Tectonic Setting for the

DCPP Region

• Los Osos tectonic

domain

• Transrotational tectonics

of WTR

• Displacement history of

SGHFZ

• Depth of seimogenic zone

(long cross sections)

• Geologic constraints on

long-term maximum

compressive stress in

the DCPP region

Geologic Setting / History

modified from McLaren

and Savage

Los Osos tectonic

domain

Nicholson et al. (1994); Geology

Plate boundary transition at 24-20 Ma

Model for CW Rotation of the WTR (modified after Hornafius et al., 1986)

N60W

33 mm/yr

N60W

52 mm/yr

(increased rate

at 12 Ma)

N27W

(change in direction

at 8-6 Ma)

Relative P-NA plate motions after Atwater and

Stock, 1989; Kriigsman et al., 1999)

extensional

transpressional:

• decreasing slip

rates on SGHFZ

transtensional:

• initiation of slip on

SGHFZ (12-10 Ma)

Model for CW Rotation of the WTR (cont.)

(modified after Hornafius et al., 1986)

post-latest Miocene rotation

continued

transpression:

• continued decrease in

slip rate on SGHFZ

*Age range for Monterey Fm (Shell

Beach) from Omarzai et al. (2001)

Colgan et al. (2012)

t r a n s t e n s i o n a

l

e x t e n s i o n a l

﹛ ⎩ t r a n s p r e s s i o n

a l

SMB

15.2 Ma

11.0 Ma *

*

15 Ma

10 Ma

5 Ma

12-10 Ma

8-6 Ma ?

⎧

Pismo Basin

Regional

Tectonic Style

Tpm

Tpp

A

B

B’ A’

A-A’

B-B’

Hall (1973)

D-D’

Tpp

Tmp

Tpp Tmp

Tmp

Net Displacement on the San Gregorio-Hosgri fault zone

Dickinson et al. (2005)

• Net RL

displacement

across SGHFZ

= 156 ± 4 km

Modified from Vicki Langenheim’s WS2 presentation (Nov. 2012)

156±4 km

4 4 ± 4

k m

(Mz)

Decrease in slip rate through time

early-Late Miocene (10-8 Ma)

25-30 mm/yr

Late Miocene to late Pliocene (8-3 Ma)

16 mm/yr

post-late Pliocene (3-0 Ma)

6 mm/yr

late Pleistocene (post-83 ka)

3.0-4.5 mm/yr*

Modified from Clark et al. (1984)

Slip History for the San Gregorio-Hosgri fault zone

(Clark et al., 1984, 1998, 1999; *Simpson et

al., 1998; *Caskey and Weber in preparation)

Net offset

150-160 km (post-10 Ma)

* assumes 12-10 Ma age for initial movement on fault

modified from Vicki Langenheim’s WS2 presentation (Nov. 2012)

Summary of Net Displacements and Average Long-term

Slip Rates along SGHFZ

Net

Displacements Average slip rates*

contraints from

potential field

correlations of

Langenheim

et al. (2012)

(154 km) (13-15 mm/yr)

Modified from Vicki Langenheim’s WS2 presentation (Nov. 2012)

Negligible offset across south end of fault at Point Conception

(Langenheim et al., 2012)

PA (PA)

Los Osos

Domain

modified from McLaren

and Savage

↿

Model for post-latest Miocene CW Rotation of the WTR

(modified after Hornafius et al., 1986)

post-latest Miocene rotation

Post-Miocene rotation of WTR

Los Osos Domain

modified from McLaren

and Savage

Long cross showing results of PG&E/EDGE (RU-3)

seismic refraction study and seismicity (after Hardebeck).

Long cross showing results of PG&E-3

seismic refraction study and seismicity (after Hardebeck).

Vittori and others (1994);

GSA Spec Pap. 292

Numerical Inversion

from Fault Slip Data (mainly within the Edna

block)

NE-NNE oriented σ1 for the

late Pliocene & Pleistocene;

mean σ1 oriented 202˚, 5˚

San Luis Range fold axes in Mio-

Pliocene rocks (after Hall, 1973,

1979)

SATSI Results – determined from Hardebeck (2010) mechanisms

using the HASH algorithm (Hardebeck and Shearer, 2006)