Browsing by Author "Kypros Pilakoutas"

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Co-seismic and Rainfall-Triggered Landslide Hazard Susceptibility Assessment for Uganda Derived Using Fuzzy Logic and Geospatial Modelling Techniques
(Springer, 2025-07) Morris Oleng; Zuhal Ozdemir; Kypros Pilakoutas
Uganda has suffered from many damaging landslides like the 1966 Rwenzori, 1994 Kisomoro and 2010 Bududa events. Despite escalating landslide risks exacerbated by rapid deforestation, urbanization and population growth coupled with a substandard building stock, comprehensive national co-seismic and rainfall-induced landslide hazard and risk maps for Uganda do not exist. This study therefore aims to conduct landslide hazard assessment and zonation for Uganda using a geospatial-based fuzzy logic methodology. In this methodology, landslide frequency ratios obtained for the 1966 Toro and 1994 Kisomoro earthquakes are assigned to the stochastic event-based probabilistic seismic hazard map derived using OpenQuake-engine. The available co-seismic and rainfall-induced landslide inventory datasets are used to derive the distribution of landslide frequency ratios based on geology, topographic slope position index, slope aspect, slope angle, distance from streams, and proximity to major active faults. The spatial distribution of fuzzy membership functions obtained from frequency ratios are overlaid and aggregated to produce landslide susceptibility maps showing relative probabilities of landslide occurrences across Uganda. Results indicate that the highest overall landslide hazard susceptibility is expected in areas comprising highly weathered outcropping rocks of precambrian granites, dominantly metasedimentary, and granulites and gneisses geologies within 40 km from major active faults; where the bedrock peak ground acceleration ≥ 0.1 g, topographic position index ≥ 3.8, slope gradient ≥ 10°, and the distance from streams ≤ 1.25 km. These findings can inform Uganda’s directorate of disaster preparedness and management towards pioneering the development of co-seismic landslide risk mitigation measures for the country.
Fault-Oriented Spatially Distributed Seismicity Model and Coseismic Landslide Hazard Assessment Framework for Uganda
(SECED, 2023-09) Morris Oleng; Zuhal Ozdemir; Kypros Pilakoutas
Uganda’s location between the western and eastern branches of the East African Rift System exposes several parts of the Sub-Saharan African country, which already suffers from landslides, to earthquakes of varying degrees. Over the past decades, many destructive seismic events e.g., the 1929 Masaka, 1966 Toro, 1994 Kisomoro and 2016 Bukoba earthquakes have caused enormous human and economic losses. Moreover, the catastrophic impacts of these events have been exacerbated by the triggered landslides around earthquake epicentres. The proliferation of a substandard building stock caused by lack of building control and obsolete seismic design guidelines coupled with rapid population growth and urbanisation exposes Uganda to a massively increasing risk from such disasters. Hence, there is an urgent need to quantify this risk so that mitigation measures can be applied. In retrospect, as the first step towards the development of a seismic risk and resilience assessment framework for Uganda, this paper holistically presents a stochastic probabilistic seismic multi-hazard model developed based on fault-oriented and spatially distributed seismicity data for Uganda. Suitable attenuation relationships are implemented using a logic tree approach to predict ground motion in both stable continental and active shallow crust geological formations. Herein, the multi-hazard assessment tool incorporates coseismic landslides into the framework for Uganda. Mean seismic hazard maps in terms of PGA are computed for 475 and 2475-year return periods, in addition to a probabilistic assessment of coseismic landslides based on various conditioning factors. The findings, which are generally consistent with previous regional studies, indicate that western Uganda is prone to higher seismicity and coseismic landslides compared with the other parts of the country. Correspondingly, the framework presented herein can be used to kick-start the update and continuous improvement of Uganda Seismic Design Code, as well as help develop a National Seismic Mitigation Strategy.
Probabilistic Earthquake Risk Assessment Framework for Uganda: Event-Based Modelling Approach
(World Conference on Earthquake Engineering, 2024-07-05) Morris Oleng; Zuhal Ozdemir; Kypros Pilakoutas
Uganda’s geology, tectonics and morphology exposes most of its territory to earthquakes of low to moderate intensities. Past earthquakes such as the 1966 Toro, 1994 Kisomoro and 2016 Bukoba events have had detrimental consequences on the socio-economic welfare and resilience of communities across Uganda. Despite earlier efforts in predicting seismic hazard in Uganda, there is no comprehensive study published on earthquake-related risks across the country. Whilst losses during the previous earthquakes were still compar-atively low, damage due to future earthquakes are likely to escalate considerably because of the proliferation of a largely substandard building stock coupled with rapid population growth and urbanisation. As a first step towards building an earthquake risk and resilience framework for Uganda, this work employs the probabilistic event-based risk calculator of OpenQuake-engine to holistically assess potential losses resulting from future earthquakes. Using a fault-oriented spatially distributed seismicity approach, a logic tree is implemented to minimise the associated epistemic uncertainties and site conditions are modelled using the shear wave velocity in the upper 30m of soil across Uganda. The building stock is largely inferred and projected from the 2014 national population and housing census and analytical vulnerability curves are selected from the GEM global database. The analysis of earthquake ruptures, hazard maps, loss exceedance curves, mean annual loss maps and aggregated asset loss statistics indicate that western Uganda is prone to the highest risk. These findings will be a huge step towards the urgent need to update the Uganda Seismic Design Code, strategically plan land use patterns, optimise earthquake insurance pricing and improve the National Policy for Disaster Preparedness and Management.
Probabilistic Seismic Hazard Assessment Framework for Uganda: A Stochastic Event-Based Modelling Approach
(Springer, 2024-01-23) Morris Oleng; Zuhal Ozdemir; Kypros Pilakoutas
Uganda lies between the eastern and western arms of the East African Rift System, the largest seismically active rift above sea level. With increasing population, urbanisation and rapid construction, seismic risk in the country is escalating fast and is compounded by the high vulnerability of the building stock and inadequate disaster prevention and mitiga- tion strategies. Hence, there is an urgent need to assess Uganda’s resilience against seis- mic risks. This paper presents a Monte-Carlo based probabilistic seismic hazard model for Uganda, as the first step towards the development of a seismic risk and resilience assess- ment framework for the country. In addition to fault segment data, earthquake catalogues are compiled for the period between 1900 and 2022 to estimate recurrence parameters for source zones in the area of interest. Area source zones incorporating focal mechanisms are used to stochastically model a national hazard framework for Uganda. A logic tree approach is applied to implement four ground motion prediction equations for both stable continental and active shallow crust geologies. Mean hazard curves, uniform hazard spec- tra, earthquake disaggregation and spectral pseudo-accelerations for major Ugandan cities are derived in addition to hazard maps for the country. The findings are largely consistent with previous regional studies and confirm that western Uganda is exposed to the highest level of seismicity. The model presented herein can be used to kick-start the update and continuous improvement of Uganda Seismic Design Code and the National Policy for Dis- aster Preparedness and Management.
Stochastic Event-Based Probabilistic Earthquake Risk Assessment Framework for Uganda: Towards Informing the National Policy for Disaster Preparedness and Management
(Springer, 2025-02) Morris Oleng; Zuhal Ozdemir; Kypros Pilakoutas
Catastrophic earthquakes in Uganda have the potential for detrimental consequences on the socio-economic welfare and resilience of communities. Despite considerable efforts in predicting earthquake risk across Africa, a national comprehensive seismic risk study for Uganda does not exist. With increasing population, urbanisation and rapid construction, seismic risk is escalating fast and is compounded by the high vulnerability of buildings and scanty disaster prevention and mitigation strategies. This study uses the probabilistic event-based risk calculator of the OpenQuake-engine to assess potential risks resulting from future earthquakes. Although the building exposure model is largely inferred and projected from the national population and housing census of 2014, total replacement costs are obtained by performing series of interviews with local engineering practitioners. Analytical vulnerability curves are selected from Global Earthquake Model (GEM) database. Seismic hazard studies confirm that western Uganda is exposed to the highest level of seismicity where peak ground accelerations on rock ground can reach up to 0.27 g over a 475-year return period. Relative to Uganda’s gross domestic product, the associated seismic risk estimates indicate mean economic loss ratios of 0.36%, 2.72% and 4.94% over 10, 50 and 100-year return periods respectively; with mean annual economic loss of US$ 74.7 million (0.34% relative to the total replacement value) and annual deaths averaging 71 persons across the whole country. It is envisaged that the findings will inform strategic land use planning patterns, earthquake insurance pricing and foster the continuous improvement of Uganda’s National Policy for Disaster Preparedness and Management.