On Mars, basins formed by tectonic processes are rare and mostly have unconstrained subsidence histories. One method for understanding this record of subsidence is through associated alluvial fans, which are sourced from uplifted areas and accumulate in downthrown basins. The source, morphology, and superposition of fan deposits can be used to reconstruct fault kinematics, the relative timing of accommodation space formation, and, in turn, the influence tectonic processes had on Martian fan formation. Here we use high-resolution orbital data sets to characterize sediment fan deposits associated with syn-tectonic sedimentation in two regions of the Valles Marineris canyons: Coprates Chasma and Juventae Chasma. These deposits comprise sediment fans on the current canyon floor and low-gradient surfaces perched several kilometers above the canyon floor. We interpret the low-gradient surfaces as remnant sediment fan deposits, which originally formed at the former canyon floor and have since been offset due to normal faulting. The preservation of vertically offset generations of sediment fan deposits supports a progressive, basinward migration of fault activity into the original hanging wall or repeat activity along a fault zone. Each episode of faulting was followed by a basinward shift in drainages, which led to fault-scarp degradation and formation of a new generation of fans. Multiple episodes of syn-tectonic sedimentation occurred during the evolution of the basins, with fluvial activity sporadically active. Our results demonstrate, for the first time on Mars, that depositional cyclicity was linked to tectonic deformation, possibly representative of regional processes throughout Valles Marineris.

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A major debate in Mars science is the nature of the early Mars climate, and the availability of precipitation and runoff. Observations of relict erosional valley networks have been proposed as evidence for extensive surface runoff around the Noachian-Hesperian boundary. However, these valley networks only provide a time-integrated record of landscape evolution, and thus, the timing, relative timescales and intensity of aqueous activity required to erode the valleys remain unknown. Here, we investigate an ancient fluvial sedimentary system in western Arabia Terra, now preserved in positive relief. This ridge, "Aram Dorsum," is flat-topped, branching,~85 km long, and particularly well preserved. We show that Aram Dorsum was an aggradational alluvial system and that the existing ridge was once a large river channel belt set in extensive flood plains, many of which are still preserved. Smaller, palaeochannel belts feed the main system; their setting and network pattern suggest a distributed source of water. The alluvial succession is up to 60 m thick, suggesting a formation time of 10 5 to 10 7 years by analogy to Earth. Our observations are consistent with Aram Dorsum having formed by long-lived flows of water, sourced both locally, and regionally as part of a wider alluvial system in Arabia Terra. This suggests frequent or seasonal precipitation as the source of water. Correlating our observations with previous regional-scale mapping shows that Aram Dorsum formed in the mid-Noachian. Aram Dorsum is one of the oldest fluvial systems described on Mars and indicates climatic conditions that sustained surface river flows on early Mars. Plain Language Summary The oldest regions of Mars contain ancient valleys, carved by running water, and sinuous ridges, often interpreted as the remnants of former riverbeds, left upstanding by erosion. These "inverted channel" systems provide insight into Mars's ancient climate and hydrologic cycle. We use high-resolution satellite images to investigate "Aram Dorsum," an 85 km long ridge system in the Arabia Terra region. Our observations show that Aram Dorsum is composed of sedimentary rocks, originally deposited in rivers or their adjacent floodplains. The Aram Dorsum sedimentary material is up to 60 m thick, which, by comparison with similar sedimentary deposits on Earth, suggests that the Aram Dorsum river system was active for between 10,000 and 10 million years. Our study also indicates that Aram Dorsum was formed around 3.9 billion years ago, an age consistent with other evidence for ancient rivers and lakes in this region. The water that flowed within the rivers at Aram Dorsum probably came from both locally and regionally generated rainfall or snowfall, rather than a single point source of water, such as large distant ice sheets. Our observations therefore point to an ancient Martian climate that supported precipitation and river flow for thousands or millions of years.

A new approach to identifying and characterising system responses of the EBS based on analysis of ensemble runs of a generic and flexible source term model is developed and applied. A discussion of issues relating to the use of this methodology as a complementary approach to existing scenario development/safety case definition is also included.

A semi-analytical model for percolation problems, called the Dynamical Network Model, is developed. Because of its semi-analytic nature, the model is more efficient than the existing numerical techniques especially for three dimensional problems and, thus, can be used to a wide range of percolation-like problems in performance assessment of radioactive waste disposal.