Surface waves were generated by the North Korean nuclear explosion of 9 October 2006 and were recorded at epicentral distances up to 34°, from which we estimated a surface wave magnitude (Ms) of 2.94 with an interstation standard deviation of 0.17 magnitude units. The International Data Center estimated a body-wave magnitude (mb) of 4.1. This is the only explosion we have analyzed that was not easily screened as an explosion based on the differences between the Ms and mb estimates. Additionally, this Ms predicts a yield, based on empirical Ms/yield relationships, that is almost an order of magnitude larger than the 0.5–1 kt reported for this explosion. We investigate how emplacement medium effects on surface wave moment and magnitude may have contributed to the yield discrepancy.