In a groundbreaking study illuminating the intricate dynamics beneath East Africa’s Turkana Depression and southern Ethiopia, researchers have harnessed an extensive array of seismological data to decode the mysteries of the region’s lithosphere and upper mantle structure. This pioneering investigation leveraged data from 38 temporary broadband seismograph stations, supplemented by permanent seismic stations, weaving a comprehensive picture of the subsurface geological architecture that has long intrigued earth scientists. The integration of these seismic networks has unlocked unprecedented insights into the seismic velocity structure, shedding light on the nature of crustal and mantle processes shaping one of the planet’s most geodynamically active regions.
Central to this research was the extraction of fundamental-mode Rayleigh-wave group velocity dispersion curves across a broad spectrum of periods—from the brief, rapid oscillations of 4 seconds to the slower 60-second waves that probe deeper beneath the surface. These observations, derived from innovative anisotropic tomographic models, were meticulously combined with long-period global Rayleigh-wave data to enhance depth resolution and spectral completeness. A three-point moving averaging technique was prudently applied, ensuring seamless transition across the short- and long-period datasets and eliminating artificial velocity fluctuations that might have masked subtle but telling signals within the Earth’s crust and upper mantle, spanning depths between 5 km and about 150 km and even extending sensitivity down to 400 km in some cases.
Not content with surface-wave analysis alone, the team incorporated receiver function data drawn from teleseismic earthquakes, which provided sharp snapshots of the seismic discontinuities beneath each station. This method, which isolates P-to-S converted phases, required rigorous quality assessment through iterative deconvolution processes, ensuring that only the most robust seismic phases contributed to the final models. By meticulously binning the receiver functions according to ray parameters and applying dual Gaussian filters, the researchers could delineate detailed lithospheric features, distinguishing between sharp and gradational boundaries with greater confidence than previously possible.
One remarkable finding emerged from the stability of the receiver functions across the TRAILS network, which exhibited minimal anisotropic complexities or backazimuthal variability, attesting to a predominantly isotropic and laterally uniform subsurface structure. This contrasts sharply with regions to the south, such as the melt-rich Afar Depression, highlighting the nuanced geological diversity within the broader East African Rift system. Some stations situated in thick sedimentary basins or overlying basalt flows presented challenges, their receiver functions obscured by low-velocity sediments or complex multiphase conversions, underscoring the importance of geologic context when interpreting seismic data.
The heart of the analysis lies in the joint inversion of these complementary seismic datasets, a sophisticated approach that mitigates the individual limitations inherent in surface-wave or receiver function methods alone. Surface waves excel at resolving absolute shear velocities and detecting thermal boundaries like the lithosphere–asthenosphere boundary (LAB), yet they lack sharp vertical resolution to define discontinuities such as the Moho precisely. Receiver functions, while adept at pinpointing impedance contrasts and relative travel times, cannot provide absolute velocity measurements, leading to ambiguity in seismic velocity models if used in isolation. By combining these methodologies through iterative least-squares inversion, the study successfully captures a robust velocity profile extending to 400 km depth, balancing model smoothness with fidelity to observed waveforms.
Key to achieving reliable inversions was the careful calibration of weighting factors controlling the relative influence of receiver functions and surface-wave dispersion data, alongside optimal damping parameters to enforce geological plausibility and stability in the solutions. The team employed a rigorous trade-off curve analysis, settling on a weighting scheme that maximized the contribution of receiver functions without compromising the high-quality dispersion curve fits. Additionally, bootstrapping protocols were implemented to quantify uncertainty and variability within the seismic models, culminating in shear-wave velocity profiles with tight confidence bounds—a level of precision that enhances interpretive power for mantle thermal and compositional states.
Beyond seismic velocity mapping, the research innovatively translated these data into mantle temperature estimates through a thermodynamic framework rooted in Gibbs free energy minimization and the stx11 database. Applying corrections for anelasticity and referencing standard Earth models like PREM and ak135, the team minimized compositional uncertainties by focusing on peridotitic mantle compositions, thereby isolating thermal effects on seismic velocities. The resulting thermal models, while acknowledging some complexities such as potential radial anisotropy or subtle metasomatic alterations, allowed for reliable delineation of the lithosphere–asthenosphere transition, corroborating seismic velocity proxies with temperature gradients that mark the shift from conductive lithospheric mantle to convecting asthenosphere.
Delineating the Moho and LAB within these seismic profiles hinged on identifying distinct velocity gradients. The Moho was inferred at the base of the steepest positive velocity gradient within crust-to-upper mantle velocities ranging from 3.8 to 4.2 km/s. For the LAB, the researchers identified the base of the high-velocity mantle lithospheric lid characterized by a pronounced negative velocity gradient transitioning to slower asthenospheric velocities. To avoid confounding the analysis with crustal heterogeneities or small-scale anomalies, velocity profiles were smoothed using Savitzky-Golay filters before computing gradients. This nuanced approach yielded both minimum and maximum depth estimates for the LAB, reflecting natural variability and measurement uncertainties.
An intriguing aspect of the study was the manual integration of thermal modeling and seismic velocity profiles to validate and refine LAB depths. By pinpointing where geotherms transition from conductive lithospheric gradients to adiabatic asthenospheric profiles, the researchers defined a thermodynamic boundary matching their seismic observations, deepening the understanding of mantle thermomechanics in the rift zone. This dual seismic-thermal perspective underscores the intricate interplay between mechanical lithospheric structure and mantle heat flow, vital for constructing comprehensive geodynamic models.
Overall, this study exemplifies how integrated seismic methodologies combined with thermodynamic modeling can unravel the complexities of lithospheric and asthenospheric architecture beneath regions poised on the threshold of geodynamic transformation. The Turkana Depression and southern Ethiopian lithosphere emerge as a mosaic of thermal and structural heterogeneities shaped by both ancient rifting episodes and ongoing tectonism. These findings not only advance regional geological understanding but also provide valuable benchmarks for global studies focused on rift evolution, mantle dynamics, and large igneous province formation.
Given the multi-dimensional datasets and advanced analytical techniques deployed, the research sets a new benchmark for seismological investigations worldwide. By sharply refining estimates of fundamental boundaries such as the Moho and LAB, it opens avenues for future exploration into how lithospheric architecture influences volcanic activity, mantle convection, and continental breakup. Furthermore, the meticulous calibration of inversion parameters and uncertainty quantification serves as a methodological template for analogous studies in other tectonically active locales.
In synthesizing these technical advances, the research underscores the paramount importance of past rifting processes in governing the development of large igneous provinces and associated tectonomagmatic phenomena. The joint inversion of seismic data paired with thermodynamic insights constitutes a powerful toolkit for decoding Earth’s deep lithospheric secrets, setting the stage for transformative discoveries in Earth sciences over the coming decades.
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Kounoudis, R., Bastow, I.D., Ebinger, C.J. et al. The importance of past rifting in large igneous province development. Nature 647, 115–120 (2025). https://doi.org/10.1038/s41586-025-09668-7
Image Credits: AI Generated
DOI: 06 November 2025
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