ALBERT

Description: We present a new set of global and local sea‐level projections at example tide gauge locations under the RCP2.6, RCP4.5 and RCP8.5 emissions scenarios. Compared to the CMIP5‐based sea‐level projections presented in IPCC AR5, we introduce a number of methodological innovations, including: (i) more comprehensive treatment of uncertainties; (ii) direct traceability between global and local projections; (iii) exploratory extended projections to 2300 based on emulation of individual CMIP5 models. Combining the projections with observed tide gauge records, we explore the contribution to total variance that arises from sea‐level variability, different emissions scenarios and model uncertainty. For the period out to 2300 we further breakdown the model uncertainty by sea‐level component and consider the dependence on geographic location, time horizon and emissions scenario. Our analysis highlights the importance of variability for sea‐level change in the coming decades and the potential value of annual‐to‐decadal predictions of local sea‐level change. Projections to 2300 show a substantial degree of committed sea‐level rise under all emissions scenarios considered and highlights the reduced future risk associated with RCP2.6 and RCP4.5 compared to RCP8.5. Tide gauge locations can show large (〉 50%) departures from the global average, in some cases even reversing the sign of the change. While uncertainty in projections of the future Antarctic ice dynamic response tends to dominate post‐2100, we see a substantial differences in the breakdown of model variance as a function of location, timescale and emissions scenario.

Description: Based on the latest GFZ release 06 of monthly gravity fields from GRACE satellite mission, area-averaged barystatic sea-level is found to rise by 2.02 mm/a during the period April 2002 until August 2016 in the open ocean with a 1000 km coastal buffer zone when low degree coefficients are properly augmented with information from satellite laser ranging. Alternative spherical harmonics solutions from CSR, JPL and TU Graz reveal rates between 1.94 and 2.08 mm/a, thereby demonstrating that systematic differences among the centers are much reduced in the latest release. The results from the direct integration in the open ocean can be aligned to associated solutions of the sea-level equation when fractional leakage derived from two differently filtered global gravity fields is explicitly considered, leading to a global mean sea-level rise of 1.72 mm/a. This result implies that estimates obtained from a 1000 km coastal buffer zone are biased 0.3 mm/a high due the systematic omission of regions with below-average barystatic sea-level rise in regions close to substantial coastal mass losses induced by the reduced gravitational attraction of the remaining continental ice and water masses.

Description: Earthquakes on intra-continental faults pose substantial seismic hazard to populated areas. The interaction of faults is an important mechanism of earthquake triggering and can be investigated by the calculation of Coulomb stress changes. Using three-dimensional finite-element models, co- and postseismic stress changes and the effect of viscoelastic relaxation on dip-slip faults are investigated. The models include elastic and viscoelastic layers, gravity, ongoing regional deformation as well as source and receiver fault zones. A parameter study with a systematic fault geometry, which is independent of a specific earthquake, shows that high coseismic stress increase occurs in along-strike prolongation of the source fault and in small areas parallel to the source fault. The coseismic slip and coefficient of friction influence the magnitude of stress changes, while the fault dip also influences the distribution. The stress changes can be explained by the spatial distribution of the coseismic strain. Differences in normal and thrust fault models are mainly caused by the different fault dips. The postseismic stress changes – caused by viscoelastic relaxation and interseismic stress increase – modify the coseismic stress changes that stress-triggering zones can change to stress-shadow zones and vice versa. Stress changes induced by viscoelastic relaxation can outweigh the interseismic stress increase so that negative stress changes can persist for decades. The lower the viscosity of the lower crust or lithospheric mantle, the more pronounced is the effect of viscoelastic relaxation in the first years. Layers with low viscosity define the area of highest postseismic velocities and hence determine relaxation and stress changes. The application of the model to the active Wasatch fault system in the eastern Basin and Range Province (Utah) is the first study in which an entire series of earthquakes on a natural fault system is simulated in a finite-element model using realistic fault geometries and palaeo-seismological data to investigate the co- and postseismic Coulomb stress changes for palaeo-earthquakes and the future evolution. The coseismic stress changes extend over all modelled fault segments. The postseismic stress changes and velocities show that the postseismic relaxation dominates the first years after the earthquake, while in the hundredth year the stress increase by the regional stress field dominates. The analysis of the stress changes since the last event per fault segment shows that the Brigham City segment (~780 bar) and Salt Lake City segment (~510 bar) have accumulated the most stress since the last earthquake. Modelled hypothetical present-day earthquakes suggest that present-day ruptures on the Brigham City segment or Salt Lake City segment could experience M ~7.1 or M ~7.0 earthquakes, respectively, which pose high seismic hazard for the metropolitan areas.

Description: Earthquakes in the brittle upper crust induce viscoelastic flow in the lower crust and lithospheric mantle,which can persist for decades and lead to significant Coulomb stress changes on receiver faults located in the surrounding of the source fault. As most previous studies calculated the Coulomb stress changes for a specific earthquake in nature, a general investigation of postseismic Coulomb stress changes independent of local geological conditions is still lacking for intra-continental dip-slip faults. Here we use finite-element models with normal and thrust fault arrays, respectively, to show that postseismic viscoelastic flow considerably modifies the original coseismic Coulomb stress patterns through space and time. Depending on the position of the receiver fault relative to the source fault, areas with negative coseismic stress changes may exhibit positive postseismic stress changes and vice versa. The lower the viscosity of the lower crust or lithospheric mantle, the more pronounced are the transient stress changes in the 1st years, with the lowest viscosity having the largest effect on the stress changes. The evolution of postseismic Coulomb stress changes is further controlled by the superposition of transient stress changes caused by viscoelastic relaxation (leading to stress increase or decrease) and the interseismic strain accumulation

Description: The Wasatch fault zone constitutes the eastern boundary of the actively extending Basin and Range Province (Utah) and poses a significant seismic hazard to the metropolitan areas along the Wasatch Range. A wealth of paleoseismological data document ∼24 surface-rupturing Mw ≥ 7 earthquakes along the Wasatch fault during the last 6400 years. Here we simulate the Holocene earthquake sequence on the Wasatch, Oquirrh-Great Salt Lake and West Valley faults using three-dimensional finite-element modeling with the goal to calculate co- and postseismic Coulomb stress changes and to evaluate the slip and magnitude of hypothetical present-day and future earthquakes. Our results show that a good fit between modeled and observed paleoevents and time-integrated slip rates can be achieved within the uncertainties of the paleoseismological record and model parameters like the fault geometry. The Coulomb stress change analysis for selected paleoearthquakes shows that maximum positive stress changes are induced on receiver faults located along-strike of the source fault, while receiver faults parallel to the source fault are generally located in stress shadow zones. Postseismic viscoelastic relaxation considerably modifies the coseismic stress changes; the resulting transient stress changes are recognizable for more than 100 yr after the event. The modeled present-day state of Coulomb stress changes shows that the Brigham City, Salt Lake City and Provo segments of the Wasatch fault are prone to failure in a Mw ≥ 6.8 earthquake. Our study shows that the simulation of an entire earthquake sequence based on a paleoseismological record is feasible and facilitates identification of possible gaps and inconsistencies in the paleoseismological record. Therefore, forward modeling of earthquake sequences may ultimately contribute to refining seismic hazard estimates.

Description: The Clarion-Clipperton Zone (CCZ) of the central Pacific is one of the few regions in the world’s oceans that are still lacking full coverage of reliable identifications of seafloor spreading anomalies. This is mainly due to the geometry of the magnetic lineations’ strike direction sub-parallel to the Earth’s magnetic field vector near the equator resulting in low amplitude magnetic anomalies, and the remoteness of the region which has hindered systematic surveying in the past. Following recently granted research licenses for manganese nodules in the CCZ by the International Seabed Authority, new magnetic data acquired with modern instrumentation became available which combined with older underway data make the identification of seafloor spreading anomalies possible for large parts of the CCZ and adjacent areas. The spreading rates deduced from the seafloor spreading patterns show a sharp increase at the end of Chron 21 (47.5 Ma) which corresponds to the age of the bend in the Hawaii-Emperor seamount chain and an associated plate tectonic reorganisation in the Central Pacific. An accurate map of crustal ages for the central-eastern Pacific based on our anomaly picks may provide a basis for improved plate tectonic reconstructions of the region.

Description: We study the interactions of ice sheets with the other components of the climate system in a new modeling system that encompasses a wide range of interactions between ice sheets, their mass balance, the solid Earth and the climate. Forcing the model with increasing greenhouse gas concentrations allows us to study the full interactions of the different climate system components and thus deepen our understanding of the processes relevant during deglaciation. The system consists of the modified Parallel Ice Sheet Model (mPISM), the VIscoelastic Lithosphere and MAntle model (VILMA), and the Max Planck Institute Earth System Model (MPI-ESM). The surface mass balance of the ice sheets is computed with an energy balance model, shelf basal melt from temperature and salinity of the adjacent ocean. By applying VILMA, sea-level change due to ice loads is calculated considering surface deformation, eustasy and geoid change. In MPI-ESM, glaciers, topography, rivers, coastlines and bathymetry adapt to changes in ice sheets and topography. The model system is forced only with transient orbital parameters and greenhouse gas concentrations. In our experiments, the retreating ice sheets leave behind vast periglacial lakes and marginal seas. Gigantic ice sheet surges into these basins lead to the formation of large ice shelves with low surface elevations causing strong melt. Where the basins are connected to the open ocean, basal melt and calving increase the ice loss at the shelves. Over time, the retarded sea-level response shrinks the periglacial basins again. This study presents first experiments that include the full range of interactions between ice sheets, solid Earth, atmosphere and ocean circulation.

Description: Investigating fault interaction plays a crucial role in seismic hazard assessment. The calculation of Coulomb stress changes allows quantifying the stress changes on so-called receiver faults in the surrounding of the fault that experienced the earthquake. A positive stress change implies that the earthquake brought the receiver fault closer to failure while a negative value indicates a delay of the next earthquake. So far, most studies focussed on stress changes for particular faults and earthquakes. Here we present a general analysis of the Coulomb stress changes on intra-continental dip-slip faults using finite-element models with normal and thrust faults arrays, respectively. Our models allow calculating coseismic (“static”) stress changes on pre-defined fault planes, whose dip and position can be varied. Gravity and ongoing regional deformation (i.e. shortening or extension) are included. The results for thrust and normal faults show that synthetic receiver faults located in the hanging wall and footwall of the source fault exhibit a symmetric stress distribution, with large areas of negative and small areas of positive Coulomb stress changes. In contrast, faults positioned in along-strike prolongation of the source fault and outside of its immediate hanging wall and footwall undergo mostly positive stress changes. The stress changes are largest at the fault tip that is closer to the source fault. Our results show that the stress change distribution depends on the fault dip while the magnitude depends on the friction coefficient and the amount of coseismic slip. The Coulomb stress changes can be explained by the spatial distribution of the coseismic strain, which shows domains of horizontal extension and shortening that alternate both at the surface and with depth. Our models allow identifying the general patterns of Coulomb stress changes on dip-slip faults, which are often concealed by the peculiarity of the specific fault or earthquake in nature.

Description: Establishing a geodynamically consistent solid-earth model component is essential to realistically simulate changes in earth deformation due to ice-load changes (GIA). For the implementation of a viscoelastic lithosphere and mantle into an earth system model, uncertainties in earth deformation due to earth structure variability and glaciation history variability have to be quantified. Using the global numerical model VILMA, we investigate the sensitivity of these two aspects on surface deformation and on the reconstruction of sea-level change. In a series of model simulations, key parameters of the earth’s viscosity structure and the possible range of ice-sheet distributions are varied. The resulting variability is analyzed in a spatial-temporal context. In addition to assess the variability at the ice margins which feeds back to the ice dynamics, we investigate the far-field response which is influenced by the paleo topography/bathymetry and, so, has an impact on ocean dynamics and coastal environments. This study is part of the ‘German climate modeling initiative’ PalMod which aims at modeling, understanding and quantification of feedbacks between climate components during the last glacial cycle.

Description: Temporal variations in the total ocean mass representing the barystatic part of present-day global-mean sea-level rise can be directly inferred from time-series of global gravity fields as provided by the GRACE and GRACE-FO missions. A spatial integration over all ocean regions, however, largely underestimates present-day rates as long as the effects of spatial leakage along the coasts of in particular Antarctica, Greenland, and the various islands of the Canadian Archipelago are not properly considered. Based on the latest release 06 of monthly gravity fields processed at GFZ, we quantify (and subsequently correct) the contribution of spatial leakage to the post-processed mass anomalies of continental water storage and ocean bottom pressure. We find that by utilizing the sea level equation to predict spatially variable ocean mass trends out of the (leakage-corrected) terrrestial mass distributions from GRACE and GRACE-FO consistent results are obtained also from spatial integrations over ocean masks with different coastal buffer zones ranging from 400 to 1000 km. However, the results are critically dependent on coefficients of degree 1, 2 and 3, that are not precisely determined from GRACE data alone and need to be augemented by information from satellite laser ranging. We will particularly discuss the impact of those low-degree harmonics on the secular rates in global barystatic sea-level.