ALBERT

Description: Forests play a crucial role by regulating the global and local weather through the exchange of atmospheric gases and water vapor. The present study aims to study the intra-annual variability of net ecosystem exchange (NEE) of carbon dioxide in a sal (Shorea robusta) dominated moist deciduous forest in India by integrating eddy covariance (EC) data and Biome-Biogeochemical Cycle (Biome-BGC) model. The study also attempts to address the spatial variability of NEE with respect to phenology. Monthly average NEE were estimated using a calibrated Biome-BGC model and the spatial NEE was mapped using random forest (RF) regression algorithm. Phenology metrics were generated using the moderate resolution imaging spectrometer (MODIS) enhanced vegetation index product (MOD13A2) and its relationship with the estimated NEE was studied. RF regression model for monthly average spatial NEE estimation was built with an R2 of 0.84 and % RMSE of 3.68%. The study revealed that the NEE at the regional scale can be estimated using the basic meteorological variables like mean temperature, vapor pressure deficit, minimum temperature and total precipitation. Biome-BGC model output showed that the sal forest of the study area acted as a net sink of carbon in almost all months of 2015, except April to June. Peak NEE value (− 2.80 to − 2.96 g C m−2 day−1) was observed during October month. Annual NEE of sal forest in 2015 was found to be − 526.87 g C m−2 year−1. With the start of season (end of June), sal forest showed an increasing trend in NEE while decreasing trend was observed at the end of season (end of October). The study showed the applicability of Biome-BGC model in Indian forest when integrated with EC data. The study also highlighted the utility of RF in capturing the spatial variability of NEE over large area.

Description: A comprehensive understanding of shale’s bedding anisotropy is crucial for shale-related engineering activities, such as hydraulic fracturing, drilling and underground excavation. In this study, seven Brazilian tests were conducted on shale samples at different bedding orientations with respect to the loading direction (0°, 45° and 90°) and the disc end face (0°, 45° and 90°). An acoustic emission (AE) system was employed to capture the evolution of damage and the temporal-spatial distribution of microcracks under splitting-tensile stress. The results show that the Brazilian tensile strength decreases with increasing bedding inclination with respect to the disc end face, while it increases with the angle between bedding and loading directions. Increasing the bedding inclination with respect to the end face facilitates the reduction in b value and enhances the shale’s resistance to microcrack growth during the loading process. Misalignment between the bedding orientation and the end face suppresses the growth of mixed tensile-shear microcracks, while reducing the bedding angle relative to the loading direction is beneficial for creating mixed tensile-shear and tensile cracks. The observed microscopic failure characteristics are attributed to the competing effects of bedding activation and breakage of shale matrix at different bedding inclinations. The temporal-spatial distribution of microcracks, characterized by AE statistics including the correlation dimension and spatial correlation length, illustrates that the fractal evolution of microcracks is independent of bedding anisotropy, whereas the spatial distribution shows a stronger correlation. The evolution features of correlation dimension and spatial correlation length could be potentially used as precursors for shale splitting failure. These findings may be useful for predicting rock mass instability and analyzing the causes of catastrophic rupture.

Description: Around 30 % of Germany's final energy consumption can be attributed to heating and cooling in the building sector. Aquifer Thermal Energy Storage (ATES) allows sustainable and climate-friendly space heating and cooling and is therefore a promising technology that can contribute to decarbonizing this sector. However, further research on ATES is needed to promote the so far limited application of this technology in Germany and other countries. This work therefore gives an overview of current ATES research sites and projects in Germany collected in the project ‘SpeicherCity’. Among other aspects, these projects address hydrogeochemical challenges, potential studies and the integration of ATES into existing energy systems. They include both low-temperature (LT) and high-temperature (HT) ATES systems. This review also provides details on reservoir characteristics and well designs of the individual sites as well as information on the research goals and methods. Based on the comprehensive German research activities on ATES compiled in this work, lessons learned from the research findings and experiences with ATES operation and permission are highlighted.

Description: Tehran stands as one of the most earthquake-prone cities globally. This vast urban center, with a population exceeding 10 million, is intersected by several active faults in its vicinity, presenting significant seismic hazards. The occurrence of two Mw ~5 earthquakes in December 2017 near Malard and May 2020 near Damavand, further underscores the urgent need for comprehensive studies in the capital of Iran. Here, we primarily focus on the 2017 and 2020 seismic events and their causative faults. Additionally, we shed light on the limitations of Tehran's seismic monitoring and active faults map by addressing examples of unidentified seismic unrest and faults. By tackling the grand challenges of seismic studies and evaluating people's and cities' preparedness for a major earthquake, we draw insights from recent earthquakes around Tehran. Results show that the Malard and Damavand earthquakes occurred on the previously unknown and Mosha faults, respectively. Sparse seismic stations limit route detection thresholds and location accuracies of seismicity near Tehran. In addition, we show that the dispersion of population and distressed fabrics in Tehran is clustered, and the vulnerability to earthquakes is linked to physical and social factors. This study bears immense importance in enhancing seismological studies and risk reduction strategies for the Tehran province. Tehran stands as one of the most earthquake-prone cities globally. This vast urban center, with a population exceeding 10 million, is intersected by several active faults in its vicinity, presenting significant seismic hazards. The occurrence of two Mw ~5 earthquakes in December 2017 near Malard and May 2020 near Damavand, which resulted in the loss of life and significant consequences, further underscores the urgent need for comprehensive studies in the capital of Iran. Here, we primarily focus on the 2017 and 2020 seismic events and their causative faults. Additionally, we shed light on the limitations of Tehran's seismic monitoring and active faults map by addressing examples of unidentified seismic unrest and faults. By tackling the grand challenges of seismic studies and evaluating people's and cities' preparedness for a major earthquake, we draw insights from recent earthquakes and the 2023 Türkiye-Syria disaster. Results show that the Malard and Damavand earthquakes occurred on the hitherto unknown and Mosha faults, respectively. Sparse seismic stations limit route detection thresholds and location accuracies of seismicity near Tehran. In addition, we show that the dispersion of population and distressed fabrics in Tehran is clustered, and the vulnerability to earthquakes is linked to physical and social factors. This study bears immense importance in enhancing seismological studies and risk reduction strategies for the Tehran metropolis.

Description: Distributed acoustic sensing (DAS), deployed on dark telecom fiber, is well‐positioned to play a significant role in seismic monitoring networks because of the combination of a large aperture, fine spatial resolution, broadband sensitivity, and the ubiquitous presence of unused telecommunication fibers in many areas of the world. In this study, we explore the feasibility of dark‐fiber array deployed in a noisy environment for detecting small explosions. We test the effectiveness of template matching for the detection of low‐frequency blasts generated by mining activities in the Imperial Valley, California. We first evaluate dark‐fiber detection performance by analyzing the relationship between detection threshold (DT) and the number of DAS channels used. We find that although, as expected, increasing the number of channels yields higher detection significance and lowers DT, the gain in performance is far from linear, with local anomalies across the DAS cable associated with zones of higher noise. We focus on investigating the types of noise affecting template matching and practical approaches mitigating anthropogenic noise that lower detection performance. Using median absolute deviation, we identify two types of noise sources affecting detection performance. Next, we design a voting scheme that selects DAS channels contributing to lowering of the DT and ensures improvement in detection when adding sequential channels. Finally, we compare dark‐fiber detection performance with nearby conventional seismometers and find that a single station can outperform up to ∼10 DAS channels. However, using the full aperture of our dark‐fiber transect allows to obtain ∼10% lower DT and yields fewer false‐positive detections than an array of four seismometers. Methodological solutions for noise assessment and channel selection allow us to fully benefit from the large aperture and dense sampling offered by dark fiber. The findings of this study are a step toward incorporating existing telecom fibers into novel explosion‐monitoring workflows.

Description: In geophysical inference problems, quantification of data uncertainties is required to balance the data‐fitting ability of the model and its complexity. The transdimensional hierarchical Bayesian approach is a powerful tool to evaluate the level of uncertainty and determine the complexity of the model by treating data errors and model dimensions as unknown. In this article, we take account of the uncertainty through the whole procedure, thus developing a two‐step fully Bayesian approach with coupled uncertainty propagation to estimate the crustal isotropic and radial anisotropy (RA) model based on Rayleigh and Love dispersion as well as receiver functions (RFs). First, 2D surface‐wave tomography is applied to determine period‐wise ambient noise phase velocity maps and their uncertainty for Rayleigh and Love waves. Probabilistic profiles of the isotropic average and RA as a function of depth are then derived at station sites by inverting the local surface‐wave dispersion and model errors and RFs jointly. The workflow is applied to a temporary seismic broadband array covering all of Sri Lanka. The probabilistic results enable us to effectively quantify the uncertainty of the final RA model and provide robust inferences. The shear‐wave velocity results show that the range of Moho depths is between 30 and 40 km, with the thickest crust (38–40 km) beneath the central Highland Complex. Positive RA (⁠⁠) observed in the upper crust is attributed to subhorizontal alignment of metamorphic foliation and stretched layers resulting from deformation. Negative RA (⁠⁠) in the midcrust of central Sri Lanka may indicate the existence of melt inclusions and could result from the uplift and folding process. The positive RA in the lower crust could be caused by crustal channel flow in a collision orogeny.

Description: The Eifel Large-N Seismic Network is a concentric network of about 80km aperture around the Laacher See. Instrumentation consists of broad band seismometers, short period instruments (1Hz eigenfrequency) and 4.5Hz geophones. While the broadband and short period stations cover the area rather homogeneously for about 12 month, the geophone stations were moved after 6 month from a layout focussed on the closer vicinity of the Laacher See onto a line crossing the network from south-west to north-east with a dense station spacing. The goal of the experiment is the structural investigation of the feeding system of the East Eifel and a detailed study of the tectonic and volcanic seismic activity in this area. After the end of embargo, data will be openly available under CC-BY 4.0 license according to GIPP-rules under network code 6E.