Detailed magnetotelluric/Audiomagnetotelluric study of the Jemez volcanic zone, New Mexico
The Jemez volcanic zone is an alignment of late Cenozoic volcanic centers located in northern New Mexico and Arizona. It trends N52/sup 0/E and is >500 km in length. Previous investigators suggest the zone is associated with elevated heat flow and anomalously low P wave velocity from 25 to 140 km depth measured along a line from Mount Taylor to the Jemez Mountains. It may also be associated with a Precambrian crustal-age boundary. A detailed study, consisting of 119 audiomagnetotelluric (AMT) and 25 magnetotelluric (MT) soundings, was performed in a 161 km/sup 2/ area located approx.50 km NW of the zone center. The AMT soundings were spaced 1.6 km apart in a grid pattern and had a frequency range from 12 Hz to 10.2 kHz. The AMT soundings were used to detect any near-surface electrical structures or lateral variations. None were found, although terrain effects near the edges of mesas were observed. Agreement between the AMT and MT results from 12 to 50 Hz was excellent. Electrical strike direction is undefined at less than 1-s period. From 1 to 100 s the average tipper strike is N30/sup 0/W, aligning with the dominant surface structures. Greater than 100 s, it rotates abruptly to approx.N60/sup 0/N. This direction represents the electrical strike within metamorphic Precambrian basement rocks and suggests control of the deep electrical structure beneath the study area by the Jemez zone. Two-dimensional MT modeling indicates three relatively homogeneous layers. The resistivity of the deepest layer, > or =15 km depth, is 50 ohm-m in the northwest but decreases to 5 ohm-m southeastward, toward the zone.
- Research Organization:
- Geophysics Group, Earth and Space Sciences Division, Los Alamos National Laboratory
- OSTI ID:
- 6560171
- Journal Information:
- J. Geophys. Res.; (United States), Journal Name: J. Geophys. Res.; (United States) Vol. 89:B5; ISSN JGREA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
150201* -- Geology & Hydrology of Geothermal Systems-- USA-- (-1989)
BASEMENT ROCK
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
ELECTRICAL SURVEYS
ELECTROMAGNETIC SURVEYS
FEDERAL REGION VI
FREQUENCY RANGE
GEOPHYSICAL SURVEYS
HZ RANGE
JEMEZ MOUNTAINS
KHZ RANGE
KHZ RANGE 01-100
LAYERS
MAGNETOTELLURIC SURVEYS
MOUNTAINS
NEW MEXICO
NORTH AMERICA
PHYSICAL PROPERTIES
SURVEYS
TWO-DIMENSIONAL CALCULATIONS
USA
VOLCANIC REGIONS