Thickness of Cenozoic Deposits of Yucca Flat Inferred from Gravity Data, Nevada Test Site, Nevada

Phelps, G.A.; Langenheim, Victoria E.; Jachens, Robert C.

doi:10.3133/ofr99310

Cited by 12 publications

(39 citation statements)

References 8 publications

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“…This inversion method is useful for predicting the relative shapes of basins, although determination of absolute basement depths is less certain because of uncertainties in the local density-depth relation for overlying sediments, and because basin-fi ll density is assumed to vary only in the vertical direction (Phelps et al, 1999). A larger issue in our case is the sparse basement exposures (critical constraints for the separation of the basement and basin-fi ll gravity fi elds) on the east side of the basin.…”

Section: -D Basin Geometrymentioning

confidence: 99%

Tectonic evolution of the Tualatin basin, northwest Oregon, as revealed by inversion of gravity data

et al. 2014

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The Tualatin basin, west of Portland (Oregon, USA), coincides with a 110 mGal gravity low along the Puget-Willamette lowland. New gravity measurements (n = 3000) reveal a three-dimensional (3-D) subsurface geometry suggesting early development as a fault-bounded pull-apart basin. A strong northwest-trending gravity gradient coincides with the Gales Creek fault, which forms the southwestern boundary of the Tualatin basin. Faults along the northeastern margin in the Portland Hills and the northeasttrending Sherwood fault along the southeastern basin margin are also associated with gravity gradients, but of smaller magnitude. The gravity low refl ects the large density contrast between basin fi ll and the mafi c crust of the Siletz terrane composing basement. Inversions of gravity data indicate that the Tualatin basin is ~6 km deep, therefore 6 times deeper than the 1 km maximum depth of the Miocene Columba River Basalt Group (CRBG) in the basin, implying that the basin contains several kilometers of low-density pre-CRBG sediments and so formed primarily before the 15 Ma emplacement of the CRBG. The shape of the basin and the location of parallel, linear basin-bounding faults along the southwest and northeast margins suggest that the Tualatin basin originated as a pull-apart rhombochasm. Pre-CRBG extension in the Tualatin basin is consistent with an episode of late Eocene extension documented elsewhere in the Coast Ranges. The present fold and thrust geometry of the Tualatin basin, the result of Neogene compression, is superimposed on the ancestral pullapart basin. The present 3-D basin geometry may imply stronger ground shaking along basin edges, particularly along the concealed northeast edge of the Tualatin basin beneath the greater Portland area.on April 4, 2014 geosphere.gsapubs.org Downloaded from

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Section: -D Basin Geometrymentioning

confidence: 99%

Tectonic evolution of the Tualatin basin, northwest Oregon, as revealed by inversion of gravity data

et al. 2014

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“…2). Phelps et al (1999) showed that lateral variations in basin-fi ll density, unless abrupt, do not change the overall modeled shape of the basin and that the method can be less effective in estimating the magnitude of basin thickness, especially in basins containing thick basalt fl ows or in areas of poor well control.…”

Section: Gravitymentioning

confidence: 99%

Geophysical framework of the northern San Francisco Bay region, California

et al. 2010

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We use geophysical data to examine the structural framework of the northern San Francisco Bay region, an area that hosts the northward continuation of the East Bay fault system. Although this fault system has accommodated ~175 km of right-lateral offset since 12 Ma, how this offset is partitioned north of the bay is controversial and important for understanding where and how strain is accommodated along this stretch of the broader San Andreas transform margin. Using gravity and magnetic data, we map these faults, many of which infl uenced basin formation and volcanism. Continuity of magnetic anomalies in certain areas, such as Napa and Sonoma Valleys, the region north of Napa Valley, and the region south of the Santa Rosa Plain, preclude signifi cant (>10 km) offset. Much of the slip is partitioned around Sonoma and Napa Valleys and onto the Carneros, Rodgers Creek, and Green Valley faults. The absence of correlative magnetic anomalies across the Hayward-Rodgers Creek-Maacama fault system suggests that this system reactivated older basement structures, which appear to infl uence seismicity patterns in the region.

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“…The method assumes no lateral density variations within the basin fill. This method is a useful tool for predicting the shapes of basins, but it can be less effective in estimating the actual magnitude of basin thicknesses because of uncertainties in the local density-depth relation and the assumption of one-dimensional variations (Phelps et al, 1999).…”

Section: Gravity Data and Basin Geometrymentioning

confidence: 99%

Basin Structure beneath the Santa Rosa Plain, Northern California: Implications for Damage Caused by the 1969 Santa Rosa and 1906 San Francisco Earthquakes

McPhee¹,

Langenheim²,

Hartzell³

et al. 2007

Bulletin of the Seismological Society of America

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Regional gravity data in the northern San Francisco Bay region reflect a complex basin configuration beneath the Santa Rosa plain that likely contributed to the significant damage to the city of Santa Rosa caused by the 1969 M 5.6, 5.7 Santa Rosa earthquakes and the 1906 M 7.9 San Francisco earthquake. Inversion of these data indicates that the Santa Rosa plain is underlain by two sedimentary basins about 2 km deep separated by the Trenton Ridge, a shallow west-northwest-striking bedrock ridge west of Santa Rosa. The city of Santa Rosa is situated above the 2km-wide protruding northeast corner of the southern basin where damage from both the 1969 and 1906 earthquakes was concentrated. Ground-motion simulations of the 1969 and 1906 earthquakes, two events with opposing azimuths, using the gravitydefined basin surface, show enhanced ground motions along the northeastern edge of this corner, suggesting that basin-edge effects contributed to the concentration of shaking damage in this area in the past and may also contribute to strong shaking during future earthquakes.

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Thickness of Cenozoic Deposits of Yucca Flat Inferred from Gravity Data, Nevada Test Site, Nevada

Cited by 12 publications

References 8 publications

Tectonic evolution of the Tualatin basin, northwest Oregon, as revealed by inversion of gravity data

Tectonic evolution of the Tualatin basin, northwest Oregon, as revealed by inversion of gravity data

Geophysical framework of the northern San Francisco Bay region, California

Basin Structure beneath the Santa Rosa Plain, Northern California: Implications for Damage Caused by the 1969 Santa Rosa and 1906 San Francisco Earthquakes

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