Josiah Ensing

University of Waikato

University of Auckland

This study is the first to use ocean noise to infer the structure of the Auckland Volcanic Fields subsurface. We ZZ cross-correlated 200 days of noisy wavefields from 12 seismometers for impulse response estimates, which we used to estimate Rayleigh wave velocity dispersion relations by multiple filter analysis. Frequency-dependent surface wave speeds with periods between 3-10s provided information on the subsurface. We inverted vs dispersion curves from 16 impulse responses, obtaining shear… Show more This study is the first to use ocean noise to infer the structure of the Auckland Volcanic Fields subsurface. We ZZ cross-correlated 200 days of noisy wavefields from 12 seismometers for impulse response estimates, which we used to estimate Rayleigh wave velocity dispersion relations by multiple filter analysis. Frequency-dependent surface wave speeds with periods between 3-10s provided information on the subsurface. We inverted vs dispersion curves from 16 impulse responses, obtaining shear velocity models that extend 0-25km deep. vs variations correlated well with crust type and surface geology. The distribution of low-vs zones has good spatial correlation with the Murihiku and Waipapa Terranes (semi-continental crust). Models with monotonically increasing vs mainly associated with the Dun Mountain Ophiolite Belt, of the Maitai Terrane (oceanic crust). The average of our 16 models also agreed with a vs model obtained by other techniques by Horspool et al., 2006. Show less

University of Auckland

The coursework component required to complete a Master of Science Degree specialising in geophysics. The course topics included advanced applied geophysical techniques (using wave and field potential methods), fluid mechanics and applications, wave propagation, hydrogeology, earthquake geology, analysis techniques in engineering geology, and geohazards.

The University of Auckland

I imaged the crust of the Auckland volcanic field using multi-component ambient seismic noise tomography. This involved estimating borehole seismometer orientations using ambient noise and earthquake generated P-waves, determining the best multi-component estimate of the Green's function, frequency-time analysis, generating speed maps using reversible jump Markov chain Monte Carlo, and inverting Rayleigh wave speeds for shear speed and depth. Using multi-component ambient noise reduced… Show more I imaged the crust of the Auckland volcanic field using multi-component ambient seismic noise tomography. This involved estimating borehole seismometer orientations using ambient noise and earthquake generated P-waves, determining the best multi-component estimate of the Green's function, frequency-time analysis, generating speed maps using reversible jump Markov chain Monte Carlo, and inverting Rayleigh wave speeds for shear speed and depth. Using multi-component ambient noise reduced out-of-line signal in the Green's functions. The resulting shear speed model is the first 3D model of the crust of the Auckland volcanic field, and is more robust and has higher resolution than previous models. Show less