SAGE05 Bryce

Gravity and Magnetic Analysis of the La Bajada fault zone: 

Gravity and Magnetic Analysis of the La Bajada fault zone Bryce Johnson New Mexico Institute of Mining and Technology

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30 Km 20 km Geologic Location: La Bajada Fault Zone - fault trends roughly north-south -extensional fault in the Rio Grande Rift Basin: consists mainly of Tertiary, Mesozoic and Paleozoic deposits. San Francisco fault N

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Looking for the extent and magnetic/gravitational properties of the La Bajada fault and physical properties of the basin bounded by the La Bajada and San Francisco faults Five east-west profiles along the La Bajada and San Francisco faults and connecting basin Both gravity and magnetic profiles Each profile is 30 km long with a 5 km separation between profiles Magnetic data both has 500 meter spacing between collection points Objective and Data

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3925 3920 3915 3910 3905 Aeromagnetic Data (Regional)

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Magnetic Profiles: 3920 and 3910 across La Bajada zone Faults???

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Filtering (Magnetic) Upward Continuation to 500 m (assuming data was taken at 300m), similar to low pass filter Subtraction from total magnetic field anomalies Result: Residual anomaly map Advantage: Shallow magnetic features are enhanced Disadvantage: Noise features are also enhanced

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La Bajada zone with filter applied Espinaso Fm. La Bajada Fault ?

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Gravity Line 3925 Line 3920 Line 3915 Line 3910 Line 3905 Data was collected with …everything. Approximately 1115 gravity stations in this area with a very uneven dispersion Corrections to Data: Tidal Drift Time Drift Latitude Correction Free-Air Correction Bouguer Correction Terrain Correction -Shawn’s Program-

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Gravity Profiles: Residual Anomaly and Inversion W E W E San Francisco fault

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Gravity Profiles continued…

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The southern most line of my regional area. Significantly smaller signal for the La Bajada Basement (Precambrian) is deepest along this profile.

Interpretation and Integration: 

Interpretation and Integration

Conclusions: 

Conclusions The La Bajada fault looses most of its magnetic and gravitational signature at its southern most point The Espinaso Formation has a strong magnetic signature in out crop Some of the Tertiary sediments (Santa Fe group) may have a magnetic signature The seismic line from SAGE 2005 may have hit the tail end of the La Bajada fault.

Acknowledgments: 

Acknowledgments SAGE students, professors and TA s Shawn Biehler for his infinite patience and beautiful programs Darcy McPhee for my great figures Team 2 for making me laugh Team 3 for going first