Measurements of ground vibrations from seismic waves illuminate Earth’s interior structure, composition, and dynamics. Our group develops leading-edge computational and analytical tools for imaging Earth’s properties from surface sediments down to the asthenospheric mantle. New technologies including fiber-optic sensing and “large-N” arrays of seismic nodes are revolutionizing the field of seismology by providing access to the full seismic wavefield and its gradients through space and time, which can be used to image the subsurface as well as to characterize noise sources. We conduct “active seismic source” experiments to impart percussive energy into the subsurface to directly image geological structures and earth materials, from subsurface depths ranging from 10’s of m to several km. Understanding of seismic noise and site response are key for identifying locations of future gravitational-wave detectors and, potentially, for removing unwanted seismic signals from existing gravitational-wave datasets.