International Journal of Geophysics

Two hundred km of 2D seismic survey was carried out at the Lesser Himalayan Thrust Belts in Dailekh district, western Nepal. The main motivation is to elucidate the geologic relationship between the known oil and gas seeps, subsurface structure, and stratigraphy in the area. This is a challenging task which is from its extreme structural and geological complexity such as thrust faulting, tight folding, steep dip layers, and strong lateral variations in seismic velocity. Seismic data were acquired with SERCEL 428XL system and processed by GEOEAST computer software. In order to increase signal-to-noise ratio (SNR), suppress interference, and search for optimum acquisition parameters, a series of comparative tests on the different charge depth and size, group interval, CDP fold, geophone array, and single high-sensitivity geophone were conducted. We also tested 2S3L (two lines shooting and three lines receiving) wide line profiling. The results indicate that single hole with charge depth of 12 m, 4-16 kg charge size (less charge size for the densely populated areas), single high-sensitivity geophone, and 1S2L wide line profiling with 132 folds are the optimum acquisition parameters. On the basis of comparative process experiment, data processing workflow consisting of data preparation, prestack denoising, amplitude compensation, deconvolution, tomography static correction, velocity analysis, residual static correction, CRS stack, poststack migration, prestack time migration (PSTM), and prestack depth migration (PSDM) was selected. Maybe affected by problem of conflicting dip in complex media, CRS stack section does not show satisfactory geological characteristics. PSTM profile has moderate signal-to-noise (S/N) ratio; the shallow, medium, and deep continuous reflections can be observed in section. More details of the geological structures can be observed in PSDM section, especially in medium and shallow layers (less than 3000 ms or 4000 m), but PSDM method is more expensive and highly time consuming than that of CRS stack and PSTM. So, the PSTM section can be reasonably used for geological interpretation. By reference to field mapping, thrust characteristics, and MT data, the final interpretation to the PSTM section identified the interfaces of 6 geological units (Paleoproterozoic Nabhisthan Fm., Paleoproterozoic Dubidanda Fm., Neogene to Late Cretaceous Surkhet group, Late Carboneferous to Early Cretaeous Gondwana group, Mesoproterozoic Upper Lakharpata group, and Lower Lakharpata group) and delineated Main Boundary Thrust (MBT), Ramgarh Thrust (RMT), Padukasthan Thrust (PT), and Dailekh Thrust (DT). The bottom of Surkhet group which is our top target zone is about 4250 meters deep.

The study area includes an area between 6° to 8°N and 11° to 15°E. Geologically, it belongs to Precambrian basement (granites, gneisses), Proterozoic, and Archean (volcanic) series, showing the main heat sources of Cameroon. The purpose of this study deals to analyze and interpret the EMAG2 magnetic data in the Adamawa area using various advanced processing techniques. Thus, the mapping and depth estimation of underground structures are realized. The analysis of aeromagnetic map of the reduction to equator (RTE) in Adamawa area reveals rapidly evolving subsurface geological presented its lithological and structural. In the same, the power spectrum-processing tool clearly emphasizes shallow and deep underground heat sources. Two magnetic source location methods (source parameter imaging and analytical signal) are used to characterize of the source. The estimated magnetic source depths from source parameter imaging (SPI) are between 0.3 km and 22 km. The analytical signal ranges from 0.2 km to 31 km. In addition, the comparative study of 2D magnetic modelling showed that the basement is affected by the faults in the main directions of N-S, NE-SW, NW-SE, and WNW-ESE. The resulting structural map based on the tectonic map of Adamawa magnetic basement is a document that can simplify future hydrological and geothermal exploration.

Tiris Village, Lamongan Volcano complex is an area that has geothermal potential. The existence of geothermal potential in this study was identified using the gravity method combined with remote sensing methods. Remote sensing method is used to obtain a map of the distribution pattern of the soil surface temperature and a map of the continuity of the straightness and fault structure. The data used in the remote sensing method is secondary data in the form of Landsat-8 imagery and DEM SRTM 1 arc. Processing of the soil surface temperature map was obtained by using thermal infrared processing NDVI. The form of continuity of the straightness or fault structure is obtained by processing Landsat-8 multispectral image data in the form of 567 band composite and DEM SRTM data form of 3D topographic modeling. The data from the composite band 567 was reviewed visually using a 3D topographic model. The gravity method is the main method in this research because it is used to obtain the residual Bouguer anomaly distribution. The residual Bouguer anomaly data was obtained by using the moving average through spectrum analysis. The residual Bouguer anomaly distribution can be used for qualitative interpretation of the distribution of the earth’s gravitational acceleration at the measurement location. The quantitative interpretation of the gravity data is based on the surface density estimation graph using the Parasnis method and 3D inversion modeling, using residual Bouguer anomaly data. The results of 3D inversion modeling provide four types of subsurface rock layers based on the density distribution value, namely, the first rock layer  g/cm³, the second rock layer  g/cm³, the third rock layer  g/cm³, and the fourth rock layer  g/cm³. The third rock layer is assumed to be reservoir rock and is estimated to be at a depth of 500–800 meters below the measurement point. The fourth rock layer is assumed to be intrusive igneous rock, which penetrates dominantly in the middle of the measurement location, which is oriented southwest, south to north, which is indicated by the high anomaly continuity on the regional Bouguer anomaly map. Based on the results of 3D inversion modeling and spectrum analysis of the average depth of the regional Bouguer anomaly, it is found that the intrusive rock layer is thought to be at a depth of 350 meters below the measurement point.

Several natural disasters such as lightning, flood, fire, epidemics, and landslides frequently occur in the Himalayan region, of Nepal. The altitude of this region ranges from 59 m to “8848.86 m”—the height of Mount Everest—along with a distance of just 160 km. As a result, there is a considerable (i.e., nearly 95°C) variation in temperature in the region. Moreover, Nepal has a heterogeneous topography. All these features influence various natural disasters including lightning activity. This paper is aimed at analyzing the variations of lightning within and across the years from January 2011 to December 2021—a total of 11 years. For this, the data were taken from the Disaster Risk Reduction (DRR) portal of the Ministry of Home Affairs (MOHA). The analysis showed that there were no lightning events in November, and the lightning density was higher in the premonsoon period of study in this region. It also showed that the number of injured people is about thrice the death of the people due to the lightning. The null occurrence of lightning in November in the Himalayan region is a contribution novel to this field.

This paper deals with recurrent events’ (REs’) impacts on foF2’s diurnal variations at Dakar station (lat: 14.8° N, long: 342.6° E, Senegal) during solar cycles 21 and 22. Data were analyzed by taking in account solar phases and seasons influence. REs generate positive storms in all seasons and on all solar phases and also weak negative storms in all seasons and at minimum and maximum solar phases. The results suggest on the one hand that vertical drift due to strong electrojet currents cannot be considered an important mechanism of positive storms and on the other hand that prereversal enhancement (PRE) phenomenon (with a delay due to Dakar station position) and equatorward thermospheric neutral winds circulation (TNWC) contribute mainly to their generation. The intense positive storms, which appear mostly at night, are observed in decreasing phase and in spring which correspond, respectively, to the solar phase and the season of maximum REs occurrence. Then, positive storms’ strength presents seasonal and solar cycle dependence and it is related to REs days occurrence. REs’ negative storms strength are linked directly with REs days’ occurrence on solar phase scale, while they are not on seasonal scale.

In the last 10 years, the community of La Mesa de Macaracas (central Panama) has experienced considerable aftershocks due to earthquakes of magnitudes up to 5.7 Mw. Although most of the community consists of single-storey houses, the agricultural development in the region has led to multistorey building projects. To determine whether the characteristics of the soils could affect future construction in the study area, 16 stations were established to measure ambient vibrations and estimate the predominant frequencies and their corresponding ratio peaks through the ambient noise spectral ratio technique. According to the site class established by the Japan Road Association, the results revealed the existence of (a) soft soil with a range of predominant frequencies between 0.7 and 1.6 Hz, (b) medium soil with a range of predominant frequencies between 2.1 and 2.4 Hz, and (c) hard soil with a range of predominant frequencies between 2.6 and 2.9 Hz. In the first type (soft), the resonance effect could affect constructions of between 6 and 14 storeys with ratio peak values (amplification factor) in the range of 2.1 and 4.3, while in the second and third types (medium and hard soils), buildings of between 3 and 5 storeys could be affected, with ratio peak values (1.5–2.0) except at the SS-9 station. These results were complemented with the values obtained in four seismic soundings carried out at the site.