Ambient noise surface wave tomography

The method is based on the extraction of surface-wave Green functions from cross-correlating sequences of ambient or background seismic noise that from the random seismic wavefield. Dispersion measurements based on ambient noise have distinct advantages over traditional earthquake-based measurements, including extensions to the band of measurements to shorter periods, generating information between any arbitrary station pairs, and shrinking lateral sensitivity kernels. The consequence is that surface wave tomography based on the cross-correlation of ambient noise promises significantly lateral and vertical resolution relative to traditional methods of surface wave tomography.

Finite-frequency surface wave tomography

Evaluate 2-D sensitivity kernel validity in predicting surface wave filed variation when propagating over a heterogeneous structure using numerical simulation. Develop a regional surface wave tomography method based on 2-D sensitivity kernels. Using normal mode Rayleigh wave data filtered and windowed from seismograms recorded at the TriNet network in southern California, I invert for phase velocities at periods from 25 to 143 s. The phase velocities are further inverted for shear wave velocity structure at depth range from the surface to 250 km.

Oceanic earthquake location using T-phase

Develop a method to locate small oceanic earthquakes and estimate their earthquake magnitude using T-phases recorded in an array of ocean-bottom seismometers. The method can locate small oceanic events with Ms magnitude as low as 2.0 with epicentral distance about 500 km from the ocean-bottom seismometers. We find there is a relatively uniform liner relationship between the surface wave magnitude and T-phase maximum amplitude.

T-phase excitation mechanism

Using a multiple-reverberation seafloor-scattering model, I model T-phase envelopes excited by a relatively shallow earthquake beneath a flat seafloor. The numerical method can accurately predict the character of T-phase shape, rapid growth followed by gradual decay.

Numerical simulation of seismic waves

With a pseudo-spectral method, I model surface wave and body wave propagation over a 3-D heterogeneous medium. The synthesized seismograms can be used to investigate a number of seismic problems, such as the tradeoff between the azimuthal anisotropy and heterogeneities that I am working on now.