Near surface sediments introduce low frequency noise into gravity models
3D geologic modeling and mapping often relies on gravity modeling to identify key geologic structures, such as basin depth, fault offset, or fault dip. Such gravity models generally assume either homogeneous or spatially uncorrelated densities within modeled rock bodies and overlying sediments, with...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
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Elsevier
2023-09-01
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| Series: | Applied Computing and Geosciences |
| Subjects: | |
| Online Access: | http://www.sciencedirect.com/science/article/pii/S2590197423000204 |
| _version_ | 1797692822421241856 |
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| author | G.A. Phelps C. Cronkite-Ratcliff |
| author_facet | G.A. Phelps C. Cronkite-Ratcliff |
| author_sort | G.A. Phelps |
| collection | DOAJ |
| description | 3D geologic modeling and mapping often relies on gravity modeling to identify key geologic structures, such as basin depth, fault offset, or fault dip. Such gravity models generally assume either homogeneous or spatially uncorrelated densities within modeled rock bodies and overlying sediments, with average densities typically derived from surface and drill-hole sampling. The noise contributed to the gravity anomaly by these density assumptions is zero in the homogeneous case and typically <200 μGal in the uncorrelated case. Rock bodies and sediments, however, show both a range of densities and spatial correlation of these densities, in both surface and drill-hole samples, and this correlation causes an increase in power in the low frequency content of the resulting gravity anomaly. Spatial correlation of densities can be modeled as a Gaussian random field (GRF), with the random field parameters derived from drill-hole and geologic map data. Data from alluvial fan sediments in southern Nevada indicate correlation lengths of up to 300 m in the vertical dimension and kilometers in the horizontal dimension. The resulting GRF density models show that the noise contributed to the measured gravity anomaly is of low frequency and can be several mGal in amplitude, contradicting the common attribution of lower frequencies to deeper sources. This low-frequency noise increases in power with an increase in sediment thickness. Its presence increases the ambiguity of interpretations of subsurface geologic body shape, such as basin analyses that attempt to quantify concealed basement fault depths, offsets, and dip angles. In the southwestern United States, where basin analyses are important for natural resource applications, such ambiguity increases the uncertainty of subsequent process modeling. |
| first_indexed | 2024-03-12T02:33:08Z |
| format | Article |
| id | doaj.art-bc4957eddc464f5c95761b0c714cf19f |
| institution | Directory Open Access Journal |
| issn | 2590-1974 |
| language | English |
| last_indexed | 2024-03-12T02:33:08Z |
| publishDate | 2023-09-01 |
| publisher | Elsevier |
| record_format | Article |
| series | Applied Computing and Geosciences |
| spelling | doaj.art-bc4957eddc464f5c95761b0c714cf19f2023-09-05T04:16:16ZengElsevierApplied Computing and Geosciences2590-19742023-09-0119100131Near surface sediments introduce low frequency noise into gravity modelsG.A. Phelps0C. Cronkite-Ratcliff1Corresponding author.; U.S. Geological Survey, P.O. box 158 Moffett Field CA, 94035, USAU.S. Geological Survey, P.O. box 158 Moffett Field CA, 94035, USA3D geologic modeling and mapping often relies on gravity modeling to identify key geologic structures, such as basin depth, fault offset, or fault dip. Such gravity models generally assume either homogeneous or spatially uncorrelated densities within modeled rock bodies and overlying sediments, with average densities typically derived from surface and drill-hole sampling. The noise contributed to the gravity anomaly by these density assumptions is zero in the homogeneous case and typically <200 μGal in the uncorrelated case. Rock bodies and sediments, however, show both a range of densities and spatial correlation of these densities, in both surface and drill-hole samples, and this correlation causes an increase in power in the low frequency content of the resulting gravity anomaly. Spatial correlation of densities can be modeled as a Gaussian random field (GRF), with the random field parameters derived from drill-hole and geologic map data. Data from alluvial fan sediments in southern Nevada indicate correlation lengths of up to 300 m in the vertical dimension and kilometers in the horizontal dimension. The resulting GRF density models show that the noise contributed to the measured gravity anomaly is of low frequency and can be several mGal in amplitude, contradicting the common attribution of lower frequencies to deeper sources. This low-frequency noise increases in power with an increase in sediment thickness. Its presence increases the ambiguity of interpretations of subsurface geologic body shape, such as basin analyses that attempt to quantify concealed basement fault depths, offsets, and dip angles. In the southwestern United States, where basin analyses are important for natural resource applications, such ambiguity increases the uncertainty of subsequent process modeling.http://www.sciencedirect.com/science/article/pii/S2590197423000204GravityLow-frequency noiseUpward continuationGaussian random fieldGaussian processVariogram |
| spellingShingle | G.A. Phelps C. Cronkite-Ratcliff Near surface sediments introduce low frequency noise into gravity models Applied Computing and Geosciences Gravity Low-frequency noise Upward continuation Gaussian random field Gaussian process Variogram |
| title | Near surface sediments introduce low frequency noise into gravity models |
| title_full | Near surface sediments introduce low frequency noise into gravity models |
| title_fullStr | Near surface sediments introduce low frequency noise into gravity models |
| title_full_unstemmed | Near surface sediments introduce low frequency noise into gravity models |
| title_short | Near surface sediments introduce low frequency noise into gravity models |
| title_sort | near surface sediments introduce low frequency noise into gravity models |
| topic | Gravity Low-frequency noise Upward continuation Gaussian random field Gaussian process Variogram |
| url | http://www.sciencedirect.com/science/article/pii/S2590197423000204 |
| work_keys_str_mv | AT gaphelps nearsurfacesedimentsintroducelowfrequencynoiseintogravitymodels AT ccronkiteratcliff nearsurfacesedimentsintroducelowfrequencynoiseintogravitymodels |