COLLOQUIUM.
For the colloquium paper “Unified scaling law for earthquakes,” by Kim Christensen, Leon Danon, Tim Scanlon, and Per Bak, which appeared in Suppl. 1, February 19, 2002, of Proc. Natl. Acad. Sci. USA (99, 2509–2513), and for the Physical Review Letters paper “Unified Scaling Law for Earthquakes,” by Per Bak, Kim Christensen, Leon Danon, and Tim Scanlon, which appeared April 29, 2002, in Phys. Rev. Lett. (88, 178501), Christensen, Danon, and Scanlon note that they were unaware that publication of papers titled “Unified Scaling Law for Earthquakes” as an Arthur M. Sackler Colloquium paper in PNAS and as a letter in Physical Review Letters violated copyright transfer and double publication policies of the journals. These authors acknowledge significant overlap in data and figures between the two papers and apologize for their oversight.