Possible tectonomagnetic effect observed from mid-1989, to mid-1990, in Long Valley caldera, California
- Geological Survey, Menlo Park, CA (United States)
Precise measurements of local magnetic fields have been obtained with a differentially connected array of three proton magnetometers in the Long Valley caldera region since 1984. Two magnetometers are located inside the caldera with a third reference magnetometer located 26 km southeast of the caldera. After correction for secular variation, it is apparent that an anomalous 2 nT decrease in the magnetic field occurred from mid-1989 to mid-1990 at the magnetometer located closest to the center of the resurgent dome inside the caldera. During this period a significant increase in geodetic strain rate of 8.5 ppm/yr was observed on the two-color geodimeter network within the caldera from October, 1989, to mid-1990 and a dramatic increase in seismic activity occurred from December, 1989 to July, 1990. A simple dilatational point-source model with pressure increasing by 52 Mpa from October 1989 to August 1990 at a depth of about 7 km beneath the center of the resurgent dome can be fit to the strain data. If this same model is used to calculate piezomagnetic fields in the caldera, the results obtained agree with the observed local magnetic field data provided the Curie point isotherm is at a depth of {le}5 km. Taken together, these magnetic, seismic and geodetic data suggest that an episode of active magmatic intrusion occurred from late 1989 to mid-1990 at a depth of about 7-8 km beneath the resurgent dome within the Long Valley caldera. Other indications of this intrusion should be evident in measurements of leveling, local gravity, and seismic imaging data.
- OSTI ID:
- 5462788
- Journal Information:
- Geophysical Research Letters (American Geophysical Union); (United States), Vol. 18:4; ISSN 0094-8276
- Country of Publication:
- United States
- Language:
- English
Similar Records
Helium isotope and gas discharge variations associated with crustal unrest in Long Valley caldera, California, 1989-1992
High-resolution microseismicity study of possible magmatic intrusion in the Long Valley Caldera
Related Subjects
58 GEOSCIENCES
CALDERAS
MAGNETIC SURVEYS
LONG VALLEY
DEPTH
GEODETIC SURVEYS
GEOLOGIC MODELS
MAGMA
MAGNETIC FIELDS
MAGNETOMETERS
MAPS
MASS TRANSFER
POSITIONING
RESERVOIR PRESSURE
SEISMICITY
STRAIN RATE
VARIATIONS
CALIFORNIA
DEVELOPED COUNTRIES
DIMENSIONS
GEOPHYSICAL SURVEYS
MEASURING INSTRUMENTS
NORTH AMERICA
SURVEYS
USA
150301* - Geothermal Exploration & Exploration Technology- Geophysical Techniques & Surveys
580000 - Geosciences