History and operational capability of the Ethiopian Seismic Station Network (ESSN)

Together with the three component short period WWSSN analog station operating at the Geophysical Observatory (AAE), five seismic stations are running in the country. FURI is one of the four three-component digital stations with a GURALP CMG 3T and STS1 broadband sensors. The other three seismic stations at Wendogenet, Dessie and Alemaya are equipped with Le -3d/5s seismometers with RefTek Data Acquisition Systems (DASs), which provide semi-broadband signals. Except AAE, all stations use GPS receivers for accurate timing and provide three-component digital record. Digital data facilitate quick interpretations of seismic signals using computers. The seismic stations are in a good position to date to monitor major seismic activities of the Ethiopian rift. The earthquake locations estimated using data from our own network are found to be reliable with reasonable accuracy. A total of 15 earthquakes are located in this pilot study of which only four are captured by the USGS (United States Geological Survey) bulletin and all lie along the rift in Afar and the main Ethiopian rift system.Key words/phrases: Ethiopian rift, seismic station network, seismicity SINET: Ethiopian Journal of Science Vol. 28 (1) 2005: 93-9

Evidence for Active Rhyolitic dike Intrusion in the Northern Main Ethiopian Rift from the 2015 Fentale Seismic Swarm

Abstract Magmatic intrusions play a vital role not only in accommodating extensional stresses in continental rifts but also in feeding volcanic systems. The location, orientation, and timescale of dike intrusions are dictated by the interaction of regional and local stresses, the effect of pre‐existing weaknesses, and the composition of magma. Observing active intrusions can provide important information regarding the interaction between magmatic processes and the tectonic stress field during continental rifting. We focus on a seismic swarm that occurred in 2015 to the northeast of Fentale volcano, in the Main Ethiopian Rift (MER), and use radar interferometry to study surface deformation associated with the seismic swarm. Interferograms show a pattern of dike‐induced deformation, with a model estimate of volume change of 33×106±0.6×106m3 at a depth range of 5.4 to 8 km. We use a small baseline subset algorithm to calculate line of sight time series and find that the displacements decay exponentially with a decay constant of ∼83 days. Coupled source‐sink models suggest that such slow dike intrusions require a high viscosity rhyolitic magma. The difference in behavior between Fentale and other caldera systems in the MER, which show multi‐year cycles of inflation and deflation, suggests fundamental differences in magma composition and architecture of the plumbing system. This is the first direct observation of a dike intrusion in the MER and provides new constraints on the temporal‐spatial patterns of stress and strain that occur during continental rifting. Whether this activity is transient or a long‐term feature associated with rift evolution is an open question

Low-frequency earthquakes beneath Tullu Moye volcano, Ethiopia, reveal fluid pulses from shallow magma chamber

The active magmatic processes beneath volcanoes in continental rifts is poorly understood. For example, until recently in the East African rift (EAR), the majority of the young volcanoes were thought to be inactive. More recent studies have shown that numerous volcanoes in the EAR are seismically active and deforming rapidly. However, an unambiguous sign of actively degassing magma hosted in shallow magma bodies has eluded most investigators. Here we present detailed analysis of the first low-frequency (LF) earthquake swarms to be observed in the Main Ethiopian Rift. The earthquakes locate to beneath Tullu Moye volcano and are directly related to the presence of a shallow magma body with a high fluid content. Using spectral modelling we show that the LF earthquakes appear to have low stress-drops (1�50 kPa) which we interpret in terms of low rupture velocities and high pore-fluid pressure. Careful relocation of the LF earthquakes place them approximately 4 km below the surface within one of two possible clusters. However, analysis of the correlation between earthquake waveforms show that each swarm contains a range of earthquake families and as such a diversity of earthquake source mechanisms. To explain these observations, we propose the seismicity is induced by H2O/CO2 fluid pulses from the shallow magma body into a highly fractured region. Fluid pulses cause high pore fluid pressures, which also cause the low rupture velocities

Local seismicity near the actively deforming Corbetti volcano in the Main Ethiopian Rift

Corbetti is currently one of the fastest uplifting volcanoes globally, with strong evidence from geodetic and gravity data for a subsurface inflating magma body. A dense network of 18 stations has been deployed around Corbetti and Hawassa calderas between February 2016 and October 2017, to place seismic constraints on the magmatic, hydrothermal and tectonic processes in the region. We locate 122 events of magnitudes between 0.4 and 4.2 using a new local velocity model. The seismicity is focused in two areas: directly beneath Corbetti caldera and beneath the city of Hawassa. The shallower 0–5 km depth below sea level (b.s.l.) earthquakes beneath Corbetti are mainly focused in EW- to NS-elongated clusters at Urji and Chabbi volcanic centres. This distribution is interpreted to be mainly controlled by a northward propagation of hydrothermal fluids away from a cross-rift pre-existing fault. Source mechanisms are predominantly strike-slip and different to the normal faulting away from the volcano, suggesting a local rotation of the stress-field. These observations, along with a low Vp/Vs ratio, are consistent with the inflation of a gas-rich sill, likely of silicic composition, beneath Corbetti. In contrast, the seismicity beneath Hawassa extends to greater depth (16 km b.s.l.). These earthquakes are focused on 8–10 km long segmented faults, which are active in seismic swarms. One of these swarms, in August 2016, is focused between 5 and 16 km depth b.s.l. along a steep normal fault beneath the city of Hawassa, highlighting the earthquake hazard for the local population

Impact of the COVID-19 pandemic on mental health care and people with mental health conditions in Ethiopia:the MASC mixed-methods study

BACKGROUND: The COVID-19 pandemic has had far-reaching effects on the mental health of populations around the world, but there has been limited focus on the impact on people with existing mental health conditions in low-income countries. The aim of this study was to examine impact of the pandemic on mental health care and people with mental health conditions in Ethiopia.METHODS: A convergent mixed methods study was conducted. We systematically mapped information from publicly available reports on impacts of the pandemic on mental health care. Monthly service utilisation data were obtained from Amanuel Mental Specialised Hospital, the main psychiatric hospital, and analysed using segmented Poisson regression (2019 vs. 2020). In-depth interviews were conducted with 16 purposively selected key informants. Framework analysis was used for qualitative data. Findings from each data source were integrated.RESULTS: In the early stages of the pandemic, participants indicated a minimal response towards the mental health aspects of COVID-19. Mental health-related stigma and discrimination was evident. Scarce mental health service settings were diverted to become COVID-19 treatment centres. Mental health care became narrowly biomedical with poorer quality of care due to infrequent follow-up. Households of people with pre-existing mental health conditions in the community reported worsening poverty and decreased access to care due to restricted movement, decreased availability and fear. Lack of reliable medication supplies increased relapse and the chance of becoming chained at home, abandoned or homeless. Caregiver burden was exacerbated. Within mental health facilities, prisons and residential units, infection control procedures did not adequately safeguard those with mental health conditions. Meanwhile, the needs of people with mental health conditions in COVID-19 quarantine and treatment facilities were systematically neglected. Only late in the day were integrated services developed to address both physical and mental health needs.CONCLUSIONS: The COVID-19 pandemic had substantial negative impacts on the lives of people with mental health conditions in Ethiopia. Future emergency response should prioritise the human rights, health, social and economic needs of people with mental health conditions. Integration of mental and physical health care would both expand access to care and increase resilience of the mental health system

Local Earthquake Magnitude Scale and b‐Value for the Danakil Region of Northern Afar

The Danakil region of northern Afar is an area of ongoing seismic and volcanic activity caused by the final stages of continental breakup. To improve the quantification of seismicity, we developed a calibrated local earthquake magnitude scale. The accurate calculation of earthquake magnitudes allows the estimation of b?values and maximum magnitudes, both of which are essential for seismic?hazard analysis. Earthquake data collected between February 2011 and February 2013 on 11 three?component broadband seismometers were analyzed. A total of 4275 earthquakes were recorded over hypocentral distances ranging from 0 to 400 km. A total of 32,904 zero?to?peak amplitude measurements (A) were measured on the seismometer’s horizontal components and were incorporated into a direct linear inversion that solved for all individual local earthquake magnitudes (ML), 22 station correction factors (C), and 2 distance?dependent factors (n, K) in the equation ML=log(A)?log(A0)+C. The resultant distance correction term is given by ?log(A0)=1.274336log(r/17)?0.000273(r?17)+2. This distance correction term suggests that attenuation in the upper and mid?crust of northern Afar is relatively high, consistent with the presence of magmatic intrusions and partial melt. In contrast, attenuation in the lower crust and uppermost mantle is anomalously low, interpreted to be caused by a high melt fraction causing attenuation to occur outside the seismic frequency band. The calculated station corrections serve to reduce the ML residuals significantly but do not show a correlation with regional geology. The cumulative seismicity rate produces a b?value of 0.9±0.06, which is higher than most regions of continental rifting yet lower than values recorded at midocean ridges, further supporting the hypothesis that northern Afar is transitioning to seafloor spreading