Edge Of Basin Research Articles

Geological structure and modeling carbonate reservoirs of kt-ii of theKozhasay field(the esatern edge of pricaspian basin

In the present work the major results of integrating data from Kozhasay field for 3D geological modeling had been described (regional geological data, exploration and production drilling results, core and cuttings data, 3D seismic data interpretation results, borehole images). The entire borehole imaging data were revised and used for fracture modeling. The hybrid fracture model was generated (discret and implicit fractures). The Kozhasay field had been under production since 2003 and it has produced 4 % of the STOIIP as for 01.01.2019. Theintegrated geological model of KT-II carbonate reservoirs was used to create hydrodynamic model of the field.

Hydrocarbon potential of the Kobylandy-Tamdy upfold of the northern edge of Pricaspian basin

In the present article geological structure of Kobylandy-Tamdy Paleozoic upfold of the Pricaspian basin is described, the upfold was discovered and delineated based on seismic exploration and drilling results. On the example of Kobylandy area hydrocarbon potential of pre-salt complex of the conjunction of the Northen and Eastern edges of Pricaspian basin was evaluated and resources were estimated. New prospective structures were delineated within the Paleozoic sedimentary cover, which can be ranked as the first priority exploration drilling targets in the region.

Does Lake Erie still have sufficient oxythermal habitat for cisco Coregonus artedi?

In Lake Erie, cisco (Coregonus artedi) once supported one of the most valuable freshwater fisheries on earth, yet overfishing caused their eventual extirpation from the lake. With warming lake temperatures, some have questioned whether Lake Erie still contains suitable oxythermal conditions for cisco. Using published oxythermal thresholds for adult cisco (which have more stringent requirements than juveniles) and oxythermal profiles from Lake Erie, we sought to answer two questions critical to cisco restoration science. First, is cisco habitat still available during the most restrictive periods? Second, what is the distribution of cisco habitat during these times? Beta regression was used to determine that cisco habitat was most limited during the month of August, and that August of 2010 was the most restrictive period in the time series. We then used Empirical Bayesian Kriging (EBK) to map the spatial extent of cisco habitat during these times. EBK maps revealed large areas of summer refugia for cisco in Lake Erie, even during the least favorable periods. Most of the Central and East Basins contain suitable habitat during the average August, yet during August of 2010, suitable conditions were limited to the eastern edge of the Central Basin and the deep waters of the East Basin. These findings aligned well with historical accounts of cisco landings. While suitable oxythermal habitat still exists for cisco in Lake Erie, future restoration efforts, if attempted, will partially depend on: 1) better management of nutrient inputs, 2) the realization of future climate scenarios, and 3) the ability of cisco to adapt to a changing lake.

Middle Triassic gastropods from the Besano Formation of Monte San Giorgio, Switzerland

For the first time gastropods from the Besano Formation (Anisian/Ladinian boundary) are documented. The material was collected from three different outcrops at Monte San Giorgio (Southern Alps, Ticino, Switzerland). The taxa here described are Worthenia (Humiliworthenia)? aff. microstriata, Frederikella cf. cancellata, ?Trachynerita sp., ?Omphaloptycha sp. 1 and ?Omphaloptycha sp. 2. They represent the best preserved specimens of a larger collection and document the presence in this formation of the clades Vetigastropoda, Neritimorpha and Caenogastropoda that were widespread on the Alpine Triassic carbonate platforms. True benthic molluscs are very rarely documented in the Besano Formation, which is interpreted as intra-platform basin sediments deposited in usually anoxic condition. Small and juvenile gastropods could have been lived as pseudoplankton attached to floating algae or as free-swimming veliger planktotrophic larval stages. Accumulations of larval specimens suggest unfavorable living conditions with prevailing disturbance in the planktic realm or mass mortality events. However, larger gastropods more probably were washed in with sediments disturbed by slumping and turbidite currents along the basin edge or storm activity across the platform of the time equivalent Middle San Salvatore Dolomite.

Seismic effects of a small sedimentary basin in the eastern Tibetan plateau based on numerical simulation and ground motion records from aftershocks of the 2008 Mw7.9 Wenchuan, China earthquake

In this study, the ground motions that can be attributed to the aftershocks of the 2008 Mw7.9 Wenchuan, China earthquake recorded in the Wudu basin, which is a small basin in the eastern Tibetan Plateau, are analyzed to investigate the seismic effect of a small sedimentary basin. In case of the Wudu basin, the site responses from the basin edge are stronger than those from the basin center; the monitoring sites located near the Wudu basin edge and the Wudu basin center are sensitive to the low-frequency (<3 Hz) and high-frequency (>5 Hz) components of ground motion, respectively. It indicates that some different seismic phenomena occurred in a small sedimentary basin compared with a large sedimentary basin. To further study the ground motion in a small sedimentary basin, a simulation of the Wudu basin was conducted using the finite element method with a viscous–elastic artificial boundary. The grid size of the surface layer of the basin is 2.5 × 2.5 m2, and high-frequency (up to 10 Hz) components of a synthetic waveform were obtained. The simulation denoted that the surface wave initially appeared in the Wudu basin edge and subsequently propagated into its interior. The near-surface soil layers, exhibiting a relatively low wave velocity, magnified the amplitude of the seismic wave in the Wudu basin. Furthermore, the numerical simulation results are basically consistent with the actual ground motion records, especially with the same predominant frequencies of ground motions at the sites located near the Wudu basin edge.

Investigating the spatial variability of ground motions during the 2017 Mw 7.1 Puebla-Mexico City earthquake via idealized simulations of basin effects

We use strong motion records of the Mw 7.1 19 September 2017 mainshock and one- and two-dimensional (1D and 2D) simulations at six stations along a linear array across Mexico City, to shed light to the site amplification and ground motion variability observed during the mainshock. The 2017 Puebla-Mexico City earthquake occurred at the edge of the flat slab segment of the subducted Cocos plate beneath central Mexico, rupturing the top half of the plate. Compared to the 1985 subduction zone event, the intraslab Mw 7.1 mainshock was characterized by a much richer high-frequency content. This characteristic transpired into site amplification of the incoming shaking by the sediments of the transition zone, contrary to the 1985 Mw 8.1 Michoácan earthquake that was amplified by the deeper lake sediments. By means of idealized 1D site and 2D basin models, this paper seeks to disentangle site response from basin resonance and basin edge diffraction effects manifesting in the ground motion records. We specifically compare ground surface observations from the 2017 Mw 7.1 event to 1D and 2D analyses in the time and frequency domain; and empirical transfer functions from several earthquakes to numerical transfer functions computed using 1D and 2D models. Comparison of empirical and simulated amplification spectra shows that, although our 2D model does not capture all the peaks and troughs of the frequency response, theory and observations are nonetheless in good agreement across the entire frequency spectrum. And while frequency peaks of the 1D and 2D models are aligned in the range f>0.2Hz, the long period (f<0.01Hz) match between simulations and observations demonstrates that the 2D model appropriately captures the effects of the largest characteristic lengths of the basin, namely the basin width. In the intermediate frequency range (0.01 Hz <f<0.2Hz), our 2D model captures the scattering of the energy by the concave shape of the basin-rock interface via spectral deamplification, albeit not as strongly as is evidenced by the observations. One-dimensional site response on the other hand cannot capture the larger scale features below 0.2 Hz, which were likely relevant to the performance of lifelines and other infrastructure networks.

Research progress on production districts of Sichuan Dao-di herbs

Dao-di herbs are the Chinese herbs which have high quality and best clinic effects. Sichuan is one of the proviences most rich in Chinese herb resources,which has 7 290 species of Chinese herbs, such as Curcumae Longae Rhizoma, Chuanxiong Rhizoma, Aconiti Lateralis Radix Praeparata, Ophiopogonis Radix, Coptidis Rhizoma, Gentianae Radix, Rhei Radix et Rhizoma, Curcumae Rhizoma, Gardeniae Fructus, ect. After textual research on materia medica of the 7 290 Chinese herbs, we find there are 86 Dao-di herbs in Sichuan, such as Chuanxiong Rhizoma from Dujiangyan, Aconiti Lateralis Radix Praeparata from Jiangyou, Fritillariae Radix, Notoptergii Rhizoma et Radix, Angelicae Dahuricae Radix from Suining, Ophiopogonis Radix from Santai, Salviae Miltiorrhizae Radix et Rhizoma from Zhongjiang, Magnoliae Officinalis Cortex from Pingwu. In China more attention is paid to the production of Dao-di herbs. In 2018, the State Administration of Traditional Chinese Medicine launched the "Construction Plan of national production base of genuine medicinal materials". Developing genuine medicinal materials in genuine production areas is one of the effective ways to ensure the quality of medicinal materials. Based on the study of geographical environment and ecological factors(altitude, climate, soil) in Sichuan province. The Dao-di herbs of Sichuan province are divided into 4 districts, including, Sichuan basin medicinal materials production area, mountain and the basin edge medicinal materials production area, Panxi medicinal materials production area, Plateau Mountain Canyon medicinal materials production area. The suitable regions and best suitable regions of the 86 Dao-di herbs in Sichuan are determined by remote sensing and GIS spatial analysis of the suitable environmental indicators of these Dao-di herbs. Our study is beneficial to the rational distribution of the production and to improvement of the quality of traditional Chinese medicine in Sichuan province.

Basin edge effect on industrial structures damage pattern at clayey basins

In this numerical study, the 2D dynamic behavior of a clayey basin and its effect on damage pattern over basin edge are investigated. To attain this goal, a fully nonlinear time domain analysis method has been applied. Then, the fragility curves of the considered two typical industrial structures for that certain point are estimated using the acceleration time histories recorded at each surface point. The results show that the use of the damage related parameters in site effect analyses, instead of amplification curves, can yield more realistic estimation of the basin dynamic response. In a distance about 150m from outcrop at the basin edge, the differences between fragility curves increase when increasing the distance from outcrop with respect to the reference rock site. Outside this region and towards the basin center, they tend to occur in rather single curves. Furthermore, to connect the structural damage to the basin edge effect, the earthquake demand value at different points for two typical structures was evaluated. It was seen that the probability of occurrence of damage increases over 250 m from outcrop, while the effect of the basin edge was limited to 150 m in case of the basin edge evaluation by using fragility curves.

Numerical investigation on overburden migration behaviors in stope under thick magmatic rocks

Quantification of the influence of the fracture of thick magmatic rock (TMR) on the behavior of its overlying strata is a prerequisite to the understanding of the deformation behavior of the earth\'s surface in deep mining. A three-dimensional numerical model of a special geological mining condition of overlying TMR was developed to investigate the overburden movement and fracture law, and compare the influence of the occurrence horizon of TMR. The research results show that the movement of overlying rock was greatly affected by the TMR. Before the fracture of TMR, the TMR had shielding and controlling effects on the overlying strata, the maximum vertical and horizontal displacement values of overlying strata were 0.68 m and 0.062 m. After the fracture, the vertical and horizontal displacements suddenly increased to 3.06 m and 0.105 m, with an increase of 350% and 69.4%, respectively, and the higher the occurrence of TMR, the smaller the settlement of the overlying strata, but the wider the settlement span, the smaller the corresponding deformation value of the basin edge (the more difficult the surface to crack). These results are of tremendous importance for the control of rock strata and the revealing of surface deformation mechanism under TMR mining conditions in mines.

Growth, overprinting, and stabilization of Proterozoic provinces in the southern Lake Superior region

New geochronologic data in the southern Lake Superior region provide key information on the timing and nature of tectonic activity that pre-and post-date initial Paleoproterozoic growth of Laurentia during the geon 18 Penokean orogeny. The obducted Pembine ophiolite formed along the edge of a Paleoproterozoic ocean basin at least 30 m.y. prior to Penokean island arc/microcontinent accretion beginning at 1860 Ma. Following Penokean orogenesis, intrusion of mafic dikes at 1817 ± 2 Ma indicate a period of extension that coincided with a 30 m.y. gap in orogenic felsic magmatism at 1835–1805 Ma (between the Penokean and Yavapai orogenies) and likely represents relaxation of Penokean compression and a tectonic switch to intra-arc extension related to initiation of Yavapai subduction. Subsequent Yavapai arc accretion (1750–1720 Ma) resulted in pervasive ductile deformation of the dikes and host rocks at temperatures of ~700 °C, previously attributed to Penokean deformation. Geon 16 Mazatzal overprinting of the accreted Penokean and Yavapai provinces was widespread but of overall lower metamorphic grade (greenschist facies), and the thermal effects of the 1476–1470 Ma shallow level Wolf River batholith was limited to a 10–15 km wide contact zone surrounding the intrusion.In contrast to the Archean Superior Province to the north, Paleoproterozoic terranes in the southern Lake Superior area experienced widespread low-temperature reheating and cooling of shallow crustal levels at ca. 1.1–1.0 Ga attributed primarily to magmatic underplating with little subsequent Neoproterozoic exhumation. In the southern Lake Superior region widespread magmatic underplating likely thickened, strengthened, and stabilized Proterozoic Penokean-Mazatzal lithosphere but destabilized Archean cratonized Superior Province lithosphere to the north.

Ambient seismic noise tomography in west-central and Southern Brazil, characterizing the crustal structure of the Chaco-Paraná, Pantanal and Paraná basins

SUMMARYSurface wave analysis provides important information on crustal structure, but it is challenging to obtain accurate/robust models in aseismic regions because of the lack of local earthquake records. In this paper, interstation empirical Green's functions retrieved by ambient seismic noise in 75 broad-band stations from 2016 January to 2018 September were used to study crustal structure in west-central Brazil. Fast marching method was applied to calculate the 2-D surface wave tomographic maps, and local dispersion curves were estimated in the period range of 4–80 s for each geographic cell. 1-D damped least squares inversion method was then conducted to obtained shear wave velocity model. Finally, the average ($\tilde{\rm V}$S) of the calculated VSV and VSH quasi 3-D models were used to characterize the crustal structure. Besides the checkerboard test resolution, a stochastic test with the effect of errors in the dispersion curves and choice of inversion parameters were carried out to better evaluate model uncertainties. Our results show a clear relation between the sedimentary thickness and geological units with the shorter period tomographic maps. Agreement has also been observed in longer periods such as the clear N–S anomaly along the Asuncion and Rio Grande Arches representing the boundary between the Chaco-Paraná and the Paraná basins. A 3-D composite velocity model shows a crustal structure consisting of three main layers. Some differences in lower crustal properties were found between the Paraná and Chaco-Paraná basins, consistent with a recently postulated, gravity-derived Western Paraná suture zone. However, no high velocities along the SW–NE axis of the Paraná basin were found to confirm proposed underplating. At the eastern edge of the Pantanal basin, the thin crust seems to be associated with a very thin (or lack of) lower crustal layer, consistent with a recently proposed crustal delamination hypothesis for the formation of the Pantanal basin.

Teleseismic Scattered‐Wave Imaging Using a Large‐N Array in the Albuquerque Basin, New Mexico

AbstractThe advent of low‐cost continuously recording cable‐free autonomous seismographs, commonly referred to as nodes, enables dense spatiotemporal sampling of seismic wavefields. We create virtual source reflection profiles using P waves from five teleseismic events recorded by the Sevilleta node array experiment in the southern Albuquerque basin. The basin geology records a structurally complex history, including multiple Phanerozoic orogenies, Rio Grande rift extension, and ongoing uplift from a midcrustal magma body. The Sevilleta experiment densified the long term, regionally sparse seismograph network with 801 single channel vertical‐component 10 Hz geophone nodes deployed at ∼300 m spacing for 14 days in February 2015. Results show sediment‐basement reflections at &amp;lt;5 km depth and numerous sub‐basin structures. Comparisons to legacy crustal‐scale reflection images from the Consortium for Continental Reflection Profiling show agreement with structural geometries in the rift basin and upper crust. Comparisons of the teleseismic virtual reflection profiles to synthetic tests using 2D finite‐difference elastic wave propagation show strong P‐to‐Rayleigh scattering from steep basin edges. These high‐amplitude conversions dominate the record sections near the western rift margin and originate at the Loma Pelada fault, which acts as the primary contact between rift‐bounding basement‐cored fault blocks and rift basin sediments. At near offsets, these signals may interfere with interpretation of upper crustal structure, but their relatively slow moveout compared to teleseismic P‐wave multiples provides clear temporal separation from sediment‐basement reflections across most of the array. The high‐signal‐to‐noise ratio of these converted Rayleigh‐wave signals suggests that they may be useful for constraining short‐period (∼1 Hz) dispersion with strong sensitivity in the uppermost ∼1 km of the rift basin sediments.

Upper crustal structures of the southeast edge of Parnaiba basin using 3D magnetotelluric data imaging

In this study, broadband magnetotelluric (MT) data are acquired from 101 stations in the southeastern edge of the Parnaiba basin in NE Brazil. The MT stations are distributed in 10 semi-parallel profiles, with NW-SE orientation. In order to characterize the internal structure of this area, we propose a geoelectric resistivity model by applying the three-dimensional (3D) inversion of this data. In this way, the time series of the horizontal electric and magnetic fields are processed using a robust technique to evaluate the impedance tensor. The dimensionality analysis that was performed indicates a predominant 3D behavior, and the full tensor components were inverted. The preferred model verified the presence of low-resistivity areas located in the upper crust. The interpretation of these areas is in relation to geodynamic events that happened in the three domains of the Borborema Province: northern, central, and southern. The low-resistivity region located in the northern domain shows that there is an association with graphite precipitation, as defined by the metamorphism in the western zone of the Seridó belt. We propose that the conductive region in the central domain is explained by the reactivation of the Pernambuco shear zone. In the southern domain, it was associated with serpentinization processes by the hydration of mafic and ultramafic rocks from the Brejo Seco complex in the context of subduction in the Neoproterozoic. In addition, the 3D resistivity model revealed the graben-like structures with predominate NE-SW direction observed in previous works. Likewise, upper crust discontinuities were shown to be associated with the Senador Pompeu and Pernambuco shear zones, which were defined previously using aerogravimetric and aeromagnetic data.

The Iberian Peninsula’s Burning Heart—Long-Term Fire History in the Toledo Mountains (Central Spain)

Long-term fire ecology can help to better understand the major role played by fire in driving vegetation composition and structure over decadal to millennial timescales, along with climate change and human agency, especially in fire-prone areas such as the Mediterranean basin. Investigating past ecosystem dynamics in response to changing fire activity, climate, and land use, and how these landscape drivers interact in the long-term is needed for efficient nature management, protection, and restoration. The Toledo Mountains of central Spain are a mid-elevation mountain complex with scarce current anthropic intervention located on the westernmost edge of the Mediterranean basin. These features provide a perfect setting to study patterns of late Holocene fire activity and landscape transformation. Here, we have combined macroscopic charcoal analysis with palynological data in three peat sequences (El Perro, Brezoso, and Viñuelas mires) to reconstruct fire regimes during recent millennia and their linkages to changes in vegetation, land use, and climatic conditions. During a first phase (5000–3000 cal. BP) characterized by mixed oak woodlands and low anthropogenic impact, climate exerted an evident influence over fire regimes. Later, the data show two phases of increasing human influence dated at 3000–500 cal. BP and 500 cal. BP–present, which translated into significant changes in fire regimes increasingly driven by human activity. These results contribute to prove how fire regimes have changed along with human societies, being more related to land use and less dependent on climatic cycles.

Carbon mass balance, isotopic tracers of biogenic methane, and the role of acetate in coal beds: Powder River Basin (USA)

A multi-isotope (C, H, O) investigation of biogenic gas (δ13C−CH4, δ13C−CO2, δD−CH4) and coal bed waters (δD, δ18O, δ13C-DIC, δ13C-acetate) was conducted along a ∼25-km basinward sampling transect in the Powder River Basin (PRB) in Wyoming and Montana (USA) to address inconsistencies among isotope fingerprinting techniques and to apply mass balance isotope modeling to biogenic coalbed methane (CBM). Results include the first published compound-specific δ13C-acetate values from a natural biogenic CBM system, providing new constraints on acetate’s role in biogenic CH4 generation. Coal bed water chemistry is anoxic and dominated by Na+ and HCO3−, with high alkalinity concentrations (14.8–33.0meq/L). The deep basin interior environment contains sulfate-free, Na+−HCO3−-dominated waters exhibiting signs of methanogenesis. CH4 and CO2 generally become 13C-enriched from the shallow basin edge to the deep basin interior (δ13C−CH4 −78.2 to −56.2‰ and δ13C−CO2 -24.7 to 4.7‰). Also, compound-specific δ13C-acetate is more positive in the basin interior compared to the basin edge setting (range −34.3 to −15.1‰). Using a steady-state mass balance isotope model, the observed variations in δ13C-CH4 and δ13C-CO2 can be explained in terms of the favorability of methanogenesis (fCH4) relative to heterotrophic bacterially-mediated non-methanogenic pathways, such as bacterial sulfate reduction, which compete with methanogenesis for substrates. At the basin interior, fCH4 exceeds 0.4, approaching its inferred limiting value hypothesized from the oxidation state of low-molecular weight compounds detected in PRB formation waters. Therefore, methanogenesis is likely a dominant biogeochemical pathway consuming substrates in the deeper coal beds. The basinward shift toward 13C-enriched acetate broadly indicates linkage between acetate, CH4, and CO2, and likely records acetate synthesis effects modified by methanogenic fractionation. These results suggest that acetate plays a role in methanogenesis in PRB coal beds (not necessarily a dominant role), while other C isotope and microbial evidence suggests that hydrogenotrophic methanogenesis is also a significant methane-producing pathway. The results of this study broadly suggest multiple viable methanogenic pathways and C cycling that affects acetate, a more complex view of coal bed geochemistry than implied by traditional C and H isotope fingerprinting of accumulated products (CH4, CO2) and coexisting water.

3D Ground Response Analysis of Simplified Kutch Basin by Spectral Element Method

The damage pattern observed during the 1819 Kutch earthquake and 2001 Bhuj earthquake of magnitude [Formula: see text] in India implied the significance of the effect of Kutch basin on seismic ground motion. In the present study, the Kutch rift basin is modeled as a simplified rectangular basin of size 150[Formula: see text]km [Formula: see text] 90[Formula: see text]km [Formula: see text] 1.5[Formula: see text]km. The shear wave velocity of the Kutch region varies from 300[Formula: see text]m/s at the surface to 800[Formula: see text]m/s at the depth of 60[Formula: see text]m. Three-dimensional ground response analysis is carried out for the simplified Kutch basin subjected to ricker wave, using the spectral element code SPEED. The soil medium is modeled through visco-elastic soil model, where the damping is represented by Quality factor. It is found out from the numerical analysis that maximum amplification of 3.6 times occurs at the corner of the basin where interference of waves reflected from multiple edges happen. The long period structures with fundamental period in the range of 1.5–2.5[Formula: see text]s located near the basin edge are found to be significantly affected by the basin effect.

Contribution of time domain electromagnetic and magnetic resonance soundings to groundwater assessment at the margin of lake chad basin, cameroon

At the edge of a semi-arid sedimentary basin, the Piedmont plain of the Mandara mountains is potentially a key area for the recharge of the Lake Chad Quaternary aquifer. We conducted two geophysical surveys based on magnetic resonance sounding (MRS) and Time-Domain Electromagnetism (TDEM) techniques for a better understanding of the aquifer structure at the piedmont scale in aim to identify preferential groundwater recharge pathways. MRS water content and electrical resistivity of the medium confirmed the very heterogeneous and clayey nature of the quaternary aquifer, limiting the recharge to the sandiest areas. Thanks to the geophysical methods, these areas have been highlighted near temporary rivers and upstream of the study area near Maroua city. Because of the thickening of the aquifer downstream, the most transmissive zones are in the mid-slope of the piedmont. The geographical distribution of aquifer properties defined by geophysics and the range of MRS water content (from <2% to 26%) may be used in the future to constrain groundwater modelling and specify the recharge of the quaternary aquifer at mountain front.

The Môn–Deemster–Ribblesdale fold–thrust belt, central UK: a concealed Variscan inversion belt located on weak Caledonian crust

Abstract The Ribblesdale fold belt, representing the Variscan inversion of the Bowland Basin, is a well-known geological feature of northern England. It represents a crustal strain discontinuity between the granite-underpinned basement highs of the northern Pennines and Lake District in the north, and the Central Lancashire High/southern Pennines, in the south. Recent seismic interpretation and mapping have demonstrated that the Ribblesdale fold belt continues offshore towards Anglesey via the Deemster Platform, beneath the Permo-Triassic sedimentary cover of the southern part of the East Irish Sea Basin. The Môn–Deemster fold–thrust belt (FTB) affects strata of Mississippian to late Pennsylvanian age. Variscan thrusts extend down into the pre-Carboniferous basement but apparently terminate at a low-angle detachment deeper in the crust, here correlated with the strongly sheared Penmynydd Zone exposed in the adjacent onshore. Up to 15% shortening is observed on seismic sections across the FTB offshore, but is greater in the strongly inverted onshore segment. Pre-Carboniferous thrusting post-dates formation of the Penmynydd Zone, and is probably of Acadian age, when basement structures such as the southward-vergent Carmel Head Thrust formed. Extensional reactivation of the Acadian structures in early Mississippian time defined the northern edge of the offshore Bowland Basin. The relatively late brittle structures of the Menai Strait fault system locally exhume the Penmynydd Zone and define the southern edge of the basin. The longer seismic records from the offshore provide insights to the tectonic evolution of the more poorly imaged FTB onshore.

Bed separation backfill to reduce surface cracking due to mining under thick and hard conglomerate: a case study.

After coal mining, the surface above a goaf may experience the discontinuous deformation under some special geological and mining conditions, such as surface cracking, surface step subsidence and collapse pits. Discontinuous deformation seriously threatens the safety of surface buildings and infrastructures. In this paper, the mechanism of discontinuous surface deformation and surface cracking due to coal mining under thick and hard conglomerate in the Huafeng coal mine was studied using a simulation test on similar materials. Bed separation backfill was then proposed to control surface cracking and to protect the Luli bridge. Because of lithological differences between the conglomerate and relatively weak red strata (beneath the conglomerate), the bed separation occurred between them with the advancement of the working face. When the bed separation span exceeded its breaking span, the conglomerate fractured, causing surface cracking of the downhill area and seriously damaging the stability of the Luli bridge. Three drilling holes were arranged along the strikes of the 1412 and 1613 working faces and nearly 387 000 m3 of backfill materials (water, fly ash and gangue powder) were injected into the bed separation space to reduce or prevent fracturing of the conglomerate. The compacted backfill body supported the conglomerate and reduced the subsidence of the basin and surface ‘rebound' deformation at the edge of the subsidence basin. Clay in the red strata expanded upon contact with water, and this further backfilled the bed separation zone and supported the conglomerate. The upper and lower structures and foundation of the bridge were reinforced using various methods. It was shown that bed separation backfill effectively controlled conglomerate movement and protected the bridge with a maximum subsidence of 251 mm. No obvious surface cracks were observed near the Luli bridge.

2D seismic response of the Duzce Basin, Turkey

The existence of the inclined bedrock at the basin edges bring about the concentration of the damages at these areas. The graben-like Duzce Basin with a low inclined subsurface topography is prone to exhibit such effects. In this study, at the first, Duzce Basin edge model is extracted from the data obtained from performed microtremor surveys as well as geotechnical investigations. Using these data, the basin stratification and shear wave velocity profile as well as the geotechnical properties of the layers is identified. Based on these data, the idealized Duzce Basin edge model is proposed. Then, to estimate the dynamic behavior of the Duzce Basin, a fully nonlinear method based on explicit finite difference scheme is performed. The basin is subjected to the collection of 16 strong ground motions with different peak ground accelerations (PGA) levels. Using the recorded acceleration at 12 surface points along the basin edge the variation of the maximum spectral amplification factor is reported. The results show that the Duzce Basin edge behavior is greatly affected by inclined bedrock. Also, the sensitivity of the different points of the basin to different periods is investigated. It is seen that in the case of the motions with the PGA of 0.2 g, this band spans between 0.1s to about 1.7s.