SE Direction Research Articles

Structural evolution and the partitioning of deformation during basin growth and inversion: A case study from the Mizen Basin Celtic Sea, offshore Ireland

AbstractThe Celtic Sea basins lie on the continental shelf between Ireland and northwest France and consist of a series of ENE–WSW trending elongate basins that extend from St George’s Channel Basin in the east to the Fastnet Basin in the west. The basins, which contain Triassic to Neogene stratigraphic sequences, evolved through a complex geological history that includes multiple Mesozoic rift stages and later Cenozoic inversion. The Mizen Basin represents the NW termination of the Celtic Sea basins and consists of two NE–SW‐trending half‐grabens developed as a result of the reactivation of Palaeozoic (Caledonian, Lower Carboniferous and Variscan) faults. The faults bounding the Mizen Basin were active as normal faults from Early Triassic to Late Cretaceous times. Most of the fault displacement took place during Berriasian to Hauterivian (Early Cretaceous) times, with a NW–SE direction of extension. A later phase of Aptian to Cenomanian (Early to Late Cretaceous) N–S‐oriented extension gave rise to E–W‐striking minor normal faults and reactivation of the pre‐existing basin bounding faults that propagated upwards as left‐stepping arrays of segmented normal faults. In common with most of the Celtic Sea basins, the Mizen Basin experienced a period of major erosion, attributed to tectonic uplift, during the Paleocene. Approximately N–S Alpine regional compression‐causing basin inversion is dated as Middle Eocene to Miocene by a well‐preserved syn‐inversion stratigraphy. Reverse reactivation of the basin bounding faults was broadly synchronous with the formation of a set of near‐orthogonal NW–SE dextral strike‐slip faults so that compression was partitioned onto two fault sets, the geometrical configuration of which is partly inherited from Palaeozoic basement structure. The segmented character of the fault forming the southern boundary of the Mizen Basin was preserved during Alpine inversion so that Cenozoic reverse displacement distribution on syn‐inversion horizons mirrors the earlier extensional displacements. Segmentation of normal faults therefore controls the geometry and location of inversion structures, including inversion anticlines and the back rotation of earlier relay ramps.

Geophysical Investigation of the Geothermal Potential Under the Largest Volcanic Cover in Anatolia: Kars Plateau, NE Turkey

In this study, Curie-point depth (CPD), geothermal gradient, radiogenic heat production, and heat flow maps were constructed based on different thermal conductivity coefficients using magnetic anomaly data for the Kars Plateau, which has the largest volcanic cover in Turkey. The bottom depths of the magnetic crust in the research area were revealed by the CPD map for the first time in this investigation. There are two apparent magnetic anomaly trends in the study area: the first is the Horasan–Senkaya–Sarikamis–Selim–Arpacay trend in the NE–SW direction, and the other is the Hanak–Ardahan–Arpacay trend in the NW–SE direction. Two other prominent elongations extend into the Ardahan–Gole–Senkaya and Kars–Digor axes. All these trends represent mountain chains and/or stratovolcanoes in the region, and no anomalies are observed around the non-volcanic outcrops. Curie depths are shallow, up to 14 km between Horasan and Kagizman towns, and 12 km in the northwestern part of the study area. Gradient values can reach 50 °C km−1 in the northwestern sector, together with the high heat flows represented by the 150 Wm−1 K−1 contours. The deepest CPD region lies between Gole and Susuz towns, where the geothermal gradient decreases to 27 °C km−1. Heat flows decrease 60 Wm−1 K−1 in the same area. An apparent gap around the Kars Plateau was observed in previous regional heat flow maps of Turkey by other authors (who used the bottom hole temperatures of boreholes and hot springs temperatures). This gap has been accurately filled from the results of this study, and geothermal exploration areas and the geothermal potential of the Kars Plateau have thus been determined for future exploration activity on the basis of the tectonic elements and earthquake data.

Tectonics controls on fluvial landscapes and drainage development in the westernmost part of Switzerland: Insights from DEM-derived geomorphic indices

This work focuses particularly on the geomorphological evidence for the tectonic controls on the development of the present-day fluvial landscapes in the westernmost part of Switzerland. The tectonic deformation was evaluated on the basis of a combined analysis of several classical geomorphic indices (hypsometric curves and integrals, transverse topographic symmetry index, and channel's bottom gradients) through high-precision DEM processing. A new optimization strategy was applied for defining geomorphic anomalies related to tectonic activity along the channels of three rivers, based on a combined investigation of topographic swath, longitudinal profiles, geological and geophysical observations. The results show that the abnormally high values of hypsometric integral are spatially occurred on the hanging walls of thrust faults, while abnormally low ones are spatially observed in the same locations of paleo-ice stream pathways. Observations obtained from transverse topographic symmetry index display asymmetries in the most of the studied drainage basins with a predominant SE direction of lateral migration. This direction is in agreement with the dominant dip-direction of the bedding planes within the study area. Abnormal changes in the channel's bottom gradients, which almost coincide in space with pronounced change in the depth of the subsurface geologic layers and in the geophysical properties, are marked by distinct topographic relief in areas where rivers flow above blind and emergent faults. Our analysis not only confirms that there is a significant tectonic control on the evolution of drainage systems, but also revealed a possible evidence for the reactivation of some inherited faults.

Present crustal deformation and stress-strain fields of North China revealed from GPS observations and finite element modelling

North China is located on the N–S seismic belt of mainland China and is characterized by dense faults and intense seismicity. We analyzed the current regional crustal deformation using GPS observations from 1999 to 2007 and 2011–2017. We then established a dynamic finite element model based on the geological structure, geophysical parameters, and GPS velocity constraints to analyze the strain-stress features. Finally, we discuss the rationality of the simulation results, the variations in crustal activity, which may have been caused by the post-earthquake impact of the 2011 Mw 9.0 Tohoku and 2008 Mw 7.9 Wenchuan earthquakes, and the geodynamics of North China. Most parts of North China exhibited extensional stress in an approximately NW–SE direction during 2011–2017. In the two study periods, the maximum shear strain rates predominantly occurred in western North China; the central and eastern parts had relatively smaller values in 2011–2017. These characteristics indicate that the post-earthquake impact of the Tohoku earthquake significantly influenced most parts (central and eastern) of North China, whereas the Wenchuan earthquake mainly affected the western part. Our work quantitatively described the variations in current crustal movement velocities, stress-strain fields, and fault activity rates in North China. These characteristics indicate that the unique tectonic environment, intense crustal activity, and earthquake-prone nature of North China require continuous research attention. The results obtained in this study not only portray the current tectonic activity deformations but also reveal recent geodynamic processes in North China.

Intergrated Seismic Stratigraphic and Structural Analysis of the Songo Songo Gas-Field, Shallow Offshore Tanzania, Using Seismic and Well Data

Seismic stratigraphy and structural analysis of seismic data, when combined with wireline data, provides vital information for hydrocarbon exploration in a prospective basin. These techniques were employed in the Songo Songo shallow coastal basin, southern Tanzania to determine stratigraphic setting, trapping mechanism, reservoirs zones. Suites of well logs from two wells (AA-1 and BB-5) and 2-D seismic data was obtained from TPDC in the study area. Lithologic interpretation and well correlation were carried out using the well log suites. Stratigraphic analysis was carried out with the well logs and 2D seismic data by using principles of sequence stratigraphy while structural interpretation was done with aid of the seismic data to produce polar plots for the different structural trends. The lithology was dominated by sand, shale, and limestone. Five sequence boundaries (SB); SB1 (Albian), SB2 (base of Coniacian-Early Campanian), SB3, (Middle Eocene), SB4 (Late Miocene) and SB5 (Quaternary)) and three maximum flooding surfaces (MFS); MFS1-(Early Cretaceous), MFS2, (Late Cretaceous), MFS3-(Early Eocene) were identified. Three main normal faulting systems (Jurassic faults, active during the Jurassic rifting phase of Madagascar, Neogene faults that occurred during Neogene east African rifting and reactivated faults which mostly were Jurassic fault reactivated by east African rifting) of NNW-SSE were recognized in the study area. The structural interpretation reveal that the gas field is dominated by normal faults that occur in the upper and lower part of Songo Songo suggesting two phases of deformation prior to development of the field. The main reservoir is developed in the Neocomian and Albian sandstones, and capped by Jurassic faults and Wami (Formation) overlying rocks. The gas is sourced from Jurassic shale known as Mtumbei Formation and stored at the main reservoir developed in the Lower Cretaceous aged Neocomian sandstone known as Kipatimu Formation, sealed by high pressured shale of upper Cretaceous known as Wami Formation. This study shows that deposition of sediment occurs in the NW – SE direction, with the thinning of sediments thickness towards well BB-5 while the stratigraphic sections show that the horizons are laterally continuous and are being strongly affected by tectonic events.

3D Static Modeling and Petrographic Aspects of the Albian/Cenomanian Reservoir, Komombo Basin, Upper Egypt

The Albian/Cenomanian reservoir is one of the two main reservoirs composing the petroleum system in the Komombo Basin. However, these reservoirs have not previously been studied in detail. Therefore, a detailed study of the reservoirs is performed. Six boreholes, three vertical seismic profiles and twenty 2D seismic lines are integrated in the Petrel™ Schlumberger modeling software to build a 3D structural model for the Albian/Cenomanian reservoir. This model represents a framework for the subsequent 3D facies and petrophysical models of the studied reservoir. The interpretation of the created maps and 3D models shows two normal fault directions: NW–SE and NE–SW, where the NW–SE direction is dominant, creating a major half-graben system. Conventional well log analyses are performed for the available wells. The results are used in subsequent facies and petrophysical modeling. The thickness of the Albian/Cenomanian reservoir ranges from about 137 to 411.5 m. Petrographic analyses were conducted on two cores retrieved from the Albian/Cenomanian cycles covering the depth interval of 1323–1352 m in well AB-5. Most of the samples consist of quartz arenite and feldspathic arenite. The 3D facies model of the reservoir shows that the sandstone has a large probability distribution in the study area compared to the shale and siltstone. The 3D petrophysical models imply that the Albian/Cenomanian reservoir has good to very good reservoir quality. The main issue for the reservoir is the high water saturation values. In contrast, the hydrocarbon saturation is restricted to some parts of the basin.

One-Dimensional Velocity Model, Station Correction and Earthquake Relocation of Local Earthquakes in the Koyna–Warna Region, India

In this paper we investigated the feasibility of using the higher-frequency waveforms to characterize the seismicity in the Koyna–Warna region, globally well-known for its reservoir-triggered earthquakes. The local seismicity and source parameters have been extensively explored by many researchers using various types of data, e.g. analog data, broadband seismological data, and deep seismic sounding data. However, here we have utilized the seismological data recorded by 97 temporary 4.5-Hz geophones to locate the local seismicity in the region. We first investigated an appropriate 1-D P-wave velocity model through the inversion of P- and S-times. In order to compensate for the thick and laterally heterogeneous basalt, we incorporated the station corrections in the 1-D velocity inversion process. The station correction varies from + 0.09 to − 0.20 s for the P-waves, with clear demarcations of positive and negative station corrections corresponding to the northern and southern regions, respectively. The patterns of positive and negative station corrections suggested that the northern part is characterized by lower velocity, while slighter higher velocities present in the southern part of the study area are relative to the estimated 1-D velocity model. The earthquake locations are further improved by using the double-difference (hypoDD) approach, which enabled us to accurately map shallow subsurface seismogenic faults in the region. The data comprises 10,062 P-wave and 9049 S-wave catalog differential times from 348 earthquakes (1.0 ≤ ML ≤ 4.5). The precisely relocated earthquakes (ERH < 0.05 km ERZ < 0.5 km and rms < 0.02 s) form the three clusters of earthquakes in the NW–SE direction along the lineaments close to Warna Reservoir. The observed seismicity trends on the surface could be due to the vertical manifestations of faults or fractures. Their alignments are confirmed by the analysis of focal mechanism which exhibits a predominant normal type of faults with one nodal plane consistent with the main alignment of the seismic events.

LAVA DOME CHANGES DETECTION AT AGUNG MOUNTAIN DURING HIGH LEVEL OF VOLCANIC ACTIVITY USING UAV PHOTOGRAMMETRY

Abstract. Lava dome changes detection during increasingly high volcanic activity are essential for hazard assessment purposes. However, it is challenging to conduct direct field measurement due to safety reason. Here, we investigate the lava dome changes of Mount Agung in Indonesia during the highest level of volcanic activity. On 22 September 2017, the rumbling and seismic activity in this volcano started increasing to the highest level for a period of time. We afterwards collected image data at lava dome area by using UAV over this time period. To accomplish the goal of change detection, we assembled and developed a fixed-wing UAV platform, i.e. Buffalo FX-79 to acquire images of Mount Agung whose elevation is roughly 3,142 m above sea level. We acquired the UAV images on two dates, i.e. Oct 19 and Oct 21 of 2017. Due to an exclusion zone surround the volcano, we could only operate the UAV at 20 km distance from the crater. With these data set, we produced three-dimensional point clouds, high-resolution Digital Elevation Model and orthophoto by using Structure from Motion (SfM) and Multi View Stereo (SfM-MVS) technique with Photoscan Pro software. From orthophoto data, we found two fluid areas at the crater's surface in NE direction (4,375.9 sq-m) and SE direction (3,749.8 sq-m). We also detected a fumarole which emitted steam and gases in the eastern part that continued for several days. In order to reveal the changes in lava dome surface, we used DEM to create cross-section profile. After that, we applied cloud to cloud comparison (C2C) algorithm to calculate the difference of lava dome based on two data set of point clouds and compared it with interferometric result from Sentinel-1A data. The data from the Sentinel-1A satellite (15 Oct – 27 Oct 2017) were processed to obtain the interferogram image of Mount Agung. This research therefore demonstrates a potential method to detect lava dome changes during high level of volcanic activity with photogrammetric methods by using UAV images. Within only two days the data were successfully acquired. From the DEM data and cross-section profile between two data set, we noticed that no significant surface change was found around the lava dome surface. Moreover, we also found that there was no significant lava dome changes and vertical displacement during these two time periods as the point cloud comparison and distance result. The average of difference distance is 2.27 cm with a maximal and minimal displacement of 255 cm and 0.37 cm respectively. This result was then validated by using InSAR Sentinel that showed small displacement, i.e 6.88 cm. It indicated that UAV photogrammetry showed a good performance to detect surface changes in centimeter fraction.

Thiessen polygon analysis and spatial pattern evolution of Neolithic cultural sites (8.0–4.0 ka BP) in Huaibei Plain of Anhui, East China

The Thiessen polygon concept was applied to analyze how Neolithic sites were gathered and the features of agriculture, living environment and transportation in the Huaibei Plain, Anhui Province, East China, in the Shishanzi cultural period (8.0–6.5 ka BP), Dawenkou cultural period (6.5–4.5 ka BP), and Longshan cultural period (4.5–4.0 ka BP). The Thiessen polygon analysis method was effective in determining the settlement center of the region and helped to confer the complex relationships among agriculture, the living environment and transportation during the Neolithic Age. From the Shishanzi cultural period to the Longshan cultural period, a growing number of small polygons showed enhancement in the degree of gathering and cultural communication. In the Dawenkou and Longshan cultural periods, the central part of Huaibei Plain was the settlement center and the distance from the center of each Thiessen polygon to its edges was decreasing. This indicates that the ancients' dependence on agriculture and development conditions increased over the three cultures. The development of Neolithic cultures was also affected by the environmental changes in the Huaibei Plain. From the Shishanzi cultural period to the Longshan cultural period, the climate tended to be dry, and the area of marsh decreased. However, there was little change in temperature, which was beneficial to the ancients' lives and production. Not only did cultural sites and small polygons increase constantly, but groups of sites and settlement centers also appeared in the central part of plain and areas along the main stream of the Huai River. The Neolithic culture developed vigorously, and the abilities of ancients to adapt to environment and transform nature gradually improved. The NW to SE direction of the small polygons’ distribution suggests the control of the ancient rivers on transportation in the Huaibei Plain.

Morphometric analysis of the drainage network of Samos Island (northern Aegean Sea): Insights into tectonic control and flood hazards

The morphometric analysis of alluvial drainage provides insights into its dynamics, erosion capacity, susceptibility to floods and possible genetic relations to tectonic faulting. In this study, we analysed the drainage system of Samos Island, located in the northern Aegean Sea. The results indicate a vulnerability to erosion and flooding events, and these intense phenomena concentrate mostly on third-order catchments. Two dissimilar drainage network systems are shown: an older drainage network system with a main NW–SE direction, which includes fourth- and fifth-order branches, and a recent drainage network system, which includes new, smaller order branches with a main NE–SW direction. The major tectonic fault orientations are NNW–SSE. The branches of the hydrographic network and faults present different directions, which indicates that the hydrographic pattern is not affected by tectonics.

Source characteristics and b-values of the Tuz Gölü Fault Zone in Central Anatolia, Turkey

We investigate significant earthquake sequences in the observation period between 2000 and 2018 along the Tuz Gölü Fault Zone in Central Anatolia. These sequences include a series of strong events with moment magnitudes (Mw) >5.0, e.g. 30 July 2005 Bala-Ankara Mw 5.2, 20 December 2007 Bala-Ankara Mw 5.7 and 26 December 2007 Mw 5.6 Afşar-Ankara earthquakes. The mainshocks are shallow focus strike-slip events with minor normal component at depths of 12–15 km. Focal depths of aftershocks range from 2 to 30 km. The focal mechanisms of the aftershocks are mainly normal faulting with variable strike-slip components. The geometry of focal mechanisms reveals a normal faulting regime with E-W and also NE-SW trending directions of T-axis in the entire activated region. A stress tensor inversion of focal mechanism data is performed to acquire a more accurate picture of the Tuz Gölü Fault Zone stress field. The stress tensor inversion results display a predominant normal stress regime with a NNE–SSW oriented maximum horizontal compressive stress (SH). According to high-resolution hypocenter relocations of the Tuz Gölü Fault Zone seismic sequences, eight clusters are revealed. The aftershock activities in the observation period between 5 March 2000 and 2 June 2018 extend from NW to SE direction. Seismic cross-sections show that a complex pattern of the hypocenter distribution with the activation of Tuz Gölü Fault Zone segments. The western clusters are associated with a fault plane trending mainly N-S and dipping towards almost vertical, while the eastern clusters are related to a fault plane trending NW and dipping towards SE direction. The best constrained focal depths are mainly confined in the crust (depth < 30 km) and range from 2 to 30 km. In this study, we compare the results of an analysis of b-values from seismicity and stress tensors of focal mechanism solutions to understand their coupling in terms of faulting and earthquake hazard implications. In particular, this comparison allows to investigate the spatiotemporal correlation between b-values and stress distributions and it is therefore able to locate fault segments that have a high potential of generating large earthquakes. According to recent seismicity, b-values range from 0.5 to 1.5 along the Tuz Gölü Fault Zone in Central Anatolia. The maximum horizontal compressive stress (SH) indicates N-S and NE-SW directions while the minimum horizontal compressive stress (Sh) displays E-W. These results represent that low stress variances are correlated with high b-values. Low b-values are predominant in areas with high stress rates, consistent with a high heterogeneity of focal mechanisms.

Sediment transport in the Luanhe River delta: grain size trend analysis

Sediment grain size in the deltaic environment of the Luanhe River (LR), Liaoning, China, contains sediment transport pathway information useful in elucidating the shoreline change and fluvialmarine interaction. In this study, we utilized numerical partitioning of the sedimentary components and geostatistical grain size trend analysis (GSTA) to define the sediment transport pattern in the Luanhe River delta (LRD) and interpolated the sediment transport pattern using content changes of end numbers (EM). EM1 (the mean grain size 7.12 Phi, fine silt), EM2 (2.37 Phi, fine sand), and EM3 (1.27 Phi, medium sand) components were identified by the numerical partitioning by GSTA. ICriging interpolation method was used to interpolate the parameters of the grain size for the regular grid, and the interpolation radius was 0.015 decimal degree. We chose 0.09 decimal degree as the characteristic distance for GSTA in the semivariogram model using the geostatistical method. The FB(-) case (finer, better sorted and more negatively skewed) was adopted in GSTA for its satisfaction in the Global Moran's I test. The result of the GSTA shows that the sediments in the south barriers (SBs) were transported to the southwest of the study area. The sediments in the north, in the SE direction of sediment transport trend from the river mouth, indicated that the sediments in the north of the study area were transported from the LR to the northern beaches, and to the south and east of the study area. The sediment transport trend that simplified by GSTA as the FB(-) case was approved by the content changes of sedimentary components (i.e. EM1, EM2, and EM3). In addition, the turbulent jet diffusion pattern indicated that the coarse sediments (EM3) were delivered by LR during the flood season, and the EM2 and EM1 were from wave and tide, respectively.

Paleogene crustal extension in the eastern segment of the NE Tibetan plateau

The Tibetan plateau experienced lateral growth in response to the India–Eurasia collision, but uncertainties remain about when and how its present-day margins were formed. It was commonly viewed that crustal shortening in the NE Tibetan plateau had commenced since the Eocene and led to reverse faulting and compressional basins. Our recent investigations of some Cenozoic intermontane basins reveal that synsedimentary normal faults occur widely in the eastern segment of the NE Tibetan plateau. Normal faulting at basin bases obviously controlled basin sedimentation and presumably resulted in footwall uplift and basement exhumation. Small-scale synsedimentary normal faults are very common in basin fill sequences although they decrease in intensity upwards and eventually vanish in the uppermost Paleogene sequences. Measurement of the attitudes of synsedimentary normal faults indicates that crustal stretching was in NW–SE direction. The NW–SE extension was consistent with Paleogene stress field of the whole North China craton, which were thought responsible for the NE–SW-trending rift basins in the interior of the North China craton, such as the Yinchuan, Weihe, and Bohai Bay rift basin systems. A broad unconformity separates Paleogene and Neogene sequences in the eastern segment of the NE Tibetan plateau, contrasting strikingly with conformable Oligocene to Middle Miocene sequences in the neighboring Ningnan and Yinchuan rift basins. It thus follows that the eastern segment of the NE Tibetan plateau had not been formed in Paleogene when it was basically dictated by crustal extension, possibly as a result of far-field effect of subduction of the western Pacific plate. End-Oligocene termination of normal faulting and the presence of a regional unconformity indicate that the eastern segment of the NE Tibetan plateau began rising at the beginning of the Miocene.

The Effects of Structural Elements on Groundwater of Wadi Yalamlam, Saudi Arabia Using Integration of Remote Sensing and Airborne Magnetic Survey

The present study aimed to develop an integrated approach that utilized field geology, remote sensing and airborne magnetic data to identify the Quaternary aquifers impounded by dykes and explain the dykes/lineaments relationship and their effects on the storage and flow of the groundwater of Sadiyah sub-basin, lower part of Wadi Yalamlam basin, Western Arabian Shield, Saudi Arabia. Field visits supported by Landsat ETM + ratio images (5/7, 5/4 and 5/1) revealed the presence of three main dyke types that can be chronologically arranged from older to younger as: Sheared mafic and acidic dykes (D1); Damm dyke complex (D2); and Ghumayqah dykes (D3). Two dykes referred to the first type (D1) were traced with depth using airborne magnetic survey crosscutting the main course of Wadi Yalamlam around Sadiyah village at high angle. According to water table elevation measurements, the aquifer of lower Wadi Yalamlam area is divided into three parts namely I, II and III. The water table elevations decreased from 158 m in the first part (I) to reach 66 m in the third part (III) of the aquifer. This drop is attributed to the effect of dykes which act as natural barriers. The study area was affected by three major fault systems as confirmed by field study and total magnetic map. Two of these systems have NE–SW to ENE–WSW and N–S to NNW–SSE directions, whereas the third one represents the Najd fault system trends in NW–SE direction. The present study identifies two locations valid for agricultural expansion lie just to the north of Sheikh Said and Abu Helal Farms.

Imaging Torfajökull's Magmatic Plumbing System With Seismic Interferometry and Phase Velocity Surface Wave Tomography

AbstractTorfajökull volcano, Iceland, has not erupted since 1477. However, intense geothermal activity, deformation, and seismicity suggest a long‐lasting magmatic system. In this paper, we use ambient noise tomography to image the magmatic system beneath Torfajökull volcano. One hundred days of ambient noise data from 23 broadband seismometers show the consistent presence of double‐frequency microseism noise with significant power between ∼0.1 and 0.5 Hz. Beamforming results indicate microseism noise with persistent higher energy propagating from west and SE directions and apparent velocities below 3 km/s. We use ambient noise seismic interferometry to retrieve Rayleigh waves, and we introduce a method to estimate the reliability of the retrieved surface waves. We find stable estimation of surface wave phase velocities between 0.16 and 0.38 Hz. Azimuthal velocity variations show a trend of higher velocities in the NE/SW direction, the strike of the rift zone intersecting Torfajökull, and orientation of erupted lavas on a NE‐SW fissure swarm. Tomographic results indicate low‐velocity anomalies beneath the volcano caldera (between −5% and −10%) and even lower velocity variations in the southeast and southwest study area (below −10%), outside the volcano caldera. Low anomalies may indicate the existence of hot material, more prominent outside the caldera outskirts. High‐velocity variations (between 5% and 10%) outline the volcano caldera between 4‐ and 5‐km depth and more pronounced velocities (between 10% and 15%) up to 5‐km depth in the north of the volcano caldera. We interpret the former as possible caldera collapse structure and the latest as solidified intrusive magma from the old preferred magma paths.

Análise dos fluxos nos aquíferos cárstico-fissurais da região da APA Carste de Lagoa Santa, MG

A área de estudos, que engloba a Área de Proteção Ambiental (APA) Carste de Lagoa Santa, se estende por 504 km2. Nesta região, ocorrem os metacalcários da Formação Sete Lagoas, composta pelos membros Pedro Leopoldo e Lagoa Santa, os quais acomodam os aquíferos cárstico-fissurais. O método de estudo envolveu o levantamento de estruturas rúpteis e de dissolução cárstica em uma malha de 9.000 m2, escala 1:300.000, com a finalidade de analisá-las e associá-las com as direções de cavernas e com direções de fluxos da água subterrânea comprovadas por testes de traçadores corantes (E-W, NE e SE), de sentido oriental. Por toda a área, a preponderância sistemática de cavernas e paleocondutos reliquiares na direção N70-90W, com caimento suave para leste, indica que esses paleocondutos resultam da dissolução ao longo da interseção das fraturas E-W, de alto ângulo, com o plano de acamamento suave, de direção NNW. Fraturas de alto ângulo de direção NE e SE também são frequentes, contudo, são raras as exposições dos paleocondutos e cavernas correlatos. Em contrapartida, embora as cavernas N-S se destaquem como mais persistentes e alongadas, assim como as E-W, não se observaram fluxos de água naquela direção (N-S). Os resultados demonstram que os parâmetros estruturais primordiais, as fraturas de alto ângulo e o acamamento, condicionam os fluxos subsuperficiais em condutos de cavernas ainda ativos no sentido oriental. No entanto, não se descarta a possibilidade de ocorrerem circulações profundas em segmentos N-S não observáveis nas zonas superiores.

Geophysical evidence for thrusting of crustal materials from orogenic belts over both sides of the Yangtze Block and its geological significance

Based on deep geophysical detections, we have reconstructed the crustal structure from the eastern margin of the Tibetan Plateau to the Jiangnan-Xuefeng orogenic belt. The results suggest that the Yangtze Block was overthrusted by crustal materials in its NW direction from the eastern Tibetan Plateau but in its SE direction from the Jiangnan orogen. These overthrusting effects control the crustal structure from the western Sichuan to the western area of the Jiangnan orogen-Xuefeng orogenic belt. The eastward extruded materials from the eastern Tibetan Plateau were blocked by the rigid basement in the Sichuan Basin, where upper-middle crust was overthrusted whereas the lower crust was underthrusted beneath the Sichuan Basin. The underthrusted unit was absorbed by crustal folding, shortening and thickening in the Yangtze Block, forming the Xiongpo and Longquan Mountains tectonic belts and resulting in the NW-directed thrusting of the Pujiang-Chengdu-Deyang fault, and the western hillsiden fault in the Longquan Mountain. These results provide resolution to the controversy where the eastward extrusion material from the Qinghai-Tibet Plateau had gone. Overall, that Yangtze Block was subjected to thrusting of the crustal materials from the orogenic belts over its both sides. This finding has implications for the study of the intracontinental orogenic mechanism in South China, the reconstruction of tectonic evolutionary history and the kinematics processes during the lateral extrusion of the Tibet Plateau.

Study of the Tide and Tidal Currents in the Bay of Bengal Based on Refined Simulations

Wan, W.; Feng, X.; Liu, Q.; Yin, B.; Yang, D., and Gao, G., 2019. Study of the tide and tidal currents in the Bay of Bengal based on refined simulations. Journal of Coastal Research, 35(1), 33–40. Coconut Creek (Florida), ISSN 0749-0208.A high-resolution, two-dimensional, hydrodynamic tidal model of the Bay of Bengal was developed using the Advanced Circulation (ADCIRC) Model to study the tide and tidal currents in the Bay of Bengal. The simulations conformed to the observations, and because of the use of a high-resolution, triangular grid, characteristics of the tide and tidal currents were computed more accurately than in previous studies. The results indicated that tides in most of the Bay of Bengal are semidiurnal, whereas those in the seas SE of Sri Lanka are mixed and predominately semidiurnal. There are two degenerate amphidromic points, one at the NE end of the head of the bay and the other at SE Sri Lanka, whereas there is an amphidromic point at the seas SE of Sri Lanka. The form of the M2 tidal current is rotary on the continental shelf and rectilinear in coastal areas and seas distant from the continental shelf. Four major tidal currents are in a NW–SE direction, in the western part of the head of the bay, and in a NE–SW direction in river estuary areas. Results from the eastern part are the opposite. The amplitudes and major axes of four tides and tidal currents increase upon entering the head of the bay, whereas those of the M2 tide are the largest.

TID Observations and Source Analysis During the 2017 Memorial Day Weekend Geomagnetic Storm Over North America

AbstractWe investigate ionospheric perturbations associated with traveling ionospheric disturbance (TID) during the geomagnetic storm on Memorial Day weekend (28 May) 2017. Results show the presence of both equatorward propagating large‐scale TIDs (LSTIDs) and poleward propagating medium‐scale TIDs. Equatorward moving TIDs are connected with enhanced auroral activity owing to geomagnetic storm conditions, while poleward TIDs are believed to be induced by local atmospheric gravity wave sources originating from convection activities near the West Coast of North America. Measurements from magnetometers located in the west, central, and east regions of North America are used to evaluate energy inputs from the auroral belt, and these observations confirm that equatorward LSTIDs are due to geomagnetic disturbance. The observed LSTID waves were characterized by some uncommon features, such as horizontal wavefront stretching from coast to coast, aligned in the NW to SE direction, and propagating to the southwest (equatorward) direction during the storm main phase period. In contrast, during the recovery phase and on other experimental control days, the observed medium‐scale TIDs were characterized with relatively smaller wavelengths aligned in the NW to SE direction and propagate primarily in the northeast (poleward) direction. Our results also reveal that LSTID waves appear to travel faster in the central continental region compared to LSTIDs in the western and eastern regions.

High-resolution lithofacies and porosity modeling of the mixed siliciclastic–carbonate deposits of the Burdigalian Dam Formation, Eastern Saudi Arabia

Conventional subsurface models of reservoir bodies are limited with respect to the good understanding of small-scale heterogeneities at inter-well spacing. Uncertainties associated with data limitation of such large-scale models can be enhanced by information from small-scale modeling. These high-resolution models may provide a realistic three-dimensional insight into their relevant subsurface reservoir setting. In this context, outcrop studies are frequently used to produce high-resolution models. In this paper, the Burdigalian Dam Formation outcrop in eastern Saudi Arabia was targeted to construct high-resolution models of lithofacies and porosity variations. These models were used to identify small-scale heterogeneities in lithofacies and porosity distribution using geostatistical modeling. Ten different lithofacies were identified and modeled. Indicator semivariogram analysis of the lithofacies showed good continuity in NW–SE direction but less continuity in NE–SW. The porosity model showed differing porosity distributions in different carbonate lithofacies. Several realizations of lithofacies and porosity models were generated and ranked against the input data set. Furthermore, the porosity variation was investigated through detailed petrography and SEM analyses for each of the studied lithofacies. The models demonstrated the presence of patterns of lithofacies and porosity variation at a small scale that cannot be obtained from conventional subsurface models. The study indicated the importance of such models in reducing the uncertainty associated with subsurface modeling as a result of data limitation.