Recent studies using data from the EarthScope Facility as well as other national and international sources show that tectonic faults exhibit a broad spectrum of slip behaviors ranging from creep to earthquakes, including several phenomena that were unknown as recently as 10 years ago. Transient fault slip (TFS) includes slow and silent earthquakes, episodic tremor and slip, creep events, low frequency earthquakes, tsunamigenic earthquakes, and postseismic fault afterslip. There appears to be a continuous spectrum of slip modes ranging from aseismic creep to earthquakes. These observations challenge the standard view of brittle faulting that has existed for the past 40 years, in which frictional slip occurs in one of only two modes: stick-slip or stable creep. Although modern friction constitutive laws predict that fault slip will exhibit a range of transient behaviors, the underlying processes are poorly understood and key constitutive parameters are poorly constrained. Moreover, existing frictional models require special conditions to produce self-sustained modes of slow slip, and phenomena such as tremor are not well described, which may indicate that additional processes are needed in the models.
A workshop on TSF and related phenomena for ~100 researchers, including post-docs, students and faculty, is being held on October 11-14, 2010, in Portland OR. The primary goals of the workshop are to: 1) provide intellectual leadership and foster critical thinking about the underlying mechanisms and physical processes responsible for TFS, 2) promote broad, community-based interest in understanding TFS, 3) seed collaborations between observational, theoretical and laboratory-based research programs, 4) discuss novel approaches for identifying new fault slip phenomena and new tectonic settings that may host transient strain release, and 5) initiate a continuing web-based virtual "institute" dedicated to TFS.
The workshop and virtual institute foster education and communication across disciplines ranging from geodesy and seismology to rock mechanics, petrology, hydrogeology, tectonics, and geodynamics and provide an opportunity for young researchers to broaden their understanding and become involved in research on a high-profile problem. Focused study of TFS should elucidate the potential role of slow and transient slip on earthquake triggering and seismic hazard assessment.
This grant supported a workshop to foster critical thinking about the spectrum of fault slip behaviors by bringing together specialists from a broad range of scientific disciplines. In the past decade, as a result of technical advances in measuring deformation of the Earth through geodesy and seismology, it was become apparent that faults slip on a much wider range of spatial and temporal scales than previously recognized. For example, slope slip events with durations of days to months accompanied by co-located seismic tremor has been observed down-dip of the region that slips in major subduction zone earthquakes (e.g. the 2011 Tohoku earthquake offshore Japan, the 2010 Maule earthquake offshore Chile, the 2004 Sumatra earthquake). The physical mechanisms causing these slow events and the interaction between the region that is slipping slowly and that which is storing up stress that will be released in a large earthquake in the future are poorly understood. The workshop, which included talks, posters and breakout sessions, was held in Portland Oregon and was attended by over 150 scientists from academia and government labs. Approximately one third of the participants were undergraduate and graduate students or post-doctoral scholars. Speakers came from many countries, including New Zealand, Japan and Italy. The workshop provided an opportunity for participants to see and discuss many exciting new results. Although the meeting focused on the scientific underpinnings for understanding these phenomena, implications for public policies related to earthquake hazards planning and response were also discussed. PDF files from most of the presentations, selected posters and summaries of the breakout discussions can be found at: www.earthscope.org/workshops
