Microearthquakes illuminate the deep structure of the endglacial Pärvie fault, northern Sweden

Lindblom, Eva; Lund, Björn; Tryggvason, Ari; Uski, Marja; Böðvarsson, Reynir; Juhlin, Christopher; Roberts, Roland

doi:10.1093/gji/ggv112

Cited by 47 publications

(52 citation statements)

References 41 publications

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“…Since the establishment of the modernized SNSN in the region in 2000, 36 microearthquakes with magnitudes in the range −0.2 to 1.4 have been recorded within 15 km of the scarp. These events do not define a linear structure, as micro-earthquakes on the postglacial faults in northern Fennoscandia tend to (Lindblom et al, 2015), and most of the events near Bollnäs seem unrelated to the scarp.…”

Section: Geological Backgroundmentioning

confidence: 96%

“…While some of them have trace lengths up to 155 km with estimated magnitudes up to 8 for the associated earthquakes (e.g. Lagerbäck and Sundh, 2008;Arvidsson, 1996;Lindblom et al, 2015), most are shorter or have less surface expression ( Fig. 1).…”

Section: Introductionmentioning

confidence: 99%

“…1). Based on the results from a reflection seismic survey, Ahmadi et al (2015) reported on the Pärvie post-glacial fault in Sweden, which they imaged down to about 8 km depth (see also Juhlin et al, 2010;Juhlin and Lund, 2011;Lindblom et al, 2015). To the best of our knowledge all known post-glacial faults have been reported to be associated with pre-existing structures (e.g.…”

Section: Introductionmentioning

confidence: 99%

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Post-glacial reactivation of the Bollnäs fault, central Sweden – a multidisciplinary geophysical investigation

et al. 2016

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Abstract. Glacially induced intraplate faults are conspicuous in Fennoscandia where they reach trace lengths of up to 155 km with estimated magnitudes up to 8 for the associated earthquakes. While they are typically found in northern parts of Fennoscandia, there are a number of published accounts claiming their existence further south and even in northern central Europe. This study focuses on a prominent scarp discovered recently in lidar (light detection and ranging) imagery hypothesized to be from a post-glacial fault and located about 250 km north of Stockholm near the town of Bollnäs. The Bollnäs scarp strikes approximately northsouth for about 12 km. The maximum vertical offset in the sediments across the scarp is 4-5 m with the western block being elevated relative to the eastern block. To investigate potential displacement in the bedrock and identify structures in it that are related to the scarp, we conducted a multidisciplinary geophysical investigation that included gravity and magnetic measurements, high-resolution seismics, radio-magnetotellurics (RMT), electrical resistivity tomography (ERT) and ground-penetrating radar (GPR). Results of the investigations suggest a zone of low-velocity and highconductivity in the bedrock associated with a magnetic lineament that is offset horizontally about 50 m to the west of the scarp. The top of the bedrock is found ∼ 10 m below the surface on the eastern side of the scarp and about ∼ 20 m below on its western side. This difference is due to the different thicknesses of the overlying sediments accounting for the surface topography, while the bedrock surface is likely to be more or less at the same topographic level on both sides of the scarp; else the difference is not resolvable by the methods used. To explain the difference in the sediment covers, we suggest that the Bollnäs scarp is associated with an earlier deformation zone, within a wide (> 150 m), highly fractured, water-bearing zone that became active as a reverse fault after the latest Weichselian deglaciation.

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Section: Geological Backgroundmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Post-glacial reactivation of the Bollnäs fault, central Sweden – a multidisciplinary geophysical investigation

et al. 2016

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“…Towards the end of the glaciation, the ice melted rapidly in northern Fennoscandia and the effective stress field changed accordingly, generating major faulting (Lagerbäck, 1978) with associated large earthquakes (M7-8.2; e.g., Muir-Wood, 1988;Arvidsson, 1996;Lindblom et al, 2015). The resulting fault scarps have been alternatively termed end-glacial scarps, post-glacial fault scarps or glacially induced fault scarps; we use the first term in this paper as it is appropriate for the Pärvie fault.…”

Section: Introductionmentioning

confidence: 99%

“…The longest of the scarps, located in northern Sweden, belongs to the Pärvie fault system and has been the focus of recent geophysical studies, including reflection and hydroacoustic seismic surveying (see Fig. 1) (Juhlin et al, 2010;Vogel et al, 2013), a temporary seismic network (Lindblom et al, 2015) and remote sensing (Mantovani and Scherneck, 2013).…”

Section: Introductionmentioning

confidence: 99%

Revealing the deeper structure of the end-glacial Pärvie fault system in northern Sweden by seismic reflection profiling

et al. 2015

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Abstract.A new seismic reflection survey for imaging deeper levels of the end-glacial Pärvie fault system in northern Sweden was acquired in June 2014. The Pärvie fault system hosts the largest fault scarp so far documented in northern Scandinavia, both in terms of its length and calculated magnitude of the earthquake that generated it. Present-day microearthquakes occur along the length of the fault scarp on the eastern side of the scarp, in general agreement with an east-dipping main fault. In the central section of the fault system, where there is a number of subsidiary faults east of the main Pärvie scarp, it has been unclear how the earthquakes relate to the structures mapped at the surface. A seismic profile across the Pärvie fault system acquired in 2007, with a mechanical hammer as a source, showed a good correlation between the surface mapped faults and moderate to steeply dipping reflections. The most pronounced reflectors could be mapped to about 3 km depth. In the new seismic survey, for deeper penetration an explosive source with a maximum charge size of 8.34 kg in 20 m deep shot holes was used. Reflectors can now be traced to deeper levels with the main 65 • east-dipping fault interpreted as a weakly reflective structure. As in the previous profile, there is a strongly reflective 60 • west-dipping structure present to the east of the main fault that can now be mapped to about 8 km depth. Extrapolations of the main and subsidiary faults converge at a depth of about 11.5 km, where current earthquake activity is concentrated, suggesting their intersection has created favorable conditions for seismic stress release. Based on the present and previous seismic reflection data, we propose potential locations for future boreholes for scientific drilling into the fault system. These boreholes will provide a better understanding of the reflective nature of the fault structures and stress fields along the faults at depth.

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Evidence for the release of long‐term tectonic strain stored in continental interiors through intraplate earthquakes

Craig

Calais

Fleitout

et al. 2016

Geophysical Research Letters

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The occurrence of large earthquakes in stable continental interiors challenges the applicability of the classical steady state “seismic cycle” model to such regions. Here we shed new light onto this issue using as a case study the cluster of large reverse faulting earthquakes that occurred in Fennoscandia at 11–9 ka, triggered by the removal of the ice load during the final phase of regional deglaciation. We show that these reverse‐faulting earthquakes occurred at a time when the horizontal strain rate field was extensional, which implies that these events did not release horizontal strain that was building up at the time but compressional strain that had been accumulated and stored elastically in the lithosphere over timescales similar to or longer than a glacial cycle. We argue that the tectonically stable continental lithosphere can store elastic strain on long timescales, the release of which may be triggered by rapid, local transient stress changes caused by surface mass redistribution, resulting in the occurrence of intermittent intraplate earthquakes.

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Microearthquakes illuminate the deep structure of the endglacial Pärvie fault, northern Sweden

Cited by 47 publications

References 41 publications

Post-glacial reactivation of the Bollnäs fault, central Sweden – a multidisciplinary geophysical investigation

Post-glacial reactivation of the Bollnäs fault, central Sweden – a multidisciplinary geophysical investigation

Revealing the deeper structure of the end-glacial Pärvie fault system in northern Sweden by seismic reflection profiling

Evidence for the release of long‐term tectonic strain stored in continental interiors through intraplate earthquakes

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