Combination of long time-series of troposphere zenith delays observed by VLBI

Within the International Very Long Baseline Interferometry (VLBI) Service for Geodesy and Astrometry (IVS), long time-series of zenith wet and total troposphere delays have been combined at the level of parameter estimates. The data sets were submitted by eight IVS Analysis Centers (ACs) and cover January 1984 to December 2004. In this paper, the combination method is presented and the time-series submitted by the eight IVS ACs are compared with each other. The combined zenith delays are compared with time-series provided by the International Global Navigation Satellite System (GNSS) Service (IGS), and with zenith delays derived from the European Centre for Medium-Range Weather Forecasts (ECMWF). Before the combination, outliers are eliminated from the individual time-series using the robust BIBER (bounded influence by standardized residuals) estimator. For each station and AC, relative weight factors are obtained by variance component estimation. The mean bias of the IVS ACs’ time-series with respect to the IVS combined time-series is 0.89 mm and the mean root mean square is 7.67 mm. Small differences between stations and ACs can be found, which are due to the inhomogeneous analysis options, different parameterizations, and different treatment of missing in-situ pressure records. Compared to the IGS zenith total delays, the combined IVS series show small positive mean biases and different long-term trends. Zenith wet delays from the ECMWF are used to validate the IVS combined series. Inconsistencies, e.g., long-term inhomogeneity of the in-situ pressure data used for the determination of VLBI zenith delays, are identified.     

Neuere Ergebnisse der Tonmineralienforschung

Ohne Zusammenfassung     

Geowissenschaften und die Zukunft des Menschen

Ohne Zusammenfassung     

Tsunami inundation in Napier, New Zealand, due to local earthquake sources

Deterministic analysis of local tsunami generated by subduction zone earthquakes demonstrates the potential for extensive inundation and building damage in Napier, New Zealand. We present the first high-resolution assessments of tsunami inundation in Napier based on full simulation from tsunami generation to inundation and demonstrate the potential variability of onshore impacts due to local earthquakes. In the most extreme scenario, rupture of the whole Hikurangi subduction margin, maximum onshore flow depth exceeds 8.0 m within 200 m of the shore and exceeds 5.0 m in the city centre, with high potential for major damage to buildings. Inundation due to single-segment or splay fault rupture is relatively limited despite the magnitudes of M_W 7.8 and greater. There is approximately 30 min available for evacuation of the inundation zone following a local rupture, and inundation could reach a maximum extent of 4 km. The central city is inundated by up to three waves, and Napier Port could be inundated repeatedly for 12 h. These new data on potential flow depth, arrival time and flow kinematics provide valuable information for tsunami education, exposure analysis and evacuation planning.     

Impact of Preboreal to Subatlantic shifts in climate on groundwater resources on the Arabian Peninsula

A large-scale numerical flow and transport model was developed for the central-eastern arid part of the Arabian Peninsula. The model was applied to a region with freshwater resources dating back to more humid periods of the past, which are faced with overexploitation today. Model inflow was based on infiltration around wadi beds and groundwater recharge. Inflow was balanced by natural outflows, such as evaporation from sabkhas, spring discharge, and discharge to the sea. Two models were developed: (1) a short-term present-day model to estimate effective model parameters, and (2) a long-term model to study the development of the groundwater resources during the Mid- and Late Holocene and the natural response of the groundwater system to changes in climate. Hydraulic model parameters (hydraulic conductivity and specific storage) were assigned with respect to geological structures. Hydraulic parameters were estimated with an inverse PEST model by calibrating against observed depression cones cause by groundwater abstraction. Sensitivity analysis demonstrated that estimated model parameters were associated with a high uncertainty at a certain distance from agricultural areas when calibration data were lacking. A long-term model starting 10,000 years BP was calibrated by spring discharge and palaeo-groundwater levels and validated using measured ¹⁴C groundwater ages. The long-model predicted that groundwater levels adapted in response to changes in precipitation. During the Mid-Holocene, which was characterized by an intensification of the monsoon season, groundwater levels increased by 10 m on the mainland within the shallow aquifers and adapted quickly to higher recharge rates. The deeper aquifers were less affected by changes in climate. Along the present-day coastline, the groundwater level rose by about 25 m due to the declined sea level in the Mid-Holocene. During this period, surface run-off was possible as groundwater levels temporarily reached the ground surface. The natural groundwater budget reacted sensitively to changes in climate. Between 10 and 3 ka, groundwater storage occurred. During the Late Holocene, at 3 ka, natural depletion of the groundwater system began, which still prevails today.     

Approaches to stress monitoring in deep boreholes for future CCS projects

There is no monitoring technology available to observe possible changes of stress in the rock mass of a CO₂ reservoir or its cap rock formations. Any development of a stress-monitoring technique must be related to the natural regional stress conditions and must be adjusted to the possibly changing in situ stress conditions due to CCS activity. As a step towards an in situ stress-monitoring probe, a lab scale device was developed and used for investigations on the practicability of a hard-inclusion tool for stress monitoring. In situ stress conditions, as deduced from the Altmark Gas Field, were applied to evaluate the efficiency and the limits of this stress-monitoring technique. At lab-scale the applied stresses resp. stress differences with moderate amounts of 9?C15?% of the vertical stress component Sv coincide sufficiently with the resulting strain answers of the hard inclusion tool (i.e., a steel tube corresponding to the liner in the borehole). Therefore, it was possible to re-calculate the stresses and to compare them with the applied ones. The resulting coincidence, however, can be disturbed at high pressure levels due to rock failure around the borehole with extended deformations. In addition, the results are influenced by the mechanical behaviour of the surrounding rock mass type. Nevertheless, a further development of a hard inclusion probe for monitoring of stress changes in deep boreholes can be successful and may be the only possible way to detect stress changes without fracturing damages in deep boreholes.     

Complexity vs. Simplicity: Groundwater Model Ranking Using Information Criteria

A groundwater model characterized by a lack of field data about hydraulic model parameters and boundary conditions combined with many observation data sets for calibration purpose was investigated concerning model uncertainty. Seven different conceptual models with a stepwise increase from 0 to 30 adjustable parameters were calibrated using PEST. Residuals, sensitivities, the Akaike information criterion (AIC and AICc), Bayesian information criterion (BIC), and Kashyap's information criterion (KIC) were calculated for a set of seven inverse calibrated models with increasing complexity. Finally, the likelihood of each model was computed. Comparing only residuals of the different conceptual models leads to an overparameterization and certainty loss in the conceptual model approach. The model employing only uncalibrated hydraulic parameters, estimated from sedimentological information, obtained the worst AIC, BIC, and KIC values. Using only sedimentological data to derive hydraulic parameters introduces a systematic error into the simulation results and cannot be recommended for generating a valuable model. For numerical investigations with high numbers of calibration data the BIC and KIC select as optimal a simpler model than the AIC. The model with 15 adjusted parameters was evaluated by AIC as the best option and obtained a likelihood of 98%. The AIC disregards the potential model structure error and the selection of the KIC is, therefore, more appropriate. Sensitivities to piezometric heads were highest for the model with only five adjustable parameters and sensitivity coefficients were directly influenced by the changes in extracted groundwater volumes.