Ambient Noise Analysis Near Hikurangi Margin, New Zealand Using an Amphibious Array

Date: 4/24/2019

Time: 05:00 PM

Room: Grand Crescent

We apply ambient noise analysis to data from the Hikurangi Ocean Bottom Investigation of Tremor and Slow Slip (HOBITSS) experiment and 32 New Zealand national seismic network (GeoNet) seismic stations to infer the seismic wave speed structure of the Hikurangi Margin and East Cape, New Zealand, regions. During the 2014-2015 HOBITSS experiment 15 ocean bottom seismometers (OBS) were deployed on the Hikurangi portion of the subduction zone off North Island New Zealand. We apply standard ambient noise data processing methods to the continuous vertical component data, including cutting daily records, calculating cross-correlation between station pairs, and stacking daily cross-correlations to obtain the Rayleigh wave Green’s function estimates. Removal of tilt and compliance noise from the OBS vertical components using the horizontal components and pressure records produced little to no improvement in this study because of the limited bandwidth of the surface wave signal. We apply frequency-time analysis (FTAN) to the stacked cross-correlations to measure Rayleigh wave group speeds. We obtain reasonable measurements for periods of 5 to 12 seconds for most of the FTAN diagrams. Asymmetry on the positive and negative lags of the cross-correlation from both the waveform and signal to noise ratio (SNR) of the FTAN results is observed for many station pairs, likely due to the distribution of noise sources. The Rayleigh wave dispersion measurements are used to invert for group velocity maps at periods from 5 to 12 seconds using a straight ray theoretic tomography method. The group velocity maps correlate with regional features mostly as expected, most notably low seismic wave speeds in the ocean and higher wave speeds on the continent, with the highest group velocities beneath the Ruakumara range of the East Cape. We invert for 1-D velocity structures at selected points, obtaining constraints on sediment and upper crustal shear velocity structure of the Hikurangi accretionary prism, as well as coastal and continental northeast North Island, New Zealand.

Presenting Author: Hongda Wang

Authors