Abstract Craton evolution plays a fundamental role in stabilizing the continental lithosphere and the long‐term evolution of Earth's surface environment. The Shanxi Rift Zone (SRZ) within the North China Craton marks an ongoing craton destruction. Detailed lithospheric structure is essential to explain craton destruction. To better understand its mechanism, we investigated the anisotropic lithospheric structure of the SRZ using surface‐wave Eikonal tomography. The results reveal strong north–south contrasts. In the northern SRZ, strong low‐velocity anomalies with weak azimuthal anisotropy are revealed in the upper mantle under the Datong volcano, implying strong mantle upwelling. In the central SRZ, the lithosphere shows higher velocity and consistent E‐W anisotropy across the rift, indicating little thermal effect. We attribute these variations, particularly the thermal structure, to Paleozoic subduction of the Paleo‐Asian Ocean along the northern margin of the craton, leading to a feasible environment for later magmatic underplating induced by the Pacific subduction.

Abstract Vapor-dominated geothermal systems provide a reliable, low-carbon source of heat and electricity, but optimizing their exploitation requires high-resolution imaging of fracture networks and fluid pathways at the reservoir scale. We analyze a dense microseismic cluster in the northwestern Geysers (California), selecting 1,276 induced earthquakes recorded between 2006 and 2015. Using inter-event interferometry and fast-marching surface-wave tomography, we retrieve Rayleigh wave phase velocities on horizontal layers at 100 m spacing and jointly invert them with previously derived local group velocities to obtain a quasi-3D shear-wave (Vs) model at ~ 100 × 100 × 10 m blocks. The resulting Vs models reveal three main types of low-velocity anomalies: (I) fault-related zones associated with fracturing and hydrothermal alteration, (II) shallow steam-cap and normal-temperature-reservoir (NTR) boundary transitions spanning depths of ~ 900–1400 m, exhibiting sharp Vs contrasts due to thermal and fluid effects, and (III) injection/engineering-related anomalies characterized by localized or vertically elongated low Vs patches. Integrating these results with induced microseismicity provides valuable insights into fracture activity, fluid migration, and stress evolution within the geothermal reservoir.

Abstract Management of water resources will be of critical importance as the effects of climate change accelerate. This implies the need to monitor water resources with high spatial and temporal resolution. One way to meet this need could be passive seismic methods using ambient seismic noise. In this study, we present a novel approach using time‐lapse probabilistic tomography to monitor a hydrological pumping test in the municipality of Nickelsdorf (Austria). We deployed a dense array of nodal seismic sensors that recorded seismic noise for approximately 4 months in early 2023. To assess changes in subsurface properties associated with the pumping, we conducted trans‐dimensional probabilistic tomography with daily time resolution using train‐generated noise. Our results show a clear correlation between water table fluctuations and shear wave velocities. We interpret this to be due to variations in saturation caused by groundwater pumping. Mapping these spatio‐temporal variations enables water resource monitoring that complements well‐based point‐wise measurements. Such an approach can lead to improved understanding of groundwater dynamics such as inflow from external water resources.

Abstract We present a surface wave tomography application based on event‐pair interferometry to investigate local (∼100 km) mid‐ocean crustal structures, with a particular focus on imaging a potential crustal solidified intrusive complex in a region lacking seismic stations. We analyzed vertical‐component IRIS data (2010–2022) from over 180 M ≥ 4.5 earthquakes. Signal pre‐processing techniques, cross‐correlation, and then stacking, were employed to extract inter‐event empirical Green's functions (EGFs). Afterward, dispersion curves were manually derived for inter‐event distances exceeding three wavelengths, and tomographic inversion was performed to obtain isotropic and anisotropic group velocity models across periods of 1–12 s. Our results at shallow depths reveal well‐resolved low‐velocity anomalies, attributed to high porosity, low density, and the presence of unconsolidated to semi‐consolidated pelagic sedimentary deposits. In contrast, at greater depths, high‐velocity regions are interpreted as parts of the volcanic plumbing system inside the oceanic crust beneath seamount volcanoes in mid‐ocean settings, highlighting the effectiveness of the method despite the limitations imposed by widely spaced global physical stations. Additionally, observed anisotropy indicates deformation around Hunga Tonga‐Hunga Haʻapai (HTHH), with fast‐direction alignment reflecting magmatic intrusions and crustal fabric influences during crust formation. The VS models highlight structural variations and anisotropic features consistent with regional tectonics and magmatic processes.

The Schwechat depression, in the Vienna Basin (VB) is currently the main target area for deep geothermal exploration in eastern Austria. Knowledge of the subsurface heavily relies on active seismic reflection profiling experiments that are expensive and logistically demanding. Affordable geophysical prospecting methods are needed to reduce subsurface uncertainty over large spatial areas. Over recent years, seismic ambient noise tomography (ANT) has proven to be a cost-effective and environment-friendly exploration technique fulfilling this need. Here, we present an ANT study of the central Vienna Basin revealing the shear-wave velocity, and shear-wave radial anisotropy structure down to 5 km beneath the surface. We deployed an array of 100 seismic nodal instruments during 5 weeks over summer 2023. We measured fundamental-mode Rayleigh and Love-wave group velocity dispersion from seismic noise correlations, and employed transdimensional Bayesian tomography to invert for isotropic Rayleigh and Love group velocity maps at periods ranging from 0.8 to 5.5 s. We then extracted Rayleigh and Love group velocity dispersion curves from the maps at all locations, and jointly inverted them for shear-wave velocity and radial anisotropy as a function of depth using a transdimensional Bayesian framework.Our shear-wave velocity model reveals a basin-like low-velocity feature, interpreted as the seismic signature of the Schwechat depression. Another low-velocity feature is observed beneath the city of Vienna, which could be of great interest for geothermal exploration. The shear-wave velocity radial anisotropy structure indicates a thin negative anisotropy layer in the top 150 meters, likely associated with water-saturated open cracks. Between 150 meters and 1.5 km depth, we observe widespread positive radial anisotropy across the entire study area, corresponding to sub-horizontal layering within the Neogene basin. At greater depths, the Schwechat depression is characterized by positive radial anisotropy, while the edges of the Schwechat depression exhibit negative radial anisotropy due to steeply dipping strata and normal faults responsible for the formation of this major depocenter in the Vienna Basin.

In spring 2024, we deployed a large seismic nodal array across the southern Vienna Basin, Austria. Using a machine-learning approach, we constructed a seismic catalog for the 60-day deployment period and reliably identified 100 events. We applied a local earthquake tomography inversion procedure to relocate the detected events and derive three-dimensional P- and S-wave velocity models and V P /V S estimates. The results reveal a low-velocity anomaly with high V P /V S estimates, corresponding to the Neogene basin structure. In contrast, high-velocity anomalies with low V P /V S estimates highlight nappe systems associated with the Alpine Orogen. Most of the relocated seismicity during the deployment is linked to the April 14 th , 2024, M ~ 3 earthquake. The mechanism for this event, along with its aftershock distribution, suggest that the rupture occurred on a normal splay fault of the Vienna Basin Transfer Fault System, situated near its intersection with the basal detachment at depth. As this area is highlighted for its geothermal resource potential, a comprehensive understanding of geological structures and potential hazards is essential for responsible resource development.

The Vienna Basin (VB) is currently the main target area for deep geothermal exploration in Austria. Knowledge of the subsurface heavily relies on active seismic reflection that are expensive and logistically demanding. Affordable geophysical prospecting methods are needed to reduce subsurface uncertainty. Over the recent years, seismic ambient noise tomography (ANT) has proven to be a cost-effective and environment-friendly exploration technique. Here, we present an ANT of the central Vienna Basin revealing the shear-wave velocity structure of the top 5 km beneath the surface. We deployed an array of ~100 seismic nodal instruments during 6 weeks over summer 2023. We measured fundamental-mode Rayleigh and Love-wave group velocity dispersion from seismic ambient noise and employed transdimensional Bayesian tomography to invert for isotropic group velocity maps at periods ranging from 0.8 to 5.5 s. We then extracted Rayleigh and Love group velocity dispersion curves from the group velocity maps at all locations and jointly inverted them for shear-wave velocity as a function of depth using a transdimensional Bayesian framework. We discuss features observed in our 3D shear-wave velocity model relevant to geothermal exploration.

The depths of mineralogical phase transitions in the mantle (at ~410 and ~660 km depth) offer crucial insights into the thermal conditions of the mantle transition zone and, by extension, the upper mantle's state and circulation. Our approach involves conducting P-to-S receiver function analysis to determine the mantle transition zone's thickness and the absolute depths of the ~410 km and ~660 km discontinuities in the Central and Eastern European region. Our workflow meticulously attends to each step, starting from data download, quality control, and culminating in the calculation of P-to-S receiver functions. We use data from multiple sources, including the AlpArray and AdriaArray Seismic Networks, the PACASE, Carpathian Basin, and South Carpathian Project temporary seismic networks, as well as the permanent stations of the Hungarian National Seismological network and of the neighboring countries. This analysis covers the time period from 2002 to 2023, involving over 860 seismological stations. Our extensive dataset, consisting of approximately 2 million three-component waveforms and over 120,000 high-quality P-to-S radial receiver functions, coupled with dense piercing-point coverage, allows us to achieve unprecedented resolution. We present Common Conversion Point cross-sections migrated with a 3D tomographic velocity model underneath the Alps, Carpathians, and the Pannonian Basin. Additionally, we aim to offer new insights into the mantle transition zone's thickness beneath intriguing regions (e.g., Vrancea zone, Alpine Tethys Ocean zone, Eastern Alps–Pannonian Basin transition zone). For a precise understanding of geodynamic processes such as slabs, mantle plumes, and volcanism, it is imperative to accurately map these boundaries.

AdriaArray is a multinational initiative to cover the Adriatic Plate and its tectonically active surroundings - including units of Adriatic origin - with a dense regional array of seismic stations. AdriaArray provides data for imaging of the crustal and upper mantle structure and for the analysis of seismic activity and hazard. It will help to understand the causes of active tectonics and volcanic fields in the region. The network consists of 1092 permanent and 436 temporary broadband stations from 23 mobile pools. A homogeneous coverage of broadband stations is achieved in an area from the Massif Central in the west to the Carpathians in the east, from the Alps in the north to the Calabrian Arc and mainland Greece in the south. The backbone network (2022-2026) is complemented by locally densified broadband deployments in the western Carpathians, along the Dubrovnik fault and in the Vrancea region. Data recorded by AdriaArray stations is transmitted in real-time to 12 nodes of the European Integrated Data Archive (EIDA) where it is accessible as a single virtual network. Regular availability and quality checks ensure high data usability. AdriaArray, the largest passive seismic experiment in Europe to date, is based on the cooperation between local network operators, mobile pool providers, technicians, engineers, field teams, researchers, students, and organizations such as ORFEUS (Observatories and Research Facilities for European Seismology) and EPOS (European Plate Observing System). The AdriaArray Seismology Group, founded in 2022, encompasses 64 institutions from 30 countries with 451 participants. Initial Collaborative Research Groups have been established to coordinate data analysis and scientific research. We present the evolution of the experiment and its objectives, describe its preparation and planning, and show maps of the AdriaArray Seismic Network, station properties and coverage. We further describe the data archiving and distribution, list the participating institutions, individuals and networks and discuss collaborative research topics.

Soil moisture is a key metric to assess soil health. Water held in the shallow subsurface between soil particles enables various biogeochemical and hydrological processes indispensable to soil functions. Potential soil moisture deficit may raise the irrigation demands, which further exacerbates the stress on the water supply. The changes in soil moisture can impact climate, further amplifying the climatic anomalies and intensifying extreme weather events. Thus, understanding soil moisture and its dynamics over time are of broad scientific interest and practical implications.Despite the vital importance of soil moisture, it still lacks sufficient means to properly assess the parameter at a regional scale, which is an essential research dimension for addressing practical issues in the agricultural and environmental sectors. Ambient noise seismology provides new possibilities to infer subsurface changes in a real-time, non-intrusive, and costless manner.In this study, we map the temporal variations in soil moisture for Central-Southern Europe with ambient seismic noise. It is the first time that the seismic method has been applied to map soil moisture at a regional scale using an ordinary seismic network setup. The method helps in bridging the resolution gap between current pointwise (e.g., tensio-, electrical- and neutron-meter) and global (e.g., satellite-based remote sensing) investigations, providing complementary information for both scientific research and public decision-making.

Understanding the nature of the Mantle Transition Zone (MTZ) can foster our knowledge about the dynamics of the Earth, especially related to the vertical heat and mass exchange between the upper and the lower mantle. The MTZ, characterized by seismic-velocity discontinuities at depths of 410 km and 660 km, is conventionally studied using seismic waves emitted by earthquakes. However, this approach suffers from a typically uneven distribution of earthquakes, biases in earthquake location, and the complexity of earthquake processes.In this study, we used body waves retrieved from ambient noise correlations to map the mantle transition zone beneath the US. We analyzed cross-correlation functions from more than 3500 seismic stations, including the EarthScope USArray stations during its deployment time frame between 2004 and 2013. We obtained clear short period (

With the accelerating global climate crisis and the ratification of the Paris Agreement in 2015, reducing our carbon footprint has become crucial, particularly in the energy sector. Geothermal energy is becoming an attractive green energy since it is baseload-capable, and highly suitable for the supply of district heating in Europe. Identifying optimal locations for deep geothermal wells is essential, but such exploration typically depends on conventional active seismic surveys, which are logistically complex and costly. The high upfront costs associated with geothermal resource exploration remain a significant barrier to the large-scale development of deep geothermal energy across Europe. This is where passive seismic methods based on ambient noise, combined with large, dense seismic nodal arrays, offer a promising solution. In Austria, the central Vienna Basin is the primary target for deep geothermal production serving the city of Vienna. Meanwhile, the southern Vienna Basin also shows potential for geothermal production for smaller cities like Wiener Neustadt in lower Austria. In Spring 2024, we deployed 181 seismic nodal sensors in two temporary deployments over an area of 400 km2. We measured fundamental-mode Rayleigh and Love-wave group velocity dispersion from seismic noise correlations and employed transdimensional Bayesian tomography to invert for isotropic Rayleigh and Love group velocity maps at periods ranging from 0.8 to 3.5 s and 0.8 to 5.5 s, respectively. We then extracted Rayleigh and Love group velocity dispersion curves from the maps at all locations and jointly inverted them for shear-wave velocity and radial anisotropy as a function of depth using a transdimensional Bayesian framework. The 3-D VSV model highlights the seismic characteristics of the Neogene basin in the southern Vienna Basin. Additionally, the 3-D shear-wave radial anisotropy model reveals several features at depth. Combined, these findings hold significant implications for early-stage geothermal exploration in the southern Vienna Basin.

The northern extension of the AdriaArray, a dense network of broadband seismic stations, covers the southeastern part of the Bohemian Massif, the Eastern Alps, the Western Carpathians, and the northernmost part of the Pannonian Basin. Considering also the previous passive experiments carried out since 2015, the existing 32 broadband permanent stations have been complemented by 89 temporary stations deployed in the collaborative effort of institutions from the Czech Republic, Poland, Austria, and Slovakia. We document the seismic station configuration, instrumental equipment, data transmission, preprocessing, and availability, as well as the general organization of the network. Since spring 2022, when the AdriaArray network started its operation, to January 2025, approximately 2.8 TB of data recorded by the temporary stations has been transmitted to the European Integrated Data Archive (EIDA), with an average completeness of 80% and real‑time operation for 91% of the stations. The network records valuable data for a wide range of Earth science studies, including earthquake location, seismic hazard assessment, and high-resolution images of the crust and upper mantle structure. As examples of data utilization, we show Moho depth variations from the Bohemian Massif to the West Carpathians and the northernmost part of the Pannonian Basin, as well as prevailing NW‑SE polarization azimuths of the fast shear waves from the splitting evaluations at stations in the broader surroundings of the Carpathians.

Soil moisture is an essential ecosystem resource and a major control of the Earth's hydrological cycle and energy balance, closely interacting with the climate system. However, investigating deep soil moisture dynamics at large scales presents significant challenges due to the sparse distribution and limited spatial representativeness of in situ monitoring networks, while various remote sensing methods mainly address surface soil moisture within the top few centimeters. This study illustrates how seismic waves can effectively detect variations in deep soil moisture. We examine continuous seismic data from 791 stations across South-Central Europe for the period 2016-2020. Our findings confirm a strong correlation between variations in seismic velocity and deep soil moisture content. Notably, the seismic observations pinpoint areas impacted by severe soil moisture deficits related to the 2016-2017 European drought event. The seismic method presented in this study offers new opportunities in addressing the observational gap of this critical environmental parameter.

This study investigates the mantle transition zone (MTZ) beneath Central and Eastern Europe using a 3-D Common Conversion Point migration of P-to-S receiver functions derived from a dense regional seismic network. The analysis focuses on the major seismic discontinuities at similar to 410, similar to 520 and similar to 660 km depth to assess their depth variations, continuity and implications for past and ongoing geodynamic processes. Our results reveal significant spatial variations in the thickness and topography of the MTZ. In the Western Alps and central Pannonian Basin, the MTZ is thickened up to similar to 280 km, deviating from the global average of similar to 250 km. This thickening is attributed to the presence of stagnant slab material in the transition zone, suggesting a long-lasting influence of past subduction, particularly of the Adria Plate and Vrancea slab. In the Carpathians and Dinarides, the 410 km discontinuity is uplifted to depths as shallow as similar to 400 km, while the 660 km discontinuity reaches depths of similar to 670-680 km in regions affected by subducted lithosphere, further supporting the presence of cold slab remnants. Additionally, the 520 km discontinuity-often intermittent or absent in global studies-is clearly imaged in many parts of the region, and found at variable depths ranging between similar to 510 and similar to 540 km. These depth anomalies suggest the presence of compositional heterogeneities and thermal variations within the MTZ, possibly linked to subducted oceanic crust or recycled lithospheric material. Evidence for mantle upwellings is also observed, particularly beneath the Pannonian Basin, where low-velocity anomalies near the 410 km discontinuity are consistent with small-scale plumes or thermal anomalies. These may be associated with post-subduction processes or intraplate volcanism. Importantly, the Alpine slab itself is not clearly detected in the transition zone, indicating that it may have already sunk below the MTZ or is not well-coupled to the upper mantle structure imaged by receiver functions. By providing new constraints on the structure of the upper mantle and its transition zone, this study refines existing models of regional tectonic evolution. Our findings emphasize the interplay between surface tectonics and deep mantle dynamics and demonstrate that the observed MTZ features preserve a strong geodynamic imprint of both past subduction and intraplate processes across the Alpine-Carpathian-Pannonian-Dinarides region.

We use an adapted approach for long-distance high temporal resolution monitoring to investigate the daily and sub-daily behavior of seismic velocity changes. We analyze four years of continuous data from AlpArray and other local networks throughout the Central-Southern Europe. Focusing on the 1 Hz frequency we calculate seismic velocity changes based on coda wave interferometry. Our results show that we can observe a consistent periodic behavior with periods of 24 h and 12 h, with a focus primarily on the latter. We attribute these changes predominantly to variations in atmospheric pressure. These changes manifest through loading effects on the unsaturated zone and alterations in the water bodies below that. By analyzing the spatial variations of this two-cycle-per-day behavior we found a strong correlation with extensively karstified water-bearing formations. This connection may contribute to the hydrological characterization of the near-subsurface in central Europe identifying large water reservoirs.

Seismic waves capture important insights into subsurface behavior. We introduce an adapted coda-wave interferometry approach to monitor the spatial variability of semi-daily periodic seismic velocity changes on a regional scale, applied to data collected across South and Central Europe. Our results reveal a broad spatial correlation between seismic velocity changes and air pressure fluctuations, suggesting that air pressure is the dominant driving force. Specifically, air pressure fluctuations modulate saturation levels within the capillary zone through the dynamic interplay between fluid and gaseous phases, producing significant seismic velocity changes. The mechanism explains the large variations observed in regions with high connectivity between the surface and saturated zone. We associate this enhanced interaction with the high vulnerability of shallow water resources. We propose inspecting semi-daily periodic seismic velocity changes as a new tool for gaining a regional view of water reservoir vulnerability.

Climate change significantly impacts groundwater resources by altering recharge rates and thus availability, making it crucial to manage these vital reserves sustainably to ensure long-term water security. In this study we seismically monitor a series of groundwater pumping tests in the municipality of Nickelsdorf (Burgenland, Austria). Due to expected increasing demand for water due to population development, wells were installed to ensure a sustainable drinking water supply in the long term. Traditionally monitored through point-wise hydrological wells, our approach combines nodal seismic sensors and ambient noise to broaden insights into subsurface processes affected by pumping activity. Seismic ambient noise was continuously recorded over three months in early 2023, including periods before, during, and after pumping. Our study evaluates various ambient noise sources and seismic signals, especially those generated by passing trains. To gain broader understanding of the subsurface processes we perform a time-lapse tomography to identify the location and strength of the velocity variations. Based on our analysis, we resolve increases/decreases in seismic velocity of around 10 % in the uppermost meters of the subsurface during pumping operations related to local reduction in the water table. This holistic approach aims at unveiling the behavior of the subsurface during and post-pumping, potentially offering a comprehensive understanding beyond individual hydrological wells.

Summary Mitigating climatic change is one of the greatest societal challenges of our time. Geothermal energy is a renewable resource potentially available anywhere at any time. However, developing geothermal projects is challenging due to high economic and geological risks caused by the lack of knowledge about the subsurface. Therefore, there is an urgent need for affordable geophysical prospection methods to reduce uncertainty, de-risk drilling, and ensure safe operations of new projects. In recent years, seismic ambient noise tomography (ANT) has proven to be a cost-effective alternative for geothermal exploration. Here, we present an ANT of the central Vienna Basin revealing the shear-wave velocity structure of the top 5 km beneath the surface. We deployed an array of ∼100 seismic nodal instruments for 6 weeks during the summer of 2023. We measured fundamental-mode Rayleigh and Love-wave group velocity dispersion from seismic ambient noise. We then used transdimensional Bayesian tomography to create a 3-D shear-wave velocity model following a 2-step approach. Finally, we discuss the features observed in our 3D shear-wave velocity model that are relevant to geothermal exploration.

The Pannonian-Carpathian-Alpine Seismic Experiment (PACASE) is a collaborative project based on a large, passive seismic network comprising 214 temporary stations. Among the primary aims are the imaging of the Earth’s crustal, lithospheric and upper mantle structure, including joint inversions; monitoring and mapping of seismic activity; and interpretation of the data from seismotectonic and geodynamic perspectives. The base of the cooperation is a high-quality, broadband seismic network covering the very centre of Europe: the Eastern Alpine and Western Carpathian Mountain ranges, the Bohemian Massif, and the sedimentary Molasse and Pannonian Basins. In this overview, we focus on the implementation and achieved field goals of PACASE, such as seismic station configuration, general network organization, data availability and access to the dataset. With selected seismological examples, we demonstrate the good usability of the records of earthquake detection, and a first publication attests to the structural imaging capability of the PACASE data. We assess the background noise level at various stations and its variations in time and space. Our aim is to collect all practical information relevant to serve as a long-term reference for the PACASE.