Rift interaction zones and the stages of rift linkage in active segmented continental rift systems

Abstract

Although much is known about the interaction of faulting and sedimentation within the basins of active segmented continental rift systems, little is known about these processes within the interaction zones of varying geometries that separate the young interacting segments. We address this problem by exploring the non-volcanic rift interaction zones (RIZ) along the humid, magma-poor juvenile western branch of EAGE KOLAWOLE Et AL. F I G U R E 1Cartoon illustrating the growth of propagating rift segments along active continental rift systems (updated and modified after Nelson et al., 1992). Note that this cartoon only features collinear and underlapping parallel rift segments. For each zone of rift segment interaction, the cartoon illustrates the pre-and post-linkage geometries of the rift segments. Also, note that cartoon represents rift segmentation and interaction at the early stages (stretching stage) of continental rifting F I G U R E 4 Eastern Africa rift basins and the major rift interaction zones. (a) Map of eastern Africa showing the different segments of the Cenozoic Western Branch (WBEARS) of the East African Rift System (and some of the Eastern branch segments). Also shown are the Mesozoic rift segments that are reactivated (e.g. LR, RR, SRZ) and unreactivated (e.g. LmR, MnR, RuR, ZR) during the current phase of Cenozoic extension.

The Malawi Active Fault Database: An Onshore‐Offshore Database for Regional Assessment of Seismic Hazard and Tectonic Evolution

“…Faults buried beneath rift sediments in Malawi have also been previously inferred from gravity and aeromagnetic data (Chisenga et al., 2019; Kolawole et al., 2018a, 2021). Where these faults are favorably oriented to the regional stresses (Williams et al., 2019), we interpret that they are active and so also include them in the MAFD; albeit, since there is no definitive evidence that they have been active during East African rifting, they are assigned a confidence level of 2 (Figure 3a, Table 1).…”

“…We infer that these faults are active as they have hosted displacement since the onset of East African rifting in Malawi or because they are buried beneath the rift valley and are favorably oriented to the regional stresses. To address the challenges of mapping such faults in the Western Branch of the EAR's, the MAFD has been compiled from a multidisciplinary data set that includes fieldwork, existing geological maps, high-resolution DEMs, 10.1029/2022GC010425 of 25 seismic surveys (Scholz et al, 2020;Shillington et al, 2016Shillington et al, , 2020, and aeromagnetic (Kolawole et al, 2018a(Kolawole et al, , 2021 and gravity data (Chisenga et al, 2019). We consider that the MAFD is currently the most complete compilation of active faults across Malawi and will be of use for future regional seismic hazard studies.…”

Geologic and geodetic constraints on the seismic hazard of Malawi’s active faults: The Malawi Seismogenic Source Database (MSSD)

“…It is distinct, but complementary to the Malawi Active Fault Database (Williams et al, 2021c). The MSSD also represents an update of the South Malawi Seismogenic Source Database (Williams et al, 2021b) due to the application of a new geodetic model (Wedmore et al, 2021), new active fault mapping (Kolawole et al, 2021a), and a more robust description of uncertainty.…”

“…The MAFD includes 90 basement-involved faults that were mapped from geological maps, high resolution digital elevation models, and 2D seismic reflection surveys Shillington et al, 2020) and that have demonstrably shown evidence of displacement during EAR activity in Malawi. The remaining 23 faults in the MAFD are buried intrarift faults inferred from aeromagnetic (Kolawole et al, 2018a(Kolawole et al, , 2021a or gravity data (Chisenga et al, 2019), and hence no definitive evidence of displacements associated with East African rifting, but are well-oriented for reactivation in the regional stress field (Dawson et al, 2018;Williams et al, 2019Williams et al, , 2021c. The MAFD contains basic geomorphic and mapping attributes following the format of the Global Earthquake Model Global Active Faults Database .…”

“…The MSSD is comparable to the Database of Individual Seismogenic Sources in Italy (Basili et al, 2008), the Taiwan Earthquake Model (Shyu et al, 2016), or the New Zealand Community Fault Model (Van Dissen et al, 2021). The MSSD is the first seismogenic source database in central and northern Malawi, and represents an update of the South Malawi Seismogenic Source Database (SMSSD; Williams et al, 2021b) because it incorporates new active fault traces (Kolawole et al, 2021a;Williams et al, 2021c), new geodetic data (Wedmore et al, 2021) and a statistical treatment of uncertainty in the logic tree approach (Sect. 3.4).…”