Locating a scatterer in the active volcanic area of Southern Peru from ambient noise cross-correlation

S U M M A R Y We report on a strong scatterer of seismic energy in the 5–10 s period range located in the volcanic arc of Southern Peru. It is superficially like an active noise source in that it produces a continuous signal that arrives earlier than the inter-station surface wave in the noise crosscorrelations. However, it is clearly determined to be a scatterer based on the coda arrivals observed in the cross-correlations, and the fact that it scatters waves from earthquake sources. Wemodel the scatterer as a cylinder approximately 5 km in diameter with a shear wave velocity 30 per cent lower than the background velocity. It is likely to exist at the depth of 5–10 km, and is located at 71.6◦W/16.1◦S with an error of 10 km, which is near the inactive volcano Nevado Chachani and the active volcano El Misti which recently erupted in 1985.