Active Deformation Constraints on the Nubia‐Somalia Plate Boundary Through Heterogenous Lithosphere of the Turkana Depression

Abstract

The role of lithospheric heterogeneities, presence or absence of melt, local and regional stresses, and gravitational potential energy in strain localization in continental rifts remains debated. We use new seismic and geodetic data to identify the location and orientation of the modern Nubia‐Somalia plate boundary in the 300‐km‐wide zone between the southern Main Ethiopian Rift (MER) and Eastern Rift (ER) across the Mesozoic Anza rift in the Turkana Depression. This region exhibits lithospheric heterogeneity, 45 Ma‐Recent magmatism, and more than 1,500 m of base‐level elevation change, enabling the assessment of strain localization mechanisms. We relocate 1716 earthquakes using a new 1‐D velocity model. Using a new local magnitude scaling with station corrections, we find 1 ≤ ML ≤ 4.5, and a b‐value of 1.22 ± 0.06. We present 59 first motion and 3 full moment tensor inversions, and invert for opening directions. We use complementary geodetic displacement vectors and strain rates to describe the geodetic strain field. Our seismic and geodetic strain zones demonstrate that only a small part of the 300 km‐wide region is currently active; low elevation and high‐elevation regions are active, as are areas with and without Holocene magmatism. Variations in the active plate boundary's location, orientation and strain rate appear to correspond to lithospheric heterogeneities. In the MER‐ER linkage zone, a belt of seismically fast mantle lithosphere generally lacking Recent magmatism is coincident with diffuse crustal deformation, whereas seismically slow mantle lithosphere and Recent magmatism are characterized by localized crustal strain; lithospheric heterogeneity drives strain localization.

Seamless Map of Depth to the Moho Interface in the Afro‐Arabian Region Using Gravity Data Derived From EGM2008

“…A relatively small uplift is observed beneath the GP, which is located west of the SMER and north of the Chamo Basin that extends south toward the Kenyan Rift. A comparison of results from earlier work (Braile et al, 1994;Kounoudis et al, 2023;Musila et al, 2023;Ogden et al, 2023;Sippel et al, 2017) with the one from this work showed that the EARs south of the MER are in an advanced stage of the rifting process than the SMER. Bonini et al (2005) also indicated that extensional structures started to develop in the Southern MER due to the northward propagation of Kenya Rift-related deformation.…”

“…The Chew Bahir basin, located at the southern end of the GP is considered to be the northernmost propagation of the Kenya Rift, which accommodates extensional deformation south of the Gofa Basin and Range (Corti, 2009 & reference therein). A belt of seismically fast velocity mantle lithosphere that forms the linking zone between the MER and EAR is usually associated with diffused crustal deformation and lacks recent magmatism (Musila et al, 2023). On the other hand, seismically slow velocity mantle lithosphere and recent magmatism in the linkage zone are characterized by localized crustal strain, which is driven by lithospheric heterogeneity.…”