Extracting Ambient Noise Dispersion in the North Western Pacific Ocean

Abstract:

Seismic constraints on the oceanic crustal structure and thickness are typically obtained from surface wave dispersion measured with teleseismic earthquakes. These measurements are, unfortunately, limited to periods of about 25s or larger and thus have a poor vertical resolution in the shallowest parts of the lithosphere. Ambient noise dispersion measurements can, however, provide data at shorter periods and valuable information about crustal structure. These measurements are widespread in continental regions where lots of seismic arrays have been deployed over the years, but less common in oceanic basins. Lin et al. (2006) demonstrated that ambient noise tomography across ocean basins is possible as long as the locally generated noise, which is stronger than in continents, is removed or reduced. In practice, it can mean that multiple years of continuous data recordings at station pairs are needed. Ma and Dalton (2016) successfully applied such method across the Indian Ocean, which improved the resolution of tomographic models in the northern Indian Ocean.

In this work, we extracted ambient noise dispersion measurements across the North Western Pacific Ocean by cross-correlating vertical component seismograms at permanent stations on ocean islands and on continents between Alaska, Japan, and Papa New Guinea. We did this for multiple sets of 1-3 years of continuous recordings from 1991 to 2014 in order to assess the stability of the results. A good signal-to-noise ratio (SNR) was obtained for multiple station pairs, and phase velocity dispersion curves were processed between 10s-100s period. A comparison of our longer period results with published phase velocity maps obtained from teleseismic earthquakes validates our measurements.