Identifying the Frequency Dependent Interactions between Ocean Waves and the Continental Margin on Seismic Noise Recordings

Zhen Guo,Yu Huang,Adnan Aydin,Mei Xue

doi:10.3390/jmse8020134

Abstract

This study presents an exploration into identifying the interactions between ocean waves and the continental margin in the origination of double-frequency (DF, 0.1–0.5 Hz) microseisms recorded at 33 stations across East Coast of USA (ECUSA) during a 10-day period of ordinary ocean wave climate. Daily primary vibration directions are calculated in three frequency bands and projected as great circles passing through each station. In each band, the great circles from all stations exhibit largest spatial density primarily near the continental slope in the western North Atlantic Ocean. Generation mechanisms of three DF microseism events are explored by comparing temporal and spatial variations of the DF microseisms with the migration patterns of ocean wave fronts in Wavewatch III hindcasts. Correlation analyses are conducted by comparing the frequency compositions of and calculating the Pearson correlation coefficients between the DF microseisms and the ocean waves recorded at selected buoys. The observations and analyses lead to a hypothesis that the continental slope causes wave reflection, generating low frequency DF energy and that the continental shelf is where high frequency DF energy is mainly generated in ECUSA. The hypothesis is supported by the primary vibration directions being mainly perpendicular to the strike of the continental slope.

Highlights

Ambient noise has been widely used to estimate the seismic site effect parameters of a site [1,2,3,4,5] and to characterize both deep and shallow subsurface structures [6,7,8,9,10,11,12,13,14,15] for its advantages as a fast, effective, and reliable tool
This study explored the role and significance of the continental slope in the interactions between the ocean waves and the continental margin as well as the resulting double-frequency (DF) microseisms recorded in ENAM
The primary vibration direction analysis of the ambient noise recordings in the study area shows that these DF microseisms originated in areas of the North Atlantic Ocean, which are generally aligned in the SE direction with the recording stations

Summary

Introduction

Ambient noise (or seismic noise) has been widely used to estimate the seismic site effect parameters (e.g., predominant frequency f 0, sediment thickness, amplification factor, etc.) of a site [1,2,3,4,5] and to characterize both deep (down to the mantle of the Earth) and shallow (within the depth of geological engineering activities) subsurface structures [6,7,8,9,10,11,12,13,14,15] for its advantages as a fast, effective, and reliable tool. The accuracies and reliabilities of the applications listed above would be strongly affected by the spatial and temporal variations of the ambient noise sources. One example is given in [16] who estimated the amplification factors in Northern Mississippi of United States applying the horizontal-to-vertical spectral ratio (HVSR, or Nakamura) method based on long term ambient noise recordings. The ambient noise with frequency greater than 0.1 Hz would be used in shallow subsurface tomography From this point of view, exploring the source locations, the spatial and temporal characteristics and the generation mechanisms of the ambient noise with frequency greater than 0.1 Hz, especially the DF microseisms, would significantly improve the application of the ambient noise in site effect evaluation and shallow subsurface tomography.

Methods

Results

Discussion

Conclusion