The goal of this project is to develop new methods of analyzing seismic data from densely spaced seismometer arrays, such as EarthScope?s USArray. A key seismological tool for answering the fundamental question of how the mantle circulates is the imaging of seismic discontinuities that are sensitive to the thermal and chemical properties of the mantle. The wealth of data provided by EarthScope allows geoscientists to study the structure of seismic discontinuities on a scale and at a level of detail that have never been possible before. The first phase of this project is funded by the EArly-concept Grants for Exploratory Research (EAGER) program, bringing together a team of seismologists with a broad range of expertise that is led by Dr. Nicholas Schmerr at the University of Maryland and Goddard Space Flight Center. The team is developing a new algorithm and suite of computational tools to analyze seismic energy that reflects from the topside of a seismic discontinuity, providing detailed upper mantle discontinuity structure at scale lengths of several hundred kilometers or less. This tool requires the use of array methodologies enabled by the dense station spacing of the USArray. Development of this new data analysis methodology should stimulate fundamental advances in understanding of the mantle in the fields of mineral physics, mantle petrology, seismology, and geodynamics, adding to the richness of information on the geological history of the mantle beneath the North American continent. The project is providing next-generation open-source scientific research tools, datasets, and measurements made freely available to the scientific community to empower a broader cross section of scientists to handle large datasets such as those provided by EarthScope. These newly developed seismological tools and discontinuity models are being disseminated to the scientific community through the PI?s website.
The goal of this project was to develop a new method for analyzing seismic data from a densely spaced seismometer array, such as EarthScope’s USArray. This project provided a key new seismological tool for answering the fundamental question of how the mantle circulates, in the form of imaging of seismic discontinuities that are sensitive to the thermal and chemical properties of the mantle. Seismic discontinuities occur where there is a rapid change in seismic velocities and density with depth; examples of such mechanisms include changes in mineralogy, composition, and mineral orientations (see attached Figure 1). The wealth of data provided by EarthScope allows geoscientists to study the structure of seismic discontinuities at a level of detail that have never been possible before. The first phase of this project was funded by the EArly-concept Grants for Exploratory Research (EAGER) program, bringing together a team of seismologists with a broad range of expertise that is being led by Dr. Nicholas Schmerr at the University of Maryland and Goddard Space Flight Center, and collaboration from around the world (Dr. Chin-Wu Chen is a professor in Taiwan, while Dr. Daoyuan Sun is a professor in China). With the support of this grant, we have successfully developed software for analyzing seismic energy that reflects from the topside of a seismic discontinuity, to study upper mantle discontinuity structure at scale lengths of several hundred kilometers or less (see attached Figure 2). The dense station spacing of the provided by the USArray enabled our study. We have begun applying this topside reflection approach to a multitude of earthquakes recorded by EarthScope to analyze the shear wave structure of both the 410 and 660 km discontinuities in the Earth, and testing hypotheses regarding the connections of such features to lateral variations in the temperature and chemistry of the mantle. The project has also revealed the presence of the topside reflections from other seismic discontinuities in the upper mantle beneath North America (see attached Figure 3). Although such features are not unexpected, they are elusive in other datasets and the topside reflections will shed considerable light on the origin(s) of these less well known seismic discontinuities. We are also taking this new technique and applying it to data from other seismic arrays, such as the Hi-Net array in Japan. More broadly, the project supported the training of an undergraduate student in seismology (Mr. Anthony Mautino), giving him experience in collecting, processing, and analyzing seismic data. He has now gone on to become a graduate student in seismology under the supervision of the PI and intends to have a career in the geosciences. The tools created here are openly shared with the scientific community.
