Rayleigh wave group velocity dispersion tomography of West Africa using regional earthquakes and ambient seismic noise
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West Africa could teach us much about the early tectonic history of Earth, but current seismic models of the regional crustal and lithospheric structure lack the resolution required to answer all but the most basic research questions. We have improved the resolution of group velocity maps of the West African Craton by complementing the uneven path distribution of earthquake-generated surface waves with surface waves reconstructed from ambient noise cross-correlations. Our joint dataset provides good spatial coverage of group velocity measurements from 20- to 100-s period, enabling us to reduce artifacts in our group velocity maps and improve their resolution. Our maps correlate well with regional geological features. At short periods, they highlight differences in crustal thickness, recent tectonic activity, and thick sediments. At long periods, we found lower velocities due to hot, thin lithosphere under the Pan-African mobile belt and faster velocities due to cold, thick lithosphere under the Man-Leo and Reguibat shields. Our higher resolution maps advance us a step towards revealing the detailed lithospheric structure and tectonic processes of West Africa.
KeywordsWest Africa Craton Rayleigh waves Dispersion Cross-correlation Ambient noise Group velocity
The research described herein used seismological data from various global networks available through the Incorporated Research Institutions for Seismology (IRIS) Data Management Center (including Africa Array (AF), GEOSCOPE (G), Global Seismograph Network (GSN-IRIS/USGS), Global Telemetered Seismograph Network (GTSN-USAF/USGS), Instituto Superior Tecnico Broadband Seismic Network (IP), IRIS PASSCAL Experiment Stations (XB), MEDNET Project (MN), Morocco-Muenster (3D), and Seismic Network of Tunisia (TT)). We are grateful to the operators of these networks for ensuring the high quality of the data and making them publicly available. Earthquake parameters were obtained from the Global CMT catalog.
Y. Ouattara was supported by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) Young Scientist Award Grant, the Lamto Geophysical Station (Ivory Cost), and the CNRS-INSU TelluS-SYSTER program. Additional support in the form of computer equipment was provided by Institut de Physique du Globe de Strasbourg (IPGS). Y. Ouattara would like to thank Professor A. Diawara, director of the Lamto Geophysical Station, for his advice and moral support in seeking a PhD in seismology in France, and Professor B. C. Sombo for accepting him in his research laboratory in Abidjan and for supervising part of his thesis work. The manuscript benefitted from constructive comments by Michael Pasyanos and Editor Mariano Garcia-Fernandez.
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