Three dimensional model of seismic velocity variation in the Earth's mantle

Abstract

Three dimensional velocity models for the earth's mantle were obtained satisfying P, S and some PcP and ScS travel time anomalies from deep focus earthquakes. A method of successive approximation was used to compute the uniform relative velocity perturbation over three dimensional blocks of size 10°×10° in longitude and latitude, and 500 km in thickness. Features of these velocity perturbations indicated that lateral heterogeneity is the most pronounced in the upper mantle and near the core‐mantle boundary. The upper mantle anomalies are correlated with surface tectonic features, but these are not correlated with deep mantle anomalies.

Deep Earth Structure: Lower Mantle and D″

“…Initial investigations of aspherical structure in the lower mantle utilized moderate-sized (hundreds to a few thousand) sets of travel time anomalies (e.g., Sengupta and Toksoz, 1976) or differential travel time observations (e.g., Jordan and Lynn, 1974;Lay, 1983) to detect systematic variations relative to standard one-dimensional models. The main challenges in resolving lower mantle heterogeneity involve the uncertainty in earthquake source locations (typically, these are approximated by solving the location problem assuming a one-dimensional velocity structure, which intrinsically leads to an incorrect location estimate and consequent artifacts in the residual arrival times) and the strength of upper mantle heterogeneities (particularly near-source structures such as subducting slabs).…”

The thermo-chemical and physical structure beneath the North American continent from Bayesian inversion of surface-wave phase velocities

“…Seismic tomography has proved to be a powerful tool to provide information on the internal structure of the Earth and has done much to advance our understanding of its dynamics. Since its advent in the late 1970s [e.g., Aki et al , 1977; Sengupta and Toksöz , 1977; Dziewonski et al , 1977], seismic images have revealed features at a lateral and radial resolution that is continuously being improved [e.g., Ritsema et al , 2011]. …”

Tomographic inversions for mantle P wave velocity structure based on the minimization of l2 and l1 norms of International Seismological Centre Travel Time Residuals

“…Early efforts to map the three-dimensional velocity structure of Earth [Aki et al, 1977;Dziewonski et al, 1977;Sengupta and Toksoz, 1976], all of which use a block parametrization, were limited in their structural detail by numerical methods that calculate the explicit inverse of the coefficient matrix. Early efforts to map the three-dimensional velocity structure of Earth [Aki et al, 1977;Dziewonski et al, 1977;Sengupta and Toksoz, 1976], all of which use a block parametrization, were limited in their structural detail by numerical methods that calculate the explicit inverse of the coefficient matrix.…”