New Mapping of Creeping FaultsNew Mapping of Creeping Faults

Bartlett Springs Fault & northern Green Valley FaultBartlett Springs Fault & northern Green Valley Fault

2009200920092009 2010201020102010

LongLong-term Monitoring of Creep Rate LongLong-term Monitoring of Creep Rate

Why?Estimate long-term aseismic moment

release rate.

Creep reduces size of future earthquake by

limiting stress accumulation and

rupture extent

Where?In SFBR at77 sites

on 11 faults

How?By annual

measurement of angular change

across ~100-200 m

aperture arrays

Who?SFSU-USGS

http://pubs.usgs.gov/of/2009/1119/ http://pubs.usgs.gov/of/2009/1119/

New Mapping of Creeping FaultsNew Mapping of Creeping FaultsBartlett Springs Fault [2009] 170-km longBartlett Springs Fault [2009] 170-km long

http://pubs.usgs.gov/ds/541/http://pubs.usgs.gov/ds/541/

northern Green Valley Fault [2010]northern Green Valley Fault [2010]Green Valley Fault:Green Valley Fault:~50 km, new mapping~130 km, total length

See the poster See the poster for detail !for detail !

Green Valley Fault, simple rupture modelGreen Valley Fault, simple rupture modelGreen Valley fault (GVF) [and Bartlett Springs fault (BSF)] contain geometric Green Valley fault (GVF) [and Bartlett Springs fault (BSF)] contain geometric irregularities (steps and bends) of ~2-3 km extent, which may tend to stop about irregularities (steps and bends) of ~2-3 km extent, which may tend to stop about half of ruptures reaching them (Wesnousky, 2008) half of ruptures reaching them (Wesnousky, 2008) ““Soft segment boundaries”Soft segment boundaries”

Green Valley fault (GVF) [and Bartlett Springs fault (BSF)] contain geometric Green Valley fault (GVF) [and Bartlett Springs fault (BSF)] contain geometric irregularities (steps and bends) of ~2-3 km extent, which may tend to stop about irregularities (steps and bends) of ~2-3 km extent, which may tend to stop about half of ruptures reaching them (Wesnousky, 2008) half of ruptures reaching them (Wesnousky, 2008) ““Soft segment boundaries”Soft segment boundaries”

NO

RTH

ER

NS

OU

TH

ER

N

Northern G

VF

Sou

thern G

VF

Historical strike-slipruptures

Historical strike-slipruptures

Wesnousky (2008)Wesnousky (2008)

Key assumption: Key assumption: each event has ~50% each event has ~50%

chance of rupture chance of rupture propagation thru a propagation thru a node, node, S or or C, and , and

continuing (at least) continuing (at least) to the next node, to the next node, unless unless terminalterminal

Key assumption: Key assumption: each event has ~50% each event has ~50%

chance of rupture chance of rupture propagation thru a propagation thru a node, node, S or or C, and , and

continuing (at least) continuing (at least) to the next node, to the next node, unless unless terminalterminal

W & & A are are terminal terminal nodes nodes

W & & A are are terminal terminal nodes nodes

Green Valley Fault, model resultsGreen Valley Fault, model resultsThe southern GVF The southern GVF (south of Berryessa) tends to rupture rarely (south of Berryessa) tends to rupture rarely (RI~1000+ yr) in large multisegment (M6.85-6.97), but more frequently in (RI~1000+ yr) in large multisegment (M6.85-6.97), but more frequently in ~M6.7 single-segment ruptures~M6.7 single-segment ruptures

The southern GVF The southern GVF (south of Berryessa) tends to rupture rarely (south of Berryessa) tends to rupture rarely (RI~1000+ yr) in large multisegment (M6.85-6.97), but more frequently in (RI~1000+ yr) in large multisegment (M6.85-6.97), but more frequently in ~M6.7 single-segment ruptures~M6.7 single-segment ruptures

Simplifying assumptions: Simplifying assumptions: 80% of ruptures unilateral (McGuire et al., 2002)80% of ruptures unilateral (McGuire et al., 2002)Creep rate 3 mm/yr; long-term rate 6 mm/yrCreep rate 3 mm/yr; long-term rate 6 mm/yr7.5 km depth of creep using equations of Savage & Lisowski7.5 km depth of creep using equations of Savage & Lisowski14 km rupture width (Waldhauser & Schaff, 2008)14 km rupture width (Waldhauser & Schaff, 2008)Mw-moment-area-slip: Hanks & Kanamori (1979), Mw-moment-area-slip: Hanks & Kanamori (1979), Wells and Coppersmith (1994)Wells and Coppersmith (1994)Ruptures nucleate at nodesRuptures nucleate at nodes i.e., steps & bends (Oglesby, 2005)i.e., steps & bends (Oglesby, 2005)

Simplifying assumptions: Simplifying assumptions: 80% of ruptures unilateral (McGuire et al., 2002)80% of ruptures unilateral (McGuire et al., 2002)Creep rate 3 mm/yr; long-term rate 6 mm/yrCreep rate 3 mm/yr; long-term rate 6 mm/yr7.5 km depth of creep using equations of Savage & Lisowski7.5 km depth of creep using equations of Savage & Lisowski14 km rupture width (Waldhauser & Schaff, 2008)14 km rupture width (Waldhauser & Schaff, 2008)Mw-moment-area-slip: Hanks & Kanamori (1979), Mw-moment-area-slip: Hanks & Kanamori (1979), Wells and Coppersmith (1994)Wells and Coppersmith (1994)Ruptures nucleate at nodesRuptures nucleate at nodes i.e., steps & bends (Oglesby, 2005)i.e., steps & bends (Oglesby, 2005)

The northern GVF The northern GVF (Hunting Creek and Berryessa sections) also tends to (Hunting Creek and Berryessa sections) also tends to rupture rarely rupture rarely (RI~1000+ yr) (RI~1000+ yr) in large multisegment (M6.85-6.97), but in large multisegment (M6.85-6.97), but more frequently in smaller (M6.2-6.6) single-segment rupturesmore frequently in smaller (M6.2-6.6) single-segment ruptures

The northern GVF The northern GVF (Hunting Creek and Berryessa sections) also tends to (Hunting Creek and Berryessa sections) also tends to rupture rarely rupture rarely (RI~1000+ yr) (RI~1000+ yr) in large multisegment (M6.85-6.97), but in large multisegment (M6.85-6.97), but more frequently in smaller (M6.2-6.6) single-segment rupturesmore frequently in smaller (M6.2-6.6) single-segment ruptures

HU

NTI

NG

CR

EEK

HU

NTI

NG

CR

EEK

BERR

Y-E

SSA

BERR

Y-E

SSA

CON

CORD

-G

REEN

VAL

LEY

CON

CORD

-G

REEN

VAL

LEY

UCERF2 sources (BSF & GVF)UCERF2 sources (BSF & GVF)revised sourcesrevised sources

Bartlett Springs fault

Hunting Cr-Berryessa Concord-Green Valley

Soft boundariesSoft boundariesTerminalTerminal

WW

PP

LL

SS CC

AA

HH

Green Valley Fault, new map & modelGreen Valley Fault, new map & modelGreen Valley fault (GVF) zone length, ~130 km Green Valley fault (GVF) zone length, ~130 km [Compared to WG03 length, 56 km] [Compared to WG03 length, 56 km]

Although longer (~130 km) ruptures are possible, creep and geometrical Although longer (~130 km) ruptures are possible, creep and geometrical discontinuities tend to limit actual rupture lengths. GVF and Bartlett Springs fault discontinuities tend to limit actual rupture lengths. GVF and Bartlett Springs fault (BSF) each contain two or more “soft” segment boundaries, which may allow (BSF) each contain two or more “soft” segment boundaries, which may allow through only about half of ruptures based on global data set (Wesnousky, 2008)through only about half of ruptures based on global data set (Wesnousky, 2008)

Large ruptures (M≥6.7) are expected to be most frequent on the main section Large ruptures (M≥6.7) are expected to be most frequent on the main section of the GVF (south of Lake Berryessa),~200 yr recurrence interval. This result of the GVF (south of Lake Berryessa),~200 yr recurrence interval. This result agrees with our millennial paleoseismic record on GVF (199 ± 82 yr, 1agrees with our millennial paleoseismic record on GVF (199 ± 82 yr, 1))

However, on the much shorter Berryessa and Hunting Creek sections, our However, on the much shorter Berryessa and Hunting Creek sections, our model suggests such large events are probably much less frequent, ~650 yr and model suggests such large events are probably much less frequent, ~650 yr and ~1400 yr estimated recurrence intervals, respectively.~1400 yr estimated recurrence intervals, respectively.

The UCERF2 sources for BSF and GVF can be greatly improved by including The UCERF2 sources for BSF and GVF can be greatly improved by including results of this new mappingresults of this new mapping

Green Valley fault (GVF) zone length, ~130 km Green Valley fault (GVF) zone length, ~130 km [Compared to WG03 length, 56 km] [Compared to WG03 length, 56 km]

Although longer (~130 km) ruptures are possible, creep and geometrical Although longer (~130 km) ruptures are possible, creep and geometrical discontinuities tend to limit actual rupture lengths. GVF and Bartlett Springs fault discontinuities tend to limit actual rupture lengths. GVF and Bartlett Springs fault (BSF) each contain two or more “soft” segment boundaries, which may allow (BSF) each contain two or more “soft” segment boundaries, which may allow through only about half of ruptures based on global data set (Wesnousky, 2008)through only about half of ruptures based on global data set (Wesnousky, 2008)

Large ruptures (M≥6.7) are expected to be most frequent on the main section Large ruptures (M≥6.7) are expected to be most frequent on the main section of the GVF (south of Lake Berryessa),~200 yr recurrence interval. This result of the GVF (south of Lake Berryessa),~200 yr recurrence interval. This result agrees with our millennial paleoseismic record on GVF (199 ± 82 yr, 1agrees with our millennial paleoseismic record on GVF (199 ± 82 yr, 1))

However, on the much shorter Berryessa and Hunting Creek sections, our However, on the much shorter Berryessa and Hunting Creek sections, our model suggests such large events are probably much less frequent, ~650 yr and model suggests such large events are probably much less frequent, ~650 yr and ~1400 yr estimated recurrence intervals, respectively.~1400 yr estimated recurrence intervals, respectively.

The UCERF2 sources for BSF and GVF can be greatly improved by including The UCERF2 sources for BSF and GVF can be greatly improved by including results of this new mappingresults of this new mapping