“…Instead, passive sources are used such as mini earthquakes within the subsurface of the earth ͑for example, from reservoir rocks cracking due to fluid-pressure changes during production͒ or heavy traffic on the surface. We will compare the passive data model with the primary-multiple model and demonstrate that crosscorrelating data, as is usually done in seismic interferometry ͑see, e.g., Claerbout, 1968;Schuster, 2001;Shapiro and Campillo, 2004;Wapenaar, 2004;Wapenaar et al, 2004;Snieder et al, 2006;Dellinger and Yu, 2009;Draganov et al, 2009͒, is only the first step in a modified version of the recently introduced estimation of primaries by sparse inversion ͑EPSI͒ method ͑van Groenestijn and Verschuur, 2009a͒. A framework to describe active and passive seismic data ͑Berkhout and Verschuur, 2009͒ proposes to find the primary impulse responses via an inversion method.…”