Dr. Klimczak co-authors paper with alumni Dr. Jupiter Cheng and Jay Mrazek.

AGU – JGR Solid Earth: "The Transition From Jointing to Faulting Observed at the Koa'e Fault Zone, Hawaii Volcanoes National Park, Hawaii"

Dr. Klimczak co-authored this paper with our alumni Dr. Jupiter Cheng and Jay Mrazek on their field work in Hawaii. They studied a fault zone on the island of Hawaii that will likely be the locus of where the flank of the volcanic edifice that makes the island will break off and raft into the Pacific Ocean. Jupiter is now a post-doc at the university of Alabama and Jay is now a hydrology assistant at Sleeping Bear Dunes National Lakeshore.

Authors: 

Dr. Hiu Ching Jupiter Cheng ^1,2 , Jay Mrazek¹, Dr. Christian Klimczak ¹

^{1 Center for Planetary Tectonics at UGA, Department of Geology, University of Georgia, Athens, GA, USA,} 

^{2 Department of Geological Sciences, University of Alabama, Tuscaloosa, AL, USA}

Abstract

Fractures can exhibit mixed modes of displacement, that is, combinations of displacements parallel and perpendicular to the fracture plane, that make a displacement-to-length (Dmax/L) scaling analysis challenging. However, such analysis is important for understanding the propagation and nature of mixed-mode fracture populations. In this study, we investigate the Dmax/L scaling relationship for fractures involving opening and shearing modes from field measurements at the spectacularly exposed Koa'e Fault Zone in Hawai'i Volcanoes National Park, Hawaii. Its major structures have prominent fault scarps and display openings of up to several meters. They are locally accompanied by monoclines and sheared and pure joints. Through structural mapping and detailed field observations, we identify a morphological continuum along the structures representing different stages in the evolution of the faults. Contrary to previous studies, our observations support that faults are formed by the downward propagation of joints that transition to faulting at depth, then creating the monoclinal flexure. Our measurements allow us to investigate the Dmax/L scaling behavior for the total mixed-mode displacement and their individual vector components, that is, reliefs and openings. The Dmax/L scaling relationships for all structure types, including pure joints, sheared joints, and faults, show a power-law relation with a near-linear dependence of maximum displacement and length. The joint apertures scale to length with a nearly linear scaling relationship, not following the widely observed square root scaling relationship that all opening-mode fractures are believed to have.

Key Points

• Fractures with mixed-mode displacements of opening and shearing complicate D_max/L scaling analysis
• Field observations indicate the Koa'e Fault Zone forms from the downward propagation of joints into faults at depth
• The D_max/L scaling relationships for all structure types, including joints and faults, show a near-linear power-law relation

Plain Language Summary

Fractures in rocks often form in complex ways, with displacements both parallel and perpendicular to the fracture plane. This makes it challenging to study how displacement relates to fracture length, but understanding this relationship is crucial for learning how these fractures form and evolve. In this study, we focused on the Koa'e Fault Zone in Hawaii, where fractures vary in length and show large openings and reliefs (elevation difference across fractures). We mapped and measured these structures, identifying different stages of the fault zone evolution. Contrary to previous research, our findings suggest that these fractures begin as surface openings that grow downward and eventually transition into faults that experience sliding. When we analyzed how the displacements of these fractures scale with their length, we found that the opening of the fractures here does not follow the widely observed square root scaling rule but instead scales linearly with length. These findings improve our understanding of how mixed-mode fractures develop and propagate in the Earth's crust, helping us better estimate how fluids move through or are stored in fractured crystalline rock.