Displacement-Length Scaling of Resurfaced Normal Faults in Iceland and Implications for Fault Growth in Large Igneous Provinces

Stephen Sheehan, Karl J. Mueller, & Madeline F. Schwarz

Published September 11, 2022, SCEC Contribution #12590, 2022 SCEC Annual Meeting Poster #181

Faults are often conceptualized as elliptical planes propagating from a central nucleation point of rock shear failure. Maximum displacement velocity occurs at the nucleation point and gradually reduces to zero at the fault tips. A common method of quantifying this relationship is to examine the spatial distribution of displacement along length, commonly referred to as Displacement - Length scaling (D:L). A source of uncertainty within this method arises from growth strata, material deposited above active faults which periodically bury finite strain markers. Growth strata typically refers to sedimentation above active faults, however Large Igneous Provinces (LIPs) also experience growth strata deposition in the form of lava flows. Iceland, part of an LIP known as the North Atlantic Igneous Province, regularly experiences basaltic lava flows that can reach meters to kilometers in depth. In this study, D:L profiles were created for 174 normal fault scarps in three postglacially resurfaced rift zones throughout Iceland. The 2m resolution ArticDEM was used for scarp profiling in addition to high resolution (1.97cm) UAS-derived DEMs. 27% of the fault profiles displayed a unique “flat-top” D:L distribution, where displacement increased rapidly at the fault tips before stabilizing at a consistent value for the majority of fault length. We propose this profile shape is unique to faults periodically resurfaced by basalt flows. The rigidity of crystalline basalt deposited above active normal faults favors vertical displacement above lateral fault propagation. Columnar jointing aids in this process, providing pre-established, homogenous anisotropic fracture networks to accommodate vertical displacement. Fault linkage at depth also plays a large role in producing flat-top D:L distributions. Faults can easily double their lengths after linkage, further favoring vertical displacement over lateral propagation until elliptical D:L ratios are re-established. On average, flat-toped faults were ~30% longer and had throws ~16% greater than other resurfaced faults. This implies flat-topped fault profiles represent mature, hard-linked structures prior to resurfacing. Subsequent displacement favors vertical propagation until scalable D:L ratios provide the stress required for lateral fault tip propagation. Implications of this research can help determine whether separate slip events result in a consistent fraction of moment release inferred from total displacement.

Citation
Sheehan, S., Mueller, K. J., & Schwarz, M. F. (2022, 09). Displacement-Length Scaling of Resurfaced Normal Faults in Iceland and Implications for Fault Growth in Large Igneous Provinces. Poster Presentation at 2022 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)