Vlasiator is a high‐performance ion‐kinetic code that is now conducting 3D hybrid‐Vlasov simulations of the global magnetosphere. We use Vlasiator to investigate the impact of a pressure pulse with southward‐oriented magnetic field on the Earth's magnetosphere. The simulation driving parameters are comparable to conditions that have led to geomagnetic storms. Our pressure pulse simulation reproduces many physical effects, namely the expansion of the auroral oval, the development of field‐aligned currents, enhanced particle precipitation near the open/closed field line boundary, and compression of Earth's magnetopause. This demonstrates the effectiveness of the hybrid‐Vlasov approach for moderate driving conditions. Our investigation of the time‐dependent magnetopause compression motivates a generalization of the existing theory. Specifically, we find that accounting for the finite transition time of the solar wind dynamic pressure improves the model's description of the magnetopause oscillations.

Large continental-scale rift valley systems provide in Ethiopia a unique setting for a range of industrial mineral deposits. However, the issues of exploration and exploitation remain expensive. It is pragmatic to look for easy techniques for locating precious metals. In this study an attempt was made to examine precious metals in the localities of the hydrothermal areas in the central Rift valley with the objective of whether thermal springs can hit mineral deposits. Thus, Filwoha, Sodere, Ambo and Wondogenet thermal spring areas were selected and specimens were collected for gold, silver, lead, manganese, cobalt, zinc, copper and iron determination. The analysis revealed that manganese was the dominant metal with the concentrations of 1980, 1510, 535 and 375 ppm in the chemical precipitates of Filwoha, Wondogenet, Ambo and Sodere areas, respectively. Zn was thelargest deposit in the chemical precipitates of Ambo and Filwoha areas with the levels of 355 and 154 ppm, respectively. The concentration of Au was 0.02 ppm in all sites whereas the level of Ag was ranged from 0.5 ppm in Filwoha to 2.2 ppm in Wondogenet. All these metals were found in good deposit range of ore grades for mining. Hence, hot spring water anomalous in Au, Mn, Zn, Pb, Cu, Co and Ag could be a proxy for precious metal searching in epithermal systems associated with thermal springs. Keywords : Epithermal system, Ethiopian Rift Valley, geochemical exploration, thermal springs Ethiopian Journal of Environmental Studies and Management Vol. 1 (3) 2008: pp. 1-7

Seismic hazard assessment for the Eastern and Southern Africa region was done using the probabilistic approach. Seismic hazard maps for 10% exceedance in 50 years, 10% exceedance in 100 years, as well as for 50 and 100 years return periods were prepared using the FRISK88M software. The area involved covers a wide region bounded by latitudes 40°S-25°N and longitudes 10°E and 55°E. Input parameters for the computations were obtained using the recent earthquake catalogue compiled by Turyomurugyendo. The catalogue which covers the time period 627-1994, contains earthquakes within the area bounded by 40°S-25°N and 10°E-55°E, with homogeneous magnitudes (M S ). Since a Poisson model of earthquake occurrence is assumed, dependent events were cleaned from the catalogue. Attenuation relations for the Eastern and Southern Africa region based on the strong motion data are virtually non-existent. However, attempts have been made recently by Jonathan and Twesigomwe to establish an average attenuation relation for the region. These relations were used in the computations. Possible uncertainties in the attenuation relations were accounted for using the logic-tree formalism. The results are presented in seismic hazard maps in terms of Peak Ground Acceleration (PGA) for the mean and the 85th percentile. The distribution of PGA values indicate relatively high hazard along the East African rift system. In the northern segments of the rift system, they exceed 250 gals for 10% probability of exceedence in 50 years.

A probabilistic seismic hazard analysis (PSHA) for the Horn of Africa is presented. Our seismicity database consists of a revised and up-to-date regional catalogue compiled from different agencies, checked for completeness with respect to time and homogenized with respect to magnitude (M-s), The seismic source zones are based on our present day knowledge of the regional seismotectonics. Among the results we present regional hazard maps for 0.01 annual probability for intensity and Peak Ground Acceleration (PGA) and hazard curves and response spectra for six economical significant sites within the region, The model uncertainties with respect to seismicity are analysed in a novel approach and form part of a sensitivity analysis that quantifies our PSHA modelling uncertainties,For 0.01 annual probability we find randomly oriented horizontal PGA that exceed just 0.2 g and MM-scale intensity VIII in the Afar depression and southern Sudan. Uncertainties amount to 20% g PGA in some cases, mainly due to attenuation uncertainties. Intensity uncertainties seldom exceed 0.5 intensity units. Relatively large seismic hazard is found for Djibouti (VIII for 0.01 annual probability), slightly lower for the port of Massawa (between VII and VIII for 0.01 annual probability) and low for the port of Assab (between VI and VII for 0.01 annual probability).

Spatial and temporal variation of b-values for the East African rift system and the southern Red Sea is studied. In general, average b-values obtained for the whole East African rift system range from 0.5 to 1.5. Mapping of b-value shows that relatively low average b-values (0.5–0.8) are observed in certain segments of the southern Red Sea, Afar Depression and north of the Western rift. If experimental laboratory works are correct then, this observation may imply that during the time interval studied here (1963–1990), parts of the northern East African rift system have been experiencing relatively high stress levels when compared with the southern part of the region. Plots of temporal variation of b-values for different segments of the rift show different behavior. These observations suggest that different rift segments are under different stress conditions which in turn may reflect the status of the ongoing rifting processes in each segment. In southern Africa, a sudden significant increase in b-value followed by a gradual decrease is observed prior to the occurrence of an intermediate-size earthquake with normal faulting mechanism. A thorough investigation of the temporal change of b-values in the southern Red Sea prior and after the occurrence of an intermediate-size earthquake with a strike-slip mechanism could not reveal such a precursory phenomena. Observations are consistent with those made by other researchers in other regions.

The seismicity of the East African Rift system and southern Red Sea is studied here. Location of earthquake epicenters in East Africa shows that there is a seismicity gap in space and time between the Main Ethiopian Rift system and the eastern rift. However, distribution of earthquake epicenters together with the energy mapping suggest a continuity of seismic activity or stress field from the Main Ethiopian Rift system to the western rift system via the southernmost rifts of Ethiopia. In general (except for some earthquakes which occurred at different complex tectonics regions) mechanisms of earthquakes studied here show dominantly normal faulting suggesting that the rift system is an extensional zone on the continent. The presence of greater focal depth earthquakes to the southern part of the rift system may indicate that softer materials at a shallower depth are present in Afar and neighboring regions than in the remaining part of the East African Rift system. This interpretation is supported by other geophysical studies (low electrical resistivity and gravity data) performed in Afar. It is also supported by low and high stress drops found for the northern part (Afar depression) and southern part of the East African Rift system, respectively.

We obtained spectral source parameters for one event on the axial trough and two events on a presumed transform fault, all in the southern part of the Red Sea. Seismic moments obtained range from 0.3 × 1025 to 15 × 1025 dyn cm. The normal fault mechanism event on the axial trough shows a low stress drop of 7 bars and average displacement of 10 cm while the strike-slip event displays a stress drop of 50 bars and average displacement of 114 cm. The aftershock of the strike-slip event with moment-magnitude 1.3 units smaller than the main event, shows lower stress drop and average displacement than those of the main event. Different mode of energy release in the epicentral areas under study indicate that different tectonic processes are involved in the two regions.

Spectral analysis of 196 short-period and long-period vertical- and horizontal-component seismograms from ten earthquakes on the central and western margin of Afar is performed to determine source parameters and discuss their tectonic implications. For the earthquakes in the regions under study, the stress drop varies from 2 to 31 bar while the seismic moment varies from 2 × 1024 to 154 × 1024 dyn cm. In general, low stress-drop values are obtained indicating the presence of softer material (especially for central Afar) at a shallower depth. It is observed that there is an increase in stress drop with the increase in moment-magnitude which in turn is obtained from the calculated average seismic moment. Energy estimates show that the mode of energy release is different in the two regions indicating that different tectonic processes are involved in the two regions. The slip rate obtained for the Serdo area is of the order of 1.6 cm/yr and is in close agreement with the spreading rate already obtained for central Afar. Spreading rates obtained earlier and that of the present study show a low spreading rate for Afar and neighbouring regions as compared to those of the other regions of the world.

Long‐period teleseismic P and S waveforms for the largest four earthquakes in the Serdo sequence are compared with synthetic seismograms to infer mechanisms, focal depths, source time functions, and dynamic energy release. For all four events studied, the mechanisms are predominantly strike slip. Depth estimates obtained for the four earthquakes by matching synthetic seismograms to the observations are found to lie between 5 and 8 km. The azimuthal variation of observed body wave duration for the main event indicates that the rupture propagated from NE to SW. Average seismic moments obtained from body wave synthetics vary from 4.6×1017 to 2.5×1018 N m. Average final displacements, stress drops, and lengths of the fault are found to lie between 0.16 and 0.56 m, 0.45 and 1.56 MPa, and 10 and 16 km, respectively. The low stress drop value obtained may indicate the presence of softer materials near the source. The energy release shows that the mode of energy release during the sequence took place in two steps, mainly by the two largest shocks.