Seismological Investigations in the Olduvai Basin and Ngorongoro Volcanic Highlands (Western Flank of the North Tanzanian Divergence)

Laura Parisi, Ian Stanistreet, Jackson Njau, Kathy Schick, Nicholas Toth, Paul Martin Mai

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Abstract We present data and results of a passive seismic experiment that we operated between June 2016 and May 2018 in the Ngorongoro Conservation Area (northern Tanzania), located on the western side of the eastern branch of the Eastern African Rift (EAR) system. The motivation for this experiment is twofold: (1) investigating the extension of the Olduvai basin, referred to also as the “Cradle of Human Mankind,” as it hosted a variety of paleoenvironments exploited by hominins during their evolution; and (2) studying the link between the fault system in the main EAR and in its western flank. We conduct detailed data-quality analysis of the seismic recordings based upon ambient noise characterization and numerical waveform simulations. Our data set is of good quality, and we observe that local magnitude can be overestimated up to at least 0.23, due to wave-amplifications effects occurring at sites with loose sedimentary material. Based on a new but simple approach using power spectral density measurements, we calculate the thickness of sedimentary basins. This allows us to map the bottom of the Olduvai paleolake confirming that its sedimentary record may be at least 200 m deeper than previously inferred from core drilling. We also map the bottom of the Olbalbal depression for the first time. In addition, we present a seismicity map of the Ngorongoro Conservation Area with unprecedented detail. The seismicity depicts the suture zone between the Tanzanian craton and the Mozambique belt and reveals that the fault system in the western flank of the rift merges at depth into a single detachment that joins the Manyara fault on the western side of the main rift valley.
Original languageEnglish (US)
JournalSeismological Research Letters
StatePublished - Sep 15 2020

Bibliographical note

KAUST Repository Item: Exported on 2020-10-01
Acknowledged KAUST grant number(s): BAS/1/1339-01-01
Acknowledgements: The authors would like to acknowledge the Tanzanian Commission for Science and Technology (COSTECH), the Department of
Antiquities, and Ngorongoro Conservation Area Authority (NCAA) for research permits. The authors thank Larau, Luigi Lombardo,
Maria Rodriguez-Mustafa, Olaf Zielke, Zheng Tang, and Max Mai for their contribution during fieldwork and Rémi Matrau for helping with Figure 9. We extensively used the ObsPy package (Beyreutheret al., 2010; Krischer et al., 2015), the database for seismological data set Jane and ObsPyck used for seismic-phase picking developed by Lion Krischer, Robert Barsch, and Tobias Megies. Generic Mapping Tool (GMT) tools were used to produce some of the figures (Wesselet al., 2013). Finally, we thank the editor, the associated editor, and two anonymous reviewers for their detailed and encouraging reviews, which helped improve our article. This work was funded by the King Abdullah University of Science and Technology (KAUST) baseline BAS/1/1339-01-01 granted to P. M. M.


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