SCEC Award Number 16234 View PDF
Proposal Category Workshop Proposal
Proposal Title Workshop Proposal: Scientific Exploration of Induced SeisMicity and Stress (SEISMS)
Name Organization
Heather Savage Columbia University
Other Participants James Kirkpatrick, McGill University
James Mori, Kyoto University
Emily Brodsky, UC Santa Cruz
William Ellsworth, Stanford University
Tom Daley, UC Berkeley
SCEC Priorities 2f, 3a, 4b SCEC Groups Seismology, FARM, Geology
Report Due Date 03/15/2017 Date Report Submitted 11/10/2017
Project Abstract
Several major fault-drilling projects have captured the interseismic and postseismic periods of earthquakes. However, near-field observations of faults immediately before and during an earthquake remain elusive due to the unpredictable nature of seismicity. The SEISMS workshop met in March 2017 to discuss the value of a drilling experiment where a fault is instrumented in advance of an earthquake induced through controlled fluid injection. The workshop participants articulated three key issues that could most effectively be addressed by such an experiment: (1) predictive understanding of the propensity for seismicity in reaction to human forcing, (2) identification of earthquake nucleation processes and (3) constraints on the factors controlling earthquake size. A systematic review of previous injection experiments exposed important observational gaps in all of these areas. The participants discussed the instrumentation and technological needs as well as faults and tectonic areas that are feasible from both a societal and scientific standpoint.
Intellectual Merit Understanding how earthquakes nucleate, propagate, and arrest is one of the major outstanding challenges in Earth Science. The difficulty with making progress on this challenge stems from our inability to directly observe faults deep in the Earth where earthquakes nucleate, as well as our inability to test existing theory at the field scale, where we expect complex feedbacks between stress, pore pressure, and slip. These parameters could be measured by borehole and surface-based instruments during an earthquake if they were deployed near the rupture source. Previous fault zone drilling projects have probed the earthquake source soon after large events (e.g. following the 1995 Kobe, 1999 Chi Chi, 2008 Wenchuan, and 2011 Tohoku earthquakes), and have enabled estimations of important parameters like stress during the earthquake (Ikeda, 2001; Ma et al., 2006; Fulton et al., 2013; Li et al., 2013). However, capturing the dynamics of an earthquake can only be achieved by instrumenting a fault prior to failure and monitoring it before, during and after slip. Because earthquakes cannot be predicted, planning for a near-source deployment is extremely challenging. One possible method to ensure success is to induce failure through controlled fluid injection, similar to earthquakes induced by wastewater injection and recent small-scale (i.e. within meters of a fault zone), controlled experiments (e.g. Guglielmi et al., 2015).
Installing instruments inside the fault through fault zone drilling is the only way to obtain the small signals deep in the Earth necessary to investigate earthquake physics. An earthquake induced on a known fault through targeted fluid injection would provide an opportunity to obtain near-field information with a dense network of instruments deployed prior to the experiment. The fault could be fully characterized before the experiment with active source seismology, borehole geophysics, surface geology, and core-based investigations. An observatory of boreholes containing strain, pore pressure, temperature sensors and down-hole seismometers constructed in advance of the experiment would collect real-time data over a large frequency band (i.e., mHz-to-kHz) close to the source from initiation to arrest.
Broader Impacts The recent escalation in induced earthquakes in North America makes an investigation like this a community priority. By defining the conditions necessary to induce an earthquake, the results would demonstrate how to prevent unintentionally induced earthquakes. A project of this scope requires significant community discussion and buy-in before going forward. The Scientific Exploration of Induced Seismicity and Stress (SEISMS) workshop was a first step in this direction. The overall goal of the workshop was to define the most significant scientific questions that could be addressed by in-situ measurements of an earthquake with borehole observatories. In addition, we discussed technological, logistical and societal hurdles, as well as how to overcome them. The outcome of this workshop includes focused understanding of the unanswered questions in earthquake and fault mechanics, as well as which questions could be addressed through fault zone drilling. Here, we outline the current state of understanding of earthquake physics, as articulated at the workshop, and provide a roadmap of questions that could be addressed through future fault zone drilling.
Exemplary Figure Figure 2