Geology & Environmental Science Colloquium: Dr. Donald M. Fisher | Professor of Geosciences; Wilson Faculty Fellow, Penn State University

How can AI improve spaceborne thermal volcano monitoring?

Presented by Dr. Donald M. Fisher | Professor of Geosciences; Wilson Faculty Fellow, Penn State University

Talk Abstract:

The greatest earthquakes occur on the plate boundary of subduction zones and are typically associated with convergent margins where sediments blanket the downgoing plate. I argue here that geochemical processes increase cohesion in the sediment between plates and are responsible for interseismic strengthening (e.g., geochemical processes such as cementation and incongruent pressure solution (i.e., low grade metamorphic reactions)). Moreover, the loss of this cohesion during earthquakes is the primary mechanism for decreasing strength faster than the elastic strain can unload during slip initiation, a key prerequisite for slip intabilities associated with earthquakes. Interseismic increases in cohesion coincide with the growth of interseismic slip deficit. This talk will describe rocks deformed along the along the plate boundary at depths of seismogenesis and subsequently exhumed. We use these observations to demonstrate that the interface experiences fluctuations in fluid pressure (crack-seal deformation, oscillatory zoning in quartz) and to quantify a pressure solution flow law, which is combined with a dislocation creep flow law for quartz-phyllosilicate mixtures and incorporated into a numerical model that depicts interseismic creep, seismicity, and fluid flow, including the fluid flow transients that occur during earthquakes. This model is rooted in the coupling between interseismic fault strengthening through the kinetics of cohesion, and permeability reduction through reduction in fracture and grain scale porosity. The model (MEFISTO- a Mineralization, Earthquake, and Fluid flow Integrated SimulatOr) includes:1) an earthquake simulator with temperature-dependent increases in cohesion, 2) a fluid flow model coupled to the earthquake simulator through the link between increasing strength (contact area) and decreasing permeability, with low strength and ambient permeability restored by ruptures of the plate interface, and 3) interseismic creep that responds to variations in stress that could drive acceleration in strain rate toward the later part of the seismic cycle. The talk will explore the predictions of this model.

Biography:

Don Fisher received his PhD from Brown University in 1988 and has been a faculty member at Penn State University ever since. His field studies of subduction zone boundaries have taken him to convergent plate boundaries around the world including Costa Rica/Panama, Kodiak Alaska, southern and northern Japan, Taiwan, New Zealand, and Sumatra.