seismicity of the irish hills/pismo block and adjacent … of the irish hills/pismo block and...

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PG&E DCPP SSHAC Study

Seismicity of the Irish Hills/Pismo Block and Adjacent Areas Marcia McLaren, PG&E Geosciences Dept, San Francisco CA Workshop 2 November 6, 2012

PG&E DCPP SSHAC Study 2

Topics to Address •Location, sense of slip, and dip of the Hosgri fault zone, with specific attention to the fault adjacent to DCPP.

•Does the distribution of seismicity provide insights on faulting beneath the Irish Hills?

•Do the San Simeon and Ragged Point earthquakes provide insights for faulting beneath the Irish Hills/Pismo block?

Note: Unless specifically referenced, all earthquake relocations shown in this presentation were provided by Dr. Jeanne Hardebeck (USGS-Menlo Park) – time period 1970- 2008.


(Modified from PG&E, 2011)

Hosgri FZ Irish Hills/Pismo Block

2003 San Simeon Eq

Ragged Point


(PG&E, 2011)

Hosgri FZ Dip and Sense of Slip

PG&E DCPP SSHAC Study 6 Irish Hills/Pismo Block

DCPP


SF SMF EF LOF SLBF/WA (projected)

LOF EF

Irish Hills/Pismo Block

DCPP


1 2

3 4

5 6

7 8

Irish Hills/Pismo Block

1 2 3

5 6

7 8

4

S

DCPP

LO

SM

E WA

PB

SLB SM S S/R S

S? S?

E E

PB

WA LO LO

LO LO

LO

LO

SLB/R

LO? LO


1

1

2

2 3

3 4

4

5

5 6

6 7 7

2003 San Simeon Earthquake Region

Gray = 1970-2008 Red = 1970- 12/2003

11/10/1990 M4.0

12/23/2003 M6.5

PG&E DCPP SSHAC Study 10 Ragged Point Area: San Simeon Eq

3/1/1972 00:00 – 8/29/1983 10:09 8/29/1983 10:10 – 12/31/1985 23:59

4 4

3

3

2

2

1

1 8/29/1983 M5.2


9/17/1991 M5.2

2

2 1

1

Ragged Point Area: Ragged Point Eq.

1/1/1986 00:00 – 9/17/1991 21:09

9/17/1991 21:10 – 11/1/1991 00:00

2


Conclusions Hosgri Fault Zone: • Location: Earthquakes epicenters locate within the HFZ, as mapped by PG&E (2011). • Sense of slip - Focal mechanisms from 3D-HASH and Fpfit USGS catalog show predominantly vertical right-

lateral strike-slip. • Dip of the Hosgri fault zone adjacent to DCPP - 80 deg. NE (+-10 deg.).

Irish Hills/Pismo Block: Does the distribution of seismicity provide insights on faulting beneath the Irish Hills? Yes. • In general, more reverse faulting along the NE side of the Pismo block, and strike-slip faulting in center and

SW end of the block. • In southern part of the IH, Los Osos fault may be a boundary to seismicity along the NE side. • In the northern part of the IH/PB seismicity patterns and focal mechanisms supports a NE-dipping fault plane

that extends SW to about the Edna fault; strike-slip faulting beneath the San Miguelito and Shoreline fault zones.

• Don’t see a ramp imaged by the seismicity patterns directly under DCPP. • Don’t see a shallow SW-dipping Los Osos fault.

San Simeon and Ragged Point earthquakes: Do the these earthquakes provide insights for faulting beneath the Irish Hills/Pismo block? • San Simeon – With new earthquake location methods (e.g. tomoDD) can see similar seismicity patterns of the

1970-2003 data near the San Simeon epicenter (two faults dipping into each other) • Ragged Point area – Not enough pre-event locations to see a meaningful pattern


Thank you

seismicity of the irish hills/pismo block and adjacent … of the irish hills/pismo block and...

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