ALBERT

Description: The ability of any satellite gravity mission concept to monitor mass transport processes in the Earth system is typically tested well ahead of its implementation by means of various simulation studies. Those studies often extend from the simulation of realistic orbits and instrumental data all the way down to the retrieval of global gravity field solution time-series. Basic requirement for all these simulations are realistic representations of the spatio-temporal mass variability in the different sub-systems of the Earth, as a source model for the orbit computations. For such simulations, a suitable source model is required to represent (i) high-frequency (i.e., subdaily to weekly) mass variability in the atmosphere and oceans, in order to realistically include the effects of temporal aliasing due to non-tidal high-frequency mass variability into the retrieved gravity fields. In parallel, (ii) low-frequency (i.e., monthly to interannual) variability needs to be modelled with realistic amplitudes, particularly at small spatial scales, in order to assess to what extent a new mission concept might provide further insight into physical processes currently not observable. The new source model documented here attempts to fulfil both requirements: Based on ECMWF’s recent atmospheric reanalysis ERA-Interim and corresponding simulations from numerical models of the other Earth system components, it offers spherical harmonic coefficients of the time-variable global gravity field due to mass variability in atmosphere, oceans, the terrestrial hydrosphere including the ice-sheets and glaciers, as well as the solid Earth. Simulated features range from sub-daily to multiyear periods with a spatial resolution of spherical harmonics degree and order 180 over a period of 12 years. In addition to the source model, a de-aliasing model for atmospheric and oceanic high-frequency variability with augmented systematic and random noise is required for a realistic simulation of the gravity field retrieval process, whose necessary error characteristics are discussed. The documentation of the updated ESA Earth System Model (updated ESM) for gravity mission simulation studies is organized as follows: The characteristics of the updated ESM along with some basic validation is presented in Volume 1. A detailed comparison to the original ESA ESM (Gruber et al., 2011) is provided in Volume 2, while Volume 3 contains the description of a strategy to derive realistic errors for the de-aliasing model of high-frequency mass variability in atmosphere and ocean.

Description: The Bohemian Massif (BM) is the largest coherent surface exposure of basement rocks in central Europe. It is a geodynamically active part of the Hercynian orogenic belt representing a collage of magmatic arcs and micro-continents caused by the collision of Laurasia (Laurentia-Baltica) and Africa (Gondwana). The general northwest direction of accretion is typical of the northern part of the Hercynian belt. Irregularly-shaped colliding blocks resulted in a very complicated structure of convergence, lithospheric subduction, and crustal shortening, followed by extensional processes and rifting. The western part of the Bohemian Massif is the well-known health and resort landscape of Bohemia, Saxonia, and Bavaria, with Karlovy Vary (Karlsbad) as the flagship of the famous spa towns of the region (Figure 1). Allegedly, the Emperor Charles IV founded the spa in the years 1347–1349 at the site, which was already well known for its hot springs. For centuries, 12 springs in Karlovy Vary ranging in temperatures between 42°C and 72°C have been exploited, especially for the treatment of digestive system disorders and metabolic diseases.

Description: We report about Self-Potential (SP) anomalies registered 150 m from the active lava dome of Merapi Volcano, which are associated with Ultra-Long-Period (ULP) seismic signals (periods 〉100 s). During a 5-month period of simultaneous SP and seismological measurements, 50 ULP events were detected seismologically. If SP time series corresponding to ULP events are aligned to the onset times of ULP-events and stacked, the resulting traces show anomalous SP with an amplitude of 5–20 mV/km and 40–60 min duration. In contrast, the anomalous signals were not present in ground temperature data nor in SP data recorded ≈1 km from the summit. SP anomalies associated with ULP-seismicity might be caused by electro-kinetic effect of fluid flow in subsurface. This result is consistent with the ULP-generation model based on seismological observations and adds new information towards the understanding of ULP-seismicity.

Description: As part of Project International Deep Profiling of Tibet and the Himalaya III, a 400-km-long, densely spaced array of 57 broadband and short-period seismic stations was deployed in central Tibet from August 1998 through May 1999. Although originally designed to image the lithosphere with teleseismic events, the array also recorded numerous local and regional seismic events. More than 900 local and regional events were detected on at least 10 stations during the 1-year deployment, and we were able to locate 267 local earthquakes. A substantial number of the events were found to cluster in or near large grabens and along known strike-slip faults, while other events show no obvious correlation with known structures. In addition to spatial clustering, at least one of the large clusters also exhibits temporal clustering that may be associated with magmatic or geothermal activity in the upper crust. The average Vp and Vs are estimated to be 5.85 and 3.35 km/sec for the upper crust and 7.0 and 3.9 km/sec for the lower crust, respectively. The 50 focal mechanisms computed from this set of events are consistent with north–south shortening and east–west extension; there are no clear indications of significant local perturbations in the regional stress field induced by the collision between India and Eurasia. The majority of the focal mechanisms indicate normal and strike-slip faulting. At least six of the newly computed focal mechanisms, however, indicate thrust faulting, which is a phenomenon not well documented previously. Ninety-nine percent of the local earthquakes have focal depths shallower than 25 km, and the locations of the few deeper events are poorly constrained. The shallow earthquake focal depths are consistent with high temperatures and proposed ductile or aseismic behavior in the middle to lower crust of central Tibet.