Most of our problems of interest can be described as a system of equations, or an inverse problem, to find models of seismic sources and Earth structure that reproduce most accurately the measured data. In global seismology, three classical concepts are typically used in the interpretation of recorded seismograms (surface/body waves and normal modes). We pioneered full spectrum seismic tomography that employs all three classical datasets of derived measurements along with full seismic waveforms, while accounting for various theoretical complexities like anisotropy and attenuation.
Surface Waves
The large-amplitude, dispersed surface waves (T 25–250 s) arriving in the first few minutes to hours of a seismogram are analyzed using characteristics that describe a wave packet such as group and phase velocity.
Body Waves
The broadband body-wave arrivals (T 1–10 s) in the first few tens of minutes of a seismogram can be analyzed using ray-theoretical methods akin to geometrical optics.
Normal Modes
Free oscillations or normal modes of the whole Earth manifest as resonance peaks in the spectra of very long seismograms. The spectral peaks at the longest periods (T ≥ 250 s) are fingerprints of various types of standing waves in the whole Earth caused by a major earthquake.
Waveforms
Full seismic waveforms can be fitted at different frequency bands but this requires a good starting model and data constraints. We utilize all other derived datasets to inform this fitting procedure.