Application of microseismic data to constraining inversion for velocity structure beneath stations in sedimentary area

The joint inversion of receiver functions and seismic surface wave dispersion has become a common technique to study the velocity structure beneath stations. The results can simultaneously match the two data sets of different resolution so that the non-uniqueness of solution has been effectively suppressed in a certain extent. However, for the present distribution of seismic stations, due to many factors, there are less effective short-period surface wave dispersion data. The horizontal resolutions of seismic tomography are low, so it is difficult to reflect the real dispersion characteristics of the local media near stations. The spatial extents reflected by these surface wave dispersions and receiver functions at different depths are also different, especially in the sedimentary region with complex lateral variations, where receiver functions and surface wave dispersion can not simultaneously achieve a good fitting result. So the constraint data, which can reflect information of media in the same spatial extent, should be used as far as possible for joint inversion. In May of 2009, we laid a small-aperture seismic array for micro-seismic observation near two mobile seismic stations in a sedimentary region on the plateau of northern Hebei province and in North China Plain, and obtained high-frequency phase velocity dispersion curves by spatial autocorrelation method. The micro-seismic dispersion curves are used as constraint on shallow velocity structure for the joint inversion of receiver functions and surface waves in sedimentary region. The inversion result shows that the constraint of high-frequency phase velocity dispersion curves may obviously improve the stability and reliability of the inversion for velocity structure in sedimentary region.