Deformation of Long Valley Caldera, eastern California, 1983-1984

Abstract

Continued deformation of the Long Valley caldera from the summer of 1983 to the summer of 1984 Is Indicated by resurveys of leveling and trilateration networks. The trilateration surveys can be explained by continued inflation (0.022 km) of a spherical magma chamber located 10 km beneath the resurgent dome plus continued right-lateral slip on the uppermost 2 km of the 1983 rupture surface in the south moat of the caldera. The leveling data suggest a minor upwarping over the resurgent dome but are dominated by a regional tilt (0.9 yrad down to the southeast) over 60 km. Although the leveling data satisfy the usual routine tests for absence of systematic error (e.g., no correlation with topography, satisfactory loop closures, satisfactory agreement between the cumulative sums of backward and forward runs), we are unconvinced that the regional tilt is real. Unusual difficulty in obtaining satisfactory section closures in the double-run sections of the leveling is the primary basis for our skepticism.

Modeling gravity and trilateration data in Long Valley, California, 1983–1984

“…This more recent peak is located essentially over the deep magma chambers identified by Savage and Clark [1982] and Rundle and Whitcomb [1984] and away from the southern end of the resurgent dome, where the uplift was concentrated during the year before. Examination of the trilateration data [Savage and Cockerham, 1984;Savage et al, 1985;Estrem et al, 1986] also confirms this basic picture of the deformation.…”

“…The trilateration data for the years 1983-1984 are given by Savage et al [1985]. The means for the line length changes are recapitulated in Table 3a; a location map for the stations is shown in Figure 3.…”

Bibliography of literature pertaining to Long Valley Caldera and associated volcanic fields

“…Emerson, D., and Eichelberger, J.C., 1980, Geology of the Long Valley Caldera, California, in Goff, F., and Waters, A.C., eds Estrem, J.E., Lisowski, M., and Savage, J.C., 1984, Deformation of Long Valley Caldera, eastern California, measured in 1983[abs]: Eos, Transactions, American Geophysical Union, v. 65, no. 45, p. 1116-1117 Estrem, J.E., Lisowski, M., and Savage, J.C., 1985, Deformation in the Long Valley Caldera, California, 1983: Journal of Geophysical Research, v. 90, no. 14, p. 12,683-12,690.…”

Deformation near the Long Valley Caldera, eastern California, 1982–1986

“…No predominant focal mechanism has been identified for these shocks. The 1984 leveling has been discussed in some detail by Savage et al [1985]. The accuracy of leveling surveys is degraded by systematic error as well as random error.…”

“…Nevertheless, we regard the entire 1984 leveling as suspect, and we will generally avoid using those data. The 1984 leveling has been discussed in some detail by Savage et al [1985].…”