Structural Geology and Geophysical Investigations Flashcards

Structural Geology

The study of how rocks deform under stress.

Fault

A planar feature in rocks along which there has been displacement.

Anticline

A fold with the limbs dipping away from the hinge.

Tensional Stress

Type of stress that causes elongation of rocks.

Brittle Deformation

Results in a fault.

Strike

Compass direction of a horizontal line on an inclined surface.

Joint

A fracture in a rock with no displacement.

Overturned Fold

Both limbs dip in the same direction, one is overturned.

Ductile Deformation

Results in a fold.

Dip

Maximum angle of the bed from the horizontal.

Syncline Fold

Has limbs that dip toward the hinge.

Normal Fault

Occurs due to tension.

Thrust Fault

A type of reverse fault.

Anticline

Arch-like fold with the oldest rocks at the core.

Strike-Slip Fault

Fault with horizontal motion.

Dip

The steepest angle of descent of a tilted bed.

Anticline Fold

Typically contains rocks that are older at the core.

Shear Stress

Usually results in folding, faulting, or jointing.

Tensile Stress

Results in an extension joint.

Bed

A structure that is NOT caused by deformation.

Hinge (of a fold)

The axis around which bending occurs.

Compressive Stress

Shortens a rock body.

Tectonic Forces

Commonly result in folds in rocks.

Brittle Deformation

Typically occurs at shallow depths.

Strike-Slip Fault

Motion is primarily horizontal.

Recumbent Fold

Has a horizontal axial plane.

Strike

The compass direction of the line formed by the intersection of a rock layer with a horizontal surface.

Dip Plane

The imaginary surface connecting points of equal dip.

Normal Fault

The hanging wall moves down relative to the footwall.

Folds, Faults, or Joints

Geological feature is most likely to form reservoirs for oil and water.

Geophysical Investigations

Primary goal is to investigate subsurface conditions.

Gravity Method

Involves measuring variations in the Earth's gravitational field.

Seismic Refraction

Primarily measures the velocity of seismic waves.

P-waves

Travel through both solids and liquids.

Resistivity Method

Best suited for detecting groundwater.

Ohm-meter

Unit used to express electrical resistivity.

Magnetic Method

Measures the Earth’s natural or induced magnetic fields.

Geophysical Methods

Main advantage is non-destructive exploration.

Electrical Resistivity Method

Primarily depends on electrical current.

Schlumberger Configuration

Commonly used in electrical resistivity surveys.

Hammer Blow

Seismic source in geophysical surveys.

Magnetometers

Used to measure magnetic field intensity.

Seismic Surveys

Ideal for locating underground cavities.

Geophones

Used to detect seismic waves.

Bouguer Anomaly Map

Shows gravity differences.

Electrical Resistivity

Affected by temperature, moisture content, and type of soil or rock.

Seismic Reflection

Relies on wave refraction at layer boundaries.

Denser Materials

Cause positive anomalies in gravity surveys.

High Resistivity Value

Generally indicates dry rock.

Dipole-Dipole Array

Current and potential electrodes are spaced equally.

Seismic Refraction

A key limitation is that it cannot detect shallow layers.

Magnetic Anomalies

Often associated with iron-rich minerals.

Geophysical Logging

The Borehole analysis.

Seismic Reflection Method

Provides information about layer thickness and depth.

Rock Density

Property influences gravity readings the most.

Electrical Method

Most sensitive to subsurface voids.

Vertical Electrical Sounding (VES)

Helps determine the depth of layers.

Gravity Method

Cannot detect Seismic velocity.

Resistivity Survey

Would be most useful in detecting Fractured zones.

Schlumberger Array

Preferred over Wenner array because it has a greater depth penetration.

Geophysical Methods

Not a limitation of cost-effectiveness.

Electrical Resistivity

Is generally low in Clay.

Geophysics

The main reason for using ____ before drilling: To reduce cost and increase accuracy.

Seismic Wave

travel faster in hard rock.

Magnetic Method

One limitation of the _____ is that it is not suitable for detecting non-metallic minerals.

Noise

The term ___ in geophysical methods refers to unwanted data interference.

Anomaly

Term _____ refers to a deviation from normal readings.

Ground Penetrating Radar (GPR)

uses radio waves.

higher Seismic velocities

typically occur in compacted rock.

Magnetic Method

is best for mapping buried metallic objects.