Tilt measurements at Long Valley caldera, California, May-August 1982

The Mammoth Lakes area in east-central California has experienced unusual seismicity and ground deformation since 1978, highlighted by four M>6 earthquakes in May 1980 and by the discovery soon thereafter of a broad uplift within Long Valley caldera. Recurrent seismic swarms during June 1980-May 1982 raised concern over the possibility of renewed volcanic activity in the foreseeable future, prompting a USGS Notice of Potential Volcanic Hazard on 28 May 1982. As part of an intensified Long Valley monitoring effort sponsored by the USGS Volcanic Hazards Program, a network of nine tilt sites was established near Mammoth Lakes in May and July 1982. This report describes those stations and presents results from three tilt resurveys during July-August 1982.