The question asks about the geophysical anomalies associated with elevated land masses that are experiencing subsidence (sinking).

Understanding Isostatic and Bouguer Anomalies

To answer this, we need to understand two key geophysical concepts:

• Isostatic Anomaly: This measures the deviation from isostatic equilibrium. Isostasy is the concept that the Earth's crust floats on the denser mantle, with elevation being supported by a thicker, less dense crustal root. A positive (+) isostatic anomaly suggests the landmass is higher than expected for its density structure, implying extra buoyancy or uplift forces. A negative (-) isostatic anomaly suggests it's lower than expected.
• Bouguer Anomaly: This is a measure of gravity after correcting for the gravitational effect of the rock layer between the measurement point and sea level. Negative (-) Bouguer anomalies typically indicate a deficiency in mass beneath the surface (e.g., low-density crust or mantle), while positive (+) anomalies indicate excess mass.

Geophysical Signatures of Elevated Land Masses

Elevated land masses, like mountain ranges or plateaus, are often supported by a thicker crustal root that is less dense than the surrounding mantle. This lower density structure typically leads to:

• A negative (-) Bouguer anomaly, because the total mass column isn't as large as expected for the elevation, or the underlying compensation is less dense.

The isostatic state can vary:

• A positive (+) isostatic anomaly over elevated terrain suggests the region is buoyant or experiencing uplift beyond what simple isostasy predicts based on density alone.

Interpreting Subsidence

When an elevated land mass undergoes subsidence, it means the land surface is sinking. If this landmass initially had a positive (+) isostatic anomaly (meaning it was elevated perhaps more than its density structure alone would justify), the subsidence could represent a relaxation process, moving towards a state of better isostatic balance. The negative (-) Bouguer anomaly often reflects the underlying crustal structure (lower density roots) which may persist even as the elevation changes.

Conclusion on Anomalies

Therefore, elevated land masses that are sinking (undergoing subsidence) are typically associated with:

• A positive (+) isostatic anomaly: Reflecting the buoyant state or extra support contributing to the initial elevation.
• A negative (-) Bouguer anomaly: Reflecting the underlying low-density compensation or mass deficit characteristic of high-standing regions.

This combination corresponds to Option C.