This chapter summarizes the book with a focus on the future of glacially triggered faulting research. The concept of glacially triggered faulting is challenged by new results from Fennoscandia documenting several episodes of fault rupture within the past 14,000 years. We speculate that some of these ruptures at known (or potential) glacially induced faults may not be due to glacially triggered faulting but may contain a signature of tectonically driven intraplate seismicity. Glacially triggered faulting cannot be totally ignored though for these episodes, since the ongoing rebound of the lithosphere is continuously increasing glacially induced stresses that can eventually be released under favourable conditions. As those conditions can only be described by a complex 4-dimensional model, simple identification of glacially induced faults is hampered. Precise dating of the younger fault ruptures is especially important to produce the necessary spatiotemporal image. The intended DAFNE drilling and subsequent in situ observations of the Pärvie Fault combined with numerical modelling will contribute to an improved understanding of the fault mechanism.

The Danish area is divided by the Fennoscandian Border Zone into a north-eastern part, which is generally tectonically stable with low seismicity marginally related to well-known fault zones, and close to no seismicity in the south-western non-shield part. Stress measurements show that lithospheric plate motion is generally responsible for the modern stress pattern. However, stress changes induced by the weight-relief from the ice sheets during the Pleistocene appears to have created tectonic instability with maximum intensity at the time of deglaciation. The Danish area is generally covered by thick successions of unconsolidated sediments, and therefore it is often difficult to observe unambiguous examples of glacially induced faults. Nevertheless, a number of examples indicate that faults in major fault zones appear to have experienced short periods of reactivation in Lateglacial and early postglacial times. In this chapter, we present an updated map of the historic earthquakes in the Danish area, selected examples of Quaternary deformation of the terrain and near-surface sediments, and suggestions for intensified future monitoring, investigations and research.

This section presents a detailed overview of soft-sediment deformation structures of possibly seismic origin in the Eastern Baltic Region. Recent studies of soft-sediment deformation structures discovered in Estonia, Latvia, Lithuania, Belarus and the Kaliningrad District of Russia demonstrated that their formation could have been caused by fluidization and liquefaction of sediments possibly triggered by palaeoearthquakes; thus, they could be interpreted as seismites. An identification of corresponding seismogenic faults is complicated though due to the rather small scale of the tectonic dislocations in the intracratonic area with up to 2.5-km thick Phanerozoic sedimentary cover. Nevertheless, a part of soft-sediment deformation structures can be interpreted as seismites and attributed to the seismic events triggered by glacial isostatic adjustment of the lithosphere during the Last (Weichselian) glacial advance and subsequent deglaciation.

Postglacial faults in northern Fennoscandia have been investigated through geophysical methods, trenching, and mapping of brittle deformation structures. Very little is known about postglacial faults through direct measurements. A few short, up to 500 m deep, boreholes exist. Plans for a scientific drilling program were initiated in 2010. The drilling target has been identified: The Pärvie Fault system is the longest known postglacial fault in the world and has been proposed to have hosted an M8 earthquake near the end or just after the last glaciation. Further, this fault system is still microseismically active. The drill sites are north of the Arctic Circle, in a sparsely populated area. Existing site survey data, established logistics, and societal relevance through the fault’s proximity to mining and energy operations make this fault system an appropriate target. The International Continental Scientific Drilling Program approved a full drilling proposal in October 2019. This chapter presents an abbreviated version of the approved proposal.

The most prominent fault scarps are found in northern Fennoscandia in the northernmost parts of Norway, Sweden and Finland. In addition, signs of glacially triggered faulting were identified in adjacent Russia. The following chapters give an overview about these faults from their identification until the very recent results that include, among other things, new reactivation dating and revised fault geometries at the surface from laser scanning.

The reactivation of glacially induced faults is linked to the increase and decrease of ice mass. But, whether faults are reactivated by glacially induced stresses depends to a large degree on the crustal stress field, fault properties and fluid pressures. The background (tectonic and lithostatic) stress field has a major effect on the potential for reactivation, as the varying stresses induced by the ice sheet affects the state of stress around the fault, bringing the fault to more stable or more unstable conditions. Here, we describe the effect of glacially induced stresses on fault reactivation under three potential background stress regimes of normal, strike-slip and thrust/reverse faulting. The Mohr diagram is used to illustrate how glacially induced stresses affect the location and the size of the Mohr circle. We review these different cases by applying an analysis of the stress state at different time points in the glacial cycle. In addition, we present an overview of fault properties that affect the reactivation of glacially induced faults, such as pore-fluid pressure and coefficient of friction.

The application of gravity gradient measurements to exploration has been growing over the past 20 years. The ability of tensor gradiometry instruments to greatly improve signal/noise when deployed on mobile platforms has transformed the usefulness of this technology. Airborne and marine Full Tensor Gradiometry (FTG) surveys have become an increasingly common part of the exploration and production toolkit. The ability of the modern instruments to provide high-resolution, spatial accuracy and very good signal/noise data has made this technology a more common part of integrated exploration and production management. The technology has a distinct cost advantage over seismic data acquisition and as such can deliver a competitive solution for imaging problems in some circumstances. There are now numerous published examples of effective use of FTG in the oil industry. The development of better instruments such as integration of direct contemporaneous measurement of conventional gravity is encouraging more interest in the technology. The potential for extending the use of FTG to reservoir monitoring and carbon dioxide sequestration assurance is likely to increase the popularity of the technology in future.

There is abundant evidence for high levels of seismic activity during deglaciation of Eastern Canada, suggesting that the seismic response of Eastern Canada to deglaciation is analogous to Fennoscandia, where numerous glacially induced faults have been confirmed. However, the Canadian record of glacially induced faults is scant. The two probable glacially induced faults that are described are few compared to the 100+ surface ruptures that are expected on statistical grounds. Alternative explanations to account for the small number of known ruptures are provided together with an interpretation of certain normal faulting that has been observed in glaciolacustrine sediments. It is recommended that the interpretation of prospective glacially induced fault features utilize a sceptical approach employing judgemental scales that reflect data limitations and associated uncertainties.

As glacially induced faults are reactivated due to a combination of tectonic and glacially induced isostatic stresses, it is interesting to model the corresponding fault slip with dedicated models. The next chapters introduce first such a modelling approach with a well-established model of glacial isostatic adjustment followed by a review of stresses to be considered in sophisticated future modelling.

The gravity and magnetic survey methods have been in use since the early days of geophysical prospecting for petroleum. They find most application in frontier exploration. In that context, regional and global datasets are often available to assist with early evaluations.

The design and execution of modern, targeted surveys has been transformed as a result of advances in instruments and the advent of satellite navigation. Imaging and interpretive techniques have been transformed by modern computer-based approaches. The potential field methods are extremely cost-effective at delineation of basins and determining structural controls on those basins, especially delineating normal faulting within rift basins. Magnetic surveys yield depth to basement and delineate any igneous rocks present. Such surveys therefore enable early decisions about cost-effective placement of seismic surveys and other intensive follow-ups.

In more mature exploration, gravity and gravity gradient data combine well with seismic data in distinguishing between alternate interpretations, thereby removing ambiguities. High-resolution magnetic data offer an effective means of fault connection in conjunction with regional seismic coverage, if shales or mudstones are present.

In a production environment, gravity logging is the most sensitive density log available, and 4D-gravity finds application in gas production and also water-flood monitoring.

Despite early studies indicating fault rupture both before and after deglaciation, it has long been hypothesized that glacially induced faults in Fennoscandia ruptured only once. The now widespread availability of high-resolution digital elevation models allows for testing this hypothesis by examining cross-cutting relationships between the scarps and both glacial and postglacial landforms. Although not widespread, such cross-cutting relationships indicate that segments of the Merasjärvi, Lainio and Pärvie faults have ruptured at least twice. The timing of the Merasjärvi ruptures is unknown; the Lainio ruptures occurred both before and after deglaciation, and at least one of the Pärvie ruptures is postglacial.

Additionally, it can be demonstrated that parallel segments of the Pärvie and Lansjärv faults ruptured at different times despite being only a few kilometres from each other. Given these results, the single rupture hypothesis must be reassessed for the high-relief scarps in northern Sweden, but it may still hold true for some of the low-relief scarps.

The chapter describes the exploration process which isfocussed on building a geological model of the subsurface which predicts the presence of hydrocarbons, and through a process of investment, reduces the uncertainty of the model so the risk of project failure is acceptable.

A staged approach for exploring for, and producing, oil and gas is described. First, explorers screen basins and find potentially prospective hydrocarbon provinces. Following this regional screening, they identify specific plays that may contain the elements for a working petroleum system (reservoir, source rocks and seal). Then, following a successful exploration programme that identified hydrocarbons, the next stage appraises the scale and productive characteristics of the discovery in order to design an effective, economic development. The traditional final stage is the production of the discovered hydrocarbons, where this is commercially attractive.In many basins the economic life of a reservoir is being extended to allow for the sequestration of carbon dioxide as a vital element in our ability to reduce carbon emissions.

The application of geophysical technologies to each stage of the exploration and production process is described through an articulation of the key problem that needs to be solved.The choice of which technology to use is determined by the geophysical property change and its scale.

Modelling of stresses that influence glacially triggered faulting has progressed substantially in the last decades with more complex models and improved modelling techniques, incorporation of a variety of relevant processes, better constraints of ice-loading history, higher model resolution and 3D geometries. Some recent developments are collected in this section to portray the scope and variability of numerical modelling relevant to glacially triggered faulting. These range from modelling of the general in situ stress field to studies on the stress field induced by glacial loading and unloading.

An appropriate estimation of the ambient background stress field is crucial for determining the effect of additional ice loading (or unloading) on pre-stressed faults. Contributions from local and far-field stress sources (topography, tectonics) need to be reconciled with in situ measurements from boreholes and fault-plane solutions from earthquakes. We describe the different types of stresses in glaciated regions with a focus on Scandinavia together with the techniques used to incorporate stresses into numerical models.