Three-Dimensional Imaging of the Crust and Upper Mantle in the Long Valley-Mono Craters Region, California, Using Teleseismic P-Wave Residuals
Teleseismic travel time residuals measured at 90 seismic stations centered on the Long Valley caldera in eastern California were inverted to obtain a three-dimensional image of the velocity structure beneath the array. Direct inversion of these data indicate that the 2- to 4-km thick low-velocity caldera fill contaminates the signal from mid-crustal velocity anomalies beneath the caldera. Thus, two methods were used to strip the effects of the upper crust from the travel time residuals: (1) ray tracing through upper crustal velocity models provided by seismic refraction experiments and gravity surveys, and (2) an iterative stripping scheme using the inversion process itself. These methods adequately remove the effects of the shallowest crustal structures, including the caldera fill. The resulting “stripped” models show two well resolved mid-crustal low-velocity bodies in the Long Valley region. The first body is centered between 7 and 20 km depth beneath the resurgent dome of the Long Valley caldera and has a volume of 150 to 600 km3. The second, with a similar volume, is centered between 10 and 20 km depth beneath the Mono Craters, about 10 km north of Long Valley. Velocity contrasts in both of these bodies are about 6 to 10%, and the features are interpreted as silicic magma chambers. Upper mantle velocities are lower than average beneath the Mono Craters, and higher than average beneath Long Valley. The high eruptive rate of the Mono Craters and these upper mantle structures suggest that the focus of volcanism is shifting north from Long Valley to the Mono Craters.
KeywordsMagma Chamber Velocity Structure Seismic Refraction Valley Region Mono Lake
Unable to display preview. Download preview PDF.
- Bailey RA (1982) Other potential eruption centers in Claifornia: Long Valley, Mono Lake, Coso, and Clear Lake volcanic fields. Calif Div Mines Geol Spec Publ 63:17–28.Google Scholar
- Cerveny V, Molotkov IA, Psencik I (1977) Ray method in seismology. Chambers Univ Press, Praque, 214 pp.Google Scholar
- Goldstein NE (1987) Proceedings of the symposium on the Long Valley caldera: A predrilling data review. Rep LBL-23940, Lawrence Berkeley Lab, Berkeley, Calif, 195 pp.Google Scholar
- Herrin E (1968) 1968 Seismological tables for P-phases. Bull Seismol Soc Am 58:1193–1241.Google Scholar
- Iyer HM, Evans JR, Zandt G, Stewart RM, Coakley JM, Roloff JN (1981) A deep low-velocity body under the Yellowstone caldera, Wyoming: delineation using teleseismic P-wave residuals and tectonic interpretation. Geol Soc Am Bull 92: Part I 792-798, Part II 1471-1646.Google Scholar
- Lachenbruch AH, Sass JH (1978) Models of an extending lithosphere and heatflow in the Basin and Range province. Geol Soc Am Mem 152:209–250.Google Scholar
- Luetgert JH (1988) User’s manual for RAY84/R83PLT interactive two-dimensional ray tracing/ synthetic seismogram package. US Geol Surv Open File Rep 88-238:80.Google Scholar
- Luetgert JH, Mooney WD (1985) Crustal refraction profile of the Long Valley caldera California, from the January 1983 Mammoth Lakes earthquake swarm. Bull Seismol Soc Am 75:211–221.Google Scholar
- Muffler LJP, Williams DL (1976) Geothermal investigations of the U.S. Geological Survey in Long Valley, California, 1972–1973. J Geophys Res 81:721–744.Google Scholar