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The noise level of kinematic Global Positioning System (GPS) coordinates is much higher than static daily coordinates. Therefore, it needs to be improved to capture details of small sub-daily tectonic deformation. Multipath is one of the dominant error sources of kinematic GPS, which the sidereal filter can mitigate. With increasing interest in applying kinematic GPS to early postseismic deformation studies, we investigate the characteristics of multipath errors and the performance of the position-domain sidereal filter using 30-s kinematic coordinates with a length of nearly 5 days. Experiments using three very short baselines mostly free from atmospheric disturbances show that multipath signature in position-domain has better repeatability at longer periods, and sidereal filtering without low-pass filtering yields a lift of power spectral density (PSD) at periods shorter than 200 s. These results recommend an empirical practice of low-pass filtering to a sidereal filter. However, a moderate cut-off period maximizes the performance of the sidereal filter because of the smaller multipath signature at longer periods. The amplitude of post-sidereal-filtered fluctuation is less than 6 mm in standard deviation, which demonstrates the nearly lowest noise level of kinematic GPS used for postseismic and other tectonic deformation studies. Our sidereal filter is proven to mitigate several peaks of power spectral density at periods up to 100,000 s, but the period dependency of PSD is not fully alleviated by sidereal filtering, which needs future investigation. Graphical Abstract

Mt. Bromo is geographically located in eastern of Java Island at 112°57'30'' longitude and 7°56' latitude, with a large area of caldera ~10 Km2. The land over the volcano is a perfect area for farming, one of the important factor affects the level of soil fertility is the most mineral rich soils. Volcanic activities at Mt. Bromo has been recorded in 1775 which characterized by small eruptions with cycles ranging from one to five years. Regarding this evidence, we tried to investigate the surface changes over the Mt. Bromo by using Time-Series InSAR with TimeFun algorithm. TimeFun is an extension of SBAS to allow incorporating various functions such as seasonal oscillations, polynomials, and step functions as generally it estimates DEM errors as well and allows missing observation. The maximum allowed baseline value is defined and used to constrain the interferogram pair by selecting manual after differential InSAR processing in single face working. The proposed analysis is based on 27 SAR data sets acquired by the ALOS/PALSAR sensors during the 2007–2017 time interval. The result shows us deformation occurred up to ~10 cm at summit of Mt. Bromo during the eruption period. Time-series monitoring of surface deformation to infer volume changes, geometries and locations of sources of deformation involved in the future eruption

We present deformation measurements of the Kirishima volcanic complex from ALOS and ALOS-2 Interferometric Synthetic Aperture Radar (InSAR) time series during 2006–2019. Shinmoe-dake deflated ∼6 cm during the 2008–2010 phreatic eruptions and inflated ∼5 cm prior to the 2017 magmatic eruption. Iwo-yama inflated ∼19 cm within the crater since January 2015 and ∼7 cm around the southern and western vents since 4 months before the 2018 eruption. These deformations can be modeled as ellipsoids at ∼700 m depth beneath Shinmoe-dake and as a sphere on top of an ellipsoid at ∼130 and ∼340 m depths beneath Iwo-yama. Combining geodetic, geoelectric, geochemical, and petrological analysis, we interpret the hydrothermal origin of the deflation at Shinmoe-dake and inflation at Iwo-yama; the hydrothermal–magmatic transition during the 2011 Shinmoe-dake eruption; and water-boiling and bottom-up pressurization as driving mechanisms of the inflation at Iwo-yama. The study highlights the imaging potential of InSAR time series on complex hydrothermal systems.

Among the 127 active volcanoes located in eastern Java, Indonesia. Mt. Bromo is the most famous active volcano, type of Mt. Bromo is a strombolian. Many aspects that make volcano an interesting, we conduct a critical and comprehensive study and analysis concerning of volcano eruption based on remote sensing and GIS approaches. Nowadays, remote sensing play an important role to observe volcanic activity and facilitate real-time information. The method used in this study is the determination level of risk in the Mt. Bromo by Pairwise Comparison method. Vulnerability parameters to be obtained from the potential of land deformation, population density, and distance from the volcano dome. In addition, we used SAR data to observe time-series land surface deformation which derived from PALSAR sensor and the images which L-band frequency characteristic on board from Advanced Land Observing Satellite (ALOS) with active microwave sensor to achieve cloud-free and day-and-night land observation. The dataset is composed of 24 SAR images, collected from 24 May 2007 to 5 July 2016 (Descending passes, HH polarization). Consequently, the information result has been created and processed at a municipal or city level including thematic maps, the database has been built, classified and analyzed by using GIS environment. The main idea is providing hazard mitigation map at Mt. Bromo to provide adequate guidance for disaster-prone areas to determine the level of disaster risk.

Spaceborne synthetic aperture radar (SAR) and ground-based radar interferometers (GBRIs) can be used to detect spatially detailed crustal deformations that are difficult to detect by on-site observations, the Global Navigation Satellite System, tiltmeters, and so on. To make such crustal deformation information readily available to those engaged in evaluating volcanic activities and researching the mechanisms, we are preparing a database within the Japan Volcanological Data Network data sharing system to store crustal deformation detected by spaceborne SAR and GBRIs (Subtheme 2-1, Project B, the Integrated Program for Next Generation Volcano Research and Human Resource Development). In this study, we examined methods to reduce atmospheric delay noise in SAR interferometry using the numerical weather model and determined the methods for resampling the analytical values of the numerical weather model and estimating atmospheric delay to efficiently determine atmospheric delay. We show that the atmospheric delay can be estimated with higher accuracy by properly combining the isobaric surface and ground surface data of the mesoscale model (MSM) provided by the Japan Meteorological Agency. We are developing a multi-type portable SAR system as a GBRI system such that it would allow campaign observations whenever increased volcanic activities are observed and acquire crustal deformation with a higher temporal resolution than spaceborne SAR for storage in the database. This system employs L-band radar, which has a higher penetrability against vegetation. Two modes of observations are possible: ground-based SAR and car-borne SAR. The prototype was fabricated to conduct experiments necessary to develop a working model. The experimental observations was carried out around Asama volcano, and we confirmed that clear fringe was obtained.

Mt. Fuji, located in central Japan near the triple junction of the Philippine Sea, Eurasia (or Amurian), and North American (or Okhotsk) plates, is one of the arc volcanoes associated with the subduction of the Pacific plate. Mt. Fuji has unique features including an average eruption rate in the last 100,000 years of 4–6 km3/ka, which is much higher than that of other volcanoes along the same arc (0.01 and 0.1 km3/ka). Basaltic rocks dominate in Mt. Fuji, while other arc volcanoes are dominated by intermediate and felsic compositions, and Mt. Fuji has erupted both explosively and effusively, with the two largest eruptions in the last 2000 years having different styles; the 864–866 CE Jogan eruption was effusive, while the 1707 Hoei eruption, the most recent eruption, was explosive. Mt. Fuji is not only interesting from a scientific point of view, but also important from a societal point of view because it is only 100 km from the Tokyo metropolitan region, one of the biggest cities in the world hosting more than 30 million people. The Hoei eruption resulted in more than a few tens of millimeters of ashfall in Tokyo by more than 150 mm. With this background, Mt. Fuji has been studied intensively using geological and geophysical methods to understand the evolution, magma plumbing system, and current activity of the volcano. This article synthesizes the current knowledge about Mt. Fuji. In particular, we provide background information required to understand the Jogan and Hoei eruptions, and discuss how to assess the size, timing, and style of the next eruption. Statistical insights suggest that the next eruption of Mt. Fuji is more likely to be voluminous with a long precursor, given a repose time of more than 300 years.

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An active volcano deforms even during its dormant period, as well as its active period, although the deformation during its dormant period has paid less attention than its active period. Here we investigated the deformation of Asama and Usu volcanoes, Japan, during their dormant periods by Synthetic Aperture Radar Interferometry. We found localized deformation in both of these volcanoes, some of which decay over time. In Usu volcano, we interpret the observed deformation as the thermal contraction of the intruded lava dome associated with previous eruptions. In Asama volcano, the observed deformation cannot be due to thermal contraction as with Usu volcano but can be interpreted as hydrothermal activity and flank instability.

Seismic interferometry is a powerful tool to monitor the seismic velocity change associated with volcanic eruptions. For the monitoring, changes in seismic velocity with environmental origins (such...

Coeruptive deformation helps to interpret physical processes associated with volcanic eruptions. Because phreatic eruptions cause small, localized coeruptive deformation, we sometimes fail to identify plausible deformation signals. Satellite synthetic aperture radar (SAR) data allow us to identify extensive deformation fields with high spatial resolutions. Herein, we report coeruptive crustal deformation associated with the 2018 Kusatsu-Shirane phreatic eruption detected by time series analyses of L-band satellite SAR (ALOS-2/PALSAR-2) data. Coeruptive deformation maps derived from SAR time series analyses show that subsidence and eastward displacement dominate the southwestern side of an eruptive crater with a spatial extent of approximately 2 km in diameter. Although we were unable to identify any significant deformation signals before the 2018 eruption, posteruptive deformation on the southwestern side of the crater has been ongoing until the end of 2019. This prolonged deformation implies the progression of posteruptive physical processes within a confined hydrothermal system, such as volcanic fluid discharge, similar to the processes observed during the 2014 Ontake eruption. Although accumulated snow and dense vegetation hinder the detection of deformation signals on Kusatsu-Shirane volcano using conventional InSAR data, L-band SAR with various temporal baselines allowed us to successfully extract both coeruptive and posteruptive deformation signals. The extracted coeruptive deformation events are well explained by normal faulting with a left-lateral slip component along a southwest-dipping fault plane rather than by a point source deflation. The inferred fault plane can be considered as a degassing pathway from the shallow hydrothermal system to the surface. We reconfirmed that SAR data is a robust tool for detecting coeruptive and posteruptive deformations, which are helpful for understanding shallow physical processes associated with phreatic eruptions at active volcanoes.

Seismic interferometry is a powerful tool to monitor the seismic velocity change associated with volcanic eruptions. For the monitoring, changes in seismic velocity with environmental origins (such...

Erta Ale Volcano erupted on 16 January 2017 in a difficult-to-access terrain in the Erta Ale volcanic range in Ethiopia. Like many other rifting ridge volcanoes, little is known about the properties of the deep magma plumbing system. Here, we analyze interferometric synthetic aperture radar data from different satellites between late January 2017 and May 2019 to study the ground deformation after the start of the intrusion to infer the possible geometry and volume change of the magma reservoir that fed the eruption. We identified volcano-wide subsidence of up to 9cm and horizontal contraction of up to ~5cm that extend from Erta Ale to neighboring volcanoes. The modeling results suggest that an off-rift NE-SW elongated mid-crustal source is required to explain the observed volcano-wide deformation, but the depth is poorly constrained and the shape is complex. We suggest the presence of vertical interactions between stacked mid-crustal magma sources. Our study demonstrates that a considerable volume of melt could have been stored in mid-crustal magma reservoirs within the slow-spreading Erta Ale Ridge to facilitate recent volcanic activity.

Seismic velocity measurements have revealed that the Tohoku-Oki earthquake affected velocity structures of volcanic zones far from the epicenter. Using a seismological method based on ambient seismic noise interferometry, we monitored the anisotropy in the Mount Fuji area during the year 2011, in which the Tohoku-Oki earthquake occurred (Mw = 9.0). Here we show that even at 400 km from the epicenter, temporal variations of seismic anisotropy were observed. These variations can be explained by changes in the alignment of cracks or fluid inclusions beneath the volcanic area due to stress perturbations and the propagation of a hydrothermal fluid surge beneath the Hakone hydrothermal volcanic area. Our results demonstrate how a better understanding of the origin of anisotropy and its temporal changes beneath volcanoes and in the crust can provide insight into active processes, and can be used as part of a suite of volcanic monitoring and forecasting tools., In this study, the authors monitor a hydrothermal fluid surge through seismic anisotropy changes at the Hakone volcanic field, Japan. The authors find the anisotropy changes to be set off by the seismic waves of the 2011 Tohoku-Oki earthquake, that reactivated the hydrothermal system.

Asama volcano is one of the most active volcanoes in Japan. Spatially dense surface deformation at Asama volcano has rarely been documented because of its high topography and snow cover around the summit. This study presents the first interferometric synthetic aperture radar (InSAR) observation of ground deformation at Asama volcano with 120 Sentinel-1 SAR images from both ascending and descending tracks and 20 descending ALOS-2 images acquired between 2014 and 2018. We exploited both persistent and distributed scatterers to overcome decorrelation of SAR signals and applied a three-dimensional unwrapping method to retrieve the displacement time series efficiently. Our observations reveal an asymmetric deformation around the volcano with two main deformation regions on the northeast and southeast flanks, respectively. The northeast flank (NEF) exhibits line-of-sight (LOS) extensions in all the three SAR datasets with maximum velocities of − 14, − 10, and − 12 mm/year for the descending ALOS-2, ascending, and descending Sentinel-1 measurements, respectively. The southeast flank (SEF) shows LOS extensions in the ascending observations and LOS shortening in the descending observations with velocities between − 12 and 9 mm/year. Decomposition of the LOS displacements reveals nearly pure subsidence at the NEF, while the SEF exhibits a substantial eastward component as well as subsidence. Comparisons of the vertical subsidence at two continuous GNSS stations near the summit crater with our InSAR observations indicate small discrepancies smaller than 4 mm/year. We interpreted that the subsidence at the NEF of Asama is primarily due to the hydrothermal activity, while the deformation at SEF is plausibly due to flank instability. We highlight that efforts should be taken to monitor the slope instability at Asama volcano in the future.

Noise-based crustal seismic velocity changes are known to be affected by environmental perturbations, such as rainfall, atmospheric pressure loading, and temperature changes. Similar to geodetic observations, these external perturbations can mask the effects of tectonic and volcanic processes. In this study, we benefit from the dense Hi-net short-period seismic network that covers the entire Japan to measure continuous changes in seismic velocities over a few years, using noise-based seismic monitoring. Some strong seasonal seismic velocity changes are observed in both southern Japan (Kyushu Island) and northern Japan (Hokkaido Island). Decreasing of seismic velocities in summer in southern Japan can be clearly explained by a model of increased crustal fluid pore pressure associated with high rainfall. In northern Japan, it is necessary to adopt a more complex model to explain the observed seismic velocity variations, which takes into account precipitation, snow depth, and sea level changes. Moreover, western and eastern Hokkaido Island show very different responses to these different external perturbations. The models developed are used to remove the seasonal components of the seismic velocity changes. The minimum remaining detectable seismic velocity change reduces to 10−5, which allows detection of crustal responses to small earthquakes that are previously hidden in the strong seasonal perturbations.

Magma is transported in the crust mainly by dike intrusions. In volcanic areas, dikes can ascend towards the free surface and also move by lateral propagation, eventually feeding flank eruptions. Understanding dike mechanics is a key to forecasting the expected propagation and associated hazard. Several studies have been conducted on dike mechanisms and propagation; however, a less in-depth investigated aspect is the relation between measured dike-induced deformation and the seismicity released during its propagation. We individuated a simple equation that can be used as a proxy of the expected mechanical energy released by a propagating dike and is related to its average thickness. For several intrusions around the world (Afar, Japan, Mt. Etna), we correlate such mechanical energy to the seismic moment released by the induced earthquakes. We obtain an empirical law that quantifies the expected seismic energy released before arrest. The proposed approach may be helpful to predict the total seismic moment that will be released by an intrusion and thus to control the energy status during its propagation and the time of dike arrest.

Development of space geodetic techniques such as Global Navigation Satellite System and Synthetic Aperture Radar in last few decades allows us to monitor deformation of Earth's surface in unprecedented spatial and temporal resolution. These observations, combined with fast data transmission and quick data processing, enable us to quickly detect and locate earthquakes and volcanic eruptions and assess potential hazards such as strong earthquake shaking, tsunamis, and volcanic eruptions. These techniques thus are key parts of early warning systems, help identify some hazards before a cataclysmic event, and improve the response to the consequent damage.

In this study we show 2D intrinsic- and scattering-Q images of Asama volcano obtained by analyzing 2320 waveforms from active data. Observed energy envelopes were fitted to the diffusion model and separate intrinsic- and scattering-Q images were produced using a back-projection method based on a Gaussian-type weighting function. Synthetic tests indicate robustness and reliability of the results. Areas of high scattering attenuation coincide with the volcanic edifice and the summit at which recent eruptions took place. The intrinsic dissipation pattern shows a strong contrast between the east and west side of the volcanic structure with the low values observed in the west interpreted as solidified magma bodies. Our results demonstrate a strong relationship between structural heterogeneities and attenuation processes in volcanic areas and confirm the effectiveness of the present technique, which can be used as an imaging tool complementary to conventional techniques.

Volcanic islands in remote settings are challenging to study with ground-based instrumentation; nevertheless it is important to define “normal” background activity at these volcanoes because they pose threats to air and sea traffic. A combination of remote sensing methods is critical to adequately characterize volcanic activity, and in this study we present space-based observations of both thermal anomalies and surface deformation at Pagan Island in the Mariana Island Arc. Mt. Pagan produced a large eruption (>0.1 km3) in 1981, and recent smaller eruptions (>0.001 km3) in 2011 and 2012 that triggered volcanic ash advisories. In this study we examine available Interferometric Synthetic Aperture Radar (InSAR) from Envisat and ALOS between October 2004 and June 2010 for precursory deformation leading up to the most recent eruptions. Although we do not observe evidence for shallow magma reservoir inflation, we do observe a zone of subsidence of up to -3 cm/yr located on the northern flank likely caused by continuing scoria compaction of 1981 eruptive deposits. CosmoSkyMed InSAR measurements spanning the October 2012 eruption also shows deposit subsidence, but no detectable co-eruptive deflation. We also present remotely-sensed thermal time series from the MODIS and ASTER instruments spanning over a decade. There are two distinct locations of anomalous surface temperatures on the island, which correlate with previously documented, fumarolically active vents at South Pagan and Mt. Pagan. Ultimately, we did not find thermal or deformation precursors for recent eruptive activity, plausibly because the volcano had an open conduit and persistent degassing during this time period. We compare and contrast the efficacy of various sensor types currently available to characterize transient dynamics at small and remote volcanic islands such as Pagan.

An energetic eruption started on 25 May 2015 from a circumferential fissure at the summit of Wolf volcano on Isabela Island, western Galapagos. Further eruptive activity within the Wolf caldera followed in mid-June 2015. As no geodetic observations of earlier eruptions at Wolf exist, this eruption provides an opportunity to study the volcano's magmatic plumbing system for the first time. Here, we use interferometric synthetic aperture radar (InSAR) data from both the Sentinel-1A and ALOS-2 satellites to map and analyze the surface deformation at four time periods during the activity. These data allow us to identify the two eruption phases and reveal strong co-eruptive subsidence within the Wolf caldera that is superimposed on a larger volcano-wide subsidence signal. Modeling of the surface displacements shows that two shallow magma reservoirs located under Wolf at ~1 km and ~5 km below sea level explain the subsidence and that these reservoirs appear to be hydraulically connected. We also suggest that the transition from the circumferential to the intra-caldera eruption may have involved ring fault activity.

We present detailed maps of local-scale 3D deformation preceding the 2018 phreatic eruption at Iwo-yama volcano (south of Kyushu Island, Japan), using a combination of airborne and spaceborne Interferometric Synthetic Aperture Radar (InSAR) data. The 3D and 2.5D deformation maps obtained at different periods allow us to successfully track their spatiotemporal evolution and to infer the transition of subsurface conditions responsible for the precursory deformation observed from 2014 to 2018. From 2014 to 2016, ground inflation depicted an axisymmetric pattern with the maximum displacement at the center of the deformed area. However, from 2016 to 2018, an inflation peak moved to the southern edge of the area deformed during 2014–2016 and became more localized, which was close to the newly generated vents in the 2018 eruption. Modeling of the inflations suggests that pressurization within a crack at a depth of 150 m beneath the Iwo-yama geothermal area caused the 2014–2016 deformation and had continued until the 2018 eruption. Modeling results highlight the persistence of the local ground inflation pattern just above the southern edge of the crack, which suggests the presence of a shallower inflation source contributing to the local inflation. Consequently, we interpret the sequence of these deformations as follows: from 2014, deeper-rooted fluid started to inject into a fluid-saturated crack at 150-m depth, which caused the 2014–2016 deformation. Then, after 2016, the crack inflation continued because of the continuous fluid injection and formed another pressurized part directly above the southern tip of the crack. Additionally, the results of the time-series analysis of the satellite InSAR data revealed that the local inflation started around April 2017 for which thermal activity including a mud emission became pronounced around the location of the local inflation. As a result of an episodic increase in supply rate of magmatic fluids from a deep magma reservoir from early 2018, a phreatic eruption finally occurred in the vicinity of the most deformed point, providing a clue for predicting future eruption sites, as was also observed in the Hakone 2015 eruption.

Quantifying the eruption potential of a restless volcano requires the ability to model parameters such as overpressure and calculate the host rock stress state as the system evolves. A critical challenge is developing a model-data fusion framework to take advantage of observational data and provide updates of the volcanic system through time. The Ensemble Kalman Filter (EnKF) uses a Monte Carlo approach to assimilate volcanic monitoring data and update models of volcanic unrest, providing time-varying estimates of overpressure and stress. Although the EnKF has been proven effective to forecast volcanic deformation using synthetic InSAR and GPS data, until now, it has not been applied to assimilate data from an active volcanic system. In this investigation, the EnKF is used to provide a “hindcast” of the 2009 explosive eruption of Kerinci volcano, Indonesia. A two-sources analytical model is used to simulate the surface deformation of Kerinci volcano observed by InSAR time-series data and to predict the system evolution. A deep, deflating dike-like source reproduces the subsiding signal on the flanks of the volcano, and a shallow spherical McTigue source reproduces the central uplift. EnKF predicted parameters are used in finite element models to calculate the host-rock stress state prior to the 2009 eruption. Mohr-Coulomb failure models reveal that the host rock around the shallow magma reservoir is trending toward tensile failure prior to 2009, which may be the catalyst for the 2009 eruption. Our results illustrate that the EnKF shows significant promise for future applications to forecasting the eruption potential of restless volcanoes and hind-cast the triggering mechanisms of observed eruptions.

Faulting processes in volcanic areas result from a complex interaction of pressurized fluid-filled cracks and conduits with the host rock and local and regional tectonic setting. Often, volcanic seismicity is difficult to decipher in terms of the physical processes involved, and there is a need for models relating the mechanics of volcanic sources to observations. Here we use focal mechanism data of the energetic swarm induced by the 2000 dike intrusion at Miyakejima (Izu Archipelago, Japan), to study the relation between the 3-D dike-induced stresses and the characteristics of the seismicity. We perform a clustering analysis on the focal mechanism (FM) solutions and relate them to the dike stress field and to the scaling relationships of the earthquakes. We find that the strike and rake angles of the FMs are strongly correlated and cluster on bands in a strike-rake plot. We suggest that this is consistent with optimally oriented faults according to the expected pattern of Coulomb stress changes. We calculate the frequency-size distribution of the clustered sets finding that focal mechanisms with a large strike-slip component are consistent with the Gutenberg-Richter relation with a b value of about 1. Conversely, events with large normal faulting components deviate from the Gutenberg-Richter distribution with a marked roll-off on its right-hand tail, suggesting a lack of large-magnitude events (Mw > 5.5). This may result from the interplay of the limited thickness and lower rock strength of the layer of rock above the dike, where normal faulting is expected, and lower stress levels linked to the faulting style and low confining pressure.

Mount Fuji has ejected a huge amount of basaltic products during the last 100,000 years. Even though the region around Mount Fuji is tectonically active, the seismicity below Mount Fuji is low, resulting in little knowledge about the seismic structure there. To gain more insight into the magma-plumbing system, we obtain the seismic structure beneath Mount Fuji by the receiver function (RF) technique. RFs at seismic stations around Mount Fuji show positive phases at ~3 and ~6 s, representing the conversion of P to S waves at a positive velocity boundary in the Philippine Sea plate. Cross sections of RF amplitudes reveal two distinct velocity boundaries around Mount Fuji, at depths of 40–50 km and 20–30 km, which we interpret to be the boundary between the crust-mantle transition layer and the uppermost mantle of the Izu-Bonin arc and the velocity discontinuity just below the region where low-frequency earthquakes (LFEs) of Mount Fuji have occurred, respectively. The velocity boundary at about 50 km depth shows a clear gap just beneath Mount Fuji. We suggest that this gap represents a weaker velocity contrast zone through which the magma of Mount Fuji ascends from the Pacific plate. A thorough grid search reveals that a low-velocity zone at depths of ~13–26 km explains all the characteristics of RFs around Mount Fuji, leading us to interpret the high-velocity boundary just below the LFE region as the lower boundary of Mount Fuji's magma chamber.

Multiple cycles of the intensive volcanic gas discharge and ground deformation (inflation and deflation) were observed at Asama Volcano, Japan, from 2000 to 2011. Magma budget of the shallow magma plumbing system was estimated on the basis of the volcanic gas emission rates and ground deformation data. Recent inflations observed in 2004 and 2008 were modeled as a dike intrusion to 2–3 km west of Asama Volcano. Previous studies proposed that magma ascends from a midcrustal magma reservoir to the dike and reaches the surface via a sinuous conduit which connects the dike to the summit. The intensive volcanic sulfur dioxide discharge of up to 4600 t/d at the volcano was modeled by magma convective degassing through this magma pathway. The volcano deflates as shrinkage of the magma in a reservoir by volcanic gas discharge. We estimated the volume change of the dike modeled based on the GPS observations, the volume decrease of the magma by the volcanic gas discharge, and the amount of degassed magma produced to calculate the magma budget. The results show that the volume decrease of the magma by the volcanic gas discharge was larger than the volume change of the dike during the inflation periods. This indicates that a significant volume of magma at least more than 2 times larger than the volume change of the dike was supplied from the midcrustal magma reservoir to the dike. The volume decrease of the dike was comparable with the volume decrease of the magma by the volcanic gas discharge during the deflation periods. The long-term deflation trend of the dike and the volume of degassed magma (108–9 m3) suggest that the degassed magma produced is not stored in the dike and the magma is mainly supplied from the midcrustal magma reservoir. In both periods, the volume of degassed magma produced was 1 order of magnitude larger than the volume change of the dike. This indicates that the actual volume of the magma supplied from the midcrustal magma reservoir is up to 1 order of magnitude larger than the volume change of the dike. These results strongly suggest that an amount of magma moved through a magma reservoir is possible to be significantly larger than volume change of the magma reservoir estimated by the geodetic observations.

Cross‐correlating seismic random signals, such as coda waves or ambient noise, at two sites can extract seismic wavefields as if a source is at one site and a receiver is at the other if certain conditions are met (e.g., Aki, 1957; Campillo and Paul, 2003). Given the recent development of dense seismic network, the last decade has witnessed the rapid emergence of imaging Earth’s local (Nagaoka et al. , 2012), regional (Shapiro et al. , 2005; Nishida et al. , 2008; Lin et al. , 2011), and global (Nishida et al. , 2009) seismic structures and their temporal changes (Brenguier, Campillo, et al. , 2008; Brenguier, Shapiro, et al. , 2008; Nagaoka et al. , 2010; Brenguier et al. , 2014) from these random signals. With this trend of research, we fortuitously found peculiar pulses in the cross correlations of the Japanese high‐sensitivity seismograph network (Hi‐net; Obara et al. , 2005) seismic records (Fig. 1). Here, we used one‐month records for January 2012 at 142 Hi‐net stations in southwest Japan. Applying a band‐pass filter of 10–20 s to correlograms reveals sharp pulses at lag times of every 60 s (Fig. 1a). Unfiltered correlograms nicely demonstrate a propagation of Rayleigh waves, but a closer look at locations where no wavetrain is extracted reveals sharp pulses at lag times of every second (Fig. 1b). Figure 1. Correlograms of ambient seismic noise aligned along the interstation distance. (a) Correlograms with a band‐pass filter between 10 and 20 s. (b) Unfiltered correlograms of a portion where no extracted wave propagation is expected. (c,d) Same as (a) and (b) but the quantization errors are subtracted from the raw data before cross correlation. (e,f) Same as (a) and (b) but the difference of ZR and RZ correlations is taken without subtraction of the quantization error. The amplitude scales of (c,e) and (d,f) are the same as those of (a) and (b), …

We measure shear wave splitting and estimate stresses of Mount Fuji, Japan, to interpret anisotropic structure and its implication for geologic processes using local crustal earthquake seismograms from 2009 to 2012. The measured fast polarizations have preferred orientations at each station with mean values of delay times

We present intrinsic- and scattering-Q attenuation images for Usu volcano (Japan) by analyzing over 1800 vertical seismograms. By fitting the observed envelopes to the diffusion model, we obtained intrinsic and scattering attenuation values at three different frequency bands. Using a back-projection method and assuming a Gaussian-type weighting function, we obtained the 2D images of intrinsic and scattering attenuation. Resolution tests confirm the robustness and reliability of the obtained images. We found that scattering attenuation is the dominant process of energy loss in the frequency range analyzed, which suggests strong spatial heterogeneity. The resultant scattering attenuation images show an increase of attenuation toward the southwest from Toya caldera, which may correspond to deepening of the basement. We also identify an area of low intrinsic and scattering attenuation at the summit of Usu volcano which could be associated with old magma intrusions. Our results demonstrate a strong spatial relation between structural heterogeneities and attenuation processes in volcanic areas and confirm the efficiency of the method which can be used together with conventional imaging techniques.

Magmatic intrusions release extensional strain in the Earth's crust upon availability of magma. Intrusions are typically accompanied by earthquake swarms and by surface faulting that is often larger than what is expected from the magnitude of the induced earthquakes. The 2000 Miyakejima dike intrusion triggered the largest volcanic earthquake swarm monitored so far, with five Ml>6 earthquakes. We analyze the seismicity and deformation induced by the Miyakejima dike with the aim of constraining the timescale and mechanisms of slow strain release during the episode. In six earthquake bursts lasting few hours and migrating at ∼1 km h−1 we find candidates for slow earthquakes. Each burst nucleated at the tips of previous bursts, suggesting stress interaction. The variability of fault plane solutions indicates that the bursts occurred on a complex system of fractures, consistent with weakly consolidated surface layers strained by spatially inhomogneous stresses that change in time, such as those induced by a dike. Based on dislocation models, we find that deformation is best explained by aseismic slip (in addition to the seismic burst), with a moment 1.3 to 2.3 times larger than the earthquakes' seismic moment, and opening of 0.20 ± 0.07 m on the dike. The aseismic slip occurred over a few hours, with moment, duration, and migration velocity consistent with that of previously observed slow slip events. We argue that the seismic bursts are likely driven by slow slip, sharing most properties with tectonic slow slip events and swarms, but occurring on a set of nonaligned faults.

The relation between unrest and eruption at calderas is still poorly understood. Aso caldera, Japan, shows minor episodic phreatomagmatic eruptions associated with steady subsidence. We analyse the deformation of Aso using SAR images from 1993 to 2011 and compare it with the eruptive activity. Although the dataset suffers from limitations (e.g. atmospheric effects, coherence loss, low signal-to-noise ratio), we observe a steady subsidence signal from 1996 to 1998, which suggests an overall contraction of a magmatic source below the caldera centre, from 4 to 5 km depth. We propose that the observed contraction may have been induced by the release of the magmatic fluids feeding the eruptions. If confirmed by further data, this hypothesis suggests that degassing processes play a crucial role in triggering minor eruptions within open conduit calderas, such as at Aso. Our study underlines the importance of defining any eruptive potential also from deflating magmatic systems with open conduit.

We use numerical modeling to investigate the proposed stress-based origin for changing anisotropy at Mount Asama Volcano, Japan. Stress-induced anisotropy occurs when deviatoric stress conditions are applied to rocks which are permeated by microcracks and compliant pore space, leading to an anisotropic distribution of open crack features. Changes to the local stress field around volcanoes can thus affect the anisotropy of the region. The 2004 eruption of Mount Asama Volcano coincided with time-varying shear wave splitting measurements, revealing changes in anisotropy that were attributed to stress changes associated with the eruption. To test this assertion, we create a model that incorporates knowledge of the volcanic stress, ray tracing, and estimation of the anisotropy to produce synthetic shear wave splitting results using a dyke stress model. Anisotropy is calculated in two ways, by considering a basic case of having uniform crack density and a case where the strength of anisotropy is related to dry crack closure from deviatoric stress. Our results show that this approach is sensitive to crack density, crack compliance, and the regional stress field, all of which are poorly constrained parameters. In the case of dry crack closure, results show that modeled stress conditions produce a much smaller degree of anisotropy than indicated by measurements. We propose that the source of anisotropy changes at Asama is tied to more complex processes that may precipitate from stress changes or other volcanic processes, such as the movement of pore fluid.

Ground deformation associated with the eruption of Lumpur Sidoarjo mud volcano between 2006 and 2011 has been investigated from Synthetic Aperture Radar images. Marked subsidence has been observed to the west of, as well as around, the vent. Line-of-sight changes in the both areas decayed since the middle of 2008 with a time constant of 1.5–2.5 years, implying that the ongoing eruption won't last long. This uniform decay time indicates that the western part is connected to the eruption center since the middle of 2008 to form a system with stationary geometry. Our observation that the decay started later to the west than around the vent suggests that the subsidence to the west has been triggered by the mud eruption. A simple modeling suggests that 1) the conduit needs to be narrower at depth than at the surface, 2) the effective rigidity of the mud needs to be lower than that estimated from the drilled sample, or both to explain the observed decay constant of the deformation.

Penginderaan jauh kini memainkan peranan penting dalam pengamatan perilaku gunung api. Penelitian ini bertujuan untuk mengamati deformasi permukaan Gunung Bromo, yang terletak di Jawa bagian Timur, Indonesia, yang masuk dalam rangkaian sistem volkanik di Taman Nasional Bukit Tengger Semeru (TNBTS). Penggunaan algoritma SAR Interferometry (InSAR) yang disebut sebagai pendekatan Small Baseline Subset (SBAS) memungkinkan perancangan peta kecepatan deformasi rata-rata dan and peta time series displacement di wilayah kajian. Teknik SBAS yang biasa menghasilkan rangkaian observasi tahap interferometrik. Ini tercatat sebagai kombinasi linear dari nilai fase SAR scene untuk setiap pixel secara tersendiri. Analisis yang dilakukan terutama berdasarkan 22 data SAR data yang diperoleh melalui sensor ALOS/PALSAR selama kurun waktu 2007–2011. Beberapa penelitian menunjukkan bahwa kemampuan analisis InSAR dalam menyelidiki siklus gunung api, terutama Gunung Bromo yang memiliki karakteristik erupsi stratovolcano dalam satu hingga lima tahun. Analisis hasil memperlihatkan adanya kemajuan dari kajian sebelumnya akan InSAR wilayah tersebut, yang lebih fokus kepada deformasi yang berpengaruh kepada kaldera. Hal ini menunjukkan bahwa penelitian ini bisa diimplementasikan pada manajemen risiko atau manajemen infrastruktur

[1] We use 2007–2011 Advanced Land Observing Satellite (ALOS) data to perform an arc-wide interferometric synthetic aperture radar (InSAR) time series survey of the Trans-Mexican Volcanic Belt (TMVB) and to study time-dependent ground deformation of four Indonesian volcanoes selected following the 2007–2009 study of Chaussard and Amelung (2012). Our objectives are to examine whether arc volcanoes exhibit long-term edifice-wide cyclic deformation patterns that can be used to characterize open and closed volcanic systems and to better constrain in which cases precursory inflation is expected. We reveal deformation cycles at both regularly active and previously inactive Indonesian volcanoes, but we do not detect deformation in the TMVB, reflecting a lower activity level. We identify three types of relationships between deformation and activity: inflation prior to eruption and associated with or followed by deflation (Kerinci and Sinabung), inflation without eruption and followed by slow deflation (Agung), and eruption without precursory deformation (Merapi, Colima, and Popocatepetl; at Merapi, no significant deformation is detected even during eruption). The first two cases correspond to closed volcanic systems and suggest that the traditional model of magmatic systems and eruptive cycles do apply to andesitic volcanoes (i.e., inflation and deflation episodes associated with magma accumulation or volatile exsolution in a crustal reservoir followed by eruptions or in situ cooling). In contrast, the last case corresponds to open volcanic systems where no significant pressurization of the magmatic reservoirs is taking place prior to eruptions and thus no long-term edifice-wide ground deformation can be detected. We discuss these results in terms of InSAR's potential for forecasting volcanic unrest.

[1] Geophysical observations and numerical studies have shown that creeping portions of faults have persistent rate-strengthening frictional properties and can act as barriers to earthquake rupture propagation. On the basis of GPS data following the 2011 MW 9.0 Tohoku-oki earthquake in Japan, we find that the evolution of afterslip and postseismic shear stress on the plate interface is inconsistent with persistent rate-strengthening frictional properties but is consistent with slip-rate-dependent frictional properties that exhibit less rate-strengthening with increasing slip rate. Such slip-rate-dependent frictional properties tend to prevent creeping regions from acting as barriers to rupture propagation and therefore could be an important factor in determining the spatial extent of individual earthquakes.

While the location and shape of magma chambers beneath active volcanoes play a key role in understanding magma transport and forecasting volcanic activity, the nature of magma chambers, particularly their shape, is not fully understood. Here we found a low velocity body too small to be detected from conventional techniques by the aid of a modern technique called seismic interferometry. Combining our result with independent observations suggests that the low velocity body is likely to represent a magma chamber. Our findings demonstrate the utility of seismic interferometry in imaging a small scale feature with a size of less than 10 km.

In this article, we summarize some recent results of measurements of temporal changes of active volcanoes using seismic noise cross-correlations. We first present a novel approach to estimate volcano interior temporal seismic velocity changes. The proposed method allows to measure very small velocity changes (≈ 0.1%) with a time resolution as small as one day. The application of that method to Piton de la Fournaise Volcano (La Reunion Island) shows velocity decreases preceding eruptions. Moreover, velocity changes from noise cross-correlations over 10 years allow to detect transient velocity changes that could be due to long-lasting intrusions of magma without eruptive activity or to pressure buildup associated to the replenishing of the magma reservoir. We also present preliminary results of noise cross-correlation waveform perturbation associated with the occurrence of dike injection and volcanic eruption. We show that such an analysis leads us to locate the areas of dike injection and eruptive fissures at Piton de la Fournaise Volcano. These recent results suggest that monitoring volcanoes using seismic noise correlations should improve our ability to forecast eruptions, their intensity and thus potential environmental impact.

Seismic noise reveals volcanic plumbing Monitoring the way in which seismic noise passes through Earth's crust after a large earthquake can clarify how volcanoes erupt. Japan has the highest-density seismic network in the world. Brenguier et al. observed reductions in seismic velocity below volcanic regions of Japan from before, to the weeks and months after the 2011 Tohoku-Oki earthquake (see the Perspective by Prejean and Haney). This indicates that pressurized fluids below volcanoes can weaken in response to dynamic stress perturbations. Science , this issue p. 80 ; see also p. 39