Attitude of Beds Attitude: A general term for the orientation of a line or plane. Attitude refers to the three dimensional orientation of planar and linear features such as a bed, a joint, a hornblende neddle or a fold. The attitude of planar features, such as beds or joints, is defined by their strike and dip.

Attitude of Linear Structures Attitude of Beds Attitude of Linear Structures The attitude of linear structures is defined by the trend & plunge (together they define a vector) Trend is the bearing of the line & Plunge is the inclination of the line. Linear structure are also defined by their pitch / rake on a given plane: Pitch / Rake: The acute angle between the line and the strike of the plane on which the line lies. Example of linear structures: Fold axis, hingeline, intersection of two planes, stretched pebbles, slickenside, other lineations. Plunge Horizontal line Line – linear structure Vertical Plane Inclined Plane Line – linear structure Horizontal line Pitch / Rake Inclined Plane

Attitude of Planar Structures Attitude of Beds Attitude of Planar Structures The attitude of planar structures is defined by the strike and dip Strike and dip describe the orientation of a plane in space. Strike is the bearing of a horizontal line on the plane (a scalar), i.e., N400E Dip is the inclination of the plane measured down. Dip is a vector; it gives the direction and amount of dip of the plane. Example for dip: 800N 80o is the amount, N is the direction. Example of planar structure: bedding, fault, fold axial plane, layering in lava, cleavage & schistosity.

Attitude of Beds Strike: Strike is the direction of a line formed by the intersection of the bedding plane with the horizontal plane. Strike is the bearing of a horizontal line on the inclined plane (a scalar). If a plane is immersed in a water, the strike line will be the water-line. Generally expressed as an angle relative to north. i.e. N370E, N120W

Attitude of Beds Dip Direction: It is the direction along which a bed dips and is perpendicular to the strike line. The dip direction is the direction that a drop of water will flow down the plane.

Attitude of Beds Dip: The dip of a bed is the angle between the bedding and horizontal plane, i.e., the amount of inclination with respect to horizontal. It is measured in a vertical plane at right angle to the strike of the bedding. It is expressed in degrees (450), or in gradient (1 in 1), or in percentage (50%).

Attitude of Beds Dip: The dip of a bed is the angle between the bedding and horizontal plane, i.e., the amount of inclination with respect to horizontal. It is measured in a vertical plane at right angle to the strike of the bedding. It is expressed in degrees (450), or in gradient (1 in 1), or in percentage (50%). HD VD d HD = Horizontal distance = 1 unit VD = Vertical Distance = 1 unit = tan d VD HD _ or, d = tan

Dipping Sedimentary Beds

Cockscomb Ridge, S. Utah Strike Dip

Attitude of Beds Two types of dip – a) True dip & b) Apparent dip True dip : The angle between a bed and a horizontal plane measured in a vertical plane lying at right angles to the strike of the bedding. It is the maximum vertical angle of an inclined structural plane. It is denoted by d Apparent dip: Apparent dip is the angle measured in any direction other than the true dip direction. The amount is always less than the true dip. It is denoted by r

Attitude of Beds tan r = tan d sin a d = true dip r = apparent dip a = azimuth angle between strike line and apparent dip direction The relation between the apparent dip and true dip is expressed by the following equation:- tan r = tan d sin a

Attitude of Beds tan r = tan d sin a d = true dip r = apparent dip a = azimuth angle between strike line and apparent dip direction C d F a r G d Derived the equation:- tan r = tan d sin a

Attitude of Beds Dip & Strike Symbols Block Diagram Map View Inclined bed Vertical bed Horizontal bed 400

Attitude of Beds

Geologic Map and Cross Section

Attitude of Beds Compass-clinometer for measuring strike & dip Silva compass Brunton compass Taking a bearing of a rock feature - e.g. strike Measuring the inclination (e.g. dip)

Steeply Dipping Beds, Pt. Arena, Ca

Field Measurements

Maps and X-sections

Geologic Maps – strike & dip (angle, direction), geologic cross-sections

Two ways of expressing attitude Attitude of Beds Two ways of expressing attitude N 460 N450E Amount of dip followed by dip direction W E AD DD S Strike followed by amount of dip with dip component N450W, 460 NE