Week 16

Question 1

Transform fault =

Answer 1

cuts whole lithosphere

Conservative plate boundary

Question 2

Transcurrent fault =

Answer 2

Intraplate

Question 3

Dextral aka

Answer 3

Right lateral

Question 4

Sinistral aka

Answer 4

Left lateral

Question 5

Types of strike-slip fault

Answer 5

Trench linked

Tear

Indent-linked
(N.B. indenter/escape tectonics)

Ridge transforms

Boundary transforms

Intracrustal S-S

Question 6

Piercing point =

Answer 6

shows offset of strike-slip

e.g. offset drainage

Question 7

Examples of strike-slip faults

Answer 7

Haiti 2010 Enriquillo-Plantain fault (7th all time deadliest earthquake)

NZ 2016 14th November Kaikoura (also thrust)

San Andreas

Question 8

What proportion of plate boundaries are strike-slip? What proportion are significantly oblique?

Answer 8

14%

45%

Question 9

Continental strike-slip

Answer 9

Andersonian wrench faults

Only form in isotropic material with vertical σ2 and conjugate sets

Question 10

Roles of S-S in collision tectonics

Answer 10

ESCAPE

TRANSFER ZONES

COLLISION ZONE BOUNDARIES

SHORTENING ARRAYS

ELEMENTS IN STRAIN PARTITIONING

e.g. Arabian plate

Question 11

Idealised strike slip

Answer 11

Assumes isotropic material

Sub-vertical deformation zone with plane strain // to displacement direction

‘Simple shear’ zone

Question 12

Characteristic structures of S-S in map view

Answer 12

1. EN ECHELON
   - offset sub// features oblique to PDZ
2. RELAY
   - if no consistent offset
3. ANASTOMOSING/BRAIDED STRUCTURE
   - tulip/palm tree in 3D
4. LEFT-STEPPING
5. RIGHT STEPPING

Question 13

Pervasive =

Answer 13

wide spreading

Question 14

Sigmoidal =

Answer 14

looks like a C or an S

Question 15

What happens as shear in the PDZ build up?

Answer 15

Structures rotate towards PDZ

Question 16

Releasing structures

Answer 16

Pull-apart basins

Basin length = displacement on fault; migration of depocentre with time

Shear sense = obliquity

Question 17

Restraining structures

Answer 17

Push-up basins

Shear sense doesn’t = obliquity

e.g. uplift in Lebanon peaks > 3000m

Question 18

Which structures are perpendicular to the z axis and // to the x axis in map view?

Answer 18

Stylolites (contractional)

Folds

Fabrics

Thrusts

Question 19

Which structures are // to z-axis and perpendicular to x axis in map view?

Answer 19

Tensile fractures

Normal faults

Question 20

Which structures are bisected by the z axis?

Answer 20

Conjugate S-S faults

- R (antithetic) and R’ (synthetic)

Question 21

Slip rate =

Answer 21

offset/age

long term

Question 22

Which offset is most recent?

Answer 22

Smallest

Question 23

Recurrence =

Answer 23

how long to build up event offset?

Add no. years to last event date

Question 24

Age =

Answer 24

offset/rate

Question 25

What does it mean if a) GPS derived velocities and b) earthquake slip vectors are not //?

Answer 25

Rotation and shortening may have taken place (with the use of S-S faults!)

Question 26

Finding the azimuth of the S-S, steps:

Answer 26

1. Could be in two directions
2. Look at offset
3. Determine 1’ auxiliary plane (i.e. not the strike plane)
4. If >180 = -90, if <180 = +90 to auxiliary plane’s strike