Investigating the Past 100 Years of Fault Zone Deformation and Frictional Variation of Kilauea’s Decollement

Abstract:

The decollement underlying the south flank of Kīlauea Volcano, Hawaii, is a major source of natural hazards to the state, as it generates major earthquakes and fatal tsunamis. It is clear that much of the region’s deformation occurs offshore and previous studies have suggested that continuous creep, slow slip events (SSEs) and major earthquakes are all occurring on the same fault plane. However, how these processes are connected and interact, and what they imply for the mechanics and evolution of the wedge and its earthquake cycle is not known. This region has been heavily monitored for decades and now has over 100 years of geodetic observations collected by a wide range of techniques such as trilateration, leveling, electronic distance measuring and GNSS, which can all be used to determine the deformation of the region throughout time. Our study collates this wealth of historical geodetic data from 1898-2018 and explores both analytical and numerical models to investigate the decollement frictional properties to determine what ranges of fault zone deformation parameters (slip, locking depth, frictional properties) adequately predict the observed secular creep rates, SSEs, and microseismicity at Kīlauea. Close inspection of the different geodetic data types reveals several key observations (1) distinctive persistent characteristics, such as evolving locked zones, of the decollement, (2) slip parameters are heavily time dependent and (3) temporal deformation rate changes are strongly linked to the earthquake cycle and changes in the locked state of the decollement prior to, and after, the 1975 Mw7.7 Kalapana earthquake. Preliminary modeling efforts are also underway to explore whether a rate-and-state friction formalism is able to describe and provide insights into the mechanics of slip on the underlying decollement and its relationship to the earthquake cycle. Moreover, consideration of Kīlauea’s complete geodetic history has important implications for improving our understanding of the mechanical and dynamical relationship between SSEs, magmatic processes, and earthquake cycle deformation transients.