5:15 PM - 7:15 PM
[STT39-P01] Influence of terrain correction using variable density distribution on gravity gradient analysis
Keywords:Gravimetry, Airborne gravity gradiometry, Geothermal, Geophysical exploration
In general, terrain correction is applied to gravity or gravity gradient data to clarify anomalies associated with the subsurface structure. The terrain correction is conducted by subtracting the effects of gravity or its gradient correlated with the topography, assuming an arbitrary surface density for rocks above sea level. Previous studies have proposed methods for estimating the surface density, including the CVUR method (Komazawa, 1995) and the ABIC minimization method (Murata, 1990), a majority of which have determined a unique value of the surface density within the entire survey area (e.g., Kusumoto, 2017). In contrast, several studies have divided the survey area into multiple small windows and performed terrain correction using the optimal surface density for each window, a procedure referred to as variable density correction (Moribayashi, 1990). The variable density correction would appear to be suitable for gravity data analysis in geothermal areas in which there are often variations in the surface density from sedimentary to volcanic rocks, in addition to steep topography.
Komazawa (2016) proposed the upward-connected residual F-T method for the surface density estimation, and attempted to the surface density distribution by applying it to the data of gravity measured on the ground surface and airborne gravity gradients. Using the horizontal components of the gradients, the estimated density distribution was found to be equivalent to that obtained from surface gravity data. However, there is further scope for investigation regarding the optimal window size for calculating surface density and the influences of the variable density correction on the analysis of gravity and gravity gradient data.
In this study, we initially investigated the optimal window size for the variable density correction of airborne gravity gradients using data obtained in the Yuzawa-Kurikoma area, which spans Akita, Iwate, Yamagata and Miyagi prefectures (JOGMEC, 2017a, b). The upward-connected residual F-T method (Komazawa, 2016) was applied for the surface density estimation, and the estimated density distribution was compared with other data sources, including geological maps. Subsequently, several types of invariants, which facilitate the extraction of subsurface structures such as faults, were calculated. In this presentation, in addition to describing our investigation of the window size, we discuss the impact of the variable density correction on the extraction of structures using gravity gradient anomalies.
Acknowledgements:
We extend special thanks to the Japan Organization for Metals and Energy Security (JOGMEC) for permission to use and publish the data compiled in the report JOGMEC HeliFALCONTM Airborne Gravity Gradiometer Survey (Project Number: 2489).
References:
Komazawa M. (1995): Gravimetric analysis of Aso volcano and its interpretation, J. Geod. Soc., Japan, 41, 17-45.
Komazawa M. (2016): Surface density derived from gradiometer data, BUTSURI-TANSA, 69, 19-28. In Japanese
Kusumoto S. (2017): Eigenvector of gravity gradient tensor for estimating fault dips considering fault type, Progress in Earth and Planetary Science, 4, 15
Murata Y. (1990): Estimation of Bouguer Reduction Density Using ABIC Minimization Method, Zishin, 2, 43, 327-339. In Japanese
Moribayashi S. (1990): A New Method for Variable Density Correction of Gravity Data, BUTSURI-Tansa, 43, 97-106. In Japanese
JOGMEC (2017a): The fiscal year 2016 airborne geophysical survey for the geothermal resources potential (Yuzawa-Kurikoma area) report, 1-185. In Japanese
JOGMEC (2017b): HeliFALCONTM Airborne Gravity Gradiometer Survey, Tohoku, Honshu Japan, Logistics and Processing Report, 1-46.
Komazawa (2016) proposed the upward-connected residual F-T method for the surface density estimation, and attempted to the surface density distribution by applying it to the data of gravity measured on the ground surface and airborne gravity gradients. Using the horizontal components of the gradients, the estimated density distribution was found to be equivalent to that obtained from surface gravity data. However, there is further scope for investigation regarding the optimal window size for calculating surface density and the influences of the variable density correction on the analysis of gravity and gravity gradient data.
In this study, we initially investigated the optimal window size for the variable density correction of airborne gravity gradients using data obtained in the Yuzawa-Kurikoma area, which spans Akita, Iwate, Yamagata and Miyagi prefectures (JOGMEC, 2017a, b). The upward-connected residual F-T method (Komazawa, 2016) was applied for the surface density estimation, and the estimated density distribution was compared with other data sources, including geological maps. Subsequently, several types of invariants, which facilitate the extraction of subsurface structures such as faults, were calculated. In this presentation, in addition to describing our investigation of the window size, we discuss the impact of the variable density correction on the extraction of structures using gravity gradient anomalies.
Acknowledgements:
We extend special thanks to the Japan Organization for Metals and Energy Security (JOGMEC) for permission to use and publish the data compiled in the report JOGMEC HeliFALCONTM Airborne Gravity Gradiometer Survey (Project Number: 2489).
References:
Komazawa M. (1995): Gravimetric analysis of Aso volcano and its interpretation, J. Geod. Soc., Japan, 41, 17-45.
Komazawa M. (2016): Surface density derived from gradiometer data, BUTSURI-TANSA, 69, 19-28. In Japanese
Kusumoto S. (2017): Eigenvector of gravity gradient tensor for estimating fault dips considering fault type, Progress in Earth and Planetary Science, 4, 15
Murata Y. (1990): Estimation of Bouguer Reduction Density Using ABIC Minimization Method, Zishin, 2, 43, 327-339. In Japanese
Moribayashi S. (1990): A New Method for Variable Density Correction of Gravity Data, BUTSURI-Tansa, 43, 97-106. In Japanese
JOGMEC (2017a): The fiscal year 2016 airborne geophysical survey for the geothermal resources potential (Yuzawa-Kurikoma area) report, 1-185. In Japanese
JOGMEC (2017b): HeliFALCONTM Airborne Gravity Gradiometer Survey, Tohoku, Honshu Japan, Logistics and Processing Report, 1-46.