Quantitative Constraints on Faulting and Fault Slip Rates in the Northern Main Ethiopian Rift. Issue 8 (8th August 2020)

• Record Type: Journal Article
• Authors: Siegburg, Melanie; Bull, Jonathan M.; Nixon, Casey W.; Keir, Derek; Gernon, Thomas M.; Corti, Giacomo; Abebe, Bekele; Sanderson, David J.; Ayele, Atalay
• Is Part Of: Tectonics. Volume 39:Issue 8(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-08-08
• Subjects: tectono‐magmatic interaction -- Boset‐Bericha Volcanic Complex -- Main Ethiopian Rift -- slip rates -- fault growth -- fault displacement; Geology, Structural -- Periodicals; 551.8
• DOI: 10.1029/2019TC006046
• Languages: English
• ISSNs: 0278-7407

Abstract

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. Key Points: Large‐scale obliquity in the northern MER increases toward Afar with transtensional kinematics The Boset magmatic segment is characterized by two main NNE orientated fault zones, bounding a nested graben Maximum slip rates are ~0.37 mm/year in ~300 Ka volcanic deposits and ~4.3 mm/year offsetting ~6 Ka lavas of Boset