A review of open software resources in python for electrical resistivity modelling

Geophysical modelling performs to obtain subsurface structures in agreement with measured data. Freeware algorithms for geoelectrical data inversion have not been widely used in geophysical communities; however, different open-source modelling/inversion algorithms were developed in recent years. In this study, we review the structures and applications of openly Python-based inversion packages, such as pyGIMLi (Python Library for Inversion and Modelling in Geophysics), BERT (Boundless Electrical Resistivity Tomography), ResIPy (Resistivity and Induced Polarization with Python), pyres (Python wrapper for electrical resistivity modelling), and SimPEG (Simulation and Parameter Estimation in Geophysics). In addition, we examine the recovering ability of pyGIMLi, BERT, ResIPy, and SimPEG freeware through inversion of the same synthetic model forward responses. A versatile pyGIMLi freeware is highly suitable for various geophysical data inversion. The SimPEG framework is developed to allow the user to explore, experiment with, and iterate over multiple approaches to the inverse problem. In contrast, BERT, pyres, and ResIPy are exclusively designed for geoelectric data inversion. BERT and pyGIMLi codes can be easily modified for the intended applications. Both pyres and ResIPy use the same mesh designs and inversion algorithms, but pyres uses scripting language, while ResIPy uses a graphical user interface (GUI) that removes the need for text inputs. Our numerical modelling shows that all the tested inversion freeware could be effective for relatively larger targets. pyGIMLi and BERT could also obtain reasonable model resolutions and anomaly accuracies for small-sized subsurface structures. Based on the heterogeneous layered model and experimental target scenario results, the geoelectrical data inversion could be more effective in pyGIMLi, BERT, and SimPEG freeware packages. Moreover, this study can provide insight into implementing suitable inversion freeware for reproducible geophysical research, mainly for geoelectrical modelling.

Modified Presplit Blast Design and its Implementation to Control Near Field Blast Vibrations

The development of urban infrastructure projects like metro rail projects in the major cities in India is one of the challenging tasks due to several site construction and operating constraints. These rapid transit systems (RTS) are conceived to minimise traffic congestion by providing commuters with fast and efficient transportation alternatives. One such project is the Phase-II of the ongoing Bangalore Underground Metrorail Project. The design and construction of the metro rail project require sound engineering judgment and field experience on envisaged strata conditions along the proposed route alignment. The important factors that govern the excavation cycle depend on Rock mass material properties, efficient blast design and construction performance. All these considerations needs to be evaluated for achieving safe, cost-effective excavation design layouts. Proper blast design and safe blasting operations play a key role in achieving good fragmentation, minimising over break and equipment downtime. Site-specific innovative methods on controlled blasting techniques are being experimented with and demonstrated to minimise the ground vibrations. The major challenge lies with the design of efficient and smooth wall blasting techniques to safeguard the old heritage buildings and other subsurface structures and utilities.

Reverse time migration with an exact two way illumination compensation

Reverse time migration (RTM) has been widely used for imaging complex subsurface structures in oil and gas exploration. However, because only the adjoint of the forward Born modeling operator is applied to the seismic data in RTM, the output migration profile is biased in terms of the amplitude. To help partially balance the amplitude performance, the RTM image can be preconditioned with the inverse of the diagonal of the Hessian operator. Yet, existing preconditioning methods do not correctly consider the receiver-side effects, assuming that the receiver coverage is infinite or the velocity model is constant. We therefore provide a comparative study aiming to give a clearer understanding on the importance of incorporating the receiver-side effects by developing a frequency-domain scattering-integral reverse time migration (SI-RTM). In the proposed SI-RTM, the diagonal of the Hessian operator is explicitly computed in its exact formulation, and the source-side wavefield and receiver-side Green’s functions are obtained by solving the two-way wave equation. The computational cost is relatively affordable when compared with the more expensive least-squares RTM. In the comparative counterpart, the diagonal of the Hessian operator is approximated by the source-side illumination. We perform two synthetic numerical examples using an overthrust model and a complex reservoir model; the final migration images were significantly improved when the receiver-side effects were accurately considered. A third application of SI-RTM on one field data set acquired from the East China Sea further demonstrates the importance of incorporating the receiver-side effects in normalizing the RTM image. Findings of this study are expected to provide a theoretical basis for improving the ability of RTM imaging of subsurface structures, thereby critically advancing the application of geophysical techniques for imaging complex environments.

Reconstruction of the late first millennium AD harbor site of Sembiran and analysis of its tradeware

The site of Sembiran on the northern coast of Bali was an important trading harbor with demonstrated intensive links to the Indian subcontinent, the Western Indian Ocean, and Mainland Southeast Asia between the second century BC and the second century AD. Using a combination of excavation and geophysical survey, we have newly mapped a dense network of subsurface structures, which we interpret to be foundations for harbor infrastructure dated to the eighth to ninth centuries AD that were subsequently covered by shoreline aggradation. An assemblage of eighth to twelfth centuries AD Chinese tradeware in dated contexts from our excavations of these shoreline structures and additional trenches further inland suggests a renewal in trade activities at Sembiran, coinciding with the growth of Chinese maritime trade in Island Southeast Asia.

Geomorphic contexts and science focus of the Zhurong landing site on Mars

As part of the Tianwen-1 mission, the Zhurong rover successfully touched down in southern Utopia Planitia on 15 May 2021. On the basis of the new sub-metre-resolution images from the High Resolution Imaging Camera on board the Tianwen-1 orbiter, we determined that the Zhurong rover landed at 109.925° E, 25.066° N at an elevation of −4,099.4 m. The landing site is near the highland–lowland boundary1 and multiple suspected shorelines2–7. Under the guidance of the remote sensing survey, the Zhurong rover is travelling south for specific in situ investigation. Supported by the six payloads on board the rover8, its initial key targets are rocks, rocky fields, transverse aeolian ridges and subsurface structures along the path. Extended investigation will aim at troughs and cones in the distance. A better understanding of the formation mechanisms of these targets may shed light on the historical volcanism and water/ice activities within the landing area, as well as the activities of the wind. These results may reveal the characteristics and evolution of the ancient Martian environment and advance the exploration of the habitability of ancient Mars.

INTEGRATED GEOPHYSICAL MAPPING OF GROUNDWATER AQUIFER FOR SPATIAL DISTRIBUTION OF GROUNDWATER DEVELOPMENT IN IPERINDO AND ITS ENVIRONS, SOUTHWESTERN NIGERIA

Assessment of groundwater potential of Iperindo area, Southwestern Nigeria was conducted by mapping spatial distribution of groundwater availability within the area and consequently locating areas of groundwater reserve to serve the community and its environs. This was achieved by integrating geophysical techniques involving landsat ETM-7 satellite data, aeromagnetic data, VLF-EM and electrical resistivity methods to delineate subsurface structures, understand the direction of groundwater flow, and detect the depth to groundwater aquifer. The result of landsat and aeromagnetic revealed some lineament intersection approximately NE-SW direction and interpreted to be potential sites for groundwater development. VLF-EM revealed geologic structures of significant hydrogeological importance at depths of 40 m to 200 m. Vertical electrical sounding (VES) confirmed high groundwater prospect in the areas with estimated depth to water table between 30 m and 100 m. The integrated results of the study revealed adequate groundwater spatial distribution for effective groundwater development in the area.

Preliminary Study of Probolinggo Active Fault in East Java Based on Gravity Method

The Gravity Method based on TOPEX satellite data is a one of geophysical method which from satellite observations. The gravity method investigate the gravitational field from one to another observation point. The principle of this method has the ability to distinguish the mass material density from its environment, so that the subsurface structure can be identified. In this research, gravity method is used to identify subsurface structures that are suspected of Probolinggo Fault and identify the rock lithology. From TOPEX we get free air anomaly and then applied the correction process to obtain Complete Bouguer Anomaly (CBA) value. The CBA value is processed interpolation to create CBA map, and then the map is filtered by butterworth to obtain regional and residual maps. The value of high gravity acceleration is 0.076 - 19.74 mGal indicating compact rocks. Meanwhile, based on the residual anomaly map, the value of smaller gravity acceleration is -0.92 - 0.9 mGal indicates lower compacting rocks with smaller mass. The gravity acceleration contrast on the residual anomaly, on the north side of fault line (0.12 mGal to 0.45 mGal) and on the south side (-0.92 mGal to -0.043 mGal), is interpreted as normal fault. Furthermore, 3D modelling shows density value less than 2 gr/cm3 we can interpret as pyroclastic fall, in between 2 gr/cm3 until 2.4 gr/cm3 is sandstone and more than 2.4 gr/cm3 is igneous rock such as andesit. 2D slicing modelling show presence the shear fault, so we can suspect this area have oblique fault with west-east direction.

Imaging Complex Subsurface Structures for Geothermal Exploration at Pirouette Mountain and Eleven-Mile Canyon in Nevada

Accurate imaging of subsurface complex structures with faults is crucial for geothermal exploration because faults are generally the primary conduit of hydrothermal flow. It is very challenging to image geothermal exploration areas because of complex geologic structures with various faults and noisy surface seismic data with strong and coherent ground-roll noise. In addition, fracture zones and most geologic formations behave as anisotropic media for seismic-wave propagation. Properly suppressing ground-roll noise and accounting for subsurface anisotropic properties are essential for high-resolution imaging of subsurface structures and faults for geothermal exploration. We develop a novel wavenumber-adaptive bandpass filter to suppress the ground-roll noise without affecting useful seismic signals. This filter adaptively exploits both characteristics of the lower frequency and the smaller velocity of the ground-roll noise than those of the signals. Consequently, this filter can effectively differentiate the ground-roll noise from the signal. We use our novel filter to attenuate the ground-roll noise in seismic data along five survey lines acquired by the U.S. Navy Geothermal Program Office at Pirouette Mountain and Eleven-Mile Canyon in Nevada, United States. We then apply our novel anisotropic least-squares reverse-time migration algorithm to the resulting data for imaging subsurface structures at the Pirouette Mountain and Eleven-Mile Canyon geothermal exploration areas. The migration method employs an efficient implicit wavefield-separation scheme to reduce image artifacts and improve the image quality. Our results demonstrate that our wavenumber-adaptive bandpass filtering method successfully suppresses the strong and coherent ground-roll noise in the land seismic data, and our anisotropic least-squares reverse-time migration produces high-resolution subsurface images of Pirouette Mountain and Eleven-Mile Canyon, facilitating accurate fault interpretation for geothermal exploration.

Seismic velocity structure of Unzen Volcano, Japan, and relationship to the magma ascent route during eruptions in 1990–1995

Subsurface structures may control the migration of magma beneath a volcano. We used high-resolution seismic tomography to image a low- P-wave velocity (Vp) zone beneath Unzen Volcano, Japan, at depths of 3–16 km beneath sea level. The top of this low-Vp zone is located beneath Mt. Fugendake of Unzen volcano, which emitted 0.21 km3 of dacitic magma as lava domes and pyroclastic flows during eruptions in 1990–1995. Based on hypocenter migrations prior to the 1990–1995 eruptions and modeled pressure source locations for recorded crustal deformation, we conclude that the magma for the 1990–1995 eruptions migrated obliquely upward along the top of the low-Vp zone. As tectonic earthquakes occurred above the deeper part of the low-Vp zone, the deep low-Vp zone is interpreted to be a high-temperature region (> 400 °C) overlying the brittle–ductile transition. By further considering Vs and Vp/Vs structures, we suggest that the deeper part of the low-Vp zone constitutes a highly crystalized magma-mush reservoir, and the shallower part a volatile-rich zone.