CAPUTO, M., P. GASPERINI, V. KEILIS-BOROK, L. MARCELLI, and I. ROTWAIN. “Earthquake’s Swarms As Forerunners of Strong Earthquakes in Italy”. Annals of Geophysics, vol. 30, no. 3-4, Nov. 1977, pp. 269-83, doi:10.4401/ag-4823.