Anant Hariharan’s research in the department of Earth, Environmental and Planetary Sciences focuses on imaging Earth’s interior with the seismic waves generated by earthquakes to understand how convection in the Earth's mantle causes plate tectonics to occur at the surface. He uses observations of ground shaking from two types of seismic surface waves, Rayleigh and Love waves.
“Some of the work in this thesis can be described as serendipitous. I came across overtone interference while noticing strange anomalies in measurements of seismic waves that I was analyzing as part of an entirely different project. Pursuing these anomalies led me to begin a rigorous study of the fascinating phenomenon of overtone interference, which represents a long-standing challenge in the study of surface-wave propagation,” shares Hariharan.
Through six chapters, Hariharan shows readers how he has developed a new way to understand and measure unique wave propagation phenomena to allow seismologists to generate new high-resolution regional images of the Earth’s interior, allowing for new improvements in both imaging quality and our understanding of deformation in the upper mantle.
Hariharan conducted a study to determine what type of overtone interference is seen in Rayleigh wave phases. He uses large datasets to find patterns in the interference. He provides an analysis of overtone interference in both Rayleigh and Love waves using both synthetic seismograms and real data to create a framework to estimate the degree of overtone contamination in any Love and Rayleigh wave measurement. Finally, he uses this framework to illustrate how and why errors in array-based Rayleigh wave phase velocity measurements are related to epicentral distance.
The second half of his work includes a focus on Love wave phase velocity measurements and demonstrates how to isolate uncontaminated data, thereby presenting the first full Love wave phase velocity maps for USArray. These maps are then used to calculate models of depth-dependent radial anisotropy beneath the continental U.S. and infer patterns of flow. He closes by highlighting manifestations of overtone interference in other surface-wave measurements including group velocities, amplification, and attenuation, explores the likelihood of overtone interference on other planets, and presents progress towards a tool for easily calculating mode and frequency-dependent surface-wave excitation.
“Anant Hariharan produced an outstanding Ph.D. dissertation that profoundly impacts the fields of seismology, tectonics, and geodynamics. His discoveries about Rayleigh and Love waves will change how surface wave researchers utilize those data sets,” shares Colleen Dalton, Associate Professor, Earth, Environmental and Planetary Sciences, who is Hariharan’s advisor.
Chapters two, three and four of his dissertation have been published as papers in the peer-reviewed journals Journal of Geophysical Research: Solid Earth, Geophysical Research Letters, and Geophysical Journal International. He is working on preparing the fifth chapter for submission to a peer-reviewed journal, and sub-sections of the sixth chapter represent the foundation for other work he hopes to publish as separate studies as well.
In addition to his primary research, Hariharan has co-authored the most comprehensive study of mantle flow beneath Greenland using the shear-wave splitting method. He also is part of a collaborative study on the mantle transition zone beneath Greenland that is nearing submission.
“My research has benefited greatly from the flexibility I’ve had as a graduate student (only possible due to the support from my advisor) to go where the science led me and pursue directions of research that seemed promising to me when they appeared, even if they were not part of my original plan. I’ve been able to appreciate new developments and excitement at every turn and stage in the process of scientific inquiry, even while a multitude of my ideas failed and had to be left behind,” says Hariharan.
He has presented multiple times at the Meeting of the American Geophysical Union (AGU),was honored with the Outstanding Student Presentation Award at the 2021 event, and won a National Science Foundation Graduate Student Fellowship Award.
In September, Hariharan will begin a postdoctoral fellowship at the University of California, Santa Barbara.
“Being selected for the Joukowsky Dissertation Award, and being in the final weeks of my graduate studies, has made me reflect upon how fortunate I’ve been in my science and scientific communities over the last several years. This dissertation would simply not have been achieved without the support of the Department of Earth, Environmental, and Planetary Sciences, the camaraderie of my fellow graduate students, the broader seismology community’s openness in sharing data and codes, and my advisor’s mentorship and flexibility.” says Hariharan.
Doctoral candidates and graduates, Dennis Hogan, Kiara Lee, Anant Hariharan, and Suvaid Yaseen were selected for the Graduate School's Joukowsky Family Foundation Outstanding Dissertation Award. Prizes are awarded at the Doctoral Ceremony on May 28, 2023.