical...
Abstract The 2005 West Off Fukuoka Prefecture Earthquake (Mj=7.0) occurred on March 20, in the northern part of Kyushu, Japan. To study aftershock activity, we deployed eleven pop-up type ocean bottom seismometers (OBSs), sixteen locally recorded temporary stations, and eight telemetered stations around epicenter region. We combined data from these permanent located area, determined hypocenter mainshock aftershocks. was northwestern central region, at a depth 9.5 km. left-lateral strike-slip...
The pore fluid pressure distribution in the focal region of 2008 Iwate-Miyagi Nairiku earthquake was investigated through an analysis diversity mechanisms. We inverted stress orientations and mechanisms directly from P-wave polarity data obtained a dense aftershock observation network other temporarily routinely operated stations. estimated orientation is consistent with that typical NE Japan. Specifically, σ 1 axis oriented WNW-ESE nearly parallel to plate convergence, 3 vertical,...