Imaging the Northern East African Rift System using a Trans-dimensional Bayesian Inversion
Abstract
The East African Rift System is an active intracontinental rift zone that exhibits crustal thinning, extension, volcanism, and seismicity. Tomographic inversion techniques allow us to interrogate seismic velocity within this rift to infer physical and compositional structure, better constrain rifting mechanisms, provide insight into the degree of strain localization, and understand the importance of magma feedbacks during extension. Questions remain concerning how extension is accommodated with depth and the degree to which it is influenced by melt or pre-existing structures. This research incorporates new data to holistically parse the structure of the rift from its axis to the western edge of the Ethiopian plateau.
We make use of Rayleigh wave phase velocities from 20-180 seconds, and P-s, S-p converted phases to map crust and upper mantle seismic wavespeeds in 3-D structure across the Main Ethiopian rift. These complementary data are jointly inverted using a trans-dimensional, hierarchical Bayesian inversion (THBI) algorithm. We employ parallel Monte Carlo Markov Chains to generate an ensemble of good-fit 1-D models at 256 seismometer stations throughout the study region; posterior probabilities derived from these ensembles offer robust uncertainty estimates for model parameters. The THBI technique offers several benefits over a simple inversion. Transdimensionality yields efficient inversion and parsimonious models. Velocity profiles are fit by adaptive splines, which dynamically change complexity and depth. We invert for data error 'hyperparameters', thus removing potential operator bias involved in user-dictated regularization. Our study captures, for the first time, the rift shoulder structure that may hold the key to understanding the geologic context of rifting. Our velocity models are used to discuss dynamics, strain accommodation, and magma distribution within this continental rifting archetype.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.T33F0409P
- Keywords:
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- 8105 Continental margins: divergent;
- TECTONOPHYSICS;
- 8109 Continental tectonics: extensional;
- TECTONOPHYSICS;
- 8120 Dynamics of lithosphere and mantle: general;
- TECTONOPHYSICS;
- 8159 Rheology: crust and lithosphere;
- TECTONOPHYSICS