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PENROSE CONFERENCE ANNOUNCEMENT
The Geological Fingerprints

of Slow Earthquakes

Santa Catalina Island, California, USA | 27 June–1 July 2021
www.geosociety.org/penrose

CONVENERS
James Kirkpatrick, McGill University, Dept. of Earth and Planetary
Sciences, Montréal, Québec, Canada, james.kirkpatrick@mcgill.ca
Melodie French, Rice University, Dept. of Earth, Environmental
and Planetary Sciences, Houston, Texas, USA, mefrench@rice.edu
John Platt, University of Southern California, Dept of Earth
Sciences, Los Angeles, California, USA, jplatt@usc.edu
Christie Rowe, McGill University, Dept. of Earth and Planetary
Sciences, Montréal, Québec, Canada, christie.rowe@mcgill.ca
David Schmidt, University of Washington, Dept. of Earth and
Space Sciences, Seattle, Washington, USA, dasc@uw.edu

COSPONSORS Little Harbour, Catalina Island, California, USA. Photo by John Paul Platt.
The Geological Society of America The geological structures that formed during slow earthquakes
National Science Foundation and are preserved in exhumed systems can provide critical
NSF-GeoPRISMS insights into the sources of slow earthquakes and how they inter-
Southern California Earthquake Center act with the regular earthquake cycle. Although different hypoth-
eses are proposed on a regular basis in the nascent field of slow
DESCRIPTION AND OBJECTIVES earthquake geology, there is no “smoking gun” evidence of slow
The discovery of slow earthquakes 20 years ago revolutionized earthquakes in the rock record. Reconciling the geophysical
the understanding of how plate motions are accommodated at major insights with geological observations is therefore an ongoing
tectonic boundaries. Slow earthquakes are a family of events that challenge, but it is increasingly clear that only field geological
include slow slip events (SSE), tectonic tremor, and low frequency observations on exhumed structures can differentiate between
earthquakes (LFE). In some systems, SSEs occur together with tec- models for slow earthquake occurrence, as geodesy and seismol-
tonic tremor. When these events occur periodically, they are known ogy cannot resolve the relevant length scales.
as episodic tremor and slip, or “ETS.” Compared to regular earth- For this conference, we solicit contributions that use geological
quakes, the slip across a fault during a slow earthquake occurs observations, lab measurements, or numerical models to aid in
slowly, but significantly faster than plate-rate creep. Slow earth- understanding the physics of slow earthquakes. We encourage
quakes are observed predominantly near the plate interface of sub- researchers studying analog systems from any tectonic setting or
duction zones and on transform plate boundary faults. They are metamorphic grade relevant to modern tremor and slow earth-
often associated with “transitional” regions at the edges of seismo- quakes in order to build a wide range of geological perspectives.
genic zones but occur both updip and downdip, so encompass a Contributions that address outstanding questions regarding defor-
wide range of pressure and temperature conditions. Understanding mation mechanisms, limits on rates of deformation, and environ-
slow earthquakes is critical to developing better constraints on mental conditions are encouraged. New multidisciplinary
regional seismic hazards and may also provide information on the approaches are needed to define the physical controls on slow
physical conditions and fault-loading rates at depth. earthquakes and to develop new insights into disparate datasets.
Seismological, geophysical, and geodetic tools have been For this conference, we aim to stimulate contributions from
applied extensively to study the range of slow earthquake types, geological-focused, particularly field-based, investigators and
where they occur, their relations to each other, and the characteris- to engage geophysicists with a range of backgrounds to define
tics that distinguish them from regular earthquakes and creep. key unknowns and debate possible models.
However, there are numerous outstanding issues regarding the
basic processes that control slow earthquake characteristics. For PRELIMINARY OUTLINE OF THEMATIC SESSIONS
example, what deformation processes and mechanisms are critical 1. Cutting-edge observations of slow earthquakes;
to their occurrence? What controls slip rates? Do all faults that 2. Current understanding of the mechanics of slow earthquakes;
host slow earthquakes share common physical characteristics? 3. Geological perspectives on slow earthquakes;
Are the multiple potential mechanisms for tremor and slow slip 4. Processes and physical properties of rocks that might be relevant
common among the different tectonic settings where these phe- to slow earthquake physics;
nomena are observed, including subduction zones and continental 5. Key unknowns in slow earthquake physics; and
transform faults? 6. The hypotheses for slow earthquake mechanisms.

26 GSA Today | September 2020