## 1. Introduction

[2] Ocean waves have long been suspected to cause microseisms [*Wiechert*, 1904] with a dominant seismic peak at twice the wave frequency [*Bernard*, 1941]. A realistic theory was only given by *Longuet*-*Higgins* [1950] and extended to random waves by *Hasselmann* [1963]. Seismic noise sources could be located with a fair degree of accuracy using large aperture seismic arrays, as demonstrated by *Haubrich and McCamy* [1969], and the contributions of the various seismic wave modes was also revealed, showing that fundamental Rayleigh and Love modes tend to dominate at frequencies less than 0.2 Hz. Still, without a full quantitative verification, the debate lingers on the distribution of noise sources, including the relative importance of shoreline reflections, and the general validity of the Longuet-Higgins–Hasselmann theory.

[3] A first detailed verification of this theory using the output of a numerical wave model was only performed recently by *Kedar et al.* [2008]. This work was limited to northwest Atlantic sources and coastal reflections were not included, although they are probably important for other regions [e.g., *Zopf et al.*, 1976; *Chevrot et al.*, 2007]. Also, recent progress in numerical wave modeling [*WISE Group*, 2007; *Ardhuin et al.*, 2010] should also result in more accurate seismic noise applications.

[4] Here we extend the work by *Kedar et al.* [2008] to the global ocean and also take into account coastal reflections. We show that a single global model of seismic noise energy radiation, with realistic ocean wave reflections and seismic attenuation factors, can explain most observed seismic noise in spectra of vertical ground motions. This validated model is then used to discuss the importance of various classes of sea state that contribute to seismic sources and to explain the different seismic noise climates observed at a few selected seismic stations.

[5] Our model is based on a state-of-the-art numerical wave model [*Ardhuin et al.*, 2010] to which coastal reflection was added, but its seismic part is simplified in many aspects. Also, we only model the spectral distribution of the seismic wave energy, without any phase information. This paper is organized as follows. After a review of the noise generation theory, the practical modeling of microseisms is described in section 2. The validity of numerical wave models for the estimation of seismic noise is discussed in section 3. General model results are then presented in section 4 with validation at a few selected locations in section 5. Perspectives for improved models are given in section 6.