Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Continuous estimation of changes in seismic velocity and seismic scattering property by passive interferometry using seismic ambient noise is a promising tool for monitoring volcanoes. To improve the usefulness of this method, it is... more
Continuous estimation of changes in seismic velocity and seismic scattering property by passive interferometry using seismic ambient noise is a promising tool for monitoring volcanoes. To improve the usefulness of this method, it is necessary not only to detect subsurface structural changes but also to quantitatively compare the estimated changes in seismic wave velocity and seismic wave scattering property with other observations, such as ground deformation. We applied passive interferometry to continuous seismic records from the Suwanosejima volcano, Japan, recorded between April 2017 and December 2021. We detected repeated significant waveform decorrelations in seismic ambient noise cross‐correlation functions (CCFs), indicating changes in seismic scattering property in the shallow areas of the volcano. These decorrelations were observed from 2 weeks to a few days before the increase in the number of explosions, suggesting that seismic scattering properties changed significantly during that period. We found that the timing of the decorrelation in seismic ambient noise CCFs and tilt changes related to magma accumulation and injection beneath Suwanosejima were well synchronized. The high correlation between the amounts of decorrelation and the tilt change during the magma accumulation period possibly suggests that a large volume of accumulated magma caused great changes in the scattering property. These results provide a significant first step toward a quantitative comparison of the amount of changes in the scattering property with the amount of magma accumulation beneath volcanoes.
Research Interests:
Research Interests:
Summary Source location determination of volcanic tremor has been a challenge in seismology due to the waveform complexity and difficulties in reading P- and S-wave arrival times. We present a method for locating volcanic tremor recorded... more
Summary Source location determination of volcanic tremor has been a challenge in seismology due to the waveform complexity and difficulties in reading P- and S-wave arrival times. We present a method for locating volcanic tremor recorded at a seismic network distributed around a volcano. The method combines the source-scanning algorithm and cross-correlation analysis. Tremor records are processed using a technique adopted from ambient seismic interferometry to obtain stacked cross-correlation functions (CCFs) for all station pairs, which are expected to show high amplitudes at the lag time that corresponds to the travel time difference between the stations. The best seismic source location is determined from the maximum of the sum of envelope amplitudes of CCFs at predicted travel time differences between all pairs of stations. This method does not compute theoretical amplitudes, assume an initial hypocenter location, or measure the arrival times. To quantitatively evaluate the accuracy of the location determination, we examine the method by using the vertical component seismic data of volcano-tectonic (VT) earthquakes recorded at six seismic stations at Izu-Oshima volcano. The VTs have been previously located by using arrival times of P- and S-waves, and the hypocenters are used as the reference for evaluation and error estimation of the method. The results show that the misfit, which is the distance between our estimated sources and the references, is about 2 km or less when using CCFs at the frequency band of 4–16 Hz which contains the dominant frequencies of direct S-waves. To test whether the method can be used for volcanic tremor, we simulate the tremors by combining the observed VTs that occurred randomly in time in a localized region. The simulated tremors are determined with location errors of approximately 1 km or less, when the sources of VTs are located within a distance of 1 km and CCFs are calculated for a minimum data length of about 2 minutes. The volcanic tremor location method we present here can be used as an alternative tool for volcano monitoring, especially to locate tremors and seismic events with no clear phase arrival.
Research Interests:
ABSTRACT Iwo-jima is a volcanic caldera located 1250 km south of Tokyo, and is part of the Izu–Ogasawara arc. An extremely high uplift rate (averaging 0.25 m/a over several hundred years) characterizes the volcanic activity of Iwo-jima.... more
ABSTRACT Iwo-jima is a volcanic caldera located 1250 km south of Tokyo, and is part of the Izu–Ogasawara arc. An extremely high uplift rate (averaging 0.25 m/a over several hundred years) characterizes the volcanic activity of Iwo-jima. This deformation is believed to be due to post caldera uplift. To investigate the mechanisms contributing to the high uplift rate, we have repeatedly conducted leveling and trilateration surveys from 1976 to 1995, and GPS surveys from 1996 to 2002. These observations have detected two patterns of continuous crustal deformation: concentric subsidence around Motoyama at the center of the Iwo-jima caldera and uplift surrounding the subsiding area. During the period from 1977 to 1995, subsidence at Motoyama reached 0.54 m and uplift in the southwestern part of the island exceeded 3 m. In addition, the island has experienced broad, episodic uplift, which amounted to more than 1 m during volcanic unrest both in 1982 and 2001. Horizontal displacements around Motoyama exhibit contraction due to the concentric subsidence, indicating the presence of a deflating source at depth. Vertical deformation dominates the displacement field during periods of broad episodic uplift, suggesting a deeper and/or more extensive source. Focusing the Motoyama area, we modeled the subsidence source simultaneously with the broad episodic uplift, which is approximated by deformation with a planar gradient, for 14 times between 1976 and 2002, using a grid search combined with a least-squares method. By assuming the subsidence source could be located at any grid point, we applied the least-squares method to calculate the intensity of subsidence source and the parameters for the uplift with a planar gradient and then selected the best-fitting source location. The best-fitting subsidence source geometries for 1998–2000 and 2000–2002 (the two time periods with GPS results) are horizontal, squared-shaped sills with side lengths of 4 and 5 km, respectively. Adopting the horizontal sill with a side length of 4 km as the deflating source, we applied this model to the 12 additional measurement epochs. Stable solutions for the source were obtained for 8 of the 12 periods. The results indicate that the deflating source is located beneath the Motoyama area with a depth ranging from 0.1 to 2.4 km over time. The average rate of sill closing from 1976 to 2002 was 0.46 ± 0.32 m/a. Our analysis also quantified the episodic broad uplift, though the available data do not permit modeling of the source of the continuous uplift surrounding the subsidence area. Considering the density structure in the caldera, the continuous subsidence and uplift may be explained by movement of volcanic fluids (probably geothermal) to balance the vertical load of the volcano, while the episodic uplift appears to be related to magmatic unrest.
Research Interests:
Assessing the relative seismic properties of volcanoes is essential because it improves our understanding of the similarity and diversity of processes occurring in magmatic and hydrothermal systems, thereby contributing to a comprehensive... more
Assessing the relative seismic properties of volcanoes is essential because it improves our understanding of the similarity and diversity of processes occurring in magmatic and hydrothermal systems, thereby contributing to a comprehensive understanding of these systems. Scattering and absorption are among the most challenging but useful parameters to obtain to discriminate volcanic structures. However, the separation of scattering from absorption generally relies on active seismic data or earthquake activity. We estimated seismic scattering and intrinsic absorption parameters of Rayleigh waves at 18 active volcanoes in Japan using seismic ambient noise. The use of cross-correlation functions enables the estimation of these parameters in volcanoes where there are no active seismic data available and with insufficient earthquake activity. The scattering and intrinsic absorption parameters from the 18 volcanoes are about two orders of magnitude larger than those in non-volcanic regions, indicating strong medium heterogeneity in the shallow regions of those volcanoes, as the Rayleigh waves in our target frequency are mainly sensitive to subsurface structures shallower than 1 km in depth. Volcanic islands and volcanoes near the coastline or lakes show the highest intrinsic attenuation and frequency dependence, likely caused by widespread water-saturated regions beneath the volcanoes. Our study highlights both similarities and differences in scattering and absorption properties across the 18 volcanoes. Further developing passive estimation capabilities to better constrain scattering and absorption parameters will allow us to distinguish differences in fracturing and pore space properties of the subsurface medium and will contribute to detailed studies of complex subsurface structures at active volcanic systems.
Research Interests:
Recent geodetic observations at active volcanoes succeeded in detecting volcano deformations prior to a small volcanic explosion. These could be used for quantitatively understanding the magma ascent processes before eruptions. We... more
Recent geodetic observations at active volcanoes succeeded in detecting volcano deformations prior to a small volcanic explosion. These could be used for quantitatively understanding the magma ascent processes before eruptions. We installed three tilt meters and one broadband seismometer within a distance of 500 m from the active craters at Stromboli volcano, Italy, in the end of May 2014, and recorded large number of tilt data associated with explosions until September. In this study, we estimate the spatio-temporal changes of magma pressure in the conduit by using these tilt data. We analyze tilts of 26 events recorded with high S/N ratio. These tilts at the three stations show uplifts toward craters from about 200 s before each explosion that is detected as an onset of seismic signal. By examining tilt vectors, we found that the tilt vectors roughly point to the direction of NE crater, and the direction of tilt vectors rotate about 5 seconds before the start of seismic signal. Th...
Research Interests:
Research Interests:
Research Interests:
Stromboli volcano in Italy is known as persistent eruptive activity (Strombolian eruptions). Its activity shifted from summit eruption to flank lava effusion in the Sciara del Fuoco on 7 August 2014. We obtain continuous seismic data... more
Stromboli volcano in Italy is known as persistent eruptive activity (Strombolian eruptions). Its activity shifted from summit eruption to flank lava effusion in the Sciara del Fuoco on 7 August 2014. We obtain continuous seismic data during the transition from Strombolian activity to the lava effusion. In this presentation we report unusual seismic waves, that is particularly observed from 22 July until the onset of flank eruptions. The unusual waveforms were looked like repeating volcanic tremor. The tremor (single wave packet) is composed of numerous repeating pulses of 4-12Hz, that having almost same amplitude. It continues for several to ten minutes, and then disappears with some large pulses (or one large pulse). Since the characteristic waves appeared repeatedly with a short pause time of a few minutes, we call this seismic activity as “woodpecker seismicity”. Individual pulses that make up the woodpecker seismicity are very similar. They are likely to be repetitions of the sa...
Research Interests:
Understanding the relationship cause/effect between tectonic earthquakes and volcanic eruptions is a striking topic in Earth Sciences. Volcanoes erupt with variable reaction times as a consequence of the impact of seismic waves (i.e.... more
Understanding the relationship cause/effect between tectonic earthquakes and volcanic eruptions is a striking topic in Earth Sciences. Volcanoes erupt with variable reaction times as a consequence of the impact of seismic waves (i.e. dynamic stress) and changes in the stress field (i.e. static stress). In 2012, three large (Mw ≥ 7.3) subduction earthquakes struck Central America within a period of 10 weeks; subsequently, some volcanoes in the region erupted a few days after, while others took months or even years to erupt. Here, we show that these three earthquakes contributed to the increase in the number of volcanic eruptions during the 7 years that followed these seismic events. We found that only those volcanoes that were already in a critical state of unrest eventually erupted, which indicates that the earthquakes only prompted the eruptions. Therefore, we recommend the permanent monitoring of active volcanoes to reveal which are more susceptible to culminate into eruption in t...
Research Interests:
Research Interests: Geology and Seismology
Research Interests:
RED SEED stands for Risk Evaluation, Detection and Simulation during Effusive Eruption Disasters, and combines stakeholders from the remote sensing, modelling and response communities with experience in tracking volcanic effusive events.... more
RED SEED stands for Risk Evaluation, Detection and Simulation during Effusive Eruption Disasters, and combines stakeholders from the remote sensing, modelling and response communities with experience in tracking volcanic effusive events. The group first met during a three day-long workshop held in Clermont Ferrand (France) between 28 and 30 May 2013. During each day, presentations were given reviewing the state of the art in terms of (a) volcano hot spot detection and parameterization, (b) operational satellite-based hot spot detection systems, (c) lava flow modelling and (d) response protocols during effusive crises. At the end of each presentation set, the four groups retreated to discuss and report on requirements for a truly integrated and operational response that satisfactorily combines remote sensors, modellers and responders during an effusive crisis. The results of collating the final reports, and follow-up discussions that have been on-going since the workshop, are given h...
Research Interests:
Research Interests:
Since Japan has 111 active volcanoes, we living there need to be prepared for the volcanic disasters that we will likely encounter in our lifetime. The Integrated Program for Next Generation Volcano Research and Human Resource Development... more
Since Japan has 111 active volcanoes, we living there need to be prepared for the volcanic disasters that we will likely encounter in our lifetime. The Integrated Program for Next Generation Volcano Research and Human Resource Development (INeVRH), a research project of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), started in 2016 and is now in its 7th year. It is approaching its final stage will be ready to make proposals that will improve our knowledge from both scientific and practical points of view. In theme A, the Japan Volcanic Data Network (JVDN) system started its function as a volcanic research platform, providing the observation and analysis data of many universities, governmental agencies, and institutes. The JVDN system promotes collaborative, multidisciplinary study. In theme B, many strategic observation techniques now deployed have revealed the characteristics of volcanoes in detail. For example, a dense seismic and magnetic survey has cl...
Research Interests:
Research Interests:
Research Interests:
Volcanic disaster is caused by the various volcanic phenomena, affecting some damages around neighbors. For the evaluation of volcanic disaster, the eruption event tree (Newhall and Hoblitt, 2002) is widely applied and we judge the... more
Volcanic disaster is caused by the various volcanic phenomena, affecting some damages around neighbors. For the evaluation of volcanic disaster, the eruption event tree (Newhall and Hoblitt, 2002) is widely applied and we judge the forthcoming phenomena from several possibilities at the event tree nodes. Each node of the event tree is defined as: node 1: unrest, 2: origin, 3: outcome, 4: magnitude, 5: phenomena, 6: sectors, 7: distance, 8: exposure and 9: vulnerability. For nodes 1 ? 7, the evaluation is based on volcanology, but for nodes 8 and 9, social factors are incorporated For the area in risk of the volcanic disasters, we made a timeand space dependent model of population, real estates, transportation infrastructures, and production bases, and evaluate its temporal evolution. Our volcanic disaster risk management system applied the RDBMS (Relational DataBase Management System). LavaSIM, lava flow simulator is used for volcanic hazard evaluation. In addition, for the evaluati...
Research Interests:
Eruption earthquakes are repeatedly observed with intervals of several minutes, hours or days associated with Strombolian or Vulcanian explosions. These eruption earthquakes generally have obscure onsets of P or S phases, which disables... more
Eruption earthquakes are repeatedly observed with intervals of several minutes, hours or days associated with Strombolian or Vulcanian explosions. These eruption earthquakes generally have obscure onsets of P or S phases, which disables us to use general hypocenter determination methods using the arrival times of these waves. In this study, we determine relative hypocenter locations of eruption earthquakes associated with repetitive eruption, using deconvolution filter and master event method. We use records of three tilt meters that are deployed near the active crater of Stromboli volcano since May 2014. We analyze tilt signals of eruption earthquakes that are recorded with a sampling frequency of 100Hz. We relate arrival time difference between a master event and slave event at each station with differences of hypocenter parameters. We use deconvolution filter to obtain arrival time difference because eruption earthquakes observed at each station have similar waveforms. However, s...
Research Interests:
The identification of anomalies in seismic wave interferometry data is important in the prediction of imminent volcanic eruptions. Herein, we propose using the local outlier probability (LoOP) method to evaluate the degree of anomaly in... more
The identification of anomalies in seismic wave interferometry data is important in the prediction of imminent volcanic eruptions. Herein, we propose using the local outlier probability (LoOP) method to evaluate the degree of anomaly in seismic wave velocities and scattering properties, estimated via seismic wave interferometry. LoOP is the likelihood that an observation is anomalous and is always in the range of 0–1 (0–100%). We quantitatively evaluated the degree of anomaly in seismic wave velocities and scattering properties before and after the eruption of Mt. Aso, Japan, in October 2016 and Mt. Shinmoedake, which lies within the Mt. Kirishima cluster of volcanoes, Japan, in 2017 and 2018. We found that LoOP exceeded 70% 2 to 3 days before Mt. Aso erupted on October 8, 2016, and it exceeded 70% 1 to 5 days before Mt. Shinmoedake erupted on October 11, 2017 and March 6, 2018. Adjusting the reference and quiet periods for the estimation of changes in seismic velocity/scattering pr...
Research Interests:
Research Interests:
Research Interests:
Stromboli volcano in Italy is a typical volcano where intermittent small eruption (Strombolian eruption) occurs.We report characteristic behavior of tilt records associated with small intermittent eruptions and its temporal change before... more
Stromboli volcano in Italy is a typical volcano where intermittent small eruption (Strombolian eruption) occurs.We report characteristic behavior of tilt records associated with small intermittent eruptions and its temporal change before the activity transition to flank lava effusion on August 7, 2014. We installed 3 tiltmeters near the summit crater of Stromboli volcano from the end of May 2014. We obtained continuous tilt records with a sampling frequency of 100Hz. Down-sampled data of 1 Hz are analyzed from June 1 to July 30 divided each 15 days. To extract volcano deformation associated with small explosion from tilt records, we firstly applied 6h highpass filter for noise removal, and then smoothed them by 50s low-pass filter. As a result, the signals associated with VLP seismic signal, which is rapid uplift and the following subsidence toward the active crater, are repeatedly observed. In addition, gradual uplift toward the active carter which has a few hundred second duration...
Research Interests:
Research Interests:
Understanding the cause/effect relationship between tectonic earthquakes and volcanic eruptions is a striking topic in Earth Sciences. Volcanoes may erupt due to the impact of seismic waves (i.e. dynamic stress) and changes in the stress... more
Understanding the cause/effect relationship between tectonic earthquakes and volcanic eruptions is a striking topic in Earth Sciences. Volcanoes may erupt due to the impact of seismic waves (i.e. dynamic stress) and changes in the stress field (i.e. static stress) with variable reaction times. In 2012, three large (Mw≥7.3) subduction earthquakes struck Central America within ten weeks; some volcanoes in the region erupted days after, meanwhile for others it took months to years to erupt. Here we show that the three earthquakes contributed to the increase in the number of volcanic eruptions during the seven years that followed. We found out that only those volcanoes that were already in a critical state of unrest effectively erupted, indicating that the earthquakes only prompted the eruptions. We recommend the permanent monitoring of active volcanoes to reveal which are more susceptible to culminate into eruption when the next large-magnitude earthquake hits a region.
Research Interests:
Stromboli volcano in Italy, one of the most active and famous volcano in the world, has been the target field of volcanology to understand eruption dynamics. From aspect of volcano seismology, broadband seismic observations have revealed... more
Stromboli volcano in Italy, one of the most active and famous volcano in the world, has been the target field of volcanology to understand eruption dynamics. From aspect of volcano seismology, broadband seismic observations have revealed that VLP(very-long-period) signals (10 ̃sec) are dominant among the seismic signals accompanying eruptions at Stromboli volcano (e.g. Neuberg et al., 1994). Chouet et al. (2003) demonstrated that inflation-deflation-inflation sequence of moment components, which represent inclined crack, is dominant at VLP signals observed at Stromboli volcano. The estimated force system was considered to represent the rise and ejection of gas slug, which causes repressurization of crack corresponding second inflation. However, most previous researches have analyzed a few VLP events having specific waveform characteristics, that were typical among their temporary observation data for days or weeks.
Research Interests:
Research Interests:
Research Interests:
Research Interests:
The hazard map of Mount Fuji regarding volcanic disasters was published in 2004. This map shows the prospective affected area of lava flows, pyroclastic flows, lahars due to snow melt, and volcanic ashes based on the results of numerical... more
The hazard map of Mount Fuji regarding volcanic disasters was published in 2004. This map shows the prospective affected area of lava flows, pyroclastic flows, lahars due to snow melt, and volcanic ashes based on the results of numerical simulations. At that time, the resolution of the Digital Elevation Model (DEM) used for simulations was 200m square. It has been 10 years since the first hazard map was published, and we have since produced higher resolution map using the laser scan of the topography. In this study, we used the higher resolution DEMs and simulated the Kenmarubi lava flow (AD1000) with the LavaSIM simulation software. The simulation results run with the finer grid size of the DEM produced a faster lava flow, and reached the foot of the mountain faster than the lava flow with the coarse grid DEM. Even though we ran the simulation with the same duration of lava flow, the lava flow spread over wider area and became thinner when the grid size of the DEM was coarse. Thus,...
Research Interests:
Research Interests:
Research Interests:
Research Interests:
A new program for the Next Generation Volcano Research and Human Resource Development started in 2016, following the government’s analysis of a volcanic disaster at Mount Ontake in 2014. One of its important purposes is the development of... more
A new program for the Next Generation Volcano Research and Human Resource Development started in 2016, following the government’s analysis of a volcanic disaster at Mount Ontake in 2014. One of its important purposes is the development of a technology that can provide visualized information of imminent volcanic hazards to the stakeholders. The latter include researchers in the Volcano Disaster Prevention Councils. Since the volcanic activity in Japan has been relatively less in the past few hundred years, larger eruptions are certainly expected to occur in the near future. Volcanic risk management has developed in Japan independently of university or institutional research, and by a national law, researchers are not allowed to officially forecast imminent volcanic eruptions. In the case of large eruptions never being observed, a close communication between the Japan Meteorological Agency and researchers becomes very important. Our project goal is issuing effective information on rea...