Brittle tectonics of the Thingvellir and Hengill volcanic systems, Southwest Iceland: field studies and numerical modeling

Abstract

This paper focuses on field studies and numerical models of fracture development in the area of the Hengill Central Volcano and its northern fissure swarm containing the Thingvellir Graben, in Southwest Iceland. Apart from additional field data on normal faults, a new detailed map of the Holocene fractures in the Thingvellir Graben is presented and used as a basis for numerical models on normal fault development. Field observations and models yield four basic results. First, hyaloclastite mountains in the area ("soft mechanical inclusions") tend to deflect or arrest propagating tension fractures and normal faults. Second, fractures with an en echelon arrangement and an overlapping configuration develop shear stress shadows and tend to prevent the linking up into larger fault segments. Third, fractures with an en echelon arrangement and underlapping configuration develop shear stress concentrations between nearby tips resulting in development of transverse shear faults (transfer fault). Fourth, colinear normal fault segments concentrate tensile stresses at their tips and encourage tip-to-tip growth into larger segments.

Revised earthquake hazard of the Hat Creek fault, northern California: A case example of a normal fault dissecting variable-age basaltic lavas

“…The westward migration of successive scarp system segments of the Hat Creek fault suggests that Cinder Butte and its underlying magmatic system may have focused the development of the active portion of the fault in the proximity of Cinder Butte. Such a model is consistent with documented examples of magmatic systems affecting fault growth and orientation in response to local stress perturbations related to magma pressure (Clifton and Schlische, 2003;Clifton and Kattenhorn, 2006;Rowland et al, 2007;Gudmundsson et al, 2009) or the topographic and mechanical attributes of volcanic constructs (Friese, 2008;Jenness and Clifton, 2009). Lava fl ows from Cinder Butte covered the northern end of the Pali scarp; however, the Active Scarp subsequently dissected these lavas and curved toward the center of Cinder Butte (Fig.…”

The Effect of Obliquity of Slip in Normal Faults on Distribution of Open Fractures

“…It is the only onshore oblique rift segment of the mid-Atlantic ridge, with the plate boundary oriented at ∼30% obliquity to spreading direction of the mid ocean ridge (Gudmundsson, 1987;Grant and Kattenhorn, 2004;Clifton and Kattenhorn, 2006;Villemin and Bergerat, 2013). The northern and western rift zones are dominated by axial spreading (Angelier et al, 1997;Friese, 2008;Sonnette et al, 2010;Hjartardóttir et al, 2012). In Thingvellir, located in the western rift zone, the rift axis trends approximately normal to the plate spreading direction at 30 • .…”

“…Consequently, dilatant faults are of great economic interest for water and geothermal energy supply (Jafari and Babadagli, 2011), geohazard assessment and geodynamics (Crone and Haller, 1991;Caine et al, 1996;Gudmundsson et al, 2001;Ehrenberg and Nadeau, 2005;Belayneh et al, 2006;Lonergan et al, 2007), or mineral deposits (Zhang et al, 2008). Dilatant fault systems occur at mid ocean ridges (Gudmundsson, 1987;Angelier et al, 1997;Wright, 1998;Friese, 2008;Sonnette et al, 2010;Trippanera et al, 2014), intra-plate volcanoes (Holland et al, 2006), continental rifts (Acocella et al, 2003;Acocella, 2014;Trippanera et al, 2015), but also in cemented carbonates and clastic sediments (McGill and Stromquist, 1979;Moore and Schultz, 1999;Ferrill and Morris, 2003;Lonergan et al, 2007;Wennberg et al, 2008;van Gent et al, 2010;. Their internal structure has been studied using analog and numerical models (Abe et al, 2011;Holland et al, 2011;Hardy, 2013;Kettermann et al, 2016).…”

Dilatant normal faulting in jointed cohesive rocks: a physical model study

“…Most prominent large-scale examples can be found not only at mid-ocean ridges (Angelier et al, 1997;Friese, 2008;Sonnette et al, 2010;Wright, 1998), intra-plate volcanoes (Holland et al, 2006), continental rifts (Acocella et al, 2003) but also in cemented carbonates and clastics (Ferrill and Morris, 2003;Moore and Schultz, 1999). They form major pathways for fluid flow, such as water, hydrocarbons or magma, and consequently are of great interest for water and energy supply, geohazard assessment and geodynamics (e.g., Belayneh et al, 2006;Caine et al, 1996;Crone and Haller, 1991;Ehrenberg and Nadeau, 2005;Gudmundsson et al, 2001;Lonergan et al, 2007).…”