Browsing by Author "Marobhe, I."

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    Active Fault Mapping in Karonga-Malawi after the December 19, 2009 Ms 6.2 Seismic Event
    (Elsevier, 2015) Macheyeki, Athanas S.; Mdala, Hassan; Chapola, Lostina S.; Manhiça, V. J.; Chisambi, Joshua; Feitio, Paulino; Ayele, Atalay; Barongo, J.; Ferdinand, Richard W.; Ogubazghi, G.; Goitom, B.; Hlatywayo, Dumisani J.; Kianji, Gladys; Marobhe, I.; Mulowezi, A.; Mutamina, Daniel; Mwano, J. M.; Shumba, Blessing; Tumwikirize, I.
    The East African Rift System (EARS) has natural hazards – earthquakes, volcanic eruptions, and landslides along the faulted margins, and in response to ground shaking. Strong damaging earthquakes have been occurring in the region along the EARS throughout historical time, example being the 7.4 (Ms) of December 1910. The most recent damaging earthquake is the Karonga earthquake in Malawi, which occurred on 19th December, 2009 with a magnitude of 6.2 (Ms). The earthquake claimed four lives and destroyed over 5000 houses. In its effort to improve seismic hazard assessment in the region, Eastern and Southern Africa Seismological Working Group (ESARSWG) under the sponsorship of the International Program on Physical Sciences (IPPS) carried out a study on active fault mapping in the region. The fieldwork employed geological and geophysical techniques. The geophysical techniques employed are ground magnetic, seismic refraction and resistivity surveys but are reported elsewhere. This article gives findings from geological techniques. The geological techniques aimed primarily at mapping of active faults in the area in order to delineate presence or absence of fault segments. Results show that the Karonga fault (the Karonga fault here referred to as the fault that ruptured to the surface following the 6th–19th December 2009 earthquake events in the Karonga area) is about 9 km long and dominated by dip slip faulting with dextral and insignificant sinistral components and it is made up of 3–4 segments of length 2–3 km. The segments are characterized by both left and right steps. Although field mapping show only 9 km of surface rupture, maximum vertical offset of about 43 cm imply that the surface rupture was in little excess of 14 km that corresponds with Mw = 6.4. We recommend the use or integration of multidisciplinary techniques in order to better understand the fault history, mechanism and other behavior of the fault/s for better urban planning in the area.
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    Aerogeophysical, Geological and Geochemical Investigation of the Late Archaean Granitoids in the Musoma- Mara Greenstone Belt, NE Tanzania
    (2008) Mshiu, Elisante E.; Maboko, Makenya A. H.; Marobhe, I.
    The Musoma Mara Greenstone Belt (MMGB) is intruded with syn-to-post orogenic suites of granitoids which range in composition from Tonalite Trondhjemite Granodiorites (TTG) to granite. High resolution aerogeophysical data surveyed by GST in 2003 has provided aeromagnetic and radiometric data that were used in this study to classify various granitoids existing in MMGB. The individual radioactive element content of K, Th and U, ternary image and K: U: Th composite classification map have been used in data presentation and interpretation. In addition the radioactive element ratios were used to enhance the radiometric signals. Based on the analysis and interpretations made on airborne radiometric, magnetic data and previous geological maps, a geophysical interpretation map was obtained. This map broadly categorized the MMGB granitoids into two types, the first granitoid type is characterized by high contents of all the three elements (K, U and Th) and low magnetic intensity (< 33997 nT). The second granitoid type is characterized by high K relative to U and Th, and higher magnetic intensity (>33997 nT). The aerogeophysical interpretation map was used as a base map for ground follow-up whereby the granite types were sampled accordingly for geochemical analysis. Geochemical classification of the two granitoid types from geophysical data interpretations further subdivided them into three types i.e. biotite granite, calcic granite and TTG. The overall analysis showed high correlation between aerogeophysical and geochemical data whereby the voluminous biotite and calcic granite are the subdivisions from the first granite type and the less voluminous TTG precisely correlated to the second granite type. Their compositional similarity in geochemistry with the northern MMGB high-K and Na-rich granitoids (Manya et al. 2007a, b) suggested tectonic setting and petrogenetic analogy. Biotite and calcic granites are inferred to have been generated from partial melting of pre-existing materials including TTG, intermediate and felsic volcanic rocks whereby TTGs were generated from partial melting of hydrous basaltic crust that transformed into garnet amphibolites.
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    Tectonic History of the Mandawa Basin: Implication from Field Structural Observations, Dem And Magnetic Data
    (2015-11-17) Mtabazi, E.; Boniface, Nelson; Marobhe, I.; Andresen, A.; Hudson, W.; Didas, M.
    Our new field structural observations, digital elevation modal (DEM), seismic and magnetic data from the Triassic-Jurassic Mandawa Basin of coastal Tanzania demonstrate tectonic results of Gondwana rifting and dextral strike slip movements associated with the rifting and drifting of Madagascar from East Africa in Jurassic time. The results reveal two major deformation events, in the history of Mandawa Basin formation, named D1 and D2 in this study. The D1 event generated the NNW-SSE trending deep-seated normal faults, and T-fractures. The geometry of these structures suggests that, the ENE-WSW extensional movements, probably associated with the rifting of Gondwanaland during Permo-Triassic time, generated them. The D2 event was the most important deformation episode, which is widely distributed on regional scale as well as on outcrop scale. The NNE-SSW, NNW-SSE and ENE-WSW Riedal shears, dextral strike slip faults, sinistral faults, normal faults and T-fractures characterize D2 event. The D2 event is probably related with the NNW dextral shear zone with NW-SE extensional movements, probably generated during the drifting of Madagascar along the Davie transform fault during the Jurassic time. The geometry of Mandawa Basin suggests pull-apart origin, generated by transtensional event, followed by successful reactivations.