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Martin B. Kalinowski, a nuclear expert at the University of Hamburg, said a magnitude of 4.7 corresponded to a nuclear explosive yield of about three to eight kilotons of high explosives, with the most likely yield being four kilotons. A blast that generated a tremor with a magnitude of 4.5 would be smaller. In contrast, the primitive bombs dropped on Hiroshima and Nagasaki had explosive yields of 15 kilotons and 22 kilotons, respectively.