Assessing the potential of syn-rift sediments for geochronological dating and its implications for the development of Makanjira-Shire basin in south Malawi Rift

The Upper Shire River basin, located within the zone of progressive interaction and linkage between the southern Malawi Rift and Shire Rift Zone, East Africa, presents an early-stage rift setting where rapid denudation processes take place and have profound influence on the geomorphological evolution of the region. The basin is key to the understanding of mechanisms involved in propagation and growthin young rifts. Although the tectonics in the region are well studied, lack of age constraints due to well-dated strata poses challenges in the understanding of the timing and mechanisms of rift evolution in this section of the south Malawi Rift. We used syn-rift sediments deposited from the rift shoulders to test the applicability of OSL and radiocarbon dating techniques in a poorly dated data-constrained region of the Malawi Rift. Our results suggest that proper sampling strategy is paramount in using the OSL technique for dating in areas of high dosage such as the one under consideration. However, the technique offers potential for use in these areas. Furthermore, we conclude from these findings that the evolution of the Upper Shire basin was triggered by tectonic movements along the Makongwa scrap that were responsible for redirecting the Likwenu River into the in the Zomba Graben through the Upper Shire at least during the Upper Pleistocene.Publisher PDFPeer reviewe

A systems-based approach to parameterise seismic hazard in regions with little historical or instrumental seismicity:Active fault and seismogenic source databases for southern Malawi

Seismic hazard is commonly characterised using instrumental seismic records. However, these records are short relative to earthquake repeat times, and extrapolating to estimate seismic hazard can misrepresent the probable location, magnitude, and frequency of future large earthquakes. Although paleoseismology can address this challenge, this approach requires certain geomorphic setting, is resource intensive, and can carry large inherent uncertainties. Here, we outline how fault slip rates and recurrence intervals can be estimated by combining fault geometry, earthquake-scaling relationships, geodetically derived regional strain rates, and geological constraints of regional strain distribution. We apply this approach to southern Malawi, near the southern end of the East African Rift, and where, although no on-fault slip rate measurements exist, there are constraints on strain partitioning between border and intra-basin faults. This has led to the development of the South Malawi Active Fault Database (SMAFD), a geographical database of 23 active fault traces, and the South Malawi Seismogenic Source Database (SMSSD), in which we apply our systems-based approach to estimate earthquake magnitudes and recurrence intervals for the faults compiled in the SMAFD. We estimate earthquake magnitudes of MW 5.4–7.2 for individual fault sections in the SMSSD and MW 5.6–7.8 for whole-fault ruptures. However, low fault slip rates (intermediate estimates ∼ 0.05–0.8 mm/yr) imply long recurrence intervals between events: 102–105 years for border faults and 103–106 years for intra-basin faults. Sensitivity analysis indicates that the large range of these estimates can best be reduced with improved geodetic constraints in southern Malawi. The SMAFD and SMSSD provide a framework for using geological and geodetic information to characterise seismic hazard in regions with few on-fault slip rate measurements, and they could be adapted for use elsewhere in the East African Rift and globally

Structural inheritance and border fault reactivation during active early-stage rifting along the Thyolo fault, Malawi

We present new insights on the geometry, initiation and growth of the Thyolo fault, an 85 km long active border fault in the southern Malawi Rift, from high-resolution topography, field and microstructural observations. The Thyolo fault is located towards the edge of the Proterozoic Unango Terrane, and is the border fault of the Lower Shire Graben, which has experienced four phases of extension since the Jurassic. Recent activity is demonstrated by an 18.6 ± 7.7 m high fault scarp, with two substantial reductions in scarp height along strike. However, the segment boundaries suggested by these displacement measurements do not coincide with changes in fault strike. Elsewhere, a ∼5 km long fault perpendicular scarp joins two overlapping sections, yet the scarp height in this linking section is similar to the bounding sections, and there is no evidence of significant pre-linkage strain accumulation. Microstructural analyses along the fault show a 15–45 m thick footwall damage zone with a 0.7 m thick core. We suggest that favourably-oriented, pre-existing shallow structures control changes in surface geometry and the narrow fault core, whereas exploitation of weak ductile zones at depth, possibly associated with the terrane boundary, control the displacement profile of the fault

Structural and Stratigraphic Controls of Malawi's Hotsprings : a Review

Active continental divergent zones such as those in the East African Rift System (EARS) hold significant potential for commercially exploitable geothermal resources. Evaluating these zones and characterizing the structural and stratigraphic controls may give insights of the most favourable locations for geothermal activity in a particular area. Due to the geological setting in the western branch of the EARS, several surface manifestations of geothermal energy mostly in the form of hotsprings have been found throughout Malawi. According to our results it seems that there is a strong correlation between the strike of the hotsprings, rock type, regional faulting and the seismic rupture in 2009. However, the country’s full potential has not been evaluated despite these hotspring manifestations throughout this rift segment. Those hotsprings with a high probability of containing easily extractable, commercially viable energy have still to be re-evaluated in order to locate the most favourable areas for geothermal exploration in the area. To achieve this, more local studies are necessary in order to understand better the stratigraphic and structural controls of the hotsprings in the studied area, in order to attract local and international investors. Therefore, the objective of this paper is to give an overview of the geological, structural, geochemical and seismic characteristics in northern Malawi for the exploration of geothermal energy. Once explored, this resource could become crucial in the country’s future development and economy

Impactos ambientais das residências secundárias em espaço rural de Ronda Alta

Este trabalho objetiva analisar impactos ambientais, decorrentes da presença de segundas residências instaladas no entorno do reservatório da Usina Hidrelétrica de Entre Rios do Sul em Ronda Alta (RS). O fenômeno iniciou após a formação do reservatório, que alagou extensa área do município de Ronda Alta, mais precisamente na década de 1980, ocorreu a ocupação do seu entorno motivada por proprietários de terras da localidade de Passo da Entrada. Na reconstrução da comunidade alguns moradores realizaram o parcelamento de solo em pequenos lotes à margem do logo, iniciando assim a construção de casas para veraneio e lazer. A metodologia utilizada no trabalho baseou-se no levantamento de bibliografia sobre a temática abordada e busca de informações através de pesquisas de campo, onde foram entrevistados oito moradores de propriedades rurais na comunidade de Passo da Entrada, além do presidente do Sindicato dos Trabalhadores Rurais e EMATER do município, além da coleta de informações com secretários municipais de Ronda Alta. As entrevistas foram conduzidas através de questionário semiestruturado atendendo os objetivos propostos neste trabalho. Os objetivos da pesquisa foram alcançados, tendo em vista os entrevistados demonstraram profundo conhecimento sobre o assunto, enquanto as respostas mantiveram proximidade nos resultados. Os entrevistados em suas intervenções concluirão que o turismo traz impactos ambientais na área de estudo e tem forte relação com o fenômeno das segundas residências, usadas para acomodar os turistas em seus veraneios; os imóveis encontra-se em áreas de preservação permanente, causador de impacto ambiental pela geração de lixo e esgoto doméstico e pelo fluxo demasiado de turistas.This work aims to analyze environmental impacts arising from the presence of second homes installed around the reservoir of the hydroelectric plant of Entre Rios South Ronda Alta (RS). The phenomenon began after the formation of the reservoir, which flooded a large area of the municipality of Ronda Alta, more precisely in the 1980s, was the occupation of your surroundings motivated by landowners in the locality of Step Input. In the reconstruction of the community some residents performed the installment of soil in small plots outside the logo, thus beginning the construction of houses for vacation and recreation. The methodology used in this work was based on the survey of literature on the topic addressed and search information through field research, were interviewed eight residents of rural properties in the community Step Input, the chairman of the Union of Rural Workers and EMATER the municipality, in addition to collecting information with municipal secretaries of Ronda Alta. The interviews were conducted through semi-structured questionnaire meeting the objectives proposed in this paper. The research objectives were achieved, in view of the respondents demonstrated deep knowledge of the subject, while the responses remained close in the results. Respondents in their interventions conclude that tourism brings environmental impacts in the study area and has a strong relationship with the phenomenon of second homes, used to accommodate tourists in their summers, the property is in permanent preservation areas, adversely impact environment for the generation of garbage and sewage and the flow of tourists too

Scarp height data and topographic profiles from the Zomba Graben, southern Malawi

Measurements of fault scarp height from five faults in the Zomba Graben, southern Malawi (Table S1-S6). Topographic profiles used to measure the height of the scarp are in Tables S7-S11. For more details of this dataset please refer to Wedmore, L. N. J., Biggs, J., Williams, J. N., Fagereng, Å. Dulanya, Z., Mphepo, F., & Mdala, H. (2020). Active fault scarps in southern Malawi and their implications for the distribution of strain in incipient continental rifts. Tectonics, 39(3), https://doi.org/10.1029/2019TC005834 Please contact the author, Luke Wedmore ([email protected]) for more details

How Do Variably Striking Faults Reactivate During Rifting? Insights From Southern Malawi

Crustal extension is commonly thought to be accommodated by faults that strike orthogonal and obliquely to the regional trend of the minimum compressive stress (σ3). Activation of oblique faults can, however, be conceptually problematic as under Andersonian faulting, it requires preexisting crustal weaknesses, high fluid pressures, and/or stress rotations. Furthermore, measurements of incremental fault displacements, which are typically used to identify oblique faulting, do not necessarily reflect regional stresses. Here, we assess oblique faulting by calculating the stress ratio (σ3/σ1, where σ1 is the maximum compressive stress), slip tendency, and effective coefficient of friction (μs′) required to reactivate variably striking normal faults under different trends of σ3. We apply this analysis to NW and NNE striking active faults at the southern end of the Malawi Rift, where NE‐SW, ENE‐WSW, E‐W, and SE‐NW σ3 trends have previously been proposed. A uniform σ3 trend is inferred for this region as recent joints sets do not rotate along the rift. With a NE‐SW trending σ3, NW‐striking faults are well oriented, however, NNE‐striking faults require μs′ 0.55. These σ3 trends are also comparable to a focal mechanism stress inversion, regional joint orientations, and previously reported geodetically derived extension directions. We therefore conclude that unlike typical models of oblique rifting, the southern Malawi Rift consists of faults that all strike slightly oblique to σ3