Kevin P Furlong

1
Kevin P Furlong Geodynamics Research Group,
Geosciences, Penn State University
Why is the San Andreas Fault System so Creepy?
2
The Hayward Fault - Creeping Earthquakes!
3

• Questions
• What controls which fault segments exhibit creep?
• Why do fault segments creep at different rates?
• Do young fault segments creep? How young?

4
Why Do Some Segments Creep?
Data from Galehouse et al.
5
Is it the Geology?
6
- 3-D Viscoelastic Model - Fault in elastic
layer allowed to slip - Patches on fault can be
locked - System driven by far field displacement
7
Effects of Locking Depth, Lithospheric Shear
Zones, and Fault Length
8
BASIX
Plate Boundary centered beneath the East Bay
Fault System
Pacific Plate (mechanical) extends beneath S.F.
Bay
9
(No Transcript)
10
Lisowski and Prescott, BSSA 1981
Decrease in San Andreas Creep is transferred to
southern Calaveras
20 mm/yr
11
Lithospheric Structure
12
Creeping Faults follow along one major strand of
plate boundary system
13
Effect of a Crustal Triple Junction
14
MODELING FAULT CREEP, LOCKED PATCHES, AND
PATTERNS OF SEISMICITY
15
(No Transcript)
16
Initiation of Fault Creep
17
(No Transcript)
18

• Summary
• Lithospheric plate boundary corridor constrains
  distribution of creeping faults
• Full-rate creeping segment marked by passage of
  the Hollister crustal triple junction
• Plate boundary localization well developed in 2
  Ma (Maacama Fault _at_ Willits)