For our first Friday Informal Seminar Hour of the academic year, Sunyoung Park, PhD Candidate at Harvard, presents "Near-Surface Compressional and Shear Wave Speeds Constrained by Body-Wave Polarization Analysis".

"Recovering the near-surface (uppermost few kilometers or less) seismic structure is challenging, especially in environments where drilling or field experiments using vibro-trucks or explosives are not practical options.  Here, we introduce a new non-invasive technique to constrain near-surface seismic structure based on the fact that the wave speed immediately beneath a seismometer controls the recorded orientations of arriving seismic waves.  The technique is applied to High-Sensitivity Seismograph Network in Japan to generate a map of near-surface compressional and shear wave speeds.  The lateral variations in wave speeds correlate with geological and physical features such as topography and volcanoes.  This technique requires minimal computation resources, and opens a new path to study the shallowest crustal structures non-invasively and inexpensively.  It can also provide a means of monitoring changes that occur within the shallow subsurface such as those associated with volcanic and hydrological phenomena."