Imperial College, United Kingdom

Slow slip events (SSEs) are a new class of shear slip found at subduction margins around the globe that have revealed the broad spectrum of fault slip behaviour. SSEs are widely acknowledged as one of the most exciting discoveries of the last decade in the Earth Sciences, and have implications for plate boundary processes and the seismic hazard posed by subduction megathrusts. Following the recent explosion of geodetic and seismological observations of SSEs, a variety of theories regarding their origin have been proposed; most of these theories consider episodic slow slip as a consequence of high fluid pressure within a conditionally stable frictional regime. Ultimately, testing theories for the fundamental physical mechanisms governing slow slip requires sampling of material by drilling into the SSE source regions and monitoring temporal changes in seismicity, strain rate, stress, geochemistry of fluids, and hydrological properties near the interface throughout the SSE cycle. The relatively close proximity of SSEs to the seafloor in locations such as New Zealand, central Japan, and Costa Rica indicates that ocean drilling studies have the potential to play an important role in revealing the physical processes behind SSE occurrence. In some cases (such as in New Zealand) direct sampling of the SSE source area may be possible. While the science is exciting, the practical issues of addressing transient slip behaviour in deep settings such as subduction zones are challenging to say the least, and will require extensive discussion, planning, and debate to define the conceptual basis for developing the science and practical strategies for achieving it. This workshop is intended to move ahead with this exciting challenge and facilitate discussion among the scientific community on ways to use ocean drilling to elucidate the processes behind slow slip event occurrence. Discussions in the workshop will include critical requirements of a drilling program to discern the physical mechanisms responsible for SSE behaviour, strategies to achieve the scientific goals, auxiliary data needed, and identifying the critical expertise needed to drill a SSE source area successfully. At the workshop, we will also develop: 1. a list of the SSE locations worldwide where drilling studies could reveal the conditions leading to SSE behaviour. - 2. a list of main scientific questions to be addressed by drilling and instrumenting subduction SSE source regions. - 3. a strategy for determining the physical processes behind the origin of SSEs via ocean drilling studies. The primary outcome from the workshop will be a widely available report that presents a conceptual framework for using ocean drilling to understand SSEs.