Every year a number of earthquakes cause devastation, much of it due to collapsing buildings, with economic impacts in the United States alone adding up to about $4.4 billion dollars a year. Earthquake cycle monitoring and earthquake forecasting is an active topic of geological research, and is crucial to guide our efforts to both prepare society and its infrastructure for earthquakes, and to also mitigate the impacts. It is not currently possible to make deterministic predictions of when and where earthquakes will happen. It is however, possible to make probabilistic forecasts about the likelihood of earthquakes happening in a specified area over a specified period. The accuracy of these statistical estimates is strongly dependent on our understanding of the history of a particular fault system, its current state, and its likely evolution. This picture is generated through historical records, current observations of the accumulation of stresses in the crust, and models that guide our understanding of where stresses are being stored and how a fault is likely to respond to them. Although each major fault has its own unique context, what we learn from studying one fault in detail moves our understanding of the broader processes forward. The frictional properties of a fault, and how these vary spatially and temporally throughout the earthquake cycle, are key parameters for understanding its likely behavior. The researchers will leverage the wealth of modern and historical geodetic data from the south flank of Kilauea Volcano, Hawaii, covering 100+ years, and use both analytical and numerical models to investigate the temporal evolution of the frictional properties of the underlying decollement and its relationship to the earthquake cycle. The Broader Impacts of this project span hazards, collaborations with the USGS and support for undergraduate and graduate students. Kilauea's decollement is a major source of natural hazards to the state, as it generates major earthquakes, like the May 4, 2018 Mw6.9 Leilani Estates earthquake, and also fatal tsunamis. Understanding its evolution and relationship to the catastrophic landslide features found throughout the islands is of great societal importance.
Current interpretation of geological and geophysical observations from Kilauea's south flank suggests that continuous creep, slow slip events (SSEs), and major earthquakes are all occurring on the same fault plane, with combinations of at least two of these processes operating simultaneously. How these processes are connected and interact, and the implications for the mechanics and evolution of the wedge and its earthquake cycle, are fundamental questions that must be answered to improve our understanding of these processes. The physical conditions at the shallow depths of the decollement make Kilauea an extremely unusual outlier compared to most other convergent margin sources of slow slip events. In addition, the SSEs here appear to occur up-dip of the locked zone, a region largely inaccessible to geodetic measurements in subduction zones. This study, therefore, offers an opportunity to gain new insights through comparing and contrasting fault processes with those elsewhere. Preliminary modeling of the current secular surface displacements suggests that the patches of the decollement creeping in these motions outline the zones that currently exhibit SSEs. This implies the currently active portion of the decollement can be mapped into four distinct zones with frictional properties that span velocity-weakening to velocity-strengthening behavior and include the transitional zone(s) that are thought to support SSEs. This project suggests that friction on the decollement can be described using a rate-and-state formalism. They will model geodetic data from different eras within the earthquake cycle to test this hypothesis and answer the following questions: 1) What ranges of parameters for the fault plane rheology adequately predict the observed secular creep rates, SSEs, and microseismicity? 2) How have these parameters evolved from the locked state prior to 1975 through to current? 3) What magmatic overpressures in the lower rift zone are compatible with flank deformation rates?
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
