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Abstract: Was the Collapse of the Akzo-Nobel Salt Mine, Retsof, New York, Triggered by an Earthquake?

Gary N. Nottis

On March 12, 1994, at 10:43:15 UTC, a 650×650^prime panel at the 1,100 foot level of the Akzo-Nobel salt mine, largest rock salt mine in the world, failed catastrophically. The coordinates of the collapse are 42.77°N and 77.86°W. The National Earthquake Information Center (NEIC) reported a Previous HitmagnitudeNext Hit of 3.6(mbLg) for the event. A mbLg Previous HitmagnitudeNext Hit is based on the amplitude of recorded Rayleigh waves. A coda-duration Previous HitmagnitudeTop(Mc) of 3.1 was also determined. The event coda is composed of body waves. An investigation of the event suggests that the earthquake and mine roof collapse are one and the same. Facts supporting that interpretation are: (1) seismic activity in an area of rare seismicity, (2) unusual concentration of energy n the 1-5 Hz range as opposed to a typical 10-40 Hz range, (3) pronounced presence of Rayleigh waves on seismograms, (4) unusually large discrepancy between the mbLg and Mc magnitudes, (5) emergent, predominately dilatational first motions, (6) very localized felt area (within 4-5 kilometers of collapse site), (7) felt intensities typically of II-III (MM) with rare IV-VI(MM), (8) significant damage to a highway bridge directly over the mine collapse, and (9) slight damage to nearby homes that includes hair-line plaster and masonry cracks. The observed felt effects are more typical of a large distant earthquake than a local earthquake. Since the March 12, 1994 event, seismic activity has continued sporadically, being most frequent and of largest intensity prior to an following the formation of two 600^prime diameter sinkholes that formed at the surface above the mine due to the dissolution of salt by water entering the mine.

AAPG Search and Discovery Article #90954©1995 AAPG Eastern Section, Schenectady, New York