Application of Image Analysis for the Identification of Prehistoric Ceramic Production Technologies in the North Caucasus (Russia, Bronze/Iron Age)

The recent advances in microscopy and scanning techniques enabled the image analysis of archaeological objects in a high resolution. From the direct measurements in images, shapes and related parameters of the structural elements of interest can be derived. In this study, image analysis in 2D/3D is applied to archaeological ceramics, in order to obtain clues about the ceramic pastes, firing and shaping techniques. Images were acquired by the polarized light microscope, scanning electron microscopy (SEM) and 3D micro X-ray computed tomography (µ-CT) and segmented using Matlab. 70 ceramic sherds excavated at Ransyrt 1 (Middle-Late Bronze Age) and Kabardinka 2 (late Bronze–early Iron Age), located in in the North Caucasian mountains, Russia, were investigated. The size distribution, circularity and sphericity of sand grains in the ceramics show site specific difference as well as variations within a site. The sphericity, surface area, volume and Euler characteristic of pores show the existence of various pyrometamorphic states between the ceramics and within a ceramic. Using alignments of pores and grains, similar pottery shaping techniques are identified for both sites. These results show that the image analysis of archaeological ceramics can provide detailed information about the prehistoric ceramic production technologies with fast data availability

Experimental Investigation on Static and Dynamic Bulk Moduli of Dry and Fluid-Saturated Porous Sandstones

Knowledge of pressure-dependent static and dynamic moduli of porous reservoir rocks is of key importance for evaluating geological setting of a reservoir in geo-energy applications. We examined experimentally the evolution of static and dynamic bulk moduli for porous Bentheim sandstone with increasing confining pressure up to about 190 MPa under dry and water-saturated conditions. The static bulk moduli (K-s) were estimated from stress-volumetric strain curves while dynamic bulk moduli (K-d) were derived from the changes in ultrasonic P- and S- wave velocities (similar to 1 MHz) along different traces, which were monitored simultaneously during the entire deformation. In conjunction with published data of other porous sandstones (Berea, Navajo and Weber sandstones), our results reveal that the ratio between dynamic and static bulk moduli (K-d/K-s) reduces rapidly from about 1.5 - 2.0 at ambient pressure to about 1.1 at high pressure under dry conditions and from about 2.0 - 4.0 to about 1.5 under water-saturated conditions, respectively. We interpret such a pressure-dependent reduction by closure of narrow (compliant) cracks, highlighting thatK(d)/K(s)is positively correlated with the amount of narrow cracks. Above the crack closure pressure, where equant (stiff) pores dominate the void space,K-d/K(s)is almost constant. The enhanced difference between dynamic and static bulk moduli under water saturation compared to dry conditions is possibly caused by high pore pressure that is locally maintained if measured using high-frequency ultrasonic wave velocities. In our experiments, the pressure dependence of dynamic bulk modulus of water-saturated Bentheim sandstone at effective pressures above 5 MPa can be roughly predicted by both the effective medium theory (Mori-Tanaka scheme) and the squirt-flow model. Static bulk moduli are found to be more sensitive to narrow cracks than dynamic bulk moduli for porous sandstones under dry and water-saturated conditions

Injection-induced fault slip and associated seismicity in the lab: Insights from source mechanisms, local stress states and fault geometry

Probing source mechanisms of natural and induced earthquakes is a powerful tool to unveil associated rupture kinematics. The source processes of failure and slip instability driven by stress loading are affected by fault geometry, but the source ruptures of injection-induced seismicity in relation to fault structures and local stress states remain poorly understood. We have conducted a series of fault reactivation and slip experiments on sandstone samples containing faults with different surface roughness (smooth saw-cut fault and fractured rough fault). We impose progressive fluid injection to induce fault slip, and simultaneously monitor the associated acoustic emission (AE) activity. Using high-resolution AE recordings, we perform full moment tensor inversion of all located AE sources, and investigate the changes of AE source characteristics associated with induced fault slip and their relation to fault roughness. For the complex and rough fault, we observe significant non-double-couple components of AE sources and a high degree of focal mechanism heterogeneity. The temporal changes of AE mechanisms associated with injection-induced fault slip on the smooth fault reveal increasing proportions of double-couple components and decreasing variability of AE focal mechanisms when approaching the onset of slip events. The observed inconsistency between the nodal planes of AE sources and the macroscopic fault plane orientation is attributed to the development of secondary fracture networks surrounding the principal slip surface. We analyze changes in the magnitude-frequency characteristics and source mechanisms of AEs with fault-normal distance, showing that for the smooth (mature) fault, Gutenberg–Richter b-value of on-fault seismicity is lower and focal mechanisms are less heterogeneous, compared to off-fault seismicity. Our results emphasize the important role of roughness-related changes in local fault geometry and associated stress heterogeneity for source mechanisms and rupture kinematics of injection-induced seismicity

Obtaining of oxidizers using physical fields

Негативные последствия использования химических технологий для очистки природных и сточных вод послужили толчком для развития более чистых технологий. Все чаще используются чистые окислители (озон, пероксид водорода) в сочетании с физическими методами. Наиболее широко применяется обработка воды ультрафиолетовым излучением. Есть много публикаций об образовании окислителей при обработке загрязненной воды ультразвуком и гидродинамической кавитацией. В данной статье исследовалось образование окислителей при воздействии физических полей (магнитное поле постоянных магнитов, электромагнитное поле ультрафиолетового излучения, акустическое поле ультразвуковых излучателей) на дистиллированную воду. Эксперименты проводились на стенде, где возможно осуществлять раздельное и совместное влияние различных комбинаций физического воздействия. Проведенные эксперименты показали, что в дистиллированной воде под действием различных электромагнитных полей и постоянного магнитного поля наблюдается генерация окислителей. Но их концентрация мала (0,03-0.07 мг/л в пересчете на перекись водорода) и для интенсификации воздействия физических полей необходимо вносить дополнительные реагенты (перекись, озон и др.). Определено, что действие магнитного поля наблюдается при индукциях магнитного поля: 80, 100, 240 и 540 мТл, и скорости потока воды через зазор магнитного аппарата 1,1 м/с, 3,3 м/с и 4,4 м/с. Максимальная концентрация окислителей наблюдалась: при гидродинамическом режиме (все реакторы отключены, работает только насос), при включенном эжекторе и индукции 540 мТл; при совмещенном УЗ+2УФ режиме при такой же индукции, но без эжектора. Количественно содержание окислителей в совмещенном режиме на 11,5 % выше, чем в гидродинамическом режиме, а энергозатраты при этом выше на 28 %. Выраженный синергетический эффект при совместном действии магнитного поля, ультразвука и ультрафиолетового излучения не получен. Устойчивый результат увеличения генерации окислителей в дистиллированной воде получен при воздействии магнитного поля в сочетании с эжектором

Strain Partitioning and Frictional Behavior of Opalinus Clay During Fault Reactivation

The Opalinus Clay (OPA) formation is considered a suitable host rock candidate for nuclear waste storage. However, the sealing integrity and long-term safety of OPA are potentially compromised by pre-existing natural or artificially induced faults. Therefore, characterizing the mechanical behavior and microscale deformation mechanisms of faults and the surrounding rock is relevant for predicting repository damage evolution. In this study, we performed triaxial tests using saw-cut samples of the shaly and sandy facies of OPA to investigate the influence of pressure and mineral composition on the deformation behavior during fault reactivation. Dried samples were hydrostatically pre-compacted at 50 MPa and then deformed at constant strain rate, drained conditions and confining pressures (pc) of 5–35 MPa. Mechanical data from triaxial tests was complemented by local strain measurements to determine the relative contribution of bulk deformation and fault slip, as well as by acoustic emission (AE) monitoring, and elastic P-wave velocity measurements using ultrasonic transmissions. With increasing pc, we observe a transition from brittle deformation behavior with highly localized fault slip to semi-brittle behavior characterized by non-linear strain hardening with increasing delocalization of deformation. We find that brittle localization behavior is limited by pc at which fault strength exceeds matrix yield strength. AEs were only detected in tests performed on sandy facies samples, and activity decreased with increasing pc. Microstructural analysis of deformed samples revealed a positive correlation between increasing pc and gouge layer thickness. This goes along with a change from brittle fragmentation and frictional sliding to the development of shear zones with a higher contribution of cataclastic and granular flow. Friction coefficient at fault reactivation is only slightly higher for the sandy (µ ~ 0.48) compared to the shaly facies (µ ~ 0.4). Slide-hold-slide tests performed after ~ 6 mm axial shortening suggest stable creeping and long-term weakness of faults at the applied conditions. Our results demonstrate that the mode of fault reactivation highly depends on the present stress field and burial history

Transient Creep of Quartz and Granulite at High Temperature Under Wet Conditions

AbstractTransient creep of crustal rocks is important to explain time‐dependent geological processes such as postseismic deformation following a large continental earthquake. While the steady‐state creep flow law parameters of quartz and feldspar, major minerals in the upper and lower crust, are well known, the physical mechanism behind transient creep and the corresponding flow law parameters are poorly understood. We quantify the flow law parameters for both quartz and granulite (mixture of plagioclase and pyroxene) under wet conditions with a nonlinear Burgers model using a Markov chain Monte Carlo (MCMC) method. Modeling results yield an activation energy of 70 ± 20 kJ/mol and a stress exponent of 2.0 ± 0.1 for transient creep of quartz aggregates. For granulite/feldspar, we find activation energies of 280 ± 30 and 220 ± 20 kJ/mol and stress exponents of 1.0 ± 0.2 and 0.9 ± 0.1 under mid (1050–1100°C) and high (1125–1150°C), temperature conditions, respectively. The stress exponents and activation energies of transient creep are consistently smaller than those of steady‐state creep for both quartz and granulite/feldspar. Combined with results for transient creep of olivine that were previously obtained (Masuti & Barbot, 2021, https://doi.org/10.1186/s40623-021-01543-9), we suggest that the activation energies and stress exponents of transient creep are smaller than those of steady‐state creep for volumetrically important silicate minerals of the crust and upper mantle. Extrapolation of the estimated flow law parameters of granulite/feldspar to natural conditions suggests that transient creep may dominate during the postseismic period and lasts longer than previously thought.Plain Language Summary: Earthquakes induce intermittent deformation of the solid Earth at rates that are higher or lower than the interseismic strain rates. When an earthquake occurs, it is accompanied by a sudden slip on the fault and a rapid stress change in the lower crust leading to an evolving rock strength. Lower crustal rocks represent a complex assembly of minerals and several different micro‐mechanisms may be activated during deformation. We use experimental data for quartz and feldspar to constrain the mechanical properties of the transient creep (i.e., stress changes with strain under constant strain rate conditions or strain changes nonlinearly with time under constant stress conditions). Based on our results, we conclude that the transient creep following an earthquake may not be as short lived as previously has been thought.Key Points: Transient creep flow law parameters of quartz and granulite are determined using a Markov chain Monte Carlo method Low stress exponent of the transient creep in silicates could be due to weak dependency of dislocation density on the stress Transient creep could be dominant during the postseismic phase of the earthquake cycle Japan Society for the Promotion of Science http://dx.doi.org/10.13039/501100001691Humboldt Research Fellowship for Postdoctoral ResearchersAlexander von Humboldt‐Stiftung http://dx.doi.org/10.13039/100005156https://doi.org/10.5281/zenodo.8304793https://doi.org/10.5281/zenodo.830476

Authors’ Reply to the Discussion by Crisci et al. (2021) on “Experimental Deformation of Opalinus Clay at Elevated Temperature and Pressure Conditions Mechanical Properties and the Influence of Rock Fabric”

This is a repond to the comments raised in Crisci´s et al. paper “Discussion on “Experimental Deformation of Opalinus Clay at Elevated Temperature and Pressure Conditions ¬ Mechanical Properties and the Influence of Rock Fabric” (2021). We are pleased to use the opportunity to clarify issues related to testing procedures and interpretation in more detail.Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347Helmholtz-Gemeinschaft http://dx.doi.org/10.13039/501100001656Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum - GFZ (4217

Creep and strain-dependent microstructures of synthetic anorthite-diopside aggregates

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