Lecture 6c Inverting Resistivity Data

Flashcards based on lecture notes about resistivity data inversion.

What type of surveys combine elements of profiling and sounding to acquire data for a two-dimensional resistivity image?

Surveys that combine different electrode central positions and different electrode separations.

What do different electrode separations provide in resistivity surveys?

Different effective depths of measurement.

What is the purpose of pseudosections in resistivity surveys?

A way of simply visualizing the measurement arrangements of apparent resistivity.

What is the key process to derive a resistivity image from apparent resistivity measurements?

Inversion modeling.

Why are initial parameter estimates needed in the inversion modeling of sounding data?

To help guide the algorithms due to the complexities involved.

What is the significance of processing data into a resistivity image?

It should help reconcile differences between measurements from different electrode configurations by accounting for array geometry.

What does the inverted resistivity model represent?

The best view of the subsurface that we can acquire from a resistivity survey.

In the iterative inversion process, what is used to assess the misfit between the model and the data at each iteration?

A forward model.

What adjustments are made if the misfit is too large in the inversion process?

Model parameters are adjusted, and another iteration is run.

When does the inversion process stop iterating?

When the iterations no longer decrease the misfit or the decreases are sufficiently small to be negligible.

What accounts for most variability in resistivity measurements, allowing resistivity images from different electrode arrangements to look similar?

Inverting the data.

Why do differences in subsurface models remain even after inverting resistivity data?

Due to different measurement sensitivities of the arrays.

What is an advantage of using the Venner array?

Higher signal strength

What must be considered when injecting tens to hundreds of thousands of volts into the ground?

Safety

What type of array will prove to be more successful in areas of abandoned mining?

Dipole-dipole array

What does the highest sensitivity show in a sensitivity map?

Areas nearest the electrodes at the surface.

What does low measurement sensitivity imply?

Greater uncertainty in the results.

How can sensitivity be used to improve visualization of inverted resistivity models?

By varying transparency to represent uncertainty.

What is a significant challenge when extending two-dimensional inversion to three dimensions?

The computational burden is much greater.

What do pseudosections provide?

Useful visualizations of apparent resistivity measurements, but they're not direct representations of subsurface resistivity.