Surface waves are the most prominent phases recorded at teleseismic distances at periods longer than 30 s, especially from shallow-focus earthquakes. Two types of surface waves are observed, distinguished by their polarization during propagation through the Earth: Love (SH) and Rayleigh (P–SV) waves, recorded on the transverse and vertical/longitudinal components, respectively. Surface wave arrivals are denoted by the orbit number (e.g. No = 1 for minor-arc L1 or R1 waves), a proxy for the number of times the wave circles around the Earth (Nc = [No – 1]/2 for odd No, No/2 otherwise). The wave trains excited by large mega-thrust earthquakes (Mw ≥ 7.5) circle the Earth multiple times (Nc ≥ 1) for many hours and manifest as discernible higher-orbit arrivals (e.g. L3–L5, R3–R5). Generation and propagation of surface waves can also be classified based on the properties of the corresponding normal modes. Fundamental-mode surface wave trains are excited more strongly by shallow and intermediate-depth earthquakes (h < 250 km) and appear well separated from other phases at teleseismic distances (> 30◦). Higher-mode or overtone vibrations are excited by deeper earthquakes and appear as faster propagating, compact wave packets that contribute to the long-period body waveforms. Characterizing surface waves and overtones is critical for the construction of elastic reference Earth models
Reference Data
- How fast do surface waves travel globally after any earthquake?
- Do we get the same information from various measurement techniques?
- Which features in the Earth are robust and can be resolved by a reference model?
Checkout out our peer-reviewed article written in collaboration with 18 scientists from 16 elite institutions in 7 countries who actively participated in the REM3D project. The project assimilated, archived, reconciled and modeled big (>200 million measurements) and diverse surface-wave datasets for global subsurface structure.
