1

Kinematics of Kinematics of Transrotational TectonismTransrotational Tectonismin the California Transverse Ranges andin the California Transverse Ranges andIts Contribution to Cumulative Slip AlongIts Contribution to Cumulative Slip Alongthe San Andreas Transform Fault Systemthe San Andreas Transform Fault System

William DickinsonWilliam Dickinson

20 April 200420 April 2004

Wrench Tectonics - Different EndWrench Tectonics - Different EndMembersMembers

(Sylvester, 1988)

2

San Andreas Slip DeficitSan Andreas Slip Deficit

Total Transform Slip in Central California:Total Transform Slip in Central California:~48 mm/yr~48 mm/yr

Average Slip Rate on SAF: ~35 mm/yrAverage Slip Rate on SAF: ~35 mm/yr

Average Shear on ECSZ: ~8-12 mm/yrAverage Shear on ECSZ: ~8-12 mm/yr

Total Deficit: <5 mm/yrTotal Deficit: <5 mm/yr

3

Conceptual ModelConceptual Model

Initial State (tInitial State (t00))

4

Constant-Width Model (tConstant-Width Model (t11))

Constant-Width Model (tConstant-Width Model (t22))

5

Initial State (tInitial State (t00))

"Pinned" Model (t"Pinned" Model (t11))

6

"Pinned" Model (t"Pinned" Model (t22))

Initial State (tInitial State (t00))

7

"Decoupled" Model (t"Decoupled" Model (t11))

"Decoupled" Model (t"Decoupled" Model (t22))

8

DynamicsDynamics

Two Models:Two Models:1.1. Side-DrivenSide-Driven

•• Requires attachment of rotating panels to shearRequires attachment of rotating panels to shearzone sides (and bottom detachment)zone sides (and bottom detachment)

2.2. Bottom-DrivenBottom-Driven•• Requires attachment of rotating panels to shearingRequires attachment of rotating panels to shearing

mantle lithosphere (and side detachment)mantle lithosphere (and side detachment)

Both could drive the "Pinned" orBoth could drive the "Pinned" or"Decoupled" models"Decoupled" models

Eastern Transverse RangesEastern Transverse Ranges

9

Western Transverse RangesWestern Transverse Ranges

10

WTR Conceptual ModelWTR Conceptual Model

Differential Block RotationDifferential Block Rotation

Rotation has been roughly constant at 5.7-5.9Rotation has been roughly constant at 5.7-5.9˚̊for the last ~15 Mafor the last ~15 Ma

Two Possibilities:Two Possibilities:1.1. Different rotation rates for each domain, but rotationDifferent rotation rates for each domain, but rotation

for the same amount of timefor the same amount of time

2.2. Equal rotation rates for each domain, but differentEqual rotation rates for each domain, but differenttimingtiming

The latter is preferred, and implies that theThe latter is preferred, and implies that thelength of the rotating panels shortens with timelength of the rotating panels shortens with time

11

Tehachapi MountainsTehachapi Mountains

12

13

Cumulative DisplacementCumulative Displacement

Tectonic RestorationTectonic Restoration

14

San Andreas Slip BudgetSan Andreas Slip Budget