bradley paul lipovsky
Publications CV Codes

Postdoctoral Fellow
Department of Earth and Planetary Sciences
Harvard University

brad_lipovsky at fas.harvard.edu
617 496 5132
20 Oxford St.
Cambridge, MA 02138

Video of presentation at MIT EAPS Friday Informal Seminar: link to Vimeo.

Link to manuscript. Abstract: The Whillans Ice Plain (WIP), West Antarctica, experiences twice-daily tidally modulated stick-slip cycles. We introduce rate-and-state friction, which is commonly used to simulate tectonic faulting, as an ice stream sliding law to describe the evolving strength of the ice-bed interface throughout these stick-slip cycles. WIP slip events have maximum sliding velocity ~0.5 mm/s, duration ~30 min, total slip ~0.5 m, and tend to be synchronized with the tides. We reproduce these characteristics using simulations that resolve the cross-stream dimension using a depth-integrated treatment of an elastic ice layer loaded by tides and upstream flow. Stick-slip cycles require rate-weakening friction. Under rate-and-state friction, steady sliding with rate-weakening friction is conditionally stable with steady sliding occurring for sufficiently narrow ice stream widths relative to a nucleation length. Stick-slip cycles occur when the ice stream is wider than the nucleation length. Near neutral stability, the ice stream is barely wider than the nucleation length and sliding occurs as slow-slip events. Our simulations suggest that the WIP is in the slow-slip regime with nucleation length nearly equal to the width of the WIP ~120 km. Slip on the WIP shows a sense of propagation and we reproduce slow, unilateral propagation by introducing a rate-strengthening region in the center of the otherwise rate-weakening ice stream. At lower effective stress, our simulations predict that the WIP would exhibit quasi-steady tidally modulated sliding as observed on other ice streams. This study provides an empirical validation of rate-and-state friction as a sliding law that captures the wide range ice stream sliding styles.

I defended my PhD, with Eric Dunham, at Stanford on August 1, 2016. I'm now in the Department of Earth and Planetary Sciences at Harvard, where I have a Department Fellowship. During my postdoc I'll be working with Jim Rice.

I'm going to be in Antarctica as part of the WISSARD project from October 31 until December 4.

This summer I'll be working with Janine Birnbaum as part of the SESUR program. Janine is going to be working on the loading conditions of the Whillans Ice Pain. She is going to keep a blog about her work, so please check in for updates.

The fate of the West Antarctic Ice Sheet is the most uncertain part of global sea level rise projections. The dynamics of fast flowing ice in this region are both scientifically fascinating and important for understanding future sea level rise. Seismic data similar to those used to understand tectonic earthquakes may provide new insights into these dynamics. Several projects are possible. (1) Seismographs recorded on the ice in Antarctica may be used to understand the physics at the bed of the ice sheet. In this project, small repeating earthquakes that occur during large-scale sliding will be used to estimate the coefficient of friction at the ice-rock interface. (2) Migrating waves of tidally modulated micro seismicity in Antarctica have been observed but the source of these events is not clear. A recently developed model of a resonating water-filled fracture will be used to analyze such microseismic catalogs to determine if they are due to the movement of fluid at the ice sheet bed. For both projects, prior programming experience in MATLAB or a high-level programming language will be essential, and introductory mechanics is recommended.

Seismic waves from the cryosphere transmit information from otherwise difficult to observe systems to distant seismometers. Despite the importance of understanding mass fluxes, cryospheric stability, and integrated climate feedbacks, the constraints offered by seismicity remain poorly incorporated in our general understanding of these topics. We invite presentations that draw on seismic analyses to better understand the dynamics and behavior of the cryosphere. We welcome theoretical, observational, and experimental results pertaining to seismic observations. Topics of interest include but are not limited to basal sliding, iceberg calving, fluid transients, tidally modulated seismicity, analysis of sea ice cover, crevassing, and seismicity within icebergs.