S U M M A R YEarthquake source parameter determination is of great importance for hazard assessment, as well as for a variety of scientific studies concerning regional stress and strain release and volcano-tectonic interaction. This is especially true for poorly instrumented, densely populated regions such as encountered in Africa, where even the distribution of seismicity remains poorly documented. In this paper, we combine data from satellite radar interferometry (InSAR) and teleseismic waveforms to determine the source parameters of the M w 5.9 earthquake that occurred on 2008 February 3 near the cities of Bukavu (DR Congo) and Cyangugu (Rwanda). This was the second largest earthquake ever to be recorded in the Kivu basin, a section of the western branch of the East African Rift (EAR). This earthquake is of particular interest due to its shallow depth and proximity to active volcanoes and Lake Kivu, which contains high concentrations of dissolved carbon dioxide and methane. The shallow depth and possible similarity with dyking events recognized in other parts of EAR suggested the potential association of the earthquake with a magmatic intrusion, emphasizing the necessity of accurate source parameter determination. In general, we find that estimates of fault plane geometry, depth and scalar moment are highly consistent between teleseismic and InSAR studies. Centroid-moment-tensor (CMT) solutions locate the earthquake near the southern part of Lake Kivu, while InSAR studies place it under the lake itself. CMT solutions characterize the event as a nearly pure double-couple, normal faulting earthquake occurring on a fault plane striking 350 • and dipping 52 • east, with a rake of -101 • . This is consistent with locally mapped faults, as well as InSAR data, which place the earthquake on a fault striking 355 • and dipping 55 • east, with a rake of -98 • . The depth of the earthquake was constrained by a joint analysis of teleseismic P and SH waves and the CMT data set, showing that the earthquake occurred in the shallow crust, at approximately 8 km depth. Inversions of ENVISAT (Environment Satellite) and ALOS (Advanced Land Observation Satellite) data place the earthquake at 9 km. A comparison of the scalar moment (9.43 ± 0.06 × 10 17 Nm from seismology and 8.99 ± 0.010 × 10 17 Nm from the joint InSAR solution) shows good agreement between the two data sets. Such an agreement is in contrast to the large discrepancies observed (up to an order of magnitude) in other places along the EAR where similar earthquake sequences are associated with magmatic intrusion. From this, we infer that the rupture was brittle and occurred with little aseismic deformation as might be expected from magma injection. Our results provide insights into the style of rifting occurring in the South Kivu Volcanic Province and hence will aid future studies on seismic risk in the context of Lake Kivu and underline the importance of systematic monitoring of the EAR area.

Abstract:Multipath interference can occur in ground-based radar data acquired with systems with a large antenna beam width in elevation in an upward looking geometry, where the observation area and the radar are separated by a reflective surface. Radiation reflected at this surface forms a coherent overlay with the direct image of the observation area and appears as a fringe-like pattern in the data. This deteriorates the phase and intensity data and therefore can pose a considerable disadvantage to many ground-based radar measurement campaigns. This poses a problem for physical parameter retrieval from backscatter intensity and polarimetric data, absolute and relative calibration on corner reflectors, the generation of digital elevation models from interferograms and in the case of a variable reflective surface, differential interferometry. The main parameters controlling the interference pattern are the vertical distance between the radar antennas and the reflective surface, and the reflectivity of this surface. We used datasets acquired in two different locations under changing conditions as well as a model to constrain and fully understand the phenomenon. To avoid data deterioration in test sites prone to multipath interference, we tested a shielding of the antennas preventing the radar waves from illuminating the reflective surface. In our experiment, this strongly reduced but did not completely prevent the interference. We therefore recommend avoiding measurement geometries prone to multipath interferences.

Maceration with sodium salts is applied to irmprove water holding capacity in squid-based products. The aim of this work was to determine how the mineral content of squid flesh is affected by maceration and further vacuum-cooking. Atlantic squids (Loligo vulgaris) from two fisheries (FAO areas No. 47 and 34) were sampled. Macrominerals (g/100 g) present in raw flesh were Na, Mg, P, S, K and Ca, while microminerals accounting for >1 mg/kg were Zn, Si, Sr, Fe, Cu, Al and Mn. As a result of maceration (3 + 1.5% w:w NaCl+ Na citrate) and vacuum-cooking (at 65 °C for 20 min), some squid minerals was removed. The levels of Cd and As were reduced by half, while Na content increased from 0.28 to 0.49 g/100 g. Maceration with sodium salts generally led to minerals leaching (except for Na) with the medium. Further cooking produced additional losses of most of the minerals present in macerated squid (except Pb and Cd). Squid microminerals were hardly removed with the cooking juice. The consumption of macerated-cooked squid covered >10% of the recommended dietary intake for Na, P, Zn, Mg and Mn, while health risks were almost negligible and mainly concerned Cd (up to 14% of the probable tolerable weekly intake). The combination of both treatments involves certain loss of most of the essential minerals but also contributes to reducing toxicological risks related to mineral intake through squid products.

No abstract