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to other segments of the EARS, because of the broad, diffuse rifting   Summary
        pattern and history of previous rifting oblique to the current-day trend
        (Brune et al., 2017; Ebinger et al., 2017).            Overall, the EARS shows variability in lithospheric topography and
                                                               reveals regions where the lithospheric structure may be affecting
        Beneath this region, the indication of a low-velocity anomaly at deep   the path of upwellings at shallow and middle-upper mantle depths.
        upper mantle and mantle transition zone depths was most prominent   However, there is also a clear sense of distinct upwellings within the
        (Fig. 3c). Directly above this, at middle upper mantle depths, a high-  upper mantle that might be sourced from a common, deeper anomaly.
        velocity feature was identified in the west beneath South Sudan, and  Our results of the upper mantle and mantle transition zone are useful
        the lowest velocities at these depths were located immediately adjacent  in understanding the spatial relationships and possible connections
        to the high-velocity feature, to the north and to the southeast and  between different segments and we hope that they will aid the overall
        southwest (Fig. 3b). Above this, at the shallowest upper mantle depths,  goal of synthesis.
        the lowest velocities were imaged to the east beneath Lake Turkana.
        At these shallowest depths to the west beneath South Sudan, slightly  Acknowledgments
        slow to average upper mantle velocity was observed, while the fastest   We thank the NSF Earth Sciences Postdoctoral Fellowship program
        structure was located to the south and southwest beneath the laterally   for supporting this research (EAR-1349684). The shear velocity model
        continuous Uganda and Bomu-Kibalan Cratons (Fig. 3a).  from Emry et al. (2019) is available through the IRIS-EMC at: http://
        This pattern may suggest that rising asthenosphere is being diverted and through
        north and south around a lithospheric structure within the middle  the GeoMapApp tool at: We thank
        upper mantle beneath South Sudan. However, it is difficult to be  Manochehr Bahavar from the IRIS-EMC and Andrew Goodwillie
        certain of the spatial relationship and possible connection between   from IEDA-GeoMapApp for helping to format the model and make
        this high-velocity feature and the Uganda and Bomu-Kibalan Cratonic   it available.
        roots located at shallower depths to the south and southwest. At this  Because our data came from ambient seismic noise, it was necessary
        this point we can only speculate whether the structure is part of a  that stations had temporally overlapping records. In this regard, the
        stable, deep lithospheric root or whether it is sinking or foundering  sparsely distributed long-term seismic deployments, such as the GSN,
        lithosphere (see discussion in Emry et al., 2019). However, we expect  GEOSCOPE, AfricaArray (see photos on the right), and MedNet
        that this feature may affect the style of rifting, patterns of magma-  were irreplaceable, and allowed us to also incorporate several 1-2
        rich vs. magma-poor extension, and connections between the Main  year (‘PASSCAL-type’) seismic deployments throughout Africa and
        Ethiopian Rift and the Eastern and Western Branches.   the surrounding regions.  ■

        a     30°         40°                b    30°          40°              c      30°         40°

                           A’   B’

       10°                          10°  5000  10°                      10°  5100  10°                      10°  5700
                                        4800                                4900                                5500
                                        4600                                4700                                5300
                                        4400  Vs (m/s)                      4500  Vs (m/s)                      4900  Vs (m/s)
                                        4200                                4300                                4700
                                        4000                                4100                                4500
        0°                          0°       0°                         0°       0°                          0°
            A     B
          123 km                              260 km                              424 km
              30°         40°                     30°          40°                     30°         40°

          A                                              A’     B                                               B’
                                                              0  dVs

        Figure 3. Three depth slices from the Turkana-South Sudan and Ethiopian Plateau regions showing shear velocity at a) 123 km, b) 260 km, and c)
        424 km, modified from Emry et al. (2019). Cross-sections correspond to lines plotted on a. Abbreviations explained in Figure 1.

        8  •  GeoPRISMS Newsletter  Issue No. 42  Spring 2019
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