Adjoint Tomography of 3-D Crustal Structure Beneath Northeast China Using Ambient Noise Derived Empirical Green’s Functions

Abstract:

We construct a new 3-D shear wavespeed model of the crust beneath northeast China based upon ambient noise adjoint tomography method [Chen et al., 2014]. Without intermediate steps of measuring phase dispersions, adjoint tomography method inverts for shear wavespeeds of the crust directly from 6 s - 40 s waveforms of Empirical Green’s functions (EGFs) of Rayleigh waves, which are derived from interferometry of two years of ambient noise data recorded by 127 NECESSArray stations. With an initial model derived from traditional asymptotic surface wave tomography method [Guo et al., 2015], adjoint tomography updates 3-D model by iteratively minimizing the frequency-dependent traveltime misfits between EGFs and synthetic Green’s functions in four pass bands: 6 s - 15 s, 10 s - 20 s, 15 s - 30 s, and 20 s - 40 s. Our new model show shear wavespeed anomalies well correlated with known tectonic units such as Xing’an-Mongolia Orogenic Belt, Changbai Mountain Range, and the basins of Songliao, Erlian, Hailer, and Sanjiang. The new model also reveals a distinct structure beneath the Tan-Lu Fault Zone - a significant low-wavespeed anomaly located in the mid-lower crust and uppermost mantle. Model resolution tests are presented for a few regions of interest for further tectonic interpretations of imaged new features in our model.