Events

Speaker: Dr. Demian M. Saffer, Professor & Department Head, Geosciences, Pennsylvania State University

Title of Seminar: "New Insights into in situ Stress State and Deformation Processes in Thrust Belts from Scientific Ocean Drilling and Long-Term Borehole Observatories" 

Abstract: In situ stress, pore fluid pressure, and tectonic strain accumulation and release within active offshore thrust belts are all fundamentally important toward understanding earthquake and tectonic processes in these dynamic systems. However, measurement of these quantities, particularly in the deep interior and the distal reaches of subduction zones and marine fold and thrust belts where they are most relevant to shallow earthquake slip and tsunami generation, remains challenging. Integrated Ocean Discovery Program (IODP) drilling offshore of Honshu, Japan has provided our clearest picture yet of in situ stress, pore pressure, and deformation within a subduction zone. Analysis of wellbore breakouts defined by logging while drilling (LWD) resistivity images, taken together with hydraulic fracturing experiments and inferences from downhole pressure and mud losses, yield robust constraints on the full stress tensor to depths of ~3 km below the seafloor (5 km below sea level), and show that – even in the hanging wall of a plate boundary thrust – the stress state is nearly isotropic, with very low differential stresses, and modestly elevated pore fluid pressure. In this same system, paired long-term borehole observatories at shallow subseafloor depths (< 1 km) document: (1) responses to ocean tidal loading and nearly drilling that constrain in situ formation hydraulic and elastic properties; and (2) repeating strain transients that represent quasi-regularly recurring slow slip events (SSE) on the plate interface that release energy equivalent to M~5–6 earthquakes over the course of days to weeks, and occur in a region previously characterized by high excess pore fluid pressure and low stress. The SSE occur near, and in some cases propagate all the way to, the subduction trench. These slip events accommodate up to 50% of the relative plate motion, and thus likely carry profound implications for seismic and tsunami hazard.

Biography: Dr. Saffer is currently a professor and department head in Geosciences at Penn State University. He received a BA in Geology from Williams College and a PhD in Earth Sciences from UC Santa Cruz. Dr. Saffer’s research focuses on sedimentary rock deformation and transport properties, specializing in laboratory measurements of permeability, elastic, and poroelastic properties; and numerical modeling of regional scale pore pressure and flow. He is one of the principal investigators in the Penn State Energy Institute’s Center for Geomechanics, Geofluids, and Geohazards (G3). Saffer has served as chief scientist on five Integrated Ocean Drilling Program expeditions, aimed at drilling into active subduction zones offshore Japan and New Zealand to collect core samples, conduct in situ downhole measurements, and design and install long-term monitoring systems. Saffer was the recipient of the Geological Society of America’s Donath Medal (young scientist award) in 2005, and the Alexander von Humboldt Foundation’s Bessel Award in 2009. He also currently serves as the chair of the GeoPRISMS program office.