Temporal and Spatial Variations in Deformation Across a Ridge-Transform Intersection, Northern Iceland

Open Access
Author:
O'Hara, Caroline Anne
Graduate Program:
Geosciences
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
November 04, 2009
Committee Members:
  • Dr Peter C La Femina, Thesis Advisor
  • Peter Christopher Lafemina, Thesis Advisor
Keywords:
  • northern Iceland
  • Husavik-Flatey fault
  • Gudfinnugja fault
  • Tjornes Fracture Zone
  • Theistareykir fissure swarm
  • ridge-transform intersection
  • terrestrial LiDAR
  • displacement variation
  • GPS
  • slip rate
  • tensile fractures
Abstract:
In this thesis I present new kinematic field and LiDAR data to investigate the temporal and spatial variation in displacement across the Gudfinnugja fault (GF) and Husavik Flatey fault (HFF) intersection in northeastern Iceland. Using kinematic structural data from the area combined with structural analysis of an ~0.5 km2 terrestrial LiDAR survey of the GF-HFF intersection, I show that accommodation at the ridge-transform intersection occurs over distances much smaller than crustal thickness (100’s of meters compared to 10’s of kilometers). This suggests localized processes are occurring at the inside corner of this intersection. I used geologic (kinematic) data to study the spatial distribution of normal faulting and mode-1 tensile fracturing magnitude and direction of displacement at the intersection. The azimuth of opening for mode-1 tensile fractures varies along strike of the GF; fractures south of the intersection along the GF indicate plate motion-parallel opening, while fractures near and north of the intersection, indicate a second, HFF-orthogonal direction of opening as well as a plate motion-parallel direction. This strain partitioning is likely a result of the intersection of the two faults. Monte Carlo experiments allowed me to calculate the displacement on the GF, ignoring the talus slope covering the scarp. Total displacement on the GF is 15.6 ± 1.2 m, with 15.2 ± 1.2 m of throw and 2.7 ± 2.1 m of heave. Using published ages of 3,000-12,000 yrs for the basaltic lava flows at the surface at the intersection, I estimated displacement rates for the Gudfinnugja fault that range from 1.9 – 6.5 mm/yr. Displacement rates for the Gudfinnugja complex range from 6.3 – 21.0 mm/yr. For the whole intersection, I calculated displacement rates of a minimum of 3.5 – 5.4 mm/yr and a maximum of 14.0 – 21.7 mm/yr. These rates are poorly constrained, but provide an initial estimate for the slip budget across the HFF-GF intersection and Northern Volcanic Zone. To study temporal variations in deformation, I supplemented the geologic data (~10 kyr) with geodetic GPS data (~10 yrs). To investigating short-term elastic strain accumulation in this region I modeled the velocity field across the HFF and GF using a 2-year geodetic data set from Jouanne et al. (2006). I found that the HFF appears to accommodate ~50% of the total plate motion, and therefore has ~10 mm/yr displacement rate. Velocity profiles across the GF show a velocity gradient with the largest velocity difference of ~15 mm/yr occurring >20 km east of the GF and of Krafla. This study not only increases our knowledge of the plate boundary in northern Iceland and ridge-transform intersections, but also provides a valuable field-test for the structural analysis of terrestrial LiDAR data.