Quantitative Constraints on Faulting and Fault Slip Rates in the Northern Main Ethiopian Rift

Abstract

The Boset magmatic segment (BMS) of the northern Main Ethiopian Rift (MER) is an ideal natural laboratory to investigate the kinematics, interaction, and rates of activity within a fault network in a magma‐rich rift. In this paper we take advantage of the availability of (1) high‐resolution remote sensing data (LiDAR, ASTER); (2) absolute age chronology on offset reference surfaces; and (3) well‐exposed active normal fault arrays to place new constraints on rift kinematics and strain distribution, and to quantify the architecture and fault slip rates at different temporal scales within a magmatic segment. We found that the rift border faults strike approximately NE, while the younger faults in the rift segments strike NNE. Analyses of geometric rift parameters show that the axial active part of the rift is transtensional with an increase of the shear component northward. The fault displacement analyses and displacement:length ratios increase toward the segment tips, suggesting a significant contribution of fault growth by linkage. In contrast, magmatism is focused on the segment center and localized to a narrow zone. Estimated fault slip rates vary, with rates of up to ~0.37 mm/year in ~0.3 Ma old rift floor deposits, whereas higher rates of up to ~4.4 mm/year are observed for faults cutting through ~6 Ka lavas. The difference in slip rates indicates short‐term variability or a very active recent episode compared to long‐term low average slip rates.

Mid‐Pleistocene to Recent Crustal Extension in the Inner Graben of the Northern Kenya Rift

“…However, our overall temporal resolution is not accurate enough to test the hypothesis of pulsed tectono‐magmatic activity on 10 5 yr timescales, as observed by Siegburg et al. (2020) in the more advanced Northern Main Ethiopian Rift.…”

“…The long‐term character of extension rates on geologic timescales, however, remains difficult to determine, especially within nascent plate boundaries, where the crust is entirely continental, and rate determinations that involve the analysis of the ocean‐floor (e.g., DeMets & Merkouriev, 2016, 2019) cannot be applied. However, if well‐preserved normal‐fault scarps in chronologically constrained rock exposures exist, the horizontal component of fault motion can be used to determine extension rates on longer timescales (e.g., Mouslopoulou et al., 2012; Muirhead et al., 2016; Shmela et al., 2021; Siegburg et al., 2020). This study takes advantage of such tectonic archives in the Northern Kenya Rift (NKR) with the aim to derive a robust long‐term extension rate for the divergence of the Victoria and Somalia Plates of the East African Rift System (EARS) during the last 0.5 m.y.…”

A systems-based approach to parameterise seismic hazard in regions with little historical or instrumental seismicity: active fault and seismogenic source databases for southern Malawi

“…There are no known historical accounts of surface-rupturing earthquakes in southern Malawi, although a continuous written record only extends to ca. 1870 (Pike, 1965;Stahl, 2010). However, in northern Malawi, the previously unrecognised St Mary Fault exhibited surface rupture following the 2009 Karonga earthquakes, a sequence consisting primarily of four shallow (focal depths < 8 km) M W 5.5-5.9 events over a 13 d period (Fig.…”

Evolution of the Alu-Dalafilla and Borale Volcanoes, Afar, Ethiopia

“…The similarity in segment morphology is potentially linked to the extension rate of Afar (~15-20 mm/yr), being at the slow end of that of slow spreading ridges (Jokat et al, 2003). The less mature MER also has magmatic segments of similar size and morphology to Afar (e.g., Ebinger & Casey, 2001;Siegburg et al, 2020) but rifting is at a slower rate (4.5 mm/yr, Bilham et al, 1999).…”