Rayleigh wave Tomography of NW Himalaya using Ambient Noise and Earthquake data

Abstract

Seismic tomography is an approach to reconstruct 2-D or 3-D velocity variation in a region of interest. This is performed using body or surface wave data from earthquake sources. Application of body wave data includes using travel time from the source to receiver, while surface waves use group or phase velocity between source and receiver at different time periods. Given the poor distribution of earthquakes (source) and seismic stations (receivers), it is difficult to obtain a well illuminated tomographic map of the region. To improve this, a new tool called seismic interferometry which uses ambient seismic noise to extract Green’s functions between pairs of stations is recently being applied to perform tomographic imaging. The approach is widely referred as Ambient noise Tomography (ANT). Seismic noise is mostly concentrated near the Earth’s surface and contains information related to Earth’s shallow structure which is generally absent in the earthquake records due to attenuation and scattering. In the recent years, ANT has been widely used to image the Earth’s crust and upper-mantle on both regional and continental scales. In this study, we combine both Earthquake and Ambient noise data recorded at 15 broadband stations in North West (NW) Himalaya to obtain a higher resolution tomographic image of the region using seismic surface waves at time periods ranging from 8-50 seconds. It is also shown that the use of ambient noise correlations in this area together with the surface wave dispersion measurements of earthquakes improves both the lateral and vertical resolution.