pure and applied geophysics最新文献

The article investigates the reliability of moment tensor (MT) inversion in time domain with use of first P-wave amplitude, a method used to determine the source mechanisms of earthquakes, across four different seismic networks. The study compares the synthetic tests results of MT inversion for two underground mining and two artificial reservoir monitoring seismic networks. The analysis was performed to assesses how consistency and accuracy of the results depend on different factors like: network configuration, events depth, velocity model, focal mechanism of event and applied noise. The findings highlight the impact of network configuration compared to other variables and data quality on the reliability of moment tensor inversion and provide insights into different factors which have to be considered to enhance MT accuracy. The significance of events depth in P-wave amplitude MT inversion and the necessity to consider velocity model influence, especially presence of high velocity gradient, is highlighted by the presented results.

The aim of the present work is to evaluate the performance of several MT-InSAR techniques based on satellite SAR data in monitoring ground deformation phenomena affecting complex scenarios such as small islands of volcanic origin. To such purpose, PS, SBAS and IPTA approaches are applied in the study of Lipari, Salina and Vulcano islands belonging to the Aeolian archipelago, southern Tyrrhenian Sea, Italy. The outcomes retrieved from each technique are then discussed in terms of intrinsic features, spatial coverage, linear trend and coherence. Moreover, the accuracy of PS, SBAS and IPTA results are evaluated by comparison with in-situ measurements from the GNSS network managed by INGV-OE and private operators considering different metrics. Experimental results show that in this case there is no preferred MT-InSAR technique in an absolute way but each of them has strengths and drawbacks that have to be taken into account in the monitoring of complex scenarios.

Changes in the integral characteristics of the global water exchange, at climatic time scales, are considered as random functions (processes). “Trajectories” obtained as the results of numerical calculations on various, from 34 to 43, climate models (participating at the CMIP-6 “historical” experiment covering the period from 1850 through 2014) are taken as realizations of these processes. Temporal variations of following annually averaged parameters are studied: (1) average evaporation from the ocean surface, (2) precipitation over the ocean, (3) “effective evaporation” from the ocean (difference “evaporation minus precipitation”, on average equal to the water transport from the ocean to land), (4) precipitation over land, (5) evaporation (evapotranspiration) from the land surface, (6) “effective precipitation” over land (or “climatic runoff”: precipitation minus evaporation), and (7) river runoff. It is shown that precipitation over the ocean and evaporation from land largely suppress the monotonous trends in the mean values of evaporation from the ocean and precipitation over land, respectively, at secular time scales. At the same time, this damping does not extend to the trends of the last few decades, which may be due to a combination of a sharp increase in global temperature with explosive volcanic eruptions that preceded this period. An analysis of the time divergence in the model trajectories of each of the components of the global water exchange, as well as the very existence of such divergences, indicates an increase in the uncertainty of processes that is not associated with anthropogenic impact on the climate system.

The Colorado River Delta is an example of a transtensional plate boundary defined by a series of en-echelon faults along the Gulf of California. Near the gulf’s mouth, the southern segment of the Cerro Prieto transform Fault (CPF) and the listric Pangas Viejas Fault (PVF) outline Montague Basin (MB), which contrasts with the pull-apart basins along the gulf’s axis. In this context, we present a series of seismic reflection profiles and known observations to illustrate the MB subsurface architecture. The imaging findings reveal concentrated deformation within the CPF and PVF regions, which exhibit a high density of faults perpendicular to the major faults. The imaging findings reveal concentrated deformation within the CPF and PVF regions, which exhibit a high density of faults perpendicular to the major faults. At the same time, in the central part of the basin, the seismoreflectors appear largely unaltered and only slightly tilted. The MB covers an area of approximately 250 km², with a length of around 90 km and a width of 30 km between the CPF to the east and the PVF to the west. Based on the data resolution, the basin's depth is believed to be over 5 km. The acoustic basement appears only on the west side of the basin, around 4 km deep. Other important observations include the Yurimori Fault running parallel to the PVF showing significant deformation at the basement level, as well as the Ometepec and La Salina Faults in the southwest oblique to the CPF, which could be the structural link with the Wagner Basin in the Gulf of California. Historical seismicity and one particular seismic profile indicate that deformation in the Indiviso fault occurred before the El Mayor-Cucapah earthquake (2010, Mw 7.2). Although the connection with the gulf’s basins is uncertain, a slight gravimetric high striking NE is observed; this is interpreted as a strike-slip zone, suggesting that the MB could become an overlap gap between marine and terrestrial basins. Our findings provide various controls for fault linkage in a transtensional setting in which continental and oceanic basins interact.

Seismic inversion has been in use for the last two decades to measure inverted impedances using an integrated data set approach. This research focuses on the application of multi-attribute seismic inversion and the geostatistical probabilistic neural network (PNN) approach for determining rock properties and litho-fluid classification in the Mehar-Mazarani Field of the Lower Indus Basin (LIB), Pakistan. The study compares five different inversion techniques, including model-based inversion (MBI), colored inversion (CI), linear sparse spike inversion (LSSI), band-limited inversion (BLI), and maximum likelihood sparse spike inversion (MLSSI). The inverted outputs, such as acoustic P-impedance (Zp), density (ρ), porosity (φ), and shale volume (Vsh), were analyzed in Paleocene and Cretaceous geological complex reservoirs to identify gas-bearing zones. The results indicated the existence of gas between 1630 and 1700 ms (ms) and corresponding depth ranges from approximately 3200 m up to 4200 m with varying thickness. Amongst the inversion techniques, MBI demonstrated greater accuracy, with inverted density volumes showing a strong correlation coefficient of 0.98 and the lowest root mean square error (RMSE) and relative error of 0.10 m/s * g/cc. A geostatistical PNN approach was employed to estimate variations in Vsh and φ within the sand reservoir. MBI again yielded more reliable results, with a strong correlation between the measured and inverted attributes. High φ and low Vsh were observed in predetermined low-impedance zones. Overall, MBI is proven to be the most accurate and reliable technique, providing clear identification of the gas occurrence. This research highlights the effectiveness of seismic inversion, particularly the application of MBI, in determining rock properties and identifying gas-bearing zones within the Mehar-Mazarani gas field.

Time-frequency analysis (TFA) technique has a powerful capacity to characterize non-stationary signals. In this paper, a highly energy concentrated TFA method, called multisynchrosqueezing-based S-transform (MSSBST), is proposed for the analysis of seismic data. Herein, we combine S-transform (ST) and multisynchrosqueezing framework by making full use of an iterative reassignment procedure to concentrate time-frequency energy in a stepwise manner. Furthermore, we derive a series of formulas about MSSBST and its inverse transform, which means that the MSSBST allows for signal reconstruction from its time-frequency representation (TFR). The numerical analysis shows that the proposed method not only can effectively enhance the time-frequency energy concentration but also can offer better performance in characterizing non-stationary signals compared with the short-time Fourier transform (STFT), ST and synchrosqueezing S-transform (SSST). Field examples further demonstrate its potential in depicting spectral anomalies related to hydrocarbon reservoir, thus, facilitating seismic interpretation.

We present the results of nearly one year of gravity recording acquired at the active caldera of Campi Flegrei (CFc). CFc is one of the three active volcanoes in the Neapolitan area (southern Italy) and is currently the most active one. In fact, the CFc is undergoing a period of unrest characterised by slow uplift of the ground, a peculiar phenomenon known worldwide as bradyseism, accompanied by seismicity and intense fumarolic emissions. Due to the increased intensity of the volcano dynamics, a permanent gravity station equipped with a gPhoneX spring gravimeter was installed to enhance the geodetic monitoring programmes. The purpose of the continuous recordings is to complement the time-lapse observations carried out periodically on networks of benchmarks, in order to continuously monitor the short-term gravity signals. We report on the various processing steps and analyses performed to obtain reliable parameters of the Earth's tides, non-tidal corrections and gravity residuals. The various methodologies employed to investigate the instrumental drift are also elucidated in depth, because it may masquerade the elusive gravity changes resulting from mass fluctuations within the volcanic and geothermal systems. Residual gravity signals, retrieved from the recordings, after reduction of body and ocean tides, polynomial drift, atmospheric, tilt and change of the Earth Orientation Parameters (EOP) effects, appear to be uncorrelated with hydrology, while they show a clear correlation with the most energetic earthquakes, that strongly characterise the current bradyseismic crisis. The residual gravity signals display peculiar trends characterized by steps or offsets (up to about 600 nm/s²) and transients in coincidence of the most energetic volcano-tectonic events (Magnitude > 2.5) and seismic swarms. The steps in the gravity residuals are likely to be of instrumental origin, while the amplitudes of the observed transients are not consistent with co-seismic or volcanological phenomena, for which there is no evidence from other monitoring techniques. Unfortunately, the lack of repeated absolute gravity measurements severely limits our ability to attribute the observed gravity variations to geological sources. From the analysis of the gravity records, reliable tidal gravity models have been derived, which will improve the accuracy of volcano monitoring by allowing a precise reduction of tidal effects for both relative and absolute gravity measurements taken in these volcanic areas.

Surface air temperature (SAT) affects both natural systems and human activities, impacting health, agriculture, energy demand, and so on. To investigate and analyze SAT over the region of interest, it is crucial to choose suitable climate models. The study commenced with the evaluation of 42 Coupled Model Intercomparison Project phase 6 (CMIP6) models’ simulations of SAT over India for annual and all four seasons (summer, southwest monsoon, northeast monsoon, and winter) during the historical period 1985 to 2014 with respect to the gridded SAT datasets obtained from the India Meteorological Department (IMD). Multi Model Mean (MMM) of 42 models was included in the evaluation. The evaluation was performed with various statistical metrics such as root mean squared error (RMSE), mean bias error (MBE), correlation coefficient (R), mean squared error (MAE), Taylor skill score (TSS), Brier skill score (BSS), and Interannual variability skill score (IVSS). By the method of estimating Comprehensive Rating Index (CRI), the top-ranking models were identified to be CMCC-CM2-SR5 for the annual and summer season, MIROC6 for the winter season, ACCESS-ESM-1-5 for the southwest monsoon, and NorESM2-LM for northeast monsoon. The novelty of this study lies in the approach of identifying the best ensemble. For each season, statistical metric-wise top-ranked models were picked to develop the best ensemble. Again, the overall ranking of the models along with the best ensemble for each season is determined by estimating CRI. It was observed that for all seasons, the best ensemble falls within the top 3 models’ category. Future projections of SAT under four shared socio-economic pathways (SSP-2.6, 4.5, 7.0, and 8.5) were also analyzed with the best ensemble obtained for each season. The results convey that, the country will witness, especially during the summer season, there will be a 1.160 °C, 1.288 °C and 2.368 °C rise in the mean SAT between historical (1985–2014) and near future (2021–2040), near and mid future (2041–2060), mid and far future (2081–2100) if the pathway, SSP5-8.5 is followed.

In the E&P industry, accurate lithology classification is an essential task for successful exploration and production. Geophysical logs provide high-resolution petrophysical properties, but core logging is expensive and traditional techniques may not accurately classify lithologies. We demonstrated a comparative analysis of six ML algorithms: k-nearest neighbor (kNN), support vector machine (SVM), decision tree (DT), random forest (RF), extreme gradient boosting (XGBoost) and artificial neural network (ANN) for the prediction of lithologies from geophysical logs. Here we analysed the wireline logs of eight wells associated with the petroliferous Lakadong-Therria formation of the Bhogpara oil field of the Assam-Arakan Basin. This formation contains eight typical lithologies, namely clay stone, sand stone, calcareous sandstone, shale, calcareous shale, carbonaceous shale, coal and limestone. Performance of the ML algorithms were evaluated through accuracy, precision, recall, F1-score and receiver operating characteristic (ROC) curve. During the training and test phases, the computed overall accuracy of the predicted ML modes exceeded 82% and 71%, respectively. The model accuracy hierarchy was ANN > XGBoost > RF > SVM > DT > kNN during training, and ANN/XGBoost > kNN > DT/RF > SVM during testing. This approach allows interpreters to select the most accurate ML model based on training phase performance. This study provided a clear insight towards generating a supplement for litholog sequence and improving the accuracy and efficiency of lithology prediction in a geologically complex petroleum reservoir using pre-received core derived litholog information at few wells.

Nowadays the salinization of freshwater resources due to seawater intrusion represent a worldwide issue. Accordingly, this study aims to identify and locate the freshwater-saltwater interface in the downstream part of the Nador wadi plain (Algeria), a coastal area characterized by a semi-arid mediterranean climate using a multi-methodologies approach including geophysical methods, hydrostatics approach, hydrochemical method, and piezometry situation. The investigation was carried out by the electrical survey and refraction seismic methods in the period of April-May 2018. Moreover, the hydrochemical and piezometry methods were used to confirm the results of the geophysical technique. The results of the present study case showed that the seawater intrusion interface is located at 420–1380 m from the shoreline. Additionally, the presence of the bedrock bulge (clay formation) at a distance ranging between 550 and 1050 m from the shoreline, plays the role of the natural hydraulic barrier for the seawater advance. The findings indicate that the identified seawater intrusion interface and the natural hydraulic barrier formed by the bedrock bulge are critical for managing groundwater resources in the Nador wadi plain. This methodology can be applied to other coastal plains worldwide to address the challenges of seawater intrusion and groundwater salinization.