Description and Objectives

The discovery of slow earthquakes twenty years ago revolutionized understanding of how plate motions are accommodated at major tectonic boundaries. Slow earthquakes are a family of events that include slow slip events (SSE), tectonic tremor, and low frequency earthquakes (LFE). In some systems, SSEs occur together with tectonic tremor. When these events occur periodically, they are known as episodic tremor and slip, or “ETS”. Compared to regular earthquakes, the slip across a fault during a slow earthquake occurs slowly, but significantly faster than plate-rate creep. Slow earthquakes are observed predominantly near the plate interface of subduction zones and on transform plate boundary faults. They are often associated with ‘transitional’ regions at the edges of seismogenic zones, but occur both updip and downdip so encompass a wide range of pressure and temperature conditions. Understanding slow earthquakes is critical to developing better constraints on regional seismic hazards and may also provide information on the physical conditions and fault loading rates at depth.

Seismological, geophysical, and geodetic tools have been applied extensively to study the range of slow earthquake types, where they occur, their relations to each other, and the characteristics that distinguish them from regular earthquakes and creep. However, there are numerous outstanding issues regarding the basic processes that control slow earthquake characteristics. For example, what deformation processes and mechanisms are critical to their occurrence? What controls slip rates? Do all faults that host slow earthquakes share common physical characteristics? Are the multiple potential mechanisms for tremor and slow slip common amongst the different tectonic settings where these phenomena are observed, including subduction zones and continental transform faults?

The geological structures that formed during slow earthquakes and are preserved in exhumed systems can provide critical insights into the sources of slow earthquakes and how they interact with the regular earthquake cycle. Although different hypotheses are proposed on a regular basis in the nascent field of slow earthquake geology, there is no “smoking gun” evidence of slow earthquakes in the rock record. Reconciling the geophysical insights with geological observations is therefore an ongoing challenge, but it is increasingly clear that only field geological observations on exhumed structures can differentiate between models for slow earthquake occurrence, as geodesy and seismology cannot resolve the relevant length scales.

For this conference, we solicit contributions that use geological observations, lab measurements, or numerical models to aid in understanding the physics of slow earthquakes. We encourage researchers studying analog systems from any tectonic setting or metamorphic grade relevant to modern tremor and slow earthquakes to build a wide range of geological perspectives. Contributions that address outstanding questions regarding deformation mechanisms, limits on rates of deformation, and environmental conditions are encouraged. New multi-disciplinary approaches are needed to define the physical controls on slow earthquakes and to develop new insights into disparate datasets. For this conference, we aim to stimulate contributions from geological-focused, particularly field-based, investigators and to engage geophysicists with a range of backgrounds to define key unknowns and debate possible models.

Preliminary Outline of Thematic Sessions

1. Cutting-edge observations of slow earthquakes

2. Current understanding of the mechanics of slow earthquakes

3. Geological perspectives on slow earthquakes

4. Processes and physical properties of rocks that might be relevant to slow earthquake physics

5. Key unknowns in slow earthquake physics

6. The hypotheses for slow earthquake mechanisms

Poster sessions will be held every evening between talks and dinner, and will continue after dinner. Group discussions and breakout sessions will accompany all of the thematic sessions to promote cross-disciplinary interactions. One of the main goals of the meeting is to provide forum for geologists and geophysicists to discuss how the existing information from the rock record should be integrated with the geophysical insights, as well as what new geological observations are needed to develop our understanding of the physics of slow slip further.