Shallow Source Research Articles

Assessment of the Potential Use of Shallow Geothermal Energy Source for Air Heating and Cooling in the Kingdom of Saudi Arabia

A large part of the total energy consumption in buildings in the Kingdom of Saudi Arabia (K.S.A.), is devoted to air cooling. This leads to high electricity costs for residents and a high amount of equivalent CO2 emissions. The work presented in this paper aims at evaluating and applying shallow geothermal energy for cooling and heating to reduce cost and environmental issues in the Kingdom. The system is based on the earth-air heat exchanger (EAHE) equipped with an air circulation fan. In this study, six cities have been selected; Madinah city, where our university is located, and five other cities representing five different climatic zones. A new parameter called “geothermal percentage” is proposed to calculate the ratio of geothermal energy to the cooling/heating total load. It has been shown that the proposed system covers part of the cooling load and the total heating needs for almost all the country’s territory. However, both heating and cooling needs can be fulfilled by the EAHE for few cities such as Guriiat and Khamis, characterized by a moderate climate.

Aeromagnetic anomalies and magnetic domains of the Jalisco Block, western Mexico

The Jalisco Block (JB) in western Mexico has been considered as a margin terrane being detached from the North American plate along the Tepic-Zacoalco rift and Colima graben. In this study, an aeromagnetic analysis of the JB and surrounding areas is performed applying a series of geophysical filters and VOXI inverse model. The JB is characterized by two aeromagnetic domains (AMD). AMD-Ia located throughout the south-central section that borders the continental margin is characterized by positive magnetic anomalies extending from the Armería river to Banderas Bay. The AMD-Ia corresponds to the Puerto Vallarta batholith emplaced in the late Cretaceous. The AMD-IIa in the northern section is marked by negative magnetic anomalies over volcanic and volcano-sedimentary rocks, extending to the southern Sierra Madre Occidental. We propose that JB tectonic boundaries correspond to the aeromagnetic AMD-Ia eastern limit and AMD-IIa northern limit. Estimated depths from the radially average power spectrum for deep magnetic sources in the AMD-Ia are in the range of 5.4 km, and for shallow sources from 0.8 to 1.2 km. For AMD-IIa depths are 10.45 km for deep sources and 0.13 km for shallow sources. Depths for deep sources from the Euler deconvolution for the AMD-Ia range from 3.3 to 4.5 km and from 3.5 to 4.9 km for the AMD-IIa. Shallow source depths in the AMD-Ia are 0.2–0.3 km and near surface for the AMD-IIa. The integrated analysis shows five aeromagnetic domains, two associated with the JB and three with the surrounding areas. The VOXI inverse model allows to estimate the dimensions and location of magnetic sources in the reduced to the pole and upward continuations.

Classification of volcanic tremors and earthquakes based on seismic correlation: application at Sakurajima volcano, Japan

SUMMARY Classification of volcanic tremors and earthquakes is an important part of volcano monitoring. Conventional classification technique relies on visual characterization of the amplitudes, frequency, or duration of seismic signals. In some cases, such classification is difficult to be maintained continuously, especially during high eruptive activities. In the present study, we develop a classification technique based on analyses of seismic wave correlation. The technique is based on a measure of spatial coherence using the distribution width of eigenvalues from the seismic covariance matrix that is referred to as ‘spectral width’. We use the spectral width characteristics to extract the frequencies where the seismic signals are the most spatially coherent. We analyse 6-month continuous seismic data at six seismic stations deployed on Sakurajima volcano, Japan. The classification is performed every 10 min to recognize volcanic tremor and B-type earthquakes, both of which show unclear onsets and are dominant at around 1–4 Hz. Their frequencies of high spatial coherence are different from each other, providing a basis for automatic classification of both types of seismic events. Our classification results show that an increase in seismic activity, particularly volcanic tremors, occurred during high eruptive activity and is well matched with the events that are routinely determined by the Japan Meteorological Agency (JMA) based on visual examination of the data. We discuss the volcanic activities by combining our classification results with those from detections and location methods based on seismic correlation. Most of the source locations of volcanic tremor and B-type earthquakes are distributed at the same region with depths of less than 4 km beneath the active craters, which are almost consistent with the source locations of explosion earthquakes and B-type earthquakes determined from P-wave onsets in the previous studies. Also, the distribution of horizontal locations is spatially elongated at shallow depths above a dyke that is inferred to extend from Aira caldera at a depth of 7–9 km. We obtain deep and shallow sources for the tremor that occurred before and after an explosive eruption, respectively. We also obtain shallow sources beneath the active crater during a continuous tremor that accompanies increasing eruptive activity. The source locations of the classified volcanic tremor and B-type earthquakes may represent the movement of magma and gas from the shallow magma chamber at 5 km depth to the active craters.

The distribution of Fe across the shelf of the Western Antarctic Peninsula at the start of the phytoplankton growing season

The Western Antarctic Peninsula (WAP) is a rapidly changing region with receding sea-ice cover. This region generally has increased phytoplankton productivity on the continental slope with a decrease observed in off-shelf waters located further northward. This study aims to improve the understanding of the distribution of iron (Fe) in this climatically important oceanic region during early sea-ice retreat, as well as the impact of receding ice cover on Fe concentrations and the importance of Fe and its sources at the beginning of the phytoplankton growth season. Five ocean transects were sampled along the Palmer Long Term Ecological Research (Pal-LTER) grid with an additional oceanward extension to access off-shelf waters during the austral spring (October and November) of 2014. High Fe inputs into the entire water column from ice melt as well as from sediments increased dissolved Fe (DFe) and total dissolvable Fe (TDFe) concentrations across the shelf (off-shelf DFe: 0.38 ± 0.30 nmol/L and TDFe: 2.23 ± 2.95 nmol/L versus shelf DFe: 1.54 ± 1.38 nmol/L and TDFe: 19.47 ± 23.82 nmol/L). The combination of meteoric meltwater and shallow sedimentary sources is strongest over the shelf and increased landward towards the WAP. Additionally, a winter sea-ice formation signature was detected in inner shelf waters that appeared to contribute to DFe concentrations. Relatively warm Circumpolar Deep Water (CDW) that flows onto the shelf through troughs is likely modified by non-reductive sedimentary input of Fe into the water column. The increase in Fe concentrations in WAP waters in early spring could trigger enhanced phytoplankton productivity across the shelf, although the highest productivity levels were observed in off-shelf waters, likely related to improved light conditions following receding sea-ice cover. The relatively high productivity levels in WAP off-shelf waters are presumably caused by two factors: (1) supply from below, and (2) the transport of Fe from the shelf to the off-shelf region. However, 80–90% of Fe introduced into shelf waters was removed from the upper water column prior to reaching off-shelf waters, reducing the influence of the coastal Fe source. Low concentrations of DFe (0.24 ± 0.26 nmol/L) in off-shelf waters (upper 100 m) of the WAP coincide with relatively elevated chlorophyll a concentrations (0.66 ± 0.56 μg/L), implying that uptake of available DFe had already occurred prior to sampling. Our results imply that the horizontal supply of DFe from the shelf as well as total DFe supply into the surface mixed layer might not be sufficiently high to support productivity in the off-shelf waters of the WAP, underlining the development of an Fe deficit early in the growth season.

There is more Wrangellia — magnetic characterization of southern Alaska crust

In southern Alaska, Wrangellia-type magnetic crustal character extends from the Talkeetna Mountains southwest through the Alaska Range to the Bristol Bay region. Magnetic data analyses in the Talkeetna Mountains showed that there are mid-crustal differences in the magnetic properties of Wrangellia and the Peninsular terrane. After converting total field magnetic anomaly data to magnetic potential, we applied Fourier filtering techniques to remove magnetic responses from deep and shallow sources. The resulting mid-crustal magnetic characterization delineates the regional magnetic potential domains that correspond to the Wrangellia and Peninsular terranes throughout southern Alaska. These magnetic potential domains show that Wrangellia-type crust extends southwest to the Iliamna Lake region and that it overlaps the mapped Peninsular terrane. Upon reconsidering geologic ties between Wrangellia, Peninsular, and Alexander terranes, we conclude that Peninsular terrane is part of what we here call Western Wrangellia. Western Wrangellia contains the Lower Jurassic Talkeetna volcanic arc and is similar to Wrangellia of the Vancouver Island area, Canada (Southern Wrangellia), which contains the Lower Jurassic Bonanza volcanic arc. Others have previously made this correlation and proposed that the Talkeetna arc-bearing part of southern Alaska was displaced from the Bonanza arc-bearing part of Canada. We generally agree and propose that about 1000 km of dextral displacement along ancestral Border Ranges fault segments and other faults of south-central Alaska separated Western Wrangellia from Southern Wrangellia. We think this displacement was mostly in the Late Jurassic and earliest Cretaceous, perhaps between about 160 and 130 Ma.

Parallel Algorithms for Solving Inverse Gravimetry Problems: Application for Earth’s Crust Density Models Creation

The paper describes a method of gravity data inversion, which is based on parallel algorithms. The choice of the density model of the initial approximation and the set on which the solution is sought guarantees the stability of the algorithms. We offer a new upward and downward continuation algorithm for separating the effects of shallow and deep sources. Using separated field of layers, the density distribution is restored in a form of 3D grid. We use the iterative parallel algorithms for the downward continuation and restoration of the density values (by solving the inverse linear gravity problem). The algorithms are based on the ideas of local minimization; they do not require a nonlinear minimization; they are easier to implement and have better stability. We also suggest an optimization of the gravity field calculation, which speeds up the inversion. A practical example of interpretation is presented for the gravity data of the Urals region, Russia.

Proportions, Timing, and Re-equilibration Progress during the 1959 Summit Eruption of Kīlauea: an Example of Magma Mixing Processes Operating during OIB Petrogenesis

AbstractPetrographic and chemical analysis of scoria samples collected during the 1959 Kīlauea summit eruption illustrates the progress of thermal and chemical homogenization of the melts, and the gradual growth and/or re-equilibration of olivine phenocrysts, over the course of the eruption. Glass compositions show that thermal equilibration was largely complete within the span of the eruption, whereas chemical homogenization was a work in progress. The olivine phenocryst population, known to contain conspicuous antecrystic components, is also hybrid within the euhedral population. The bulk of the olivine reached the level of the erupting magma on November 18–19, 1959. Zoning patterns in olivine phenocrysts show that initially unzoned grains developed normal zoning by the end of the eruption. Reverse zoning in relatively Fe-rich olivine phenocrysts (interpreted as cognate to the stored magma) was progressively eliminated from November 21 to December 19, 1959, by diffusive re-equilibration between crystals and melt. Toward the end of the eruption, the only olivine composition in direct contact with the melt was Fo84–86, with the original rim compositional heterogeneity gone in 4–5 weeks’ time. Activity in December 1959 differed from that in November, as high fountaining events were more closely spaced and almost all samples were picritic, with bulk MgO ≥16·5 wt%. Three different levels were in play during the 1959 eruption: a deep source for high-MgO melts and forsteritic (Fo87–89) olivines, an intermediate source for the bulk of the stored magma, and a shallower source for the most differentiated magma. This model is consistent with geophysical, petrological and chemical observations. Comparison of the 1959 eruption with results from older explosive deposits suggests that stored and recharge melts and olivine from the deeper parts of Kīlauea’s plumbing are similar in composition to those observed or inferred in the 1959 eruption, so they behave similarly during extrusive and explosive periods alike.

The Spatio-temporal Tectonic Condition and Microzonation Map of Malang Region after the 2021 M6.1 Malang Earthquake for Disaster Risk Mitigation

The M6.1 earthquake which hit Malang and its surroundings in 2021 resulted in fatalities and over 10,400 damaged houses. Several seismicity studies have been carried out for Malang region, but no specific studies have implied the M6.1 Malang earthquake yet. This study addresses such gap by investigating the Spatio-temporal b-value of Gutenberg-Richter Law and generating the microzonation maps of spectral acceleration by considering the effects of the M6.1 Malang earthquake. The earthquake data compiled from the national and international earthquake catalogs were homogenized into a moment magnitude scale. The b-value analysis was calculated using the Maximum Likelihood method and spatio-temporal mapping. Several ground motion prediction equations (GMPEs) were selected for subduction and shallow crustal earthquake sources to generate probabilistic seismic hazard analysis (PSHA). PSHA was conducted using the 2% probability of exceedance in 50 years. The results show that the b-value after the M6.1 Malang earthquake still tends to decrease, indicating a relatively-high stress level which accommodates the potential for large earthquakes in the future. The microzonation maps for Malang region show that the southern part of Malang has a higher spectral acceleration value than the others. Therefore, these findings can be considered in the future disaster mitigation plan.

Geochemical characteristics and possible sources of crude oils in the Baiyun deep-water area of the Pearl River Mouth Basin, South China Sea

Two classification methods, the distribution of biomarkers and the alternating least squares (ALS) chemometric analysis were used to investigate the genetic characteristics of oils collected from the Baiyun deep-water area of the Pearl River Mouth Basin in the South China Sea. Results of the two methods were generally consistent that most of the oils were originated from the shallow lacustrine source rocks, but oils from the West Sub-Sag (WSS) and the South Sub-Sag (SSS) have a distinct geochemical characteristic with low abundances of bicadinanes and oleanane, and relatively lighter δ13C value (<−28.0‰). The ALS chemometric analysis can quantitatively determine the sources of the oils. It shows that mixing has commonly occurred between the oils, and three end-member oils were identified (i.e., EM1, EM2, and EM3), which were derived from the semideep–deep Wenchang Formation source rocks that are characterized by a predominance of C27 steranes and low concentrations of bicadinanes and oleanane, the shallow lacustrine Enping Formation source rocks in the Main Sub-Sag (MSS) that are rich in bicadinanes but depleted in oleanane, and the shallow lacustrine Wenchang and/or Enping formations source rocks in the East Sub-Sag (ESS) that have a relatively high abundance of bicadinanes, a moderate content of oleanane, and a predominance of C29 steranes, respectively. The oils from the Panyu Low Uplift (PLU) are dominated by >83% of EM2 oil. Oils from the SSS and WSS are dominated by EM1 oil (68.0%–93.1%). Oils from the ESS and eastern part of the MSS (E-MSS) are mixed oils consisting mainly of EM2 and EM3 oil, with an increasing proportion of EM3 moving from the E-MSS to central ESS. The maturity of the oils was assessed based on diamondoid indices, and oils from the PLU have the highest maturities (1.43%–1.59% Rc), whereas oils from the SSS have the lowest maturities (1.23%–1.25% Rc), corresponding to the different maturities of their source rocks. The semideep–deep lacustrine oils discovered in the WSS and SSS highlight the hydrocarbon generation potential of these types of source rocks in the Wenchang Formation, where further oil exploration should be focused.

In Situ Bioremediation of a Chlorinated Hydrocarbon Plume: A Superfund Site Field Pilot Test

The North Railroad Avenue Plume, discovered in 1989, contained chlorinated solvent groundwater plumes extending over 23.5 hectares (58 acres) and three hydrostratigraphic units. The source contaminant, tetrachloroethene, stemmed from release at a dry cleaner/laundromat business. The anaerobic biodegradation byproducts trichloroethene, isomers of dichloroethene (DCE), and vinyl chloride were detected in groundwater samples collected prior to remedial action. The impacted aquifers are the sole source drinking water aquifers for the communities near the site. Following the remedial investigation and feasibility study, the selected alternative for full-scale remedial action at the site was enhanced reductive dichlorination (ERD) focused on four treatment areas: the shallow source zone, the shallow hotspot area, the shallow downgradient area, and the deep zone. Pilot testing, which was conducted in the source zone and hotspot areas, is the subject of this paper. The primary objectives of the pilot test were to obtain the necessary information to select an ERD treatment formulation, dose, and frequency of dosing for use during full-scale remedial action, as well as to refine the site’s hydrogeologic conceptual site model and design parameters. Four (4) test cells, each of which contained well pairs of injection and downgradient extraction wells, were used to test ERD bio-amendment formulations: ethyl lactate, dairy whey, emulsified vegetable oil (EVO), and a combination of EVO and a hydrogen gas infusion. A conservative tracer, bromide, was added to the recirculation flow to record tracer breakthrough, peak, and dissipation at extraction wells. The results of these dipole tracer tests were used to reassess the hydraulic conductivity and hydrodynamic dispersity used in the remedial design. In addition to water quality analyses of contaminants and substrates, groundwater samples were also analyzed for biological analyses before, during, and after the addition of bioamendment. Analyses of phospholipid fatty acids and deoxyribonucleic acid (DNA) extracts from fresh groundwater samples informed decisions on the capacity for complete ERD without DCE stalling and tracked the shifts in the bacterial and archaeal taxonomy and phylogeny stemming from the addition of bioamendments. The pilot test concluded that EVO was the most suitable, considering (1) support of the native microbial consortia for ERD, (2) mechanics and hydraulics of the remediation system, and (3) sustainability/retention of the substrate in the subsurface. Along with EVO, the addition of a nutrient broth derived from brewery waste accelerated and sustained the desired conditions and microbial diversity and population levels. The pilot test results were also used to assess the utilization kinetics of the injected substrates based on total organic carbon (TOC) concentrations measured in the groundwater. After determining that substrate utilization followed Monod kinetics, a TOC threshold at 300 milligrams per liter, equivalent to approximately twice its half-saturation constant was established. Full scale treatment dosing and dose frequency were designed around this threshold, assuming the maximum substrate utilization would yield optimum ERD.

Sr-Nd isotope geochemistry and petrogenesis of ca. 2.26–2.25 Ga and ca. 2.08 Ga mafic dyke swarms from the Dharwar craton, India: Insights into their mantle sources and geodynamic implications

Whole-rock and Sr-Nd isotopic data on the N-S to NNE-SSW trending ca. 2.26–2.25 Ga Ippaguda-Dhiburahalli and the N-S, NW-SE to NE-SW trending ca. 2.08 Ga Devarabanda mafic dyke swarms of the Dharwar craton have been studied. The ca. 2.26–2.25 Ga dykes are linear in nature and contain markedly high SiO2 (53.27–55.85 wt%) and Mg# (60–67) with low TiO2 (0.56–0.61 wt%) contents. While the ca. 2.08 Ga dykes are emplaced in a radiating fashion and contain relatively low SiO2 (47.34–52.67 wt%) and Mg# (34–53) with high TiO2 (0.67–2.11 wt%) contents. The multi-element patterns for both the dyke swarms reflect enrichment in the large-ion lithophile elements (LILEs) and depletion in the high-field-strength elements (HFSEs) with prominent negative Nb-Ta and Ti anomalies. Furthermore, samples of the ca. 2.26–2.25 Ga swarm are relatively more enriched than the ca. 2.08 Ga samples, which is supported by the Nd-isotopic signature. εNd(t) values in the ca. 2.26–2.25 Ga samples vary between −4.5 and 2.4, whereas in the ca. 2.08 Ga dykes it varies between −0.6 and 0.2. The parental magmas are derived from a MORB-like depleted mantle source for both the dyke swarms. Moreover, the interaction between primary melt and the metasomatized sub-continental lithospheric mantle (SCLM) is suggested for the ca. 2.26–2.25 Ga swarm, whereas, the ca. 2.08 Ga swarm show imprints of crustal contamination. The trace element modelling suggests that the ca. 2.26–2.25 Ga swarm were derived from a relatively low (≤5%) degree of partial mantle melting as compared to the ca. 2.08 Ga swarm with a high (~10–15%) degree of partial mantle melting. A deeper mantle source is suggested for the ca. 2.26–2.25 Ga swarm (Garnet/Spinel >80/20), whereas the ca. 2.08 Ga swarm were derived from a relatively shallower mantle source (Garnet/Spinel ~40/60–80/20). The TDM model age for the ca. 2.26–2.25 Ga swarm is supportive of the Neoarchean convergence-related growth of the Dharwar craton, possibly created an enriched lithospheric mantle reservoir. Absence of OIB like plume component in the ca. 2.08 Ga swarm defines the plume centre not precisely below the cratonic lithosphere of the Dharwar craton but several hundred kilometers away from the cratonic margin.

Modeling long-term volcanic deformation at Kusatsu-Shirane and Asama volcanoes, Japan, using the GNSS coordinate time series

Long-term deformation of Kusatsu-Shirane and Asama volcanoes in central Japan were investigated using Global Navigation Satellite System (GNSS) measurements. Large postseismic deformation caused by the 2011 Tohoku earthquake—which obscures the long-term volcanic deformation—was effectively removed by approximating the postseismic and other recent tectonic deformation in terms of quadrature of the geographical eastings/northings. Subsequently, deformation source parameters were estimated by the Markov Chain Monte Carlo (MCMC) method and linear inversion, employing an analytical model that calculates the deformation from an arbitrary oriented prolate/oblate spheroid. The deformation source of Kusatsu-Shirane volcano was found to be a sill-like oblate spheroid located a few kilometers northwest of the Yugama crater at a depth of approximately 4 text {km}, while that of Asama was also estimated to be a sill-like oblate spheroid beneath the western flank of the edifice at a depth of approximately 12 text {km}, along with the previously reported shallow east–west striking dike at a depth of approximately 1 text {km}. It was revealed that (1) volume changes of the Kusatsu-Shirane deformation source and the shallow deformation source of Asama were correlated with the volcanic activities of the corresponding volcanoes, and (2) the Asama deep source has been steadily losing volume, which may indicate that the volcano will experience fewer eruptions in the near future.

Potential Eruption and Current Activity of Anak Krakatau Volcano, Indonesia

Anak Krakatau Volcano is located in the Sunda Strait known for its paroxysmal eruption in 1883. During the January - November 2019 period, seismicity was dominated by types of quakes which indicated the occurrence of magma supply (VA and VB), near-surface volcanic activity (LF, Hybrid, Harmonic Tremors), and volcanic activity above the volcanic surface (eruptions, emission, and continuous tremors). In the period December 2019 - July 2020, there was an increase in the types of quakes near the surface (LF, Hybrid) and the types of quakes on the surface (emission and continuous tremors). Volcanic deformation monitors changes in tilt over the 2019-2020 period associated with pressure releases before, during and after the eruption. The results of GPS data modeling, the shallow pressure source is at a depth of 0.22 km below sea level. Volcanic activity until July 2020 was dominated by activity near and above the volcanic surface associated with the growth of lava domes. The volcanic system of Anak Krakatau is currently an open system, with the potential for eruptions. Strengthening the early warning system for the eruption of Anak Krakatau is important in mitigating efforts and understanding its eruption potential

Quantifying the influence of the range and motion of shipping sources on the ray-based blind deconvolution (RBD) algorithm

The ray-based Blind Deconvolution (RBD) can estimate the relative arrival-times of the channel impulse responses (CIRs) between a shipping source (acting as a shallow source of opportunity) and a remote receiver array (e.g., a short bottom-mounted vertical line array (VLA)) [Durofchalk & Sabra, JASA Vol. 147(3), p. 1927–1938, 2020]. Previous RBD studies primarily estimate the phase of the unknown source by using beamforming on the (most energetic) direct path, which is only observable at short ranges for a shipping source in typical downward refracting environments. Alternatively, when dealing with long range sources of opportunity and only bottom-interacting multipath arrivals can reach the VLA (i.e., exceeding the range when the direct path is observable), the general performance of the RBD algorithm remains to be evaluated. In this study, numerical simulations and experimental validation (using short bottom mounted VLAs) are used in conjunction to investigate the maximal detection range of shipping sources of opportunity per multipath arrivals as a function of frequency, Doppler effect and anisotropy of the shipping source, and the implications for the accuracy of the relative arrival time of the CIR estimated with RBD.

Inflation and Asymmetric Collapse at Kīlauea Summit During the 2018 Eruption From Seismic and Infrasound Analyses

AbstractCharacterizing the large M4.7+ seismic events during the 2018 Kīlauea eruption is important to understand the complex subsurface deformation at the Kīlauea summit. The first 12 events (May 17–May 26) are associated with long‐duration seismic signals and the remaining 50 events (May 29–August 2) are accompanied by large‐scale caldera collapses. Resolving the source location and mechanism is challenging because of the shallow source depth, significant nondouble‐couple components, and complex velocity structure. We demonstrate that combining multiple geophysical data from broadband seismometers, accelerometers, and infrasound is essential to resolve different aspects of the seismic source. Seismic moment tensor solutions using near‐field summit stations show the early events are inflationary. Infrasound data and particle motion analysis identify the source of inflation as the Halema'uma'u reservoir. For the later collapse events, two‐independent moment tensor inversions using local and global stations consistently show that asymmetric slips occur on inward‐dipping normal faults along the northwest corner of the caldera. While the source mechanism from May 29 onwards is not fully resolvable seismically using far‐field stations, infrasound records, and simulations suggest there may be inflation during the collapse. The summit events are characterized by both inflation and asymmetric slip, which are consistent with geodetic data. Based on the location of the slip and microseismicity, the caldera may have failed in a “see‐saw” manner: small continuous slips in the form of microseismicity on the southeast corner of the caldera, compensated by large slips on the northwest during the large collapse events.

West Antarctic mantle deduced from mafic magmatism

Abstract Distinct mantle compositions recorded in primitive West Antarctic magmatic rocks vary by tectonic setting and time. Deep asthenospheric mantle-plume sources or shallow metasomatized mantle sources may operate either coincidently or independently to supply melts for magmatism. For example, contemporaneous subduction and plume dynamics produced the Ferrar–Karoo Large Igneous Province; subduction-related melting followed by slab-rollback or melting of slab-hosted pyroxenite explains Antarctic Peninsula volcanism through time; Marie Byrd Land magmatism results from plume materials variably mixed with subduction-modified mantle; while magmatism in Victoria Land and western Ross Sea is best explained by plate dynamics and melting of asthenospheric and metasomatized lithospheric sources, and not by an upwelling plume. Element and isotopic ratios show a fundamental change between Marie Byrd Land and Victoria Land mantle domains. Specifically, Pb isotopes indicate that Victoria Land magmatism sources have a stronger focal zone (FOZO) mantle component, while Marie Byrd Land magmatism possesses more of the high μ = high 238 U/ 204 Pb (HIMU) mantle component that leads to high 206 Pb/ 204 Pb over time. The chemical and isotopic heterogeneity of relatively unfractionated igneous rocks in West Antarctica reflects fundamental differences in mantle domains and melting conditions. This mantle variability coincides with changes in crustal structure and composition, and has a geophysical signature that is manifest in seismic data and tomographic models.

Identification of suitable sites for open and bore well using ground magnetic survey

The study aims to identify a suitable site for open and bore well in a farmhouseusing ground magnetic survey in south India. It also aims to define depth to granitoid and structural elements which traverse the selected area. Magnetic data (n=84) measured, processed and interpreted as qualitative and quantitatively. The results of total magnetic intensities indicate that the area is composed of linear magnetic lows trending NE-SW direction and circular to semi-circular causative bodies. The magnetic values ranged from −137 nT to 2345 nT with a mean of 465 nT. Reduction to equator shows significant shifting of causative bodies in the southern and northern directions. Analytical signal map shows exact boundary of granitic bodies. Cosine directional filter has brought out structural element trending NE-SW direction. Results of individual profile brought to light structurally weak zone between 90 m and 100 m in all the profile lines. Sudden decrease of magnetic values from 2 042 nT to 126 nT noticed in profile line 6 between 20 m and 30 m indicates fault occurrence. Magnetic breaks obtained from these maps were visualized, interpreted and identified two suitable sites for open and bore well. Radially averaged power spectrum estimates depth of shallow and deep sources in 5 m and 50 m, respectively. Euler method has also been applied to estimate depth of granitoid and structural elements using structural indexes 0, 1, 2, and 3 and found depth ranges from 90 m. Study indicates magnetic method is one of the geophysical methods suitable for groundwater exploration and site selection for open and borewells.

Rayleigh Wave Propagation in the Bighorn Mountains Region, Wyoming

ABSTRACT Short-period Rayleigh waves, Rg, provide strong constraints on the depth of shallow seismic events and are of interest for monitoring small explosions. Characterizing the seismic sources that generate Rg requires an understanding of how shallow crustal structure affects Rayleigh wave propagation. In support of these efforts, this study utilizes observed waveforms from small shallow explosions recorded on temporary seismic network deployments in the Bighorn region, Wyoming. We study regional near-surface geology by measuring changes in surface-wave amplitude and polarization during propagation through basins, foothills, and mountains. We develop additional insight by carrying out surface-wave eigenfunction analyses and numerical-wave simulations, which together reproduce many characteristics seen in the observed waveforms. Our results show how sedimentary basins in the Bighorn region allow for amplified prograde-polarized higher-mode and retrograde-polarized fundamental-mode Rayleigh waves, whereas adjacent mountains only support retrograde motion. These different modes provide distinct constraints on the Earth structure and source characteristics, potentially enabling targeted inversions in future studies. Our findings provide insight into Rg propagation through complex near-surface geology, improving our understanding of shallow propagation and source effects that are relevant to explosion monitoring efforts.

Seismoelectric and Electroseismic Modeling in Stratified Porous Media With a Shallow or Ground Surface Source

AbstractFor a shallow or ground surface source and receiver at the same level or close depth, it is very difficult or computationally inefficient to simulate seismoelectric or electroseismic wave‐fields in stratified porous media by current reflectivity methods, such as the Luco‐Apsel‐Chen generalized reflection and transmission method (LAC GRTM). In this work, the peak‐trough averaging method which has been proved effective and efficient in dealing with this kind of computational problem is adopted to update the seismoelectric and electroseismic modeling algorithm based on LAC GRTM. After thoroughly verifying the accuracy and computational efficiency of the updated algorithm, we utilize it to numerically investigate both the electroseismic and seismoelectric couplings. Snapshots of electroseismic wave‐fields indicate evanescent electroseismic conversion, a reverse process of evanescent seismoelectric conversion, dominates at relatively larger ratios of seismic wavelength to interface depth, whereas the interfacial radiation electroseismic conversion is more prominent for the opposite situation. Our seismoelectric modeling results demonstrate that electric signals can arrive at the ground surface a few milliseconds earlier than their causative seismic signals due to evanescent seismoelectric conversion. This is the first modeling result considering source‐receiver geometries on the surface capable of explaining similar phenomena reported in geophysical field observations of seismically induced electrokinetic effects over a long history. The updated algorithm offers an accurate and efficient tool for forward modeling and will benefit interpretations of field observations as well as future inversion studies.

Mare Domes in Mare Tranquillitatis: Identification, Characterization, and Implications for Their Origin

AbstractMare domes, small shield volcanoes typically &lt;∼30 km diameter, are part of the spectrum of lunar volcanic features that characterize extrusive basalt deposits. We used new spacecraft data to document these in Mare Tranquillitatis, among the oldest maria and the site commonly interpreted as an ancient degraded non‐mascon impact basin. We found 283 known and suspected mare domes, with the majority (n = 229) concentrated on a broad, ∼450 km circular topographic rise in eastern Mare Tranquillitatis. The domes (median diameter 5.6 km, height 68 m, volume 0.7 km3) contain summit pits (74%; median diameter 0.8 km), and exhibit minor compositional variability between domes and surrounding flows, suggesting that domes both supply and are embayed by these flows. Based on their characteristics and associations, we interpret the small shield volcanoes to have been built from individual low‐volume (&lt;∼10–100 km3), low volatile content, short duration, cooling‐limited eruptions. The ∼450 km broad volcanic rise is ∼920 m high (volume ∼1.6 × 105 km3) and is interpreted to be built from multiple occurrences of small shield eruptions, a shield plains volcanism style. This implies a shallow mantle source region capable of supplying distributed dike‐emplacement and eruption events over an area of 1.75 × 105 km2 early in mare volcanism history (∼3.7 Ga). The difference between Mare Tranquillitatis and younger mare‐filled mascon basins is attributed to the more ancient thermal state and crustal structure of the viscously relaxed Tranquillitatis basin, and a shallower broad magma source region present in earlier lunar thermal history.