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A Shallow Attenuating Anomaly Inside The Ring Fracture Of The Valles Caldera, New Mexico
Abstract Spectral ratios of teleseismic direct and
Spectral ratios of teleseismic direct and scattered P waves observed in the Valles Caldera, New Mexico, show a systematic pattern of low amplitudes at sites inside the caldera relative to sites on or outside the ring fracture. Waveforms recorded at caldera stations are considerably more complex than those recorded outside the caldera. The data used in this study were collected during a passive seismic monitoring experiment conducted in 1987. Twenty-four teleseismic events were recorded on two linear arrays spanning the caldera. To first order, the pattern of low amplitudes did not vary with source incidence angle or azimuth of approach, and could not be explained by anomalous amplification at the ring fracture. This observation suggests the presence of a shallow, attenuating zone associated with the caldera fill material inside of the ring fracture. We estimated the general features of the caldera�s near-surface structure for the two-dimensional vertical cross section beneath the array, using a modification of the Aki-Larner discrete-wavenumber method to forward model the observed amplitude variations. Our results indicate that the caldera fill material must be subdivided into at least two distinct zones: a strongly attenuating lower zone, extending to depths in excess of 4 km, and a mildly attenuating surface layer. To fit the data we had to assign an unrealistically low value to seismic Q in the deeper attenuating anomaly. We attribute this to the inability of the Aki-Larner method to account for strong re-direction of energy away from the caldera due to local heterogeneity that we could not include within the low-Q anomaly. This interpretation is consistent with the pervasive, fractured hydrothermal system that is known to exist in the caldera fill material.
own to exist in the caldera fill material.  +
Author Peter M. Roberts  + , Keiiti Aki  + , Michael C. Fehler  +
Citation Peter M. Roberts,Keiiti Aki,Michael C. Fehler. 1995. [[A Shallow Attenuating Anomaly Inside The Ring Fracture Of The Valles Caldera, New Mexico]]. Journal of Volcanology and Geothermal Research. 67(1):79-99.  +
Document type Journal Article  +
Foaf/Page http://www.sciencedirect.com/science/article/pii/037702739400100U  +
Link http://www.sciencedirect.com/science/article/pii/037702739400100U  +
Name A Shallow Attenuating Anomaly Inside The Ring Fracture Of The Valles Caldera, New Mexico  +
PublicationDate 1995  +
Publisher Journal of Volcanology and Geothermal Research  +
ReferenceGenre Geothermal  +
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A Shallow Attenuating Anomaly Inside The Ring Fracture Of The Valles Caldera, New Mexico + , A Shallow Attenuating Anomaly Inside The Ring Fracture Of The Valles Caldera, New Mexico + , A Shallow Attenuating Anomaly Inside The Ring Fracture Of The Valles Caldera, New Mexico + , A Shallow Attenuating Anomaly Inside The Ring Fracture Of The Valles Caldera, New Mexico + , A Shallow Attenuating Anomaly Inside The Ring Fracture Of The Valles Caldera, New Mexico +
Categories References , Geothermal References , Reference Materials
Modification date
"Modification date" is a predefined property that corresponds to the date of the last modification of a subject and is provided by Semantic MediaWiki.
14:46:41, 22 May 2014  +
hide properties that link here 
Valles Caldera - Redondo Geothermal Area + , Valles Caldera - Sulphur Springs Geothermal Area + ReferenceForRobertsAkiFehler1995
Modeling-Computer Simulations At Valles Caldera - Redondo Geothermal Area (Roberts, Et Al., 1995) + , Modeling-Computer Simulations At Valles Caldera - Sulphur Springs Geothermal Area (Roberts, Et Al., 1995) + , Teleseismic-Seismic Monitoring At Valles Caldera - Redondo Geothermal Area (Roberts, Et Al., 1995) + , Teleseismic-Seismic Monitoring At Valles Caldera - Sulphur Springs Geothermal Area (Roberts, Et Al., 1995) + Reference material
 
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