Common Contracts
1 similar null contracts
Agreement INGV-DPC 2007-2009June 10th, 2010
In Eq. [3], ω is angular frequency, R is hypocentral distance, and c the corresponding wave speed. Rewriting [3] in terms of wavelengths yields R/λ >> 1, where λ = 2πc/ω. We see once more that the far-field condition depends on the characteristic frequency (or wavelength) of seismic radiation: depending on the frequency content of the signal, we may be in the far-field for high-frequencies at a particular observer location, while for the low frequency wave field the same location experiences near-field effects. In the limit, for zero-frequency waves, i.e. the static displacement, all points on the Earth are, theoretically, in the near-field domain. However, for many practical purposes, a standard statement is that for frequencies above 1Hz, the far-field condition is fulfilled for distances larger than 10 km (Madariaga, 2009).
