Continental Deep Drilling Research Articles

Zircon U[sbnd]Pb geochronology and geochemistry of hot subduction volcanic suite in the deep bore-hole well-core KBH-5: Evidence of Neoarchean Shimoga greenstone belt beneath the Cretaceous Deccan Traps, India

The continents across Earth have grown through accretion and amalgamation of plume-generated oceanic plateaux and subduction-originated magmatic arcs. The evidence of such evolutionary processes is well preserved in the greenstone belts of Canada, South Africa, China, Australia and India. Unlike accretion that leads to lateral growth of the continents, flood basalt volcanism results in the superposition of large volumes of dense mafic material above relatively less dense sialic upper continental crust. The resulting density inversion is liable to generate tectonic stresses resulting in faulting of under burden along weak planes. The nature of the crust obscured beneath flood basalt provinces that have accumulated over the past 500 My in Large Igneous Provinces (LIPs) has remained enigmatic, largely because of the voluminous lava pile that deters access to the concealed basement, unless otherwise retrieved through deep continental drilling. Here, we present in situ zircon UPb geochronology and bulk-rock geochemistry of a volcanic sequence discovered at −400 m m.s.l in the deep bore-hole well-core KBH-5 of the southwestern Deccan Traps, India. The ∼300 m thick metavolcanic succession includes a basalt – Nb-enriched basalt – andesite – Mg-andesite – dacite – adakite suite. The zircons yielded a 2.58 Ga U-Pb age for the suite, which also incorporates entrained zircon xenocrysts of 2.7 Ga age from a preexisting juvenile material during its emplacement. The bore-hole KBH-5 is located on an NNW-SSE trending normal fault, paralleling a series of major faults west of the Western Ghat Escarpment. Although the crustal block plummeted ∼1000 m downward along the fault plane, the geochemical attributes of the metavolcanic rocks are thoroughly comparable to those reported in the Medur Formation of the Shimoga greenstone belt, ∼300 km south of KBH-5 in the western Dharwar craton. Our study provides the first physical evidence of Dharwar greenstone belt(s) extending further beneath the Deccan Traps, which was previously only speculative based on short-wavelength gravity highs. The metavolcanic sequence evolved in a subduction-related back-arc tectonic regime and accreted to the active continental margin of India in the Neoarchean. Unveiling of potentially similar scenarios in cratons elsewhere entrapped beneath the vast canopy of continental flood basalts, would reveal new crustal growth events during the Archean -Proterozoic transition across the Earth.

Behavior of helium diffusion sinks in apatite: Evidence from continuous ramped heating analysis of borehole and well-characterized samples

Diffusion sinks have been proposed to explain the complex high-temperature 4He release often seen in Continuous Ramped Heating (CRH) analysis of apatites, which often correlates with over-dispersed and anomalously old (U-Th)/He ages. In this work, we first conducted CRH experiments with various ramping rates and cycled CRH experiments that confirm that the high-temperature 4He release from diffusion sinks is systematically temperature sensitive at laboratory time scales. We then analyzed apatite grains from the KTB borehole (German Continental Deep Drilling program) that have well-constrained thermal histories to test whether different thermal histories could alter the trapping of 4He at geologic time scales. The KTB samples show large intra-sample single-grain age dispersion, with most ages being older than predictions from a 4He radiation-damage diffusion model RDAAM. Individual grains from shallower depths show complex 4He outgassing behaviors, including the expected low-temperature volume-diffusion loss, sudden release spikes, and a higher- temperature-dependent component. Grains from the current partial retention zone and greater depths retain considerable helium and exhibit exclusively complex outgassing behavior dominated by high-temperature release in the laboratory. KTB samples show a systematic difference with depth in the proportion of low- and high-temperature gas-release gas components. Deeper samples, having long open-system thermal histories, contain a greater proportion of 4He that appears to have been trapped compared to the simpler volume-diffusion behavior exhibited by shallower samples that experienced a simpler monotonic cooling history. While greatly reduced, the high-temperature component is still present in the highest-temperature samples analyzed, well hotter than the partial retention zone. These observations confirm that in apatite trapping and release of helium from sinks is temperature dependent at geological time scales as well. This supports the suggestion that additional thermal-history information from apatites might be obtained using 4He/3He analysis, with laboratory release of 3He providing information about trap distribution and kinetics and 4He providing information about the geologic thermal history.

Upper crustal structure at the KTB drilling site from ambient noise tomography

Summary In this study, we show results from ambient noise tomography around the KTB (Kontinentales Tiefbohrprogramm der Bundesrepublik Deutschland), a continental deep drilling site located at the western edge of the Bohemian Massif, within the Variscan belt of Europe. At the KTB site, crustal rocks have been drilled down to 9 km depth. Before the drilling activity started, several active seismic surveys had been performed to explore its surroundings during the 1980s and early 1990s, in the frame of an extensive exploration of the area aimed at unravelling the characteristics of the continental lower crust that is exposed at surface in this location. Despite the exploration campaigns held at and around the KTB drilling site, there are important targets that are worth further investigation; these are related in particular to the obduction of lower crustal units to the surface, and to the mechanism of orogenic processes in general. Here we present a new 3-D shear wave velocity model of the area from cross-correlations of ambient seismic noise. The model is obtained by a unique data set composed of 2 yr of continuous data recorded at nine 3-component temporary stations (installed from July 2012 to July 2014) located on top and around the drilling site, and together with the data from 19 permanent stations throughout the region. This paper is focusing on the upper crustal layers, and we show velocity variations at short scales that correlate well with known geological structures in the region of the KTB site, at the surface and at depth. These are used to discuss features that are less well-resolved at present.

Borehole magnetic fabric anomalies in KBH 07 Deccan basalt core from Deep Continental Drilling, western Maharashtra, India

Borehole magnetic fabric anomalies in KBH 07 Deccan basalt core from Deep Continental Drilling, western Maharashtra, India

Generalized crack damage stress thresholds of hard rocks under true triaxial compression

The rock failure process can be characterized by several distinct stress thresholds: the crack closure stress σcc, crack initiation stress σci, crack damage stress σcd and peak stress σp. Seventy-one true triaxial compression tests were conducted to investigate the crack damage stress σcd, which is the stress at the onset of unstable crack development and dilation. Two empirical models are developed to predict the crack damage stress σcd using the intermediate principal stress σ2 and the minimum principal stress σ3. In addition, the proposed models are validated by ten results derived from the German Continental Deep Drilling Program (KTB) deep hole amphibolite. A comparison with other failure criteria also indicates the accuracy and simplicity of the proposed models. The proposed composite models show that the crack damage stress σcd gradually increases with increasing intermediate principal stress σ2 and minimum principal stress σ3. The physical meanings and ranges of six material parameters are analyzed and explained. Both the influence of the tangent Young’s modulus E and strain characteristics on the crack damage stress σcd and the inhomogeneity of the tested specimens are discussed in this paper.

Probing crustal anisotropy by receiver functions at the deep continental drilling site KTB in Southern Germany.

ABSTRACTSeismic anisotropy is a unique observational tool for remotely studying deformation and stress within the Earth. Effects of anisotropy can be seen in seismic data; they are due to mineral alignment, fractures or layering. Seismic anisotropy is linked to local stress and strain, allowing modern geophysics to derive geomechanical properties from seismic data for supporting well planning and fracking. For unravelling anisotropic properties of the crust, the teleseismic receiver functions methodology has started to be widely applied recently due to its ability in retrieving the three‐dimensional characteristics of the media sampled by the waves. The applicability of this technique is tested here by a field test carried out around the Kontinental Tiefbohrung site in southeastern Germany. We compare our results to previous investigations of the metamorphic rock pile of the Zone Erbendorf‐Vohenstrauss, drilled down to 9 km depth, which sampled an alternating sequence of paragneiss and amphibolite, in which a strong foliation has been produced by ductile deformation. The application of the receiver functions reveals the presence of two distinct anisotropic layers within the metamorphic rock pile at 0–4 km and below 6 km depth, with up to 8% anisotropy; the depth of these two layers corresponds to the location of mica‐rich paragneiss which show intense foliation, and finally proves the relation between the signal in the receiver functions, rock texture and presence of cracks. We have now the capability of providing insights from passive seismic data on geomechanical properties of the rocks, useful for geological exploration and engineering purposes, which will help influencing expensive drilling decisions thanks to future application of this seismic technique.

A Probabilistic Approach to Injection‐Induced Seismicity Assessment in the Presence and Absence of Flow Boundaries

AbstractInduced seismicity models that do not account for the effects of flow boundary conditions and uncertainty in initial stresses on the seismicity rate fail to predict the seismicity observed in real‐world injection sites. We present a model for the probabilistic assessment of induced seismicity that incorporates in situ stresses, pressure, and reservoir boundary conditions. The model considers a randomly distributed network of faults undergoing frictional failure due to pressure‐induced effective stresses. A semianalytical method is used to capture the effect of flow boundary conditions on pressure and seismicity rate based on pressure diffusion and Mohr‐Coulomb failure. We compare the model predictions with induced seismicity observations in Paradox Valley and German Continental Deep Drilling Program. We demonstrate that differences in the flow boundary conditions can drastically change the seismic response to injection. The strongest difference is observed for a closed boundary reservoir for which the induced seismicity rate increases exponentially.

Active microbial biofilms in deep poor porous continental subsurface rocks

Deep continental subsurface is defined as oligotrophic environments where microorganisms present a very low metabolic rate. To date, due to the energetic cost of production and maintenance of biofilms, their existence has not been considered in poor porous subsurface rocks. We applied fluorescence in situ hybridization techniques and confocal laser scanning microscopy in samples from a continental deep drilling project to analyze the prokaryotic diversity and distribution and the possible existence of biofilms. Our results show the existence of natural microbial biofilms at all checked depths of the Iberian Pyrite Belt (IPB) subsurface and the co-occurrence of bacteria and archaea in this environment. This observation suggests that multi-species biofilms may be a common and widespread lifestyle in subsurface environments.

Magnetic Mineralogical Variability along Deccan Trap Basalt Borehole (KBH07), Koyna Deep Continental Drilling Program, Western Maharashtra, India

ABSTRACT A 1248 m long core (KBH 07, 17°18'07" N; 73°47'28.2"E, 960m above msl) drilled up to basement in the Deccan traps from Koyna region was sampled at ∼10m interval for magnetic mineralogical studies. Analysis of routine rock magnetic parameters (mass specific magnetic susceptibility: χlf, frequency dependence of susceptibility: χfd, susceptibility of anhysteretic remanance: χARM, saturation isothermal remanance: SIRM, remanance coercivty: B(0)CR, SoftIRM, HardIRM, S-Ratio, SIRM/χlf, χARM/χlf) and density (σ, gm/ cc) depicted significant higher order temporal variation. The χlf varies between 13 and 309 x 10−8m3/kg and is independent of density variation. The χARM, B(0)CR and S-Ratios indicate majority of SD-PSD ferrimagnets with episodes of MD ferrimagnetic concentration and few hard coercivity components. The giant plagioclase lath bearing (GPB) horizons show highest variability of ferrimagnetic concentration marked by anomalous peaks. Overall the variability of rock magnetic parameters independent of lava flow units suggest that the changeover in magnetic mineral concentration, composition and domain size occur at major episodes in magma composition (e.g., primary source, crustal contamination and fractional crystallization). The studied parameters are therefore examined to mark intervals of (i) magma compositional changes, (ii) zones of oxidative conditions and (iii) rapid/slow cooling intervals demanding detailed petrologic studies. We identified one I order trend, four II order cycles and eight III order cycles for the purpose of correlation. Notable peak in χlf at 650-700m, the changeover in rock magnetic parameters at ∼930 m and ∼280 m can facilitate marker intervals while several higher order variations can be adopted for high resolution correlation to other boreholes in the region. The complex variation in rock magnetic parameters independent of flow units reflect temporal magnitudes of compositional variability, cooling and emplacement history that needs detailed petro-mineralogical attempts; and the present data is useful for high order inter-core correlations under the deep drilling program.

Improved structural characterization of the Earth's crust at the German Continental Deep Drilling Site using advanced seismic imaging techniques

AbstractThis paper describes the principles of three novel seismic imaging techniques and their application to two deep seismic reflection data sets from the vicinity of the German Continental Deep Drilling Site (KTB). These imaging techniques are based on Kirchhoff prestack depth migration and use an inherent restriction of the migration operator to focus the wavefield to its actual reflection point. For Fresnel volume migration, the emergent angle at the receivers is estimated and then used to propagate the wavefield back into the subsurface along which the Fresnel volume is determined. The migration operator is restricted to this volume, thereby focusing the image to the part of the isochrone which physically contributes to the reflection. For coherency migration, the coherency of the wavefield at neighboring traces is calculated and used as a weighting factor within the migration integral, leading to a comparable focusing to the reflection point. For coherency‐based Fresnel volume migration, both approaches are combined, resulting in an even more focused seismic image with significantly increased image quality. We applied these methods to two seismic data sets from the area around the KTB: a survey with standard split‐spread geometry (KTB8502) and a sparse data set with a small number of source points in combination with short receiver lines (INSTRUCT93). The focusing approaches yield major improvements in the final images for both data sets. Incoherent noise and migration artifacts are reduced and the visibility of crustal structures is strongly enhanced, allowing for an improved geologic and tectonic characterization.

Geothermal modelling of faulted metamorphic crystalline crust: a new model of the Continental Deep Drilling Site KTB (Germany)

The area of the 9.1-km-deep Continental Deep Drillhole (KTB) in Germany is used as a case study for a geothermal reservoir situated in folded and faulted metamorphic crystalline crust. The presented approach is based on the analysis of 3-D seismic reflection data combined with borehole data and hydrothermal numerical modelling. The KTB location exemplarily contains all elements that make seismic prospecting in crystalline environment often more difficult than in sedimentary units, basically complicated tectonics and fracturing and low-coherent strata. In a first step major rock units including two known nearly parallel fault zones are identified down to a depth of 12 km. These units form the basis of a gridded 3-D numerical model for investigating temperature and fluid flow. Conductive and advective heat transport takes place mainly in a metamorphic block composed of gneisses and metabasites that show considerable differences in thermal conductivity and heat production. Therefore, in a second step, the structure of this unit is investigated by seismic waveform modelling. The third step of interpretation consists of applying wavenumber filtering and log-Gabor-filtering for locating fractures. Since fracture networks are the major fluid pathways in the crystalline, we associate the fracture density distribution with distributions of relative porosity and permeability that can be calibrated by logging data and forward modelling of the temperature field. The resulting permeability distribution shows values between 10-16 and 10-19 m(-2) and does not correlate with particular rock units. Once thermohydraulic rock properties are attributed to the numerical model, the differential equations for heat and fluid transport in porous media are solved numerically based on a finite difference approach. The hydraulic potential caused by topography and a heat flux of 54 mW m(-2) were applied as boundary conditions at the top and bottom of the model. Fluid flow is generally slow and mainly occurring within the two fault zones. Thus, our model confirms the previous finding that diffusive heat transport is the dominant process at the KTB site. Fitting the observed temperature-depth profile requires a correction for palaeoclimate of about 4 K at 1 km depth. Modelled and observed temperature data fit well within 0.2 degrees C bounds. Whereas thermal conditions are suitable for geothermal energy production, hydraulic conditions are unfavourable without engineered stimulation.

3D fracture networks in the crystalline upper crust ‐ A new seismic model of the Continental Deep Drilling Site (South Germany)

ABSTRACTBased on three‐dimensional seismic reflection data, we present the first comprehensive three‐dimensional model of the fault and fracture inventory of the crystalline upper crust penetrated by the Continental Superdeep Drillhole (Kontinentale Tiefborung, Oberpfalz, Southeast Germany). The investigated volume spans ∼19×19 km2 down to 16‐km depth. It can be regarded as a typical example of metamorphic crust that has undergone numerous phases of ductile and brittle deformation since the start of the Variscan orogeny. We developed an automated workflow for identifying and quantifying the crustal fracture network in order to prepare a basis for an assessment of fluid pathways and geothermal potential of crystalline crust. The workflow comprises the following steps: determination of (i) a three‐dimensional model of major faults by structural tensor analysis and (ii) a three‐dimensional model of middle‐scale fractures by log‐Gabor filtering and image processing; (iii) validation of results by comparison with geophysical borehole data, with independent seismic and seismicity data; and (iv) definition of a three‐dimensional fracture density function serving for a statistical assessment of fracture connectivity and “relative permeability.” This assessment is based on probabilistic fractionation and percolation theories. The derived three‐dimensional distribution of “relative permeability” may be used as a kernel function for inverting hydraulic permeability from hydrothermal field experiments. By comparing borehole and three‐dimensional seismic data, we could confirm that the faults and fractures of the Kontinentale Tiefbohrung area follow a fractal law that is consistent with Turcotte's fractionation model. An important conclusion from this is that upscaling and downscaling between one‐dimensional borehole and three‐dimensional seismic data appear possible. The corresponding one‐, two‐, and three‐dimensional fractal dimension are about 0.8, 1.9, and 2.8, respectively.

OSL-thermochronometry of feldspar from the KTB borehole, Germany

The reconstruction of thermal histories of rocks (thermochronometry) is a fundamental tool both in Earth science and in geological exploration. However, few methods are currently capable of resolving the low-temperature thermal evolution of the upper ∼2 km of the Earth's crust. Here we introduce a new thermochronometer based on the infrared stimulated luminescence (IRSL) from feldspar, and validate the extrapolation of its response to artificial radiation and heat in the laboratory to natural environmental conditions. Specifically, we present a new detailed Na-feldspar IRSL thermochronology from a well-documented thermally-stable crustal environment at the German Continental Deep Drilling Program (KTB). There, the natural luminescence of Na-feldspar extracted from twelve borehole samples (0.1–2.3 km depth, corresponding to 10–70 °C) can be either (i) predicted within uncertainties from the current geothermal gradient, or (ii) inverted into a geothermal palaeogradient of 29±2 °C km−1, integrating natural thermal conditions over the last ∼65 ka. The demonstrated ability to invert a depth–luminescence dataset into a meaningful geothermal palaeogradient opens new venues for reconstructing recent ambient temperatures of the shallow crust (<0.3 Ma, 40–70 °C range), or for studying equally recent and rapid transient cooling in active orogens (<0.3 Ma, >200 °C Ma−1 range). Although Na-feldspar IRSL is prone to field saturation in colder or slower environments, the method's primary relevance appears to be for borehole and tunnel studies, where it may offer remarkably recent (<0.3 Ma) information on the thermal structure and history of hydrothermal fields, nuclear waste repositories and hydrocarbon reservoirs.

Intrinsic and scattering attenuation as derived from fluid induced microseismicity at the German Continental Deep Drilling site

Hydraulically induced microseismicity is used to study high-frequency attenuation properties (6–72 Hz) in an enhanced geothermal system. Intrinsic and scattering attenuation are separated by jointly inverting seismogram envelopes for structural parameters, source and site effects. Modelling of synthetic envelopes is based on radiative transfer theory. To speed up inversion, an analytical solution of the radiative transfer equation for a 3-D isotropic scattering medium is implemented. In order to compensate for the actual anisotropic scattering, a smoothing algorithm is applied to introduce envelope broadening and peak delay. The approach is tested with seismic data from four fluid-induced earthquakes (Mw ≤ 1) recorded by a temporary seismic network at the German Continental Deep Drilling (KTB) site at epicentral distances of less than 20 km. Full S-wave envelopes are inverted in 12 overlapping frequency bands with centre frequencies between 1.5 and 72 Hz. With data sampling at 200 Hz and high-frequency S-wave sources, attenuation estimates are obtained for the rarely probed frequency range between 30 and 70 Hz. From the inversion, we infer average values of the transport scattering coefficient g*, and the intrinsic absorption parameter b, as well as corresponding quality factors Qs and Qi. By comparison with attenuation estimates from regions with different tectonic activities, we see that both Qs and Qi for the investigated geothermal region fit best to moderate scattering and intrinsic regimes as obtained in tectonically active regions. A comparison with a regional attenuation model for southern Germany proves that attenuation estimates are scale-dependent. To compare intrinsic and scattering attenuation in the KTB region the transport mean free path (TMFP) and the absorption length (la) are calculated. For both, we find a clear frequency dependence proportional to f −0.8 (TMFP) and f −0.3 (la). TMFP decreases from 340 km at 6 Hz to 60 km at 72 Hz, whereas absorption length drops from 40 to 20 km, respectively. Thus, intrinsic absorption dominates over scattering attenuation by at least one order of magnitude. The influence of scattering becomes more significant towards higher frequencies. Moreover, comparing the apparent attenuation (inverse sum of TMFP and la) to values estimated with the spectral ratio technique, achieves a good agreement with mean deviations in the order of 3–5 per cent. From the frequency dependence of TMFP, it can be inferred that a von Karman-type of random medium with a Hurst exponent of κ = 0.11 is a good model for representing the stimulated reservoir at the KTB. The fractal distribution of scatterers agrees well with results derived from independent analysis of acoustic logs.

Curating the web’s deep past – Migration strategies for the German Continental Deep Drilling Program web content

On timescales beyond the life of a research project, a core task in the curation of digital research data is the migration of data and metadata to new storage media, new hardware, and software systems. These migrations are necessitated by ageing software systems, ageing hardware systems, and the rise of new technologies in data management. Using the example of the German Continental Deep Drilling Program (KTB) we outline steps taken to keep the acquired data accessible to researchers and trace the history of data management in KTB from a project platform in the early 1990ies through three migrations up to the current data management platform. The migration steps taken not only preserved the data, but also made data from KTB accessible via internet and citable through Digital Object Identifier (DOI). We also describe measures taken to manage hardware and software obsolescence and minimise the amount of maintenance necessary to keep data accessible beyond the active project phase. At present, data from KTB are stored in an Open Archival Information System (OAIS) compliant repository based on the eSciDoc repository framework. Information packages consist of self-contained packages of binary data files and discovery metadata in Extensible Mark-up Language (XML) format. The binary data files were created from a relational database used for data management in the previous version of the system, and from websites generated from a content management system. Metadata are provided in DataCite, GCMD-DIF, and ISO19139/INSPIRE schema definitions. Access to the KTB data is provided through download pages which are produced by XML transformation from the stored metadata.

Tracing of paleo-shear zones by self-potential data inversion: case studies from the KTB, Rittsteig, and Grossensees graphite-bearing fault planes

AbstractThis paper describes a new method for tracing paleo-shear zones of the continental crust by self-potential (SP) data inversion. The method falls within the deterministic inversion framework, and it is exclusively applicable for the interpretation of the SP anomalies measured along a profile over sheet-type structures such as conductive thin films of interconnected graphite precipitations formed on shear planes. The inverse method fits a residual SP anomaly by a single thin sheet and recovers the characteristic parameters (depth to the toph, extension in deptha, amplitude coefficientk, and amount and direction of dipθ) of the sheet. This method minimizes an objective functional in the space of the logarithmed and non-logarithmed model parameters (log(h), log(a), log(k), andθ) successively by the steepest descent (SD) and Gauss-Newton (GN) techniques in order to essentially maintain the stability and convergence of this inverse method. Prior to applying the method to real data, its accuracy, convergence, and stability are successfully verified on numerical examples with and without noise. The method is then applied to SP profiles from the German Continental Deep Drilling Program (Kontinentales Tiefbohrprogramm der Bundesrepublik Deutschla - KTB), Rittsteig, and Grossensees sites in Germany for tracing paleo-shear planes coated with graphitic deposits. The comparisons of geologic sections constructed in this paper (based on the proposed deterministic approach) against the existing published interpretations (obtained based on trial-and-error modeling) for the SP data of the KTB and Rittsteig sites have revealed that the deterministic approach suggests some new details that are of some geological significance. The findings of the proposed inverse scheme are supported by available drilling and other geophysical data. Furthermore, the real SP data of the Grossensees site have been interpreted (apparently for the first time ever) by the deterministic inverse scheme from which interpretive geologic cross sections are suggested. The computational efficiency, analysis of the numerical examples investigated, and comparisons of the real data inverted here have demonstrated that the developed deterministic approach is advantageous to the existing interpretation methods, and it is suitable for meaningful interpretation of SP data acquired elsewhere over graphitic occurrences on fault planes.

A non-extensive view of the Pressure Stimulated Current relaxation during repeated abrupt uniaxial load-unload in rock samples

Laboratory experiments have confirmed that the application of uniaxial stress on rock samples is accompanied by the production of weak electric currents, named Pressure Stimulated Currents (PSCs). In the present work the PSC emissions in marble and amphibolite (from the German Continental Deep drilling) samples are studied in the frame of non-extensive statistical mechanics, after having applied sequential loading-unloading cycles. It was ascertained that by increasing the sequential order of the loading-unloading cycle, the emitted PSC exhibits q-exponential behavior with a non-additive entropy parameter q which decreased in each applied uniaxial load-unload cycle. The behavior of the Tsallis q-parameter leads to the conclusion that fracturing is a subadditive process with hierarchically constrained dynamics. Furthermore, assuming an assembly of relaxed subdomains created due to microfracture, a non-extensive behavior of the observed macroscopically PSC relaxation is discussed in the frame of a superstatistical approach.

Fuzzy Logic Determination of Lithologies from Well Log Data: Application to the KTB Project Data set (Germany)

Fuzzy logic has been used for lithology prediction with remarkable success. Several techniques such as fuzzy clustering or linguistic reasoning have proven to be useful for lithofacies determination. In this paper, a fuzzy inference methodology has been implemented as a MATLAB routine and applied for the first time to well log data from the German Continental Deep Drilling Program (KTB). The training of the fuzzy inference system is based on the analysis of the multi-class Matthews correlation coefficient computed for the classification matrix. For this particular data set, we have found that the best suited membership function type is the piecewise linear interpolation of the normalized histograms; that the best combination operator for obtaining the final lithology degrees of membership is the fuzzy gamma operator; and that all the available properties are relevant in the classification process. Results show that this fuzzy logic-based method is suited for rapidly and reasonably suggesting a lithology column from well log data, neatly identifying the main units and in some cases refining the classification, which can lead to a better interpretation. We have tested the trained system with synthetic data generated from property value distributions of the training data set to find that the differences in data distributions between both wells are significant enough to misdirect the inference process. However, a cross-validation analysis has revealed that, even with differences between data distributions and missing lithologies in the training data set, this fuzzy logic inference system is able to output a coherent classification.

A multidisciplinary Earth science research program in China

Because China occupies a large and geologically complex region of central and eastern Asia, the country may hold the keys to resolving many basic problems in the Earth sciences, such as how continental collision with India produced China's interconnected array of large intraplate structures, and what links exist between these structures and natural resources. To learn more, the Chinese government has launched SinoProbe, a major research initiative focusing on multidisciplinary imaging of the three‐dimensional (3‐D) structure and composition of the Chinese continental lithosphere and its evolution through geologic history. This effort is also motivated by China's need for a comprehensive and systematic evaluation of its natural resources and a better understanding of potential geohazards. SinoProbe is funded by the Chinese Ministry of Finance, managed by the Chinese Ministry of Land and Resources, and organized by the Chinese Academy of Geological Sciences. More than 960 investigators and engineers are currently involved with the program, not counting international collaborators. Most of them are affiliated with the Chinese Academy of Geological Sciences, the Chinese Academy of Sciences, the Ministry of Education (i.e., universities), and the China Earthquake Administration. The initial phase of the program (2008–2012), with funding equivalent to about US$164 million, is testing the feasibility of new technologies in geophysical and geochemical exploration and deep continental drilling by focusing on a series of profiles (Figure 1).

Neural network modeling and an uncertainty analysis in Bayesian framework: A case study from the KTB borehole site

A new probabilistic approach based on the concept of Bayesian neural network (BNN) learning theory is proposed for decoding litho‐facies boundaries from well‐log data. We show that how a multi‐layer‐perceptron neural network model can be employed in Bayesian framework to classify changes in litho‐log successions. The method is then applied to the German Continental Deep Drilling Program (KTB) well‐log data for classification and uncertainty estimation in the litho‐facies boundaries. In this framework, a posteriori distribution of network parameter is estimated via the principle of Bayesian probabilistic theory, and an objective function is minimized following the scaled conjugate gradient optimization scheme. For the model development, we inflict a suitable criterion, which provides probabilistic information by emulating different combinations of synthetic data. Uncertainty in the relationship between the data and the model space is appropriately taken care by assuming a Gaussian a priori distribution of networks parameters (e.g., synaptic weights and biases). Prior to applying the new method to the real KTB data, we tested the proposed method on synthetic examples to examine the sensitivity of neural network hyperparameters in prediction. Within this framework, we examine stability and efficiency of this new probabilistic approach using different kinds of synthetic data assorted with different level of correlated noise. Our data analysis suggests that the designed network topology based on the Bayesian paradigm is steady up to nearly 40% correlated noise; however, adding more noise (∼50% or more) degrades the results. We perform uncertainty analyses on training, validation, and test data sets with and devoid of intrinsic noise by making the Gaussian approximation of the a posteriori distribution about the peak model. We present a standard deviation error‐map at the network output corresponding to the three types of the litho‐facies present over the entire litho‐section of the KTB. The comparisons of maximum a posteriori geological sections constructed here, based on the maximum a posteriori probability distribution, with the available geological information and the existing geophysical findings suggest that the BNN results reveal some additional finer details in the KTB borehole data at certain depths, which appears to be of some geological significance. We also demonstrate that the proposed BNN approach is superior to the conventional artificial neural network in terms of both avoiding “over‐fitting” and aiding uncertainty estimation, which are vital for meaningful interpretation of geophysical records. Our analyses demonstrate that the BNN‐based approach renders a robust means for the classification of complex changes in the litho‐facies successions and thus could provide a useful guide for understanding the crustal inhomogeneity and the structural discontinuity in many other tectonically complex regions.