Active volcanoes are often deformed by magmatic activity occurring at depth. Here, we report the deformation of Mount Fuji, central Japan, in relation to hydrological activity induced by rain. Through an analysis of the daily coordinates of global navigation satellite system stations deployed around Mount Fuji, we detected transient surface uplift of 1-2 cm correlated with heavy rains and deduced that this is caused by the expansion of shallow aquifers within Shin-Fuji lava layers. Such hydrological inflation of the volcano, lasting for a day or two, occurs within similar to 25 km of the summit. The uplift gradually decays with distance and is replaced by large-area subsidence through rainwater loading beyond the end of these lava layers. Understanding such "cold" volcanic inflation assists in the correct interpretation of "hot" changes associated with magmatic forcing mechanisms.

Active volcanoes often deform by magmatic activities at depth. Here we report that they deform also by hydrological activities induced by rains. By analyzing the daily coordinates of global navigation satellite system stations deployed around the Fuji volcano, the highest mountain of the country in central Japan, we detected transient surface uplift of 1-2 centimeters correlated with heavy rains. We consider they were caused by the expansion of shallow aquifers within Shin-Fuji lava layers. Such hydrological inflation of the volcano, lasting for a day or two, occurs within ~25 km from the summit. The uplift gradually decays with distance and is replaced with large-area subsidence by rainwater loading beyond the end of these lava layers. Subsidence is proportional to daily rains, rather than cumulative rains, suggesting dynamic equilibrium of precipitation and run-off. Understanding such ‘cold’ deformation of active volcanoes would help us correctly interpret ‘hot’ ones by magmatic activities.

We studied ionospheric changes associated with the 2025 March 28 Myanmar earthquake (M(w)7.7) using global navigation satellite system receivers to measure ionospheric electrons, as a part of the project to predict earthquake precursors. The total electron contents above the fault changed their trends similar to 36 min before the earthquake, with the positive anomaly reaching similar to 1 per cent of the background. These quantities fit well with the past similar to 20 cases despite relatively large day-to-day variability due to high-geomagnetic activities. The positive anomaly was sandwiched by two negative anomalies to the north and the south, suggesting within-ionosphere electron transportation along geomagnetic fields possibly driven by surface positive electric charges released from the fault.

Hydrological surface loads, such as snowpack and soil moisture, are the main drivers of seasonal crustal movements as seen by space geodetic techniques. In addition to that, seawater sometimes exerts additional forces for coastal stations, and the atmosphere often plays an important role for stations within continents. Here we report a case in and around the Arabian Peninsula. Despite little seasonal hydrological changes there, stations show fairly uniform seasonal vertical crustal movements, characterized by ~ 1 cm winter subsidence, over the entire region. We found that they are mainly driven by the atmospheric loading. Differences in their amplitudes are compensated by large and moderate seasonal ocean mass changes in the Red Sea and the Persian Gulf (also called the Arabian Gulf), respectively, resulting in fairly uniform amplitudes of the winter subsidence in this region.

The East Anatolian Fault in southern Turkey ruptured on 6 February 2023, causing a Mw 7.8 earthquake. Another large earthquake of Mw 7.5 occurred to the north of the first event similar to 9 h later. Here we look for ionospheric precursors immediately before these earthquakes, like those found similar to 40 min before the 2011 Tohoku-oki earthquake, Japan, by using the total electron content data obtained by global navigation satellite system receivers. Considering that the changes are small, we first inferred the leading times and the intensities of the anomalies using their empirical relationship with Mw from similar to 20 past large earthquakes. For the first earthquake, we found that a positive change of TEC trends started similar to 23 min before the rupture and that the anomaly reached similar to 2 % of the background. These values were consistent with past events. On the other hand, medium-scale traveling ionospheric disturbance activity hampered convincing detec (c) 2024 COSPAR. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

Near-field ionospheric total electron content records before and after the 15 January 2022 eruption of the Hunga-Tonga Hunga-Ha'apai submarine volcano were studied using GNSS total electron content data. The data started showing positive departures from the afternoon smooth decreasing trend similar to 1 h before the eruption. This anomaly is localized around the volcano, i.e., it decays as we go away from the volcano. The signature resembles the one that preceded the 2011 Tohoku-oki earthquake. However, a detailed investigation of ionospheric anomalies from a dense GNSS array in New Zealand showed a large-scale traveling ionospheric disturbance propagating toward Tonga, excited by a moderate geomagnetic storm on the previous day. This suggests that the anomaly around the volcano immediately before the eruption was caused by the arrival of this disturbance at Tonga just at the eruption time.

The 2023 Elbistan (Mw 7.6) earthquake, the second event of the Kahramanmaraş, Türkiye doublet, occurred by bilateral sub‐ and supershear fault ruptures toward northeast and southwest, respectively. Utilizing the data from a dense network of global navigation satellite system (GNSS) receivers in Türkiye, we investigated the Rayleigh surface wave signatures in the ionosphere. We found significantly larger signals to the southwest of the epicenter that cannot be explained by the satellite line‐of‐sight geometry. This strong beam toward southwest, possibly caused by the supershear rupture, was also supported by observations with seismometers and GNSS kinematic solutions. Our finding demonstrates that Rayleigh wave signatures in ionosphere contain rich information on earthquake source processes.

Crustal response to the 2024 September heavy rain episode in the northern Noto Peninsula, Central Japan, was studied using a dense network of global navigation satellite system receiving stations. Over the region in and around the Noto Peninsula, the regionally integrated subsidence was proportional to the daily rain, i.e., 0.1 km3 volumetric subsidence occurred in response to 1 Gt daily rain. The subsidence lasted for only a day or so. These findings are consistent with past cases of elastic response of the Japanese Islands lithosphere to rain loading. We also found that a small island, to the north of the peninsula, subsided by a few centimeters on heavy rain days. This cannot be explained by terrestrial water storage loads within the island. Rainwater may have remained partly in the ocean surrounding the island and depressed the ocean floor as a surface load.

The Wenchuan earthquake (Ms8.0), which struck Sichuan Province, China, on 12 May 2008, was one of the most devastating seismic events in recent Chinese history. It resulted in the deaths of nearly 90,000 people, left millions homeless, and caused widespread destruction of infrastructure across a vast area. In addition to the severe ground shaking and surface rupture, a variety of unusual atmospheric/ionospheric and geophysical phenomena were reported in the days and hours leading up to the earthquake. Notably, iridescent clouds were observed just before the earthquake at three distinct locations approximately 450–550 km northeast of the epicenter. These clouds appeared as fragmented rainbows located beneath the sun and were characterized by their short lifespan, lasting only 1–10 min. Moreover, they exhibited striped patterns within the iridescent regions, suggesting the influence of an external electric field. These features cannot be adequately explained by the well-known meteorological phenomenon of circumhorizontal arcs, raising the possibility of a different origin. The formation mechanism of these clouds remains unclear. In this study, we explore the hypothesis that the iridescent clouds were precursory phenomena associated with the impending earthquake. Specifically, we examine a potential causal relationship between the appearance of these clouds and the geological environment of the earthquake source. We propose a novel model in which electrical disturbances generated along the fault system immediately before the mainshock propagated upward and interacted with the ionosphere, resulting in the creation of a localized electric field. This electric field, in turn, induced electro-optic effects that altered the scattering of sunlight and projected iridescent patterns onto cirrus clouds, leading to the observed phenomena.

The Global Geodetic Observing System (GGOS) is the response of the international geodetic community, organised under the umbrella of the International Association of Geodesy (IAG), to the need to monitor changes in the Earth system continuously. GGOS is Geodesy’s contribution to the Global Earth Observation System of Systems (GEOSS) by providing the reference frames needed for all position-dependent observations, thus the foundation for most Earth observations, and measuring changes in the Earth's shape, size, gravity field and rotation over time and space. GGOS is built on the Scientific Services of the IAG (IGS, IVS, ILRS, IDS, IERS, IGFS, ISG, PSMSL, IGETS, IDEMS, ICGEM, BGI) and the products they derive on an operational basis for Earth monitoring using space- and ground-based geodetic techniques. A key objective of GGOS is to realise an integrating framework that moves from the provision of technique-specific products to a level of combined, integrated products as the basis for a consistent modelling and interpretation of Earth system processes and interactions. This is necessary to ensure a coherent Earth monitoring system that contributes significantly to a better understanding of global change and its impacts on the environment and society. This is being achieved through strong international and multidisciplinary cooperation, focusing on (1) bringing together different geodetic observing techniques, services and analysis methods to guarantee that the same standards, conventions, models and parameters are used in all data analysis and modelling of Earth system processes; (2) combining geometric, gravimetric, and Earth rotation observations in data analysis and data assimilation to jointly estimate and model all necessary parameters representing the different elements of the Earth system; (3) identifying science and societal needs that can be addressed by (new) geodetic products and define the requirements for accuracy, time resolution, and consistency of these products; (4) identifying service gaps and developing strategies to fill them; and (5) promoting and enhancing the visibility of Geodesy by improving the accessibility of geodetic observations, information and products to the widest range of users and their attribution. This contribution summarises recent achievements, ongoing activities, and main challenges for the near future.

Lands covered with snow often subside in winter by amounts detectable with modern space geodetic surveys. Such seasonal crustal subsidence would consist of numerous subsidence episodes associated with large and small snowfalls. To verify this, we study crustal subsidence of global navigation satellite system receiving stations associated with four heavy snowfall episodes 2018-2022 in Hokkaido, northern Japan. After removing common mode errors, we have detected step-like subsidence up to similar to 2.5 mm of these stations. We also calculated their expected subsidences using the snow depth data from dense meteorological sensors and the load Green's function. They are consistent with each other when we assume the average snow density of 400 kg/m(3). Hence, snow loading signals are basically removable if adequate snow depth data are available. We also show that snow accretion to antenna radomes causes significant false subsidence signals, which can be distinguished by monitoring signal-to-noise ratios of the microwave signals from satellites. over a it is difficult to remove the rainwater

The phenomenal discovery by Heki (Geophys Res Lett 38(17), 2011) [1] regarding an anomaly in the ionosphere a few minutes before a major earthquake has given hope. It has been a decade, and this research continues to develop and the latest development is the disclosure of the preseismic structure in three-dimensional. Based on the results of 3D tomography, this anomaly has positive (electron increase) in the lower and negative (electron decrease) components in the upper ionospheres. Muafiry and Heki (J Geophys Res Space Phys 125(10), 2020) [2] then suspected that the mechanism for this phenomenon was due to the transfer of electrons from the upper to the lower layer of the ionosphere triggered by surface electric charge. Nevertheless, this structure has only been identified in two significant earthquake events, the 2015 Illapel and the 2011 Tohoku-Oki Earthquakes to name. Further research regarding the existence of these two anomaly components needs to be explored extensively for other large earthquakes. In this study, an attempt to obtain these two components before the 2010 Maule Earthquake is conducted. Using phase difference of the microwave GPS signals from networks in some South American countries, the positive and negative components of the anomaly in the ionosphere before the earthquake are recorded in GPS-TEC time series. However, due to limited ray-path of GPS station-satellite signal pairs penetrated into the 3D tomography voxels, the negative anomaly component is not identified clearly at higher altitude as was previously found in two other large earthquakes. Such problem occurs because limited navigation satellites and stations are available at this time.

AbstractCombining the total electron content (TEC) data from two nationwide Global Navigation Satellite System (GNSS) networks in Japan with the L-band synthetic aperture radar (SAR) data, we reveal the fine spatial and temporal structure of a daytime sporadic-E (Es) episode in Shikoku, Japan. The snapshot of the Es is derived not only from interferometric SAR (InSAR) but also from multiple aperture interferometry (MAI), the latter of which performs better in isolating the fine spatial structure. The GNSS TEC maps indicate that the Es episode is accompanied by a primary east–west elongated (up to ~ 180 km) southward migrating TEC striation with a speed of ~ 90 m/s and ~ 10–20 km widths in the north–south direction. As previously suggested by the GNSS TEC time series, the present InSAR and MAI data independently confirm that electron density in the primary striation gradually increases from the frontal leading edge but abruptly drops in the trailing edge. MAI-based TEC map confirms multiple TEC striations as previously suggested in GNSS TEC time-series, which are reminiscent of the quasi-periodic (QP) echoes in nighttime Es detected by the middle and upper atmosphere (MU) radar, but the periodicity is not as clear as that observed by MU radar. The Kelvin–Helmholtz (KH) instabilities around the wind shear of neutral winds could be responsible for the QP TEC striations. Graphical abstract

Continuous Plinian eruptions often excite atmospheric modes of similar to 3.7 and similar to 4.4 mHz, which are observed as harmonic oscillations of ionospheric total electron content (TEC) by global navigation satellite system (GNSS) receivers. Such TEC oscillations started shortly after the great eruption of the Hunga Tonga-Hunga Ha'apai (HTHH) submarine volcano at similar to 4:14 UT, on 2022 January 15. Here I analyse GNSS data at stations within similar to 4000 km from the volcano to study temporal and spatial distribution of such atmospheric modes. Strong similar to 3.7 mHz TEC oscillations in near fields started shortly after the eruption onset and propagated outward with the sound speed from HTHH. Later such TEC oscillations became strong again with the amplitude peak at the distance similar to 1400 km from HTHH. Such far field oscillations occurred also above New Zealand and the Solomon Islands, similar to 3000 km from HTHH. Their amplitudes seem correlated with those of the 0S29 solid earth mode, suggesting that vertical surface vibrations underneath may play a role in maintaining the atmospheric mode. Onset of the far field TEC oscillations are synchronized with the local sunrise, possibly controlled by diurnal changes in the ionospheric electron density.

Ionospheric disturbances associated with large earthquakes can be observed with global navigation satellite system (GNSS) receivers on the ground as changes in total electron content (TEC). In addition to coseismic disturbances -10 min after earthquakes caused by acoustic-gravity waves from epicenters, there have been reports on changes immediately before very large earthquakes. We show such disturbances for the 2008 Wenchuan earthquake (M w 7.9), China, started - 37 min before the main shock and reached -5 percent of the background value. The results of past -20 cases with M w 7.3 or more exhibit simple relationships that the leading times scale with fault lengths and the intensities of the anomalies relative to the backgrounds scale with fault areas. We demonstrate that the anomaly immediately before the 2008 Wenchuan earthquake fits well with these trends but with slightly longer leading time and stronger intensity. (c) 2024 COSPAR. Published by Elsevier B.V. All rights reserved.

Influence of the geomagnetic field on ionospheric disturbances associated with acoustic waves has been widely reported and unanimously agreed upon for the mid-latitude north and mid-latitude south regions, while elaborate studies in this regard are scarce for the polar and equatorial regions. In this study, we present a holistic overview that characterizes the ionospheric directivity from a global perspective considering observations from various natural case studies and anthropogenic phenomena and compare the results with the numerically simulated TEC anomaly. Our focused approach highlights that ionospheric directivity is omnidirectional and bidirectional (or dual-beam) for magnetically polar and equatorial regions, respectively. The mid-latitude north and south domains were also looked upon where the ionospheric directivity is strongly unidirectional (or single-beam). Further, the results of our numerical simulation model appear to complement well with the observations. (c) 2024 COSPAR. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

Abstract The cyclonic phenomenon, particularly typhoons within the 100° E to 180° E longitude region, bring significant devastation through intense rainfall and strong winds, causing secondary effects like landslides and floods upon landfall. This results in infrastructural damage and loss of life, ranking storm-related disasters, including typhoons, second only to earthquakes in casualties, emphasizing the need for a robust observation system. While higher income countries benefit from established radar and meteorological stations for continuous monitoring, this study highlights the critical necessity for an additional monitoring system in lower income countries. We investigate the applicability of Interferometric Synthetic Aperture Radar (InSAR) during typhoon landfall, particularly in densely vegetated areas where longer wavelengths like L-band (for instance, the Advanced Land Observing Satellite (ALOS/PALSAR) and ALOS-2/PALSAR-2) are suitable. By analyzing typhoon occurrences and confirming landfall using weather radar from 2007 to 2011 (ALOS/PALSAR observation period) and 2014 to 2023 (ALOS-2/PALSAR-2 observation period), our study successfully identifies the landfall of the Jebi typhoon on September 4, 2018. InSAR processing reveals significant phase gradients linked to dense water vapor during landfall, corroborated by comparisons with sea-level Zenith Wet Delay (ZWD) from Global Navigation Satellite System (GNSS) data and hourly precipitation rates from the Automated Meteorological Data Acquisition System (AMeDAS). The concurrence of InSAR results with ZWD values and rainfall data from meteorological stations validates the potential of L-band InSAR in observing typhoon landfalls.

Seasonal movements of global navigation satellite system (GNSS) stations in Northeast (NE) Japan are mainly driven by elastic loading of snow, reaching a few meters deep along the western flank of the backbone range. Here we study them in a comprehensive manner to solve remaining problems. GNSS stations in the inland area show sharp and strong subsidence peaks in winter and remain flat in other seasons, a response consistent with the snow loading. On the other hand, those close to coasts show broad and weak winter subsidence peaks. This needs additional loads in spring to retard the rapid decay of snow loading. We propose that rice fields work as natural reservoirs until early summer and evaluate quantitative consistency of the hypothesis. We also found that some stations show abnormally large winter subsidence that cannot be explained by snow loading alone. Here we examine two factors, i.e., groundwater extraction in winter for melting snow on roads, and snow accretion onto GNSS antenna radomes. We also evaluate seasonal ocean water mass changes in the Japan Sea using GRACE satellite gravimetry data. We found its role in seasonal crustal movements in NE Japan quite small.

Vertical crustal movements associated with large earthquakes excite various kinds of atmospheric waves. They propagate upward and often disturb ionosphere. Here, I report a case for the 2024 January 1 Mw7.5 earthquake that occurred in the northern tip of the Noto Peninsula, Central Japan, using a dense network of multi-GNSS receivers. A rectangular-shaped positive anomaly of ionospheric total electron content emerged ∼9 min after the mainshock. The initial sharp peak was composed of two acoustic wave pulses excited at the two ends of the fault spanning ∼100 km. It was followed by a series of smaller-amplitude broad peaks, the largest of which was possibly excited by a slow fault rupture near the NE edge of the fault ∼8 min after the mainshock. These signatures become large where the wavefronts overlap with those of medium-scale traveling ionospheric disturbances, suggesting possible enhancement of the coseismic signals by downward displacements of high electron density regions in the ionosphere.