Surface wave eikonal tomography in heterogeneous media using exploration data



Surface wave tomography often involves the construction of phase (or group) velocity maps through linearized inversion of measured phase (group) arrival times. Such inversions require a priori information about the medium (that is, a reference model) to calculate source–receiver paths as well as regularization. Surface wave eikonal tomography bypasses these limitations and has the advantage of being simple to implement and use, with virtually no input parameters. It relies on the accurate measurement of phase arrival time, which can be challenging for dispersive waves and complex waveforms. We present a measurement method based on the evaluation of phase arrival time differences at nearby receivers. We show, using an exploration data set, that the produced Rayleigh wave velocity maps are in agreement with results from traditional tomography. The latter reveals less detail, however, because of the regularization needed to accommodate for the heterogeneity of the study area and noise in the data. Eikonal tomography requires averaging over results from multiple sources to produce a proper image; for the scattering environment considered we estimate that a source spacing of 200 m is sufficient. Finally, we show that combining seismic interferometry and eikonal tomography is effective when the source coverage is inadequate.