EAR-PF: Exploring the evolution of faults and friction through dense repeater event catalogs

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Dr. William Frank has been granted an NSF Earth Sciences Postdoctoral Fellowship at the Massachusetts Institute of Technology (MIT) to investigate the ever-changing conditions at seismic faults using rapidly repeating earthquakes as in in situ probe. The evolving activity rates of rapidly repeating seismic events that can emit tens of events in several minutes provide a unique and direct window to seismically active faults and can shed light on what properties, such as temperature, pressure, or fluid pressure, control how friction evolves through time. Thanks to recent advances in the systematic search for repeating earthquakes, Dr. Frank will extend novel detection algorithms to different geological contexts. After detecting millions of events and consolidating them into regional catalogs, comparisons between different seismic contexts will help to better understand the common mechanisms of repeating earthquakes and what controls how a fault ruptures. In addition to detection techniques, there have been a number of new methodologies that will benefit from dense catalogs of collocated events and will help better constrain repeating earthquake mechanics. Taking advantage of the unique Undergraduate Research Opportunity Program at MIT, Dr. Frank will also mentor an undergraduate student who will develop the skills to make use of the high performance computing architectures necessary for modern seismology and adapt the developed detection algorithms to a dataset as his/her own personal project.The matched-filter search is a powerful tool to detect the multiplets, or family of events, of a single source using a previously identified event as a template. A systematic detection of template events to use as matched-filters is, however, necessary to obtain a wide and dense coverage of repeating sources. Both volcanoes and industrial injection/production sites are known to generate a significant amount of seismicity, but identified events have yet to be regrouped into families of repeating multiplets in many regions around the world. Such seismically active environments will be investigated through dense event catalogs generated by a continuous and systematic search first for templates and then for multiplets. In addition to the systematic cataloging of repeating seismicity in different geological contexts, Dr. Frank will also attempt to better constrain the spectral characteristics of repeating earthquakes as we still do not fully understand what makes repeating earthquakes reactivate at such rapid rates and how they differ from more typical earthquakes. Using recent spectral estimation methods to take advantage of the collocated nature of multiplets, he will separate the spectral contributions of the source, the path, and the site from the recorded seismograms to better constrain the properties of repeating earthquake sources.