  In this paper, we present an upper limit of $\Omega_{\rm GW}<1.2\times
10^{8}$ on an isotropic stochastic gravitational-wave (GW) background
integrated over a year in the frequency range 0.05 Hz - 1 Hz, which improves
current upper limits from high-precision laboratory experiments by about 9
orders of magnitude. The limit is obtained using the response of Earth itself
to GWs via a free-surface effect described more than 40 years ago by F.J.
Dyson. The response was measured by a global network of broadband seismometers
selected to maximize the sensitivity.
