Deformation in the White Mountain seismic gap, California-Nevada, 1972-1982

A 100×40 km trilateration network extending from Bishop, California, to near Hawthorne, Nevada, crosses the east end of the Long Valley caldera, site of renewed magma inflation in the 1979–1980 interval, and spans most of the White Mountain seismic gap. The network was surveyed in 1972, 1973, 1976, 1979, 1980, and 1982. The 1980 survey may be contaminated by a scale error. In addition, leveling surveys across the caldera have been run in 1932, 1957, 1975, 1980, 1982, and 1983. Interpretation of the deformation is complicated by the occurrence of the May 1980 Mammoth Lakes earthquake sequence (four earthquakes M_L≥6) at the south edge of the caldera as well as other moderate earthquakes within the White Mountain seismic gap. The vertical deformation is largely accounted for by 0.10‐ to 0.15‐km³ expansion of a spherical magma chamber 8–10 km beneath the resurgent dome within the Long Valley caldera sometime between July 1979 and September 1980 with an additional expansion of perhaps 0.05 km³ between September 1980 and July 1982. Some additional sources of deformation within the aftershock zone of the Mammoth Lakes earthquakes seem to be required to explain the horizontal deformation. We show that right‐lateral slip on vertical faults extending WNW from each of the three largest earthquakes in the Mammoth Lakes sequence provides the required additional deformation, but this solution is by no means unique. There are simply too few data to define the rather complex deformation that apparently occurred within the aftershock zone. There is little doubt, however, that inflation of a magma chamber beneath the resurgent dome within the Long Valley caldera was involved in the deformation.