Quantitative assessment of the flow properties and mechanical stability of naturally fractured rock is frequently practiced across the mining, petroleum, geothermal, geological disposal, construction, and environmental remediation industries. These fluid and mechanical behaviours are strongly influenced by the connectivity of the fracture system and the size of the intact rock blocks. However, these are amongst the more difficult fracture system properties to characterise and honour in numerical simulations. Nonetheless, they are still the product of interactions between fractures that can be conceptualised as a series of deformation events following geomechanical principles. Generating numerical models of fracture networks by simulating this deformation with a coupled and evolving rock mass and stress field is a significant undertaking. Instead, large scale fracture network models can be ‘grown’ dynamically according to rules that mimic the underlying mechanical processes and deformation history. This paper explores a computationally efficient rules-based method to generate fracture networks, demonstrates how different types of fracture patterns can be simulated, and illustrates how inclusion of fracture interactions can affect flow and mechanical properties. Relative to methods without fracture interaction and in contrast to some other rules-based approaches, the method described here regularises and increases fracture connectivity and decreases flow channelling.

Plain Language Summary The “critical zone”—the life‐sustaining part of the Earth that extends from the top of the tree canopy to the bottom of permeable bedrock—is essential for ecosystems and agriculture. The opening of bedrock fractures and onset of water‐rock interaction are crucial to the formation of the critical zone. Within the bedrock, the intensities of horizontal regional forces and vertical gravitational forces typically increase with depth. These force intensities, or stresses, are modified by surface effects associated with topography, the weight of overlying seawater and sediment, and by groundwater pressure. However, the influence of these surface effects on fractures has been difficult to observe because comprehensive fracture data sets are rare. In this study, we examine whether, and to what depths, bedrock may fracture under the influence of stress associated with surficial conditions. We compare bedrock stress calculations with ~50,000 fractures from 18 cores reaching depths of 600 m at Forsmark, Sweden. We find that the present‐day stress field influences the opening of fractures to depths of 500 m, contributing to the formation of the critical zone and the preparation of rock for weathering hundreds of meters beneath the surface, much deeper than previously thought.

We provide a GIS data inventory of confirmed and proposed glacially-induced faults. Stresses, perturbated as a response to the advance and retreat of continental ice sheets and glaciers, can reactivate pre-existing faults. Previously referred to as "PostGlacial Faults" (PGFs), these faults are now called "Glacially-Induced Faults" (GIFs). More than a dozen kilometre-long and several metre-high fault-scarps have been identified in northern Fennoscandia since extensive investigations started in the 1960s and 1970s. Similar faults, but by far not of such dimensions, have also been described in eastern Canada. In other formerly glaciated areas in Europe, e.g., the southern parts of Sweden, Norway and Finland, the southern Baltic Sea, Denmark, northern Germany and Poland, and the Baltic countries, GIFs have rarely been observed and discussed in the literature. However, the number of studies with reliable field evidence for proposing such faults has increased considerably in recent years. The estimated fault movements are of minor magnitude, though, as compared with those in northern Fennoscandia. The database contains the confirmed GIFs in northern Fennoscandia including north-western Russia. The geological surveys in Norway, Sweden and Finland analysed recent LiDAR (Light Detection And Ranging) data from their countries, which helped uncover new faults and revise the geometry of the existing ones. In addition, we include several proposed GIFs outside this area, e.g., in southern Sweden, Denmark and Germany. Ongoing work suggests the occurrence of GIFs in Iceland, Canada and Antarctica. The database will be continually updated, considering new results. A summarized description of the GIF in this database is given in: Steffen, H., Olesen, O., and Sutinen, R. (2021). Glacially-Triggered Faulting. Cambridge University Press, Cambridge, UK, ca. 450 pp., expected publication February 2021. The book: https://doi.org/10.1017/9781108779906 The database: https://doi.pangaea.de/10.1594/PANGAEA.922705