pure and applied geophysics最新文献

The three-dimensional attenuation structure and frequency-dependent attenuation layered model are proposed for constraining seismic hazards and exploring the presence of an intra-crustal high conductive (ICHC) layer in the Himachal Himalaya, India. Using acceleration data recorded in the Himachal Himalaya, this work quantifies the attenuation characteristics in the form of shear-wave quality factor (Q_β). The low Q_β values (ranging 10–60) depict an aqueous fluid zone starting from a depth of ~ 11 km. This aqueous fluid identified in the study region closely resembles the ICHC layer identified by other researchers in its adjacent area. The geometry of the Main Himalayan Thrust (MHT) is explored in terms of the obtained attenuation model, which suggests the absence of a ramp structure of MHT below the Main Central Thrust (MCT) in the study region. The presence of an aqueous fluid zone identified at 11–20 km depth may be one of the possible reasons for high seismicity in the Himalayan seismic belt. This work also suggests a frequency-dependent shear wave attenuation (Q_β(f)) model of the form Q_of ⁿ for six different layers of 5 km thickness each. The obtained layered model suggests low Q values, i.e., (49 ± 16) f ^(0.60±0.12) for layer 3 (10–15 km) and (27 ± 11) f ^(0.99±0.18) for layer 4 (15–20 km), corresponding to the aqueous fluid in the study region. The obtained Q_β(f) model appraises the region’s seismic hazard by describing the heterogeneity and tectonic activity level in the present study region.

This study mainly focuses on the relationship between Total Totals index (TTI) and other thunderstorm related parameters over Kerala region, India. This study has been carried out on thunderstorm days for the pre-monsoon season during the time period 2017–2022. The thunderstorm related parameters such as lightning, K Index (KI), Humidity Index (HI), Total precipitable water (TPW), Rainfall to Lightning Ratio (RLR), Maximum updraft speed (MUS), Lifted Index (LI), Convective available potential energy (CAPE), Dew point depression (DPD), Cloud fraction (CF) and Temperature Difference (TempDiff) have been considered for the analysis. For a better understanding between TTI and thunderstorm indices, two distinct regions D1 (10.8°-12.4° N, 75.2°-76.8° E) and D2 (9.2°-10.8° N, 76.2°-77.8° E) of Kerala state were selected as the study region. The results reveal that D2 region (135 days) showed more lightning activity than D1 region (88 days). A significant positive trend has been seen between TTI and KI parameters. RLR & TPW parameters showed a significant negative trend with TTI parameter. MUS exhibits positive trend whereas LI showed negative trends with TTI on lightning days over both regions. This study also shows that the CAPE and DPD showed an increasing trend with TTI during lightning days. We also utilized Random forest technique to study the relationship between various thunderstorm related parameters.

Curie depth plays an important role in the study of geological structures and resource exploration. Conventional methods usually employ a fixed window size for estimation, often resulting in significant inaccuracies. To overcome this deficiency, a new adaptive window Curie depth calculation approach is proposed, which can automatically select the optimal window size across a range of diverse geological conditions to achieve a more precise Curie depth. We validated the new approach using synthetic data, demonstrating that the average error of the bottom depth of the model was reduced compared to traditional methods. Subsequently, we applied the new method to real magnetic data from the South China Block, and a new Curie depth result was obtained and verified using measured ground heat flow data. The mean square error between the derived results and the measured ground heat flow was found to be lower than that of the Curie depth inversed by previous researchers. The adaptive window Curie depth calculation method presented herein exhibited high adaptability and accommodated various geological features. For the South China Block, the Curie depths exhibited a smooth and continuous pattern in stable regions such as cratons, while displaying a distinct uplift in the junction region between fault zones and blocks. This method can not only accurately capture the Curie depth variations across large areas, but also vividly highlight subtle changes in the Curie depth within smaller regions, demonstrating the superiority of this new approach.

This study examines the structure of the Lofoten Anticyclone, located in the Lofoten Basin of the Norwegian Sea. The high-resolution ROMS model is used for hydrodynamic modeling of the Lofoten Basin circulation. The dynamics of the Lofoten Vortex are investigated using the Lagrangian methods, where trajectories of passive tracers advected by the model velocity field are calculated, and Lagrangian indicators are computed for the studied region. Lagrangian markers initially located both in the core and on the periphery of the Lofoten Vortex are considered, showing different behaviors. Lagrangian markers in the core move along closed trajectories with angular velocities depending on their distance from the eddy's center. Those initially on the periphery form a series of S-shaped folds and twists, entering and exiting the eddy. We refer to this process as “ventilation of the vortex periphery”. We demonstrated that particles leave the core and periphery of the eddy intermittently rather than uniformly over time, and the statistics of this process are analyzed. Additionally, it was found that the center of the Lofoten Vortex not only drifts cyclonically at an average speed of 3.8 cm/s but also oscillates in the horizontal plane, with the amplitude increasing in the eastern part of the Vortex’s movement area.

For the statistical characterization of the random heterogeneity of the solid earth medium, we have measured the distribution of fractional fluctuations of well log data after removing the slowly varying background variation. The well log data used are P- and S-wave velocities and mass density acquired in Japan: three data sets for the thick sedimentary layers of the Kanto Plain and two data sets for the Kujyu volcanic area of Kyushu. The estimated kurtosis is much greater than 3 for most cases, which is difficult to explain with a normal distribution. This suggests that the random fluctuations should be looked at from a broader perspective. We note the fact that the generalized central limit theorem leads to stable distributions, which are broad enough to include normal and Cauchy distributions as special cases. When the stable, normal, and Cauchy distributions are applied to the histograms of the observed fractional fluctuations, the stable distribution is found to be the most appropriate among the three distributions in most cases, where the stability parameter (alpha) ranges from 1.5 to 2. These case studies demonstrate that the stable distribution faithfully describes the thick tails of the observed fractional fluctuations as the result of a geological sedimentation process without removing them as outliers.

Rupture dynamics along a relatively wide fault zone intersecting an underground tunnel is studied in the framework of recently developed damage-breakage rheological model. The propagating rupture produces rock damage and granulation in the process zone ahead of the rupture front, where intense torsion is simulated. It also produces an out-of-fault damage zone, of which the volume is calculated and compared with analytical predictions using the point source approximation. Interaction between propagating rupture and tunnel significantly enhances stresses around the tunnel leading to its failure with significant implosive component. Tunnel failure may occur with a certain delay after the rupture front passed, depending on the initial tunnel strength. This time delay is defined by the time needed to accumulate damage in the rock mass around the tunnel. In some cases such tunnel failure maybe interpreted as an independent implosive seismic event. Model results provide an insight into the near- and intermediate fields of seismic radiation produced by seismic sources close to and intersecting an underground tunnel. Energy dissipation in the process zone in front of the propagating rupture due to the damage–breakage mechanism significantly affects the S-wave radiation in the direction of the rupture propagation. On top of that the tunnel failure process, especially if it is surrounded by relatively weak and damaged rock, significantly reduces S-wave radiation also in the directions normal to the fault zone.

Ground penetrating radar (GPR) has been widely used to assess asphalt and pavement, especially in quality testing for newly constructed roads. However, its usage has been limited in regard to aged roads. Thus, this study focuses on the applicability of GPR to extract diverse information regarding structure, thickness, and various conditions, including the moisture content of an aged road section that has undergone repeated renewals. First, two methods were employed to calculate the thickness and dielectric values; the reflection amplitude and ground truth methods. The analysis was done by RADAN 7 software. Based on the findings, the average error of thickness on the same day between continuous GPR and the core data were 2.87% and 8.72%, respectively. Second, dielectric analysis of three structural units was performed under different moisture conditions. As a result, the average dielectric values of macadam (3, 3.3, and 4), surface asphalt layer (4, 7.06, and 8.31), and cement-treated base (4.83, 10.88, and 11.88) were determined under dry, medium-wet, and wet conditions, respectively. The volumetric water difference (f) within the pavement was also estimated. As for the asphalt, macadam, and cement-treated base, the difference in the volume fraction of water (f) was 0.06, 0.01, and 0.1, respectively, under dry and wet conditions, and 0.04, 0.004, and 0.09, respectively, under dry and medium-wet conditions. Overall, the findings demonstrate that reasonably accurate assessments of the pavement thickness, structure, dielectric values, and amplitude of aged roads can be achieved by using a GPR survey under various conditions.

This study examines the impact of storm surges, infragravity waves, wider area seiches and natural harbour oscillations (harbour seiches) on port operations in the Baltic Sea, with a particular emphasis on the Port of Klaipėda, all during the severe storm that occurred from November 22–24, 2023. The study examines the interplay between meteorological factors, such as changes in air pressure and wind speed and direction, and the coastal geography of the area. Wind speeds during the storm reached a maximum of 29.7 m/s, and air pressure dropped for f ~ 50 hPa, with a corresponding sea level rise of approximately 40 cm due to the combined effects of storm surges and long waves. The research findings indicate that it was precisely long waves, which were generated offshore and amplified by the port's distinctive resonance characteristics and coastal topography, that were the primary cause of operational disruptions, creating hazardous conditions that necessitated the closure of the port. The port's elongated and narrow inlet played a pivotal role in the amplification of these waves, rendering it particularly vulnerable to resonance-induced oscillations. The research yielded several key findings, including identifying long waves (long ocean waves, wider area seiches, harbour seiches, and infragravity waves) with periods ranging from 12 to 13 h to 2–4 min, which posed significant risks to vessels moored at the port. Furthermore, the occurrence of simultaneous sea level fluctuations between Klaipėda and Karlshamn indicated the presence of seiches with period of 12,4 h across the Baltic Sea, thereby further complicating port operations. These results underscore the critical need for improved forecasting and mitigation strategies to enhance the safety and efficiency of port activities during severe weather events.

Large short-term changes in air temperature affect the functioning of living organisms in the environment and human activities. For this reason, a study of extreme positive and negative 10 min temperature changes and their causes related to atmospheric circulation was undertaken. Air temperature data for January in the period 2001–2017 in southern Poland (Sosnowiec) were analysed. Extreme ultra-short-term temperature changes were considered to be values less than or equal to 0.1 percentile (extreme temperature drops) and greater than or equal to 99.9 percentile (extreme temperature increases). The extreme ultra-short-term negative air temperature change was − 7.2°C/10 min, while the positive change was + 3.5 °C/10 min. Extreme ultra-short-term negative air temperature changes in southern Poland in January occur most frequently with the advection of air from the west (43% of cases), the inflow of maritime Polar old (transformed) air over Poland (25% of cases), western cyclonic (Wc) and north-western cyclonic (NWc) situations, a total of 34% of cases), the passage of the atmospheric front over southern Poland (59% of cases), especially a cold front (68% of cases with a front). Extreme ultra-short-term positive changes of air temperature in southern Poland in January occur most frequently with the advection of air from the south-west (43% of cases), the inflow of continental Polar air (42% of cases), anticyclonic situations (72% of cases), the occurrence of a high-pressure wedge over southern Poland (26% of cases), situations without atmospheric front (80% of cases). The direction of advection plays a secondary role in determining the values of extreme short-term changes in air temperature. More important is the speed of the influx of this air mass. Extreme ultra-short-term temperature changes are partly explained by circulation conditions. Rapid temperature changes can also occur as a result of small-scale processes in the atmosphere.

Diffracted wavefield carries high-resolution information about subwavelength geological structural elements crucial for imaging small-scale subsurface discontinuities. However, the presence of strong reflection often obscures weak diffraction, limiting the effective use of diffraction in depicting detailed small-scale structures. To obtain a high-resolution diffraction image, we present a novel two-phase diffraction separation method that combines pattern-based method and energy attenuation function of stationary reflection in migrated dip-angle gathers. In the first phase, the pattern-based method utilizes pattern operator to characterize non-stationary features of reflection in dip-angle gathers and effectively eliminates the reflection outside the stationary point. In the second phase, the energy attenuation function based on dip angle is used to further attenuate residual reflection near the stationary point. The conflicting dip angle often reduces the performance of dip-based energy attenuation methods. We introduce the covariance rate criterion to adaptively adjust the conflicting dip angle, so that the energy attenuation function can more accurately attenuate the residual reflection. The numerical experiment conducted on classic Sigsbee 2B model validates the efficacy of the proposed method in suppressing strong high-slope reflection while preserving details of small-scale faults and scatterers. The real data application demonstrates the performance of the method to highlight deep fractures, presenting additional potential reservoir-related structural insights.