11:45 AM - 12:00 PM
[S14-2-06] Phase speed measurements of multi-mode surface waves using a broad-band array: Application to USArray
Recent deployment of dense broadband seismic networks enables us to delineate high-resolution regional 3-D upper mantle images using surface waves, although many of surface-wave dispersion analysis with seismic arrays have primarily employed the fundamental mode only. To enhance the vertical resolution of 3-D S-wave models, higher-mode information can be of great help. However, their phase speed analysis is intrinsically difficult, since the wave trains of several modes are generally overlapped each other in an observed seismogram. Modal separation is not a straightforward issue because several higher-modes share similar group speeds, but it can be possible by utilizing multi-mode surface waves propagating across a dense linear seismic array aligned along the great-circle path. In this study, we develop an efficient method for measuring the phase speeds of the fundamental- and higher-mode surface waves based on an array-based analysis in the frequency-wavenumber domain with varying group-speed time window. The method is then applied to USArray, to map the phase speed distributions of each mode and frequency.
Extensive synthetic experiments suggest that the measured phase speeds using a linear array well represent the average structural features around the centroid of stations in the linear array. Thus, the measured multi-mode phase speeds are used as a representation of the average phase speeds around the centroid location of each station group. In this way, the phase speed distributions in North America are mapped using the measured phase speeds. Preliminary phase speed maps well reflect the major structural features of the upper mantle beneath the United States, regardless a relatively small number of employed seismic events. This method of multi-mode phase speed measurements can be of use to construct regional 3-D upper mantle models with enhanced vertical resolution.
Extensive synthetic experiments suggest that the measured phase speeds using a linear array well represent the average structural features around the centroid of stations in the linear array. Thus, the measured multi-mode phase speeds are used as a representation of the average phase speeds around the centroid location of each station group. In this way, the phase speed distributions in North America are mapped using the measured phase speeds. Preliminary phase speed maps well reflect the major structural features of the upper mantle beneath the United States, regardless a relatively small number of employed seismic events. This method of multi-mode phase speed measurements can be of use to construct regional 3-D upper mantle models with enhanced vertical resolution.