Northeast Trending Research Articles

Preliminary Observations of the 5 April 2024 Mw 4.8 New Jersey Earthquake

Abstract On 5 April 2024, 10:23 a.m. local time, a moment magnitude 4.8 earthquake struck Tewksbury Township, New Jersey, about 65 km west of New York City. Millions of people from Virginia to Maine and beyond felt the ground shaking, resulting in the largest number (>180,000) of U.S. Geological Survey (USGS) “Did You Feel It?” reports of any earthquake. A team deployed by the Geotechnical Extreme Events Reconnaissance Association and the National Institute of Standards and Technology documented structural and nonstructural damage, including substantial damage to a historic masonry building in Lebanon, New Jersey. The USGS National Earthquake Information Center reported a focal depth of about 5 km, consistent with a lack of signal in Interferometric Synthetic Aperture Radar data. The focal mechanism solution is strike slip with a substantial thrust component. Neither mechanism’s nodal plane is parallel to the primary northeast trend of geologic discontinuities and mapped faults in the region, including the Ramapo fault. However, many of the relocated aftershocks, for which locations were augmented by temporary seismic deployments, form a cluster that parallels the general northeast trend of the faults. The aftershocks lie near the Tewksbury fault, north of the Ramapo fault.

An Improved Fracture Seismic Method for identifying the drilling targets of medium-deep geothermal resources: A case study on heishan geothermal area

The Heishan geothermal area is located at southern area of the gigantic rock body of the Lincang Granite in western Yunnan, where the groundwater system and geothermal fluids are mainly distributed along the Heishan-Hejian fault with exposed temperatures ranging from 85 °C to 99 °C and an average geothermal gradient exceeding 49 km/ °C, showing a high potentiality for power generation. In order to understand its origin and distribution characteristics and to identify favorable drilling targets for further exploration and development, this study conducted analyses and characterizations of the ground water system, thermal structures, and heat storage fracture network through using the improved fracture seismic method. The results indicate that the distribution of vertical fracture network of Heishan geothermal area is mainly controlled by a set of secondary northeast trending faults, which govern the hydraulic circulation in the geothermal area together with the northwest-southeast trending main structures. Horizontally, the well-connected fracture network is predominantly distributed at depths ranging from 1500 to 2000 m, exhibiting a trend of thermal convergence from northwest to southeast. Therefore, the southern part of the Heishan geothermal area, particularly the high energy intensity zone at depths of 2000 to 2500 m, represents a favorable drilling targets. Furthermore, this underground fracture characterization method can be also applied to improve the success rate of directional reservoir transformation of enhanced geothermal system (EGS) and effectively monitor it.

Using Stochastic Point Pattern Analysis to Track Regional Orientations of Magmatism During the Transition to Cenozoic Extension and Rio Grande Rifting, Southern Rocky Mountains

AbstractThe southern Rocky Mountains in Colorado and northern New Mexico hosted intracontinental magmatism that developed during a tectonic transition from shortening (Laramide orogeny, ca. 75 to 40 Ma) through extension and rifting. We present a novel approach that uses stochastic weighted bootstrap simulations of a large set of new and historical geochronology data to better understand how regional anisotropies responsible for focusing magma emplacement evolved through time. This technique can detect subtle trends in directional distributions, including multi‐modal orientations, and can be filtered from regional to local scales. Our results indicate that magmatism followed first the northeast trend of the Colorado mineral belt between 75 and 40 Ma and deviated afterward. These deviations vary depending on the scale of the analysis. At the smallest scale we evaluated (<75 km), the orientation of magmatism from 45 to 30 Ma rotated counter‐clockwise before aligning with the north‐south trend of the modern Rio Grande rift. Larger, regional‐scale analyses indicate magma centers between 40 to 35 Ma and 25 to 20 Ma were dominantly oriented southwest‐northeast, whereas magmatism between 35 and 25 Ma had north‐south orientation. The large areal footprint of magmatism and shifting regional patterns suggest that ancient zones of weakness in the North American lithosphere accommodated magma flow at different moments in time, rather than controlled by a retreating interface of the Farallon and North American plates.

Sediment‐hosted disseminated gold mineralization at the Gegalaw deposit in Central Myanmar

AbstractGegalaw is one of the gold deposits situated in the Sagaing Fault zone, which marks the boundary between the Central Myanmar Basin to the west and the Mogok metamorphic belt to the east. The gold mineralization is mainly confined along northeast striking faults between carbonaceous silty limestone of the Kywethe Chaung Formation and carbonaceous and calcareous shale of the Eocene Male Formation. Hydrothermally induced dissolution breccia associated with progressive silica replacement increase near the northeast trending faults. The hydrothermal alteration associated with the mineralization is silicification in addition to illite‐kaolinite argillic alteration, of which illite is dated by the K‐Ar method as 40.26 ± 0.91 Ma. Sulfide minerals contained in the ores are mainly pyrite and arsenopyrite, with minor to trace amounts of marcasite, chalcopyrite, and sphalerite, among which pyrite and arsenopyrite are the hosts of gold. Pyrite and arsenopyrite are divided into diagenetic and hydrothermal stages, based on their mineral textures. Diagenetic stage pyrites are framboidal (Py1A) and coalescent framboidal (Py1B). Those of the hydrothermal stage are zoned pyrite with porous cores (Py2) and compact rims (Py4). In addition, euhedral homogeneous pyrites with or without compact rim are present (Py3). Some pyrites show pseudomorphs of ilmenite (Py3i) and carbonate minerals, possibly ankerite (Py3c). Arsenopyrites are also divided into porous, sooty arsenopyrite (Apy1), and compact arsenopyrite (Apy2) that co‐exists with Py3 and Py4 pyrites. Electron probe microanalysis for sulfides indicates that Py1A and Py1B are deficient in Fe while Py2, Py3 and Py4 are deficient in S compared to stoichiometry of pyrite. Such deficiencies are compensated by metal ions such as Co2+ and Ni2+ for Py1A, As2+ for Py1B, and As1− for Py2, Py3, and Py4. Arsenic equilibrium temperature of Apy2‐Py3 pairs shows a mode range of 250–270°C. Detected gold concentrations (~650 ppm) in arsenian pyrite (Py2, Py3, and Py4) indicate that gold in pyrite are below the solubility, suggesting that gold is present as solid‐solution in pyrite. Sulfur isotopic values of the pyrites in the unaltered host rocks are −18.9‰ and −8.9‰, and those of the pyrites from the hydrothermal altered rocks range from −17.3‰ to −0.5‰. These similar negative δ34S ranges of the pyrites suggest that the source of sulfur is dominated in biogenic reduction origin. Nevertheless, the two relatively heavier sulfur isotopic values (−4.9‰ and −0.5‰) suggest a contribution of an external hydrothermal fluid source. The research results indicate that gold mineralization occurred by infiltration of auriferous reduced hydrothermal fluids into the carbonaceous silty limestone and carbonaceous and calcareous shale through northeast trending secondary faults of the dextrally moving Sagaing Fault system and the fluids reacted with framboidal pyrite as well as iron‐bearing minerals in the host rocks to precipitate gold‐bearing arsenian pyrite. The age of hydrothermal illite suggests a link to the right‐lateral strike‐slip movement of the Sagaing Fault that is related to the collision of the Indian and Asian plates.

ANALYSIS AND QUANTITATIVE ASSESSMENT OF GEODIVERSITY AT KARYA MURNI, GORONTALO, INDONESIA

Karya Murni is one of the areas in the northern arm of Sulawesi that has been tectonically influenced. Tectonic processes have implications for the formation of rocks and geological features that have the potential to be developed into geodiversity sites. The development of geological features as a geodiversity site in aspiring geopark Gorontalo can protect valuable geological features from frequent degradation. This research aims to analyze and conduct quantitative assessments of geological diversity in Karya Murni, Gorontalo. The research method used is field observation, laboratory analysis, and geodiversity assessment. Field observations included observing landform, collecting rock samples, and measuring geological structures. Field observations were also carried out to observe aspects of the geodiversity assessment which included science, education, tourism, and risk degradation. Laboratory analysis consists of geomorphological analysis, petrographic analysis, and geological structure data analysis. Geodiversity assessment uses the Geological Survey Center of Indonesia assessment. The results suggest that the geomorphology of the study area can be divided into four geomorphic units - the volcanic hills, denudational hills, Karst hills, and fluvial plain units. The stratigraphy of the research area is divided into four units from the age of the early Eocene to the Holocene - the andesite lava, volcanic breccia, reef limestone, and alluvial deposit units. The geological structure of the study area is a trending northeast–southwest to northwest–southeast. Active faults at the location of the study area consist of the Apitalawu normal fault. At recent states, generally geosites of the Karya Murni have moderate scientific values, the low educational and touristic values and high risk of degradation. The geodiversity potential of the research area can be utilized for further research and education.

Reassessment of Geophysical Investigation of Zinc(Z), Cupper (Cu) and Lead (Pb) Potential Mineralization Deposits using Aeromagnetic Data in Wase Middle Benue Trough, Nigeria

Abstract: This effort aims to delineate structures responsible for exploring mineral resources in the Wase middle Benue trough area of Northcentral, Nigeria by evaluating the aeromagnetic data over that region. Oasis Montaj version 6.4 was used to qualitatively and quantitatively evaluate the aeromagnetic data. Techniques for Source Parameter Imaging (SPI) interpretation, including First Vertical Derivative, Analytical Signal, Upward Continuation, and Tilt Derivative, were used in the study. Analytic signal and tilt derivative maps showed different patterns of magnetic signatures independent of magnetization direction with amplitude ranging from 0.1 to 0.2nT/m and -1.3 to 1.4nT/m. They also showed qualitative interpretation applied aids enhance linear features at the expense of deep intrusive bodies like lineaments, fractures, and fault zones which trend Northeast Southwest (NE- SW) in the map of the study area. The boundaries of the geologically interesting anomalies were noticeably accentuated by the upward continuation done at 2 km. Nonetheless, this provides an approximation of the depth of the source of magnetic signatures in the area. The depth measured by SPI ranged from 103.9 to 1473.0 m. In the Eastern and Western regions of the region, respectively, shallow and deep-seated bodies are seen. The depth of the analysis was about 2000m, in conclusion, it was believed that the linear characteristics in the area that are trending northeast to southwest are possible structures for the prospecting of mineral deposits like zinc, copper, and lead

Detecting geothermal anomalies using Landsat 8 thermal infrared remote sensing data in the Ruili Basin, Southwest China.

With the recent increase in global focus on green energy, the application of thermal infrared remote sensing data for the detection of geothermal anomalies has attracted wide attention as it can overcome the difficulty of using only ground surveying. This study aimed to highlight areas of geothermal anomalies with land surface temperature (LST) time series data in winter derived from thermal infrared remote sensing. To extract LST anomaly areas in the Ruili Basin for geothermal prospecting, nine types of data on the study area in winter during 2014 ~ 2021 from Landsat 8 were analyzed. Landsat 8 LST inversion data based on the mono-window algorithm (MWA) can be used to identify hot springs, volcanoes, and other heat-related phenomena. Superimposing LST anomalies for each cycle through drilling data, excluding the heat island effect, geothermal anomaly regions could be plotted. The results show that the accuracy of MWA LST varied within 2K, which is acceptable for geothermal energy and higher than those of the radiative transfer equation (RTE) algorithm and MODIS LST products. Three high-LST regions in the southeast of the study area were identified as geothermal anomaly areas (A, B, and C), and region B was further verified through a comprehensive field investigation of geothermal wells, supplemented by the temperature gradient (TG) method. The findings reveal that the distribution of geothermal anomaly areas and high-LST areas are highly consistent with the northeast trending fault structure; faults act as thermal channels and help in accurately detecting local LST anomalies. Overall, the infrared remote sensing method proved to be a valid technique for detecting LST anomalies. Considering the synergy between thermal infrared surface detection and subsurface exploration methods, the identification of known geothermal fields (B) and other possible areas (A and C) has significance in the upscaling of local geologic information to regional prospecting, thus providing a direction for future geothermal research.

Light on the origin of the verdete siltstone, Bambuí group, central Minas Gerais state, Brazil

The Verdete is a variety of a greenish siltstone that occurs occasionally at different stratigraphic levels of the Serra da Saudade Formation, Bambuí Group (Neoproterozoic to Cambrian age). The main rock types related to the Verdete are potassium rich and show the follow mineralogy: quartz, illite/glauconite, orthoclase, albite, ilmenite, fluorapatite and dawsonite. Conventionally, the Verdete has been considered as formed by diagenetic processes in transgressive conditions at calm water environments. However, the present research based on different data considers the Verdete as result of potassic metasomatism in preexisting detritic sedimentary rock (siltstone, fine sandstone and greywacke). The main arguments that support the potassic metasomatic alteration hypothesis are: i) coincidence of the Verdete main occurrences with geophysical anomalies interpreted as alkaline intrusions in depth; ii) presence of dawsonite which is one hydrothermal sodium carbonate; iii) local presence of brecciated facies of phosphorite cross cutting the Verdete facies; iv) lateral discontinuity of the beds and v) microscopic evidence of substitution in coarser facies. The potassic fluids percolated in fracture zone in a northeast trend in the main area of occurrence in central Minas Gerais State (Cedro do Abaeté Town), and besides this region there are also incidence in other areas. The Verdete is considered as a possible source of potassium to be applied to agromineral or industrial supply for fertilization production. In this way, the understanding of its origin must be important to develop new processes or improve the methods to the potassium recover (chemical, biological and thermal routes).

Geophysics and origin of the Deniliquin multiple-ring feature, Southeast Australia

Major geophysical elements of the Deniliquin multiple-ring feature, a spatially distinct buried structure in mainland southeast Australia, suggest it represents the deep-seated root zone of a large impact structure from which the upper levels, including the original crater, central uplift and associated breccia, have been eroded. Principal features include (A) a multiple ring total magnetic intensity (TMI) pattern; (B) a central quiet magnetic zone; (C) circular Bouguer gravity patterns; (D) an underlying mantle Moho rise about 10 km shallower than under the adjacent Tasman Orogenic Belt; (E) radial faults associated with magnetic and demagnetized anomalies. The minimum radius of the TMI ring is ~260 km, including a central circular quiet magnetic zone about ~120 km in radius. In the east the feature is faulted against the Early Paleozoic Lachlan Orogenic belt whereas in the west it deflects the northwest and northeast trending Early Cambrian ~525–514 Ma Kanmantoo Group. An interpretation of the Deniliquin multiple-ring feature in terms of an orocline is inconsistent with the discontinuity between the feature and surrounding regional structural trends. Limits on the age of the Deniliquin feature are defined by the onset of the Adelaide fold belt at 514 +/− 5 Ma (Foden et al., 1999) and the ~427–417 Ma age of intrusive Silurian granites. Basement drill cores within the Deniliquin multiple-ring feature show Boehm lamellae but did not reveal shock metamorphic textures. Based on its multiple-ring structure, structural distinction from surrounding regional structural trends, occurrence of a central quiet magnetic zone, an underlying shallower Moho and radial faults associated with magnetic bodies, we suggest the Deniliquin multiple-ring feature may represent the deep seated root zone of a large impact structure.

Lithostratigraphy of the Bumbeni Complex and its associated subdivisions, South Africa

Abstract The Bumbeni Complex represents an Early Cretaceous volcanic complex that developed at the southern termination of the Lebombo mountain range in northern KwaZulu-Natal, South Africa. The volcano-sedimentary complex intrudes and disconformably overlies the Lebombo Group of the Karoo Large Igneous Province. The volcano-stratigraphy is defined by an assemblage of volcanic and volcaniclastic rocks as well as late stage quartz-syenite intrusions. Based on current geological and geophysical studies the complex is considered to represent the remnants of a collapsed cauldron structure. The stratigraphic succession is intricate and laterally discontinuous, comprising mafic and felsic lava flows, welded and non-welded tuffs, ignimbrites, lahar deposits, rhyolite domes and dykes and coarse-grained syenitic rocks. Rhyolite dome formation and collapse, and associated plinian eruptions and column collapse, were largely responsible for the variety of volcaniclastic rocks, including classic air-fall tuff deposits. The complex forms part of a northeast trending volcanic basement lineament known as the Bumbeni Ridge defined by aeromagnetic data.

The Broken Hill Block, a new structure and mineral exploration target areas

The Broken Hill Block contains the Paleoproterozoic Willyama Supergroup, host to the world-renowned lead–zinc–silver deposits known as the Line of Lode. A new large-scale geological structural interpretation has been developed based on the construction of 11 regional-scale cross-sections and one longitudinal section. Over an extended period of major folding during the Olarian Orogeny, two distinct sets of regional folds were produced. The longitudinal folds are of similar-type and mostly trend northeast. The cross-folds are subtle, mostly trend at right angles to the longitudinal folds and are open-style. Longitudinal folds in or near the Line of Lode have been reinterpreted. A newly interpreted major slump fold, central to the Line of Lode, allows correlation of rock units from east to west. The well-known Western Anticline and Eastern Syncline, which host the main Line of Lode, are normal drag folds, formed during the initial folding with their axes folded by the later slump folding. The lead lodes are older than the zinc lodes. We interpret previously mapped longitudinal folds, as formed by successive pulses within the one tectonic event. This resulted in increased folding complexity on a local scale, but not a regional scale, and with no substantive impact on the regional structure. Pitch and plunge data were used to identify 23 cross-folds, some more than 50 km long. Away from the Line of Lode, the new structure is simpler than previous interpretations and with no tectonic inversion of the stratigraphy, other than gravity slumping, and no regional-scale nappe structures. The combination of cross-folds and longitudinal folds has produced regional-scale domes and troughs throughout the block. The intersection of longitudinal fold axes with cross-fold crests are proposed to be particularly prospective for metallic sulfides with 25 named and prioritised mineral exploration target areas identified. The cross-folding has caused the ore bodies to plunge steeply to great depths north of the Line of Lode. Further to the northeast, the plunge is reversed bringing strata, containing potential northern extensions of the Line of Lode, closer to the surface. The retrograde schist zones, which are regional-scale faults or shears that have undergone retrograde metamorphism, postdate the longitudinal and cross-folding and are not considered to be related to thrust structures. Displacement of strata and structures is evident across the zones and is generally well understood. KEY POINTS A new set of regional folds, termed cross-folds, has been identified. In the Line of Lode, large-sale longitudinal folds include a major slump fold. The stratigraphic sequence is not inverted; nappes are for the most part not present. Broken Hill-type lead–zinc–silver deposits are preferentially found close to the intersection of longitudinal and cross-fold axes.

A newly recognised 1860–1840 Ma tectono-magmatic domain in the North Australia Craton: Insights from the Tennant Region, East Tennant area, and the Murphy Inlier

New U-Pb monazite ages from amphibolite-facies metasedimentary rocks from the Tennant Region, Murphy Inlier and intervening East Tennant area, together with existing data, reveal the presence of an 1860–1840 Ma tectono-magmatic domain over 600 km long towards the centre of the North Australian Craton. In-situ ion probe U-Pb dating of biotite-hosted monazite in amphibolite-facies schist in the Tennant Region yielded an age of 1858 ± 7 Ma, which is attributed to north–south shortening (D1) at 1860–1855 Ma. Existing data indicate that D1 was associated with east–west trending, upright folds and mostly low-grade, regional metamorphism (M1) in the Tennant Region and the Murphy Inlier. The D1 event preceded voluminous and widespread felsic magmatism between 1855 and 1845 Ma. This included the emplacement of the Tennant Creek Supersuite, as well as the Yungkulungu Formation and equivalent stratigraphy, in the Tennant Region and in East Tennant, and the Nicholson Granite and Cliffdale Volcanics in the Murphy Inlier. Newly determined monazite ages from amphibolite-facies schist from the East Tennant area and the Murphy Inlier constrain a second episode of deformation and metamorphism (D2/M2) to ∼ 1845 Ma, coincident with the cessation of widespread magmatism. D2 is characterised by regional southeast to northeast trending shear zones. Phase equilibria modelling reveals that peak pressure–temperature (P–T) conditions during M2 in the East Tennant area were 2.8–3.3 kbar and 655–680 °C, indicating an extremely high apparent geothermal gradient (>190 °C/kbar) that was likely influenced by the preceding magmatism. Existing data indicate that D2 also affected the Tennant Region, where it coincided with significant Cu-Au-Bi mineralisation, albeit at significantly lower P–T conditions (sub-greenschist facies) than in the East Tennant area. The development of the 1860–1840 Ma tectono-magmatic domain, extending from west of the Tennant Region to east of the Murphy Inlier, marks an intermediate step in the migration of tectonism in the North Australia Craton, from the Arnhem Province in the north at 1880–1860 Ma to the Aileron and Tanami provinces in the south by ca. 1830 Ma.

A methodology for estimating accurate velocity field of NigNET based on new ITRF realization

This contribution presents a new velocity field describing the crustal motion of Nigeria from more than 5years continuous GNSS data at 8 of 14 permanent stations distributed across the country. GAMIT/GLOBK GNSS processing software was used for processing. The horizontal velocity field of NigNET stations which showed a North-East trend and the selected IGS stations were obtained from cleaned position time series of daily GNSS solutions. The velocity describe the horizontal and vertical motion the selected 8 GNSS stations assuming Flicker +White noise model, which optimally describes the geophysical error source of the adopted GNSS stations. Bland and Altman statistical method shows that residual velocity solutions of our study and others (in ITRF2008) and also MORVEL plate motion model are in agreement.

Хавчуу Ам Ордын Судалгаанд Геофизикийн Аргуудыг Хэрэглэсэн Байдал

When comparing the exploration results thus far from Khavchuu with those of known mineralisation and mineral deposits in the region. The occurrence of north to north-east trending, low angle, thrust faults which also coincide with resistivity and chargeability highs, magnetic lows, As anomalies and positive Au chip samples, issimilar to that observed and documented at Boroo. The resistivity anomalies generated have been interpreted as being associated with an area of silicification or quartz veining and from the dipole-dipole results these seem to occur as shallowly dipping structures similar to those hosting the Boroo mineralisation. The chargeability highs could be interpreted as regions of sulphide mineralisation and coincide with many of the anomalous areas again as with Boroo, although in the southern area the near surface chargeability low becomes a chargeability high with depth suggesting a degree of sulphide destruction during weathering in the upper regions. Magnetic lows could be interpreted again as zones of weathering and associated destruction of magnetite in granites or sulphides in mineralised regions. Assuming that any mineralisation at Khavchuu will exhibit a similar refractory component, this broad weathering could be of significant economic importance.

High-rate very-long-period seismicity at Yasur volcano, Vanuatu: source mechanism and decoupling from surficial explosions and infrasound

SUMMARYYasur volcano, Vanuatu is a continuously active open-vent basaltic-andesite stratocone with persistent and long-lived eruptive activity. We present results from a seismo-acoustic field experiment at Yasur, providing locally dense broad-band seismic and infrasonic network coverage from 2016 July 27 to August 3. We corroborate our seismo-acoustic observations with coincident video data from cameras deployed at the crater and on an unoccupied aircraft system (UAS). The waveforms contain a profusion of signals reflecting Yasur’s rapidly occurring and persistent explosive activity. The typical infrasonic signature of Yasur explosions is a classic short-duration and often asymmetric explosion waveform characterized by a sharp compressive onset and wideband frequency content. The dominant seismic signals are numerous repetitive very-long-period (VLP) signals with periods of ∼2–10 s. The VLP seismic events are ‘high-rate’, reoccurring near-continuously throughout the data set with short interevent times (∼20–60 s). We observe variability in the synchronization of seismic VLP and acoustic sources. Explosion events clearly delineated by infrasonic waveforms are underlain by seismic VLPs. However, strong seismic VLPs also occur with only a weak infrasonic expression. Multiplet analysis of the seismic VLPs reveals a systematic progression in the seismo-acoustic source decoupling. The same dominant seismic VLP multiplet occurs with and without surficial explosions and infrasound, and these transitions occur over a timescale of a few days during our field campaign. We subsequently employ template matching, stacking, and full-waveform inversion to image the source mechanism of the dominant VLP multiplet. Inversion of the dominant VLP multiplet stack points to a composite source consisting of either a dual-crack (plus forces) or pipe-crack (plus forces) mechanism. The derived mechanisms correspond to a point-source directly beneath the summit vents with centroid depths in the range ∼900–1000 m below topography. All mechanisms suggest a northeast trending crack dipping relatively shallowly to the northwest and indicate a VLP source centroid and mechanism controlled by a stable structural geologic feature beneath Yasur. We interpret the results in the framework of gas slug ascent through the conduit responsible for Yasur explosions. The VLP mechanism and timing with infrasound (when present) are explained by a shallow-buffered top-down model in which slug ascent is relatively aseismic until reaching the base of a shallow section. Slug disruption in this shallow zone triggers a pressure disturbance that propagates downward and couples at the conduit base (VLP centroid). If the shallow section is open, an explosion propagates to the surface, producing infrasound. In the case of (the same multiplet) VLPs occurring without surficial explosions and weak or no infrasound, the decoupling of the dominant VLPs at ∼900–1000 m depth from surficial explosions and infrasound strongly indicates buffering of the terminal slug ascent. This buffering could be achieved by a variety of conditions at or directly beneath the vents, such as a high-viscosity layer of crystal-rich magma, a debris cap from backfill, a foam layer, or a combination of these. The dominant VLP at Yasur captured by our experiment has a source depth and mechanism separated from surface processes and is stable over time.

Temporal and Spatial Analysis of PM2.5 and O3 Pollution Characteristics and Transmission in Central Liaoning Urban Agglomeration from 2015 to 2020

The central Liaoning urban agglomeration is an important heavy industry development base in China, and also an important part of the economy in northeast China. The atmospheric environmental problems caused by the development of heavy industry are particularly prominent. Trajectory clustering, potential source contribution (PSCF), and concentration weighted trajectory (CWT) analysis are used to discuss the temporal and spatial pollution characteristics of PM2.5 and ozone concentrations and reveal the regional atmospheric transmission pattern in central Liaoning urban agglomeration from 2015 to 2020. The results show that: (1) PM2.5 in the central Liaoning urban agglomeration showed a decreasing trend from 2015 to 2020. The concentration of PM2.5 is the lowest in 2018. Except for Benxi (34.7 µg/m3), the concentrations of PM2.5 in other cities do not meet the standard in 2020. The ozone concentration in Anshan, Liaoyang, and Shenyang reached the peaks in 2017, which are 68.76 µg/m3, 66.27 µg/m3, and 63.46 µg/m3 respectively. PM2.5 pollution is the highest in winter and the lowest in summer. The daily variation distribution of PM2.5 concentration showed a bimodal pattern. Ozone pollution is the most serious in summer, with the concentration of ozone reaching 131.14 µg/m3 in Shenyang. Fushun is affected by Shenyang intercity pollution, and the ozone concentration is high. (2) In terms of spatial distribution, the high values of PM2.5 are concentrated in monitoring stations in urban areas. On the contrary, the concentration of ozone in suburban stations is higher. The high concentration of ozone in the northeast of Anshan, Liaoyang, Shenyang to Tieling, and Fushun extended in a band distribution. (3) Through cluster analysis, it is found that PM2.5 and ozone in Shenyang are mainly affected by short-distance transport airflow. In winter, the weighted PSCF high-value area of PM2.5 presents as a potential contribution source zone of the northeast trend with wide coverage, in which the contribution value of the weighted CWT in the middle of Heilongjiang is the highest. The main potential source areas of ozone mass concentration in spring and summer are coastal cities and the Bohai Sea and the Yellow Sea. We conclude that the regional transmission of pollutants is an important factor of pollution, so we should pay attention to the supply of industrial sources and marine sources of marine pollution in the surrounding areas of cities, and strengthen the joint prevention and control of air pollution among regions. The research results of this article provide a useful reference for the central Liaoning urban agglomeration to improve air quality.

Geophysics Appearance of The South China Sea

<p class="AbstractText">South China Sea (SCS) is underlain by sediments of an average density 2.10 g/cm<sup>3</sup> of 2 km thickness at its central part up to 10 km in the margins. The basement rock is the upper and lower crust of densities 2.67 and 2.85 g/cm<sup>3</sup> respectively of varying thicknesses. The thinnest crustal rock is at the centre of SCS that is called the South China Sea Basin (SCSB). The Mohorovicic discontinuity is about 15 km depth below the SCSB. Heatflow values in this basin vary from 2 to 3.5 HFU.</p><p class="AbstractText">Lineations of total magnetic anomaly are generally in a west-east direction covering the whole study area. However, an elongated northeast-southwest lineation of dipole anomaly separates the west-east anomaly patterns in the north from those in the south. This feature is also observed in the gravity map. These elongated patterns of the total magnetic features are in coincident with the occurrences of seamounts inferred being remnant of extinct seafloor spreading. Because of this spreading a crustal extension had taken place that separated Kalimantan from the mainland of China to restore its present position. A paleomagnetic study result confirms this hypothesis.</p><p class="AbstractText">The Palawan trench is marked by north-east trending magnetic and gravity anomaly that is inferred being traces of a remnant subduction zone. This anomaly forms a boundary between the Zengmu also called the Sarawak basin and the SCSB. Here, heat flow value is 1 to 2 HFU. This value in coincident with gravity gradient of 2.5 mGal/km also represents an active subduction of the Manila trench north of the Palawan Island. The Manila trench is supposed to be the energizing source of volcanism and earthquake in the Phillippines. Free-air and Bouguer anomaly of the order of 50 to 60 mGal and magnetic of about 100 nT represent the Zengmu basin in the Sunda Shelf. This basin is underlain by sediments of 2.10 g/cm<sup>3</sup> of 8 km thickness and also crustal rock which is much thicker than the one underneath the SCSB. Strong topographic relief at the surfaces of sedimentary layer and the crustal rock is very my much associated with normal faulting that may cause fluctuation of the free-air values.</p><p class="AbstractText">The continental margins of Sarawak and the Sunda Shelf are areas of hydrocarbon deposits now still in production, whereas the offshores Vietnam and Hainan are promising target for hydrocarbon exploration.</p>

DISTRIBUTION OF SUBSURFACE QUATERNARY SEDIMENT IN SOUTH BINTAN ISLAND WATERS AS A POTENTIAL HEAVY MINERAL PLACER OR RARE EARTH ELEMENT DEPOSIT BASED ON SEISMIC INTERPRETATION

Bintan Island is one of the areas traversed by the Southeast Asian granitoid belt which is known to have the potential for heavy mineral placer deposits. Due to the dwindling presence of heavy mineral placer deposits in land areas, it is necessary to look for the potential presence of heavy mineral placer deposits in water areas. Searching for placer heavy mineral deposits accomodation in these waters requires subsurface mapping.The method used in this subsurface mapping is a single channel seismic method with a total of 179 lines in the direction of northeast – southwest and west – east. The results of this seismic recording are then interpreted the boundaries of the seismic facies unit and distributed using the kriging method. Furthermore, the thickness calculates by using the assumption velocity 1600 m/s.Based on the facies unit boundaries that have been interpreted, the quaternary sediments that formed in the study area are divided into 2 types of units, namely: Unit 2 which is estimated to be fluvial – transitional sediment, and Unit 1 which is estimated to be transitional sediment – shallow sea. There is also a difference in thickness patterns in these two units, where unit 2 shows a pattern of sediment thickening that resembles a paleochannel trending northeast – southwest, while unit 1 is relatively uniform.From the results of this study, it can be said that the area that has potential for heavy mineral placer deposits is in the west - center of the southern waters of Bintan Island. Where the potential for heavy mineral placer deposits should be in the paleochannel deposits that are part of Unit 2.

The Storfjorden, Svalbard, Earthquake Sequence 2008–2020: Transtensional Tectonics in an Arctic Intraplate Region

AbstractAn earthquake sequence in the Storfjorden offshore area southwest of Spitsbergen in the Svalbard archipelago initiated with a 21 February 2008 magnitude Mw 6.1 event. This area had previously not produced any significant earthquakes, but between 2008 and 2020, a total of ∼2800 earthquakes were detected, with ∼16 of them being of moderate size (ML≥4.0). Applying double-difference relocation to improve relative locations reveals that the activity is linked to several subparallel faults striking southwest–northeast that extend across the entire crust. The southwest–northeast trend is also found as a possible fault plane from regional moment tensor inversion. The solutions range from oblique normal in the center of the cluster to pure strike slip farther away and are consistent with the compressional σ1 axis roughly in the east–west direction and plunging 57°, and the extensional σ3 axis subhorizontal trending north–south. The mainshock fault is steeply dipping to the southeast, but several other faults appear to be near vertical. The existence of oblique, right-lateral strike-slip motion on southwest–northeast-trending faults with a normal component and pure normal faulting events in between suggests transtensional tectonics that in and around Storfjorden result in activation of a complex fault system.

Seismic illumination of small-throw seismogenic faults, Anadarko Basin, Oklahoma

Substantial increase in the occurrence of injection-induced seismicity across Central and Eastern United States in the past decade, has highlighted a need for novel approaches to geophysical subsurface imaging of potentially seismogenic faults. Active clusters of seismicity illuminate linear fault segments within the sedimentary cover and crystalline basement that were unknown until seismicity began. Such surprises are due to the limited availability of 3D seismic reflection surveys and the difficulty of imaging relatively shallow earthquake events from sparse seismic monitoring arrays. The Sooner Trend Anadarko Basin Canadian Kingfisher Counties (STACK) play of the Anadarko Basin, Oklahoma, provides an opportunity to investigate these earthquake-prone basement faults. Modern high-quality seismic data acquired to map unconventional resource plays in the STACK enable us to assess the detailed subsurface structure. Furthermore, because of increased earthquake risk from anthropogenic activities in the past decade, state regulatory agencies have deployed a dense array of seismic monitoring stations, which allows us to integrate earthquake data with seismic reflection data for analysis of active faulting. We have mapped structural deformation using a suite of seismic attributes, including multispectral coherence, volumetric curvature, and aberrancy, in a 3D seismic reflection data set covering 625 sq mi of the STACK area. To unravel the relationship between the structures and seismicity, we use relocated locally recorded earthquakes and compute the focal mechanism solution for the events. Our results reveal previously unmapped small-throw (<120 m) fault segments with dominant north–south, northwest, and northeast trends, most of which extend from the basement up into the shallower sedimentary Hunton and Woodford Formations. Because of the small offset, we find that aberrancy and the curvature attribute best illuminate the basement-rooted faults in the sedimentary cover. Fault segments with significant vertical offset are better illuminated by band-limited multispectral coherence. We argue that the inherited structure of these faults makes them mostly illuminable by flexure-related seismic attributes, especially within the sedimentary cover. The integration of the illuminated faults with relocated earthquakes and focal mechanism solutions shows that the illuminated faults that have hosted intrasedimentary and/or basement seismicity are reactivated by strike-slip faulting. We hypothesize that careful attribute mapping of faults and related flexures, integrated with recent seismic activity data, and an understanding of the local stress and geomechanical properties, can help mitigate seismic hazards in similar intraplate geological settings where small-throw faults predominate.