Tectonics, volcanism, landscape structure and human evolution in the African Rift

Tectonic movements and volcanism in the African Rift have usually been considered of relevance to human evolution only at very large geographical and chronological scales, principally in relation to longterm topographic and climatic variation at the continental scale. At the more loca1 scale of catchment basins and individual sites, tectonic features are generally considered to be at worst disruptive and at best incidental features enhancing the preservation and exposure of early sites. We demonstrate that recent lava flows and fault scarps in a tectonically active region create a distinctive landscape structure with a complex and highly differentiated topography of enclosures, barriers and fertile basins. This landscape structure has an important potential impact on the co-evolution of prey-predator interactions and on interspecific relationships more generally. In particular, we suggest that it would have offered unique opportunities for the development of a hominid niche characterised by bipedalism, meat-eating and stone tool use. These landscape features are best appreciated by looking at areas which today have rapid rates of tectonic movement and frequent volcanic activity, as in eastern Afar and Djibouti. These provide a better analogy for the Plio-Pleistocene environments occupied by early hominids than the present-day landscapes where their fossil remains and artefacts have been discovered. The latter areas are now less active than was the case when the sites were formed. They have also been radically transfomed by ongoing geomorphological processes in the intervening millennia. Thus, previous attempts to reconstruct the local landscape setting adjacent to these early hominid sites necessarily rely on limited geological windows into the ancient land surface and thus tend to filter out small-scale topographic detail because it cannot be reliably identified. It is precisely this local detail that we consider to be of importance in understanding the environmental contribution to co-evolutionary developments

The Red Sea, Coastal Landscapes, and Hominin Dispersals

This chapter provides a critical assessment of environment, landscape and resources in the Red Sea region over the past five million years in relation to archaeological evidence of hominin settlement, and of current hypotheses about the role of the region as a pathway or obstacle to population dispersals between Africa and Asia and the possible significance of coastal colonization. The discussion assesses the impact of factors such as topography and the distribution of resources on land and on the seacoast, taking account of geographical variation and changes in geology, sea levels and palaeoclimate. The merits of northern and southern routes of movement at either end of the Red Sea are compared. All the evidence indicates that there has been no land connection at the southern end since the beginning of the Pliocene period, but that short sea crossings would have been possible at lowest sea-level stands with little or no technical aids. More important than the possibilities of crossing the southern channel is the nature of the resources available in the adjacent coastal zones. There were many climatic episodes wetter than today, and during these periods water draining from the Arabian escarpment provided productive conditions for large mammals and human populations in coastal regions and eastwards into the desert. During drier episodes the coastal region would have provided important refugia both in upland areas and on the emerged shelves exposed by lowered sea level, especially in the southern sector and on both sides of the Red Sea. Marine resources may have offered an added advantage in coastal areas, but evidence for their exploitation is very limited, and their role has been over-exaggerated in hypotheses of coastal colonization

Novel Approaches for Aligning Geospatial Vector Maps

The surge in data across diverse fields presents an essential need for advanced techniques to merge and interpret this information. With a special emphasis on compiling geospatial data, this integration is crucial for unlocking new insights from geographic data, enhancing our ability to map and analyze trends that span across different locations and environments with more authenticity and reliability. Existing techniques have made progress in addressing data fusion; however, challenges persist in fusing and harmonizing data from different sources, scales, and modalities. This research presents a comprehensive investigation into the challenges and solutions in vector map alignment, focusing on developing methods that enhance the precision and usability of geospatial data. We explored and developed three distinct methodologies for polygonal vector map alignment: ProximityAlign, which excels in precision within urban layouts but faces computational challenges; the Optical Flow Deep Learning-Based Alignment, noted for its efficiency and adaptability; and the Epipolar Geometry-Based Alignment, effective in data-rich contexts but sensitive to data quality. In practice, the proposed approaches serve as tools to benefit from as much as possible from existing datasets while respecting a spatial reference source. It also serves as a paramount step for the data fusion task to reduce its complexity

Aftershock Sequences Modeled with 3-D Stress Heterogeneity and Rate-State Seismicity Equations: Implications for Crustal Stress Estimation

In this paper, we present a model for studying aftershock sequences that integrates Coulomb static stress change analysis, seismicity equations based on rate-state friction nucleation of earthquakes, slip of geometrically complex faults, and fractal-like, spatially heterogeneous models of crustal stress. In addition to modeling instantaneous aftershock seismicity rate patterns with initial clustering on the Coulomb stress increase areas and an approximately 1/t diffusion back to the pre-mainshock background seismicity, the simulations capture previously unmodeled effects. These include production of a significant number of aftershocks in the traditional Coulomb stress shadow zones and temporal changes in aftershock focal mechanism statistics. The occurrence of aftershock stress shadow zones arises from two sources. The first source is spatially heterogeneous initial crustal stress, and the second is slip on geometrically rough faults, which produces localized positive Coulomb stress changes within the traditional stress shadow zones. Temporal changes in simulated aftershock focal mechanisms result in inferred stress rotations that greatly exceed the true stress rotations due to the main shock, even for a moderately strong crust (mean stress 50 MPa) when stress is spatially heterogeneous. This arises from biased sampling of the crustal stress by the synthetic aftershocks due to the non-linear dependence of seismicity rates on stress changes. The model indicates that one cannot use focal mechanism inversion rotations to conclusively demonstrate low crustal strength (≤10 MPa); therefore, studies of crustal strength following a stress perturbation may significantly underestimate the mean crustal stress state for regions with spatially heterogeneous stress

Earthquake nucleation in the lower crust by local stress amplification

Deep intracontinental earthquakes are poorly understood, despite their potential to cause significant destruction. Although lower crustal strength is currently a topic of debate, dry lower continental crust may be strong under high-grade conditions. Such strength could enable earthquake slip at high differential stress within a predominantly viscous regime, but requires further documentation in nature. Here, we analyse geological observations of seismic structures in exhumed lower crustal rocks. A granulite facies shear zone network dissects an anorthosite intrusion in Lofoten, northern Norway, and separates relatively undeformed, microcracked blocks of anorthosite. In these blocks, pristine pseudotachylytes decorate fault sets that link adjacent or intersecting shear zones. These fossil seismogenic faults are rarely >15 m in length, yet record single-event displacements of tens of centimetres, a slip/length ratio that implies >1 GPa stress drops. These pseudotachylytes represent direct identification of earthquake nucleation as a transient consequence of ongoing, localised aseismic creep

GENERATIVE ADVERSARIAL NETWORKS AS A NOVEL APPROACH FOR TECTONIC FAULT AND FRACTURE EXTRACTION IN HIGH-RESOLUTION SATELLITE AND AIRBORNE OPTICAL IMAGES

Abstract. We develop a novel method based on Deep Convolutional Networks (DCN) to automate the identification and mapping of fracture and fault traces in optical images. The method employs two DCNs in a two players game: a first network, called Generator, learns to segment images to make them resembling the ground truth; a second network, called Discriminator, measures the differences between the ground truth image and each segmented image and sends its score feedback to the Generator; based on these scores, the Generator improves its segmentation progressively. As we condition both networks to the ground truth images, the method is called Conditional Generative Adversarial Network (CGAN). We propose a new loss function for both the Generator and the Discriminator networks, to improve their accuracy. Using two criteria and a manually annotated optical image, we compare the generalization performance of the proposed method to that of a classical DCN architecture, U-net. The comparison demonstrates the suitability of the proposed CGAN architecture. Further work is however needed to improve its efficiency. </jats:p

Fault Trace Corrugation and Segmentation as a Measure of Fault Structural Maturity

International audienceAs faults grow over time and become more “mature,” some of their geometrical and mechanical properties evolve, and these changes modify earthquake behavior. It is thus of prime importance to know the degree of structural maturity of a fault that is likely to produce large earthquakes. Although this concept is extensively used, there is no common definition or metric to measure the structural maturity of a fault. We analyzed the heterogeneity of the surface traces of 13 large seismogenic faults whose maturity is known qualitatively. We measured the corrugations and step-over segmentation of the traces from ∼100 m to the fault length scale. Corrugations and some properties of the segmentation are found to vary with fault structural maturity. We provide scaling relationships that quantify the structural maturity of a fault based on its surface trace. These results should help in parameterizing source faults in earthquake models