SANS: Publicly Available Daily Multi-Scale Seismic Ambient Noise Source Maps

Abstract

Seismic ambient noise sources have received increased attention recently, creating new possibilities to study the Earth's subsurface and the atmosphere-ocean-solid Earth coupling. In efforts to locate such noise sources using nonlinear finite-frequency inversions, methodological developments such as pre-computed wavefields and spatially variable grids were necessary. These make inversions feasible for the secondary microseismic sources in a frequency range up to 0.2 Hz on a daily basis. By obtaining a starting model for the inversion using Matched Field Processing (MFP) we are able to further steer the inversion toward acceptable global noise source models and improve the final result. Analysis of 1 year of daily inversions shows the seasonal variations of the secondary microseisms and their dependence on the atmosphere-ocean-solid Earth coupling due to storm-induced ocean waves. We present a web framework, seismic ambient noise sources (SANS, sans.ethz.ch), where daily regional- to global-scale SANS maps for the secondary microseisms are made available to the public. This enables the implementation of time-variable noise source distributions into full-waveform ambient noise tomography and time-dependent subsurface monitoring methods. Additionally, it can act as a reference for other studies that locate secondary microseismic sources on a larger scale.