The evolution of triple junctions: from failure to success

Divergent triple junctions are stable plate margins where three spreading ridges meet. Although it is accepted that this configuration is inherited from an earlier phase of continental rifting, how post-breakup triple junctions emerge from the separation of two plates remains unclear. By documenting the strain rate history recorded in the three rift-arms of several modern and ancient triple junctions, we show that deformation is episodic and localized in only one or two rifts at any given time. We further investigate this behavior in three-dimensional (3D) analog experiments of rifting, under a range of kinematic boundary conditions and containing a variety of pre-existing lithospheric heterogeneities. Deformation in the experiments is characterized by strain jumps and rift abandonment, comparable to natural observations. Boundary rotation during extension induces oblique stretching directions, along-strike strain gradients and forces significant strain jump to reduce the number of rifts segments active. Models that comprise lithospheres ranging from homogenous to containing a triple junction-like pre-existing heterogeneities, never developed a three-armed rift, where all rift segments are active at same time, at any stage. Our experimental results indicate that, unlike mature, successful, and stable oceanic triple junctions, early-stage continental rifting progresses through unstable “double-junctions” characterized by repeated strain jumps and rift failures and reactivations.

Shortcut Faults and Lateral Spreading Activated in a Pull-Apart Basin by the 2018 Palu Earthquake, Central Sulawesi, Indonesia

Our understanding of pull-apart basins and their fault systems has been enhanced by analog experiments and simulations. However, there has been scarce interest to compare the faults that bound pull-apart basins with surface ruptures during earthquakes. In this study, we investigated the effects of a 2018 earthquake (Mw 7.5) on a pull-apart basin in the Palu–Koro fault system, Sulawesi Island, Indonesia, using geomorphic observations on digital elevation models and optical correlation with pre- and post-earthquake satellite images. A comparison of active fault traces determined by geomorphology with the locations of surface ruptures from the 2018 earthquake shows that some of the boundary faults of the basin are inactive and that active faulting has shifted to basin-shortcut faults and relay ramps. We also report evidence of lateral spreading, in which alluvial fan materials moved around the end of the alluvial fan. These phenomena may provide insights for anticipating the location of future surface ruptures in pull-apart basins.

Shortcut Faults and Lateral Spreading Activated in a Pull-Apart Basin by the 2018 Palu Earthquake, Central Sulawesi, Indonesia

Our understanding of pull-apart basins and their fault systems has been enhanced by analog experiments and simulations. However, there has been no opportunity to compare the faults that constitute pull-apart basins with surface ruptures during earthquakes. In this study, we investigated the effects of a 2018 earthquake (Mw 7.5) on a pull-apart basin in the Palu-Koro fault system, Sulawesi Island, Indonesia, using geomorphic observations in digital elevation models, optical correlation with pre- and post-earthquake satellite images. A comparison of active fault traces determined by geomorphology with the locations of surface ruptures from the 2018 earthquake shows that some of the boundary faults of the basin are inactive and that active faulting has shifted to basin-shortcut faults and relay ramps. We also report evidence of lateral spreading, in which alluvial fan materials moved around the end of the alluvial fan. These phenomena may provide insights for anticipating the location of future surface ruptures in pull-apart basins.

Visual Studies Workshop Press : a website description of process-based and experimental books

This applied thesis project deals with a selection of fifty books published by the Visual Studies Workshop (VSW) Press in the 1970s and 1980s. The selection of books can be found in the Independent Press Archive that is currently held in the Research Center at the Visual Studies Workshop (VSW) in Rochester N.Y. The objective for this applied project is to facilitate access and describe the selection of books through the construction of a website. The thesis is divided into two parts, a website description of the books and an analytical paper. The website will allow for visual access to some important experiments with the book format, analog experiments that were revolutionary in their time. The analytical paper includes a discussion of the decisions made while selecting and digitizing the books for the website. This thesis project will add to the current knowledge about VSW Press by providing a snapshot view of how the book format was utilized by artists and students working at VSW at a particular moment in history, a historical period in which photography media and publication were undergoing a time of remarkable growth.

Visual Studies Workshop Press : a website description of process-based and experimental books

This applied thesis project deals with a selection of fifty books published by the Visual Studies Workshop (VSW) Press in the 1970s and 1980s. The selection of books can be found in the Independent Press Archive that is currently held in the Research Center at the Visual Studies Workshop (VSW) in Rochester N.Y. The objective for this applied project is to facilitate access and describe the selection of books through the construction of a website. The thesis is divided into two parts, a website description of the books and an analytical paper. The website will allow for visual access to some important experiments with the book format, analog experiments that were revolutionary in their time. The analytical paper includes a discussion of the decisions made while selecting and digitizing the books for the website. This thesis project will add to the current knowledge about VSW Press by providing a snapshot view of how the book format was utilized by artists and students working at VSW at a particular moment in history, a historical period in which photography media and publication were undergoing a time of remarkable growth.

Differential Erosion and Sedimentation Process at the Longmenshan Foreland Basin, Eastern Margin of the Tibetan Plateau: Evidence From Analog Experiments

We use analog experiments to investigate the influence of rapid filling of a foreland basin system during the development of a fold-and-thrust belt, in particular, the change of erosion–sedimentation along the strike in the Longmenshan foreland basin. A negative relationship between wedge geometries and the magnitude of erosion can be found; increased erosion results in out-of-sequence thrusting and fault reactivation in the wedge hinterland, to limit the forelandward propagation of the wedge. In contrast, increased sedimentation facilitates the forelandward propagation of the wedge. We focus on a natural example of the Longmenshan foreland basin, where a change in erosion–sedimentation along the strike during the Late Cretaceous to Cenozoic is well documented. The comparison between our model and seismic sections indicates that such along-strike variation results in a rejuvenated foreland basin restricted to the southwestern part of the western Sichuan Basin in the Cenozoic.

Centrifuge Experiments of the Initiation of Self-Sustaining Subduction

<p>The post-Triassic age of all oceanic lithospheres indicates the efficiency and the sustainability of lithospheric subduction, which consumes the basaltic seafloor and recirculates it in the upper mantle. Since at present the initiation of subduction is very rare, comprehension of this cardinal process should be carried through modeling – numeric or analog. While deciphering processes through numeric modeling is commonly comprehensive, the analog models can determine major factor that constrain a tectonic procedure. Analog centrifuge experiments were applied to initiate self-sustained modelled subduction, trying to determine the critical factors that trigger its early stages.</p><p>Analytically we presumed that where densities of two lithospheric plates, juxtaposed across a weakness zone, exceed a critical value, then the denser lithosphere eventually will drive underneath the lighter one, provided the friction across the interface is not too high. Consequently, analog experiments were carried out in a centrifuge at acceleration of ca. 1000 g., deforming miniaturized models of three layers representing the asthenosphere, the ductile and the brittle lithosphere. The lithospheres were modeled to include lighter and denser components, juxtaposed along a slightly lubricated contact plane, where the density difference between these components was ca. 200 kg/m<sup>3</sup>. No mechanism of lateral force was applied in the experiment (even though such a vector exists in nature due to the seafloor spreading at the oceanic ridges), to test the possibility of subduction in domains where such a force is minor or non-existent.</p><p>The analog experiments showed that the penetration of the denser modeled lithosphere under the lighter one led to extension and subsequent break-up of the over-riding plate. That break-up generated seawards trench rollback, normal faulting, rifting, and formed proto-back-arc basins. Lateral differential reduction of the friction between the juxtaposed plates led to the development of arcuate subduction zones. The experimental miniaturization, and subsequent numerical and analytical modeling, suggest that the observed deformation in the analog models could be meaningful to the planet as well.</p><p>Constraints of the analog experimentation setting did not enable the modeling of the subduction beyond the initial stages, but there is ground to presume that at depths of 40-50 km, metamorphic processes of the generation of eclogites would change the initial mineralogy on the subducting plate. Reactions with water would convert basalts into metamorphic serpentinites and schists. Higher temperatures and pressures would melt parts of the subducted slab to generate felsic magmas, which would ascend towards the surface diapirically due to their lighter density. Alternately, low availability of H<sub>2</sub>O would gradually alter the oceanic basalt and gabbro into eclogite, which would sink into the mantle due to its increased density.</p>

Proposing "analogy experiment" as a sub-category of "analog experiment" in earth science

<p>In the earth and planetary sciences, the term "analog experiment" indicates laboratory experiments that use analog materials to investigate natural processes. Scaled experiments constitute a representative sub-category of analog experiments. They are designed to have the same dominant dimensionless parameter in the same range as the targeted natural processes. Other primary uses of analog experiments are education and outreach. Reproducing similar phenomena in front of the audience is useful in explaining the essence of the complex dynamics of natural processes. However, it is often the case that we do not fully understand the physics of the experimental systems or the targeted natural phenomena. In such cases, especially when the process is complex, it is difficult to guarantee the scaling similarity. When we take such laboratory phenomena as a research subject of earth science, we encounter critical comments about the scaling issue.</p><p>Nevertheless, I think it scientifically important to consider questions like follows. What is the mechanism of the experimental phenomena? Why the behaviors of the experiment look similar to the natural phenomena? To what extent the laboratory and the natural systems are similar. To indicate experimental studies to elucidate these questions, I would like to define "analogy experiment" as a new sub-category of analog experiments.  Some recent experiments are presented as examples.</p>