New Mapping of Creeping Faults

1. 2009 2010 New Mapping of Creeping Faults Bartlett Springs Fault & northern Green Valley Fault

2. How? By annual measurement of angular change across ~100-200 m aperture arrays Long-term Monitoring of Creep Rate Who? SFSU-USGS Why? Estimate long-term aseismic moment release rate. Creep reduces size of future earthquake by limiting stress accumulation and rupture extent Where? In SFBR at 77 sites on 11 faults http://pubs.usgs.gov/of/2009/1119/

3. Bartlett Springs Fault [2009] 170-km long New Mapping of Creeping Faults http://pubs.usgs.gov/ds/541/ northern Green Valley Fault [2010] Green Valley Fault: ~50 km, new mapping ~130 km, total length See the poster for detail !

4. 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 half of ruptures reaching them (Wesnousky, 2008) “Soft segment boundaries” Historical strike-slip ruptures Green Valley Fault, simple rupture model NORTHERN Northern GVF SOUTHERN Wesnousky (2008) Southern GVF Key assumption: each event has ~50% chance of rupture propagation thru a node, S or C, and continuing (at least) to the next node, unless terminal W & A are terminal nodes

5. HUNTING CREEK • The southern GVF (south of Berryessa) tends to rupture rarely (RI~1000+ yr) in large multisegment (M6.85-6.97), but more frequently in ~M6.7 single-segment ruptures BERRY-ESSA • The northern GVF (Hunting Creek and Berryessa sections) also tends to rupture rarely (RI~1000+ yr) in large multisegment (M6.85-6.97), but more frequently in smaller (M6.2-6.6) single-segment ruptures CONCORD- GREEN VALLEY Green Valley Fault, model results • Simplifying assumptions: • 80% of ruptures unilateral (McGuire et al., 2002) • Creep rate 3 mm/yr; long-term rate 6 mm/yr • 7.5 km depth of creep using equations of Savage & Lisowski • 14 km rupture width (Waldhauser & Schaff, 2008) • Mw-moment-area-slip: Hanks & Kanamori (1979), • Wells and Coppersmith (1994) • Ruptures nucleate at nodes • i.e., steps & bends (Oglesby, 2005)

6. revised sources Terminal Soft boundaries Hunting Cr- Berryessa UCERF2 sources (BSF & GVF) W Bartlett Springs fault L Concord- Green Valley H S C P A

7. Green Valley fault (GVF) zone length, ~130 km • [Compared to WG03 length, 56 km] • Although longer (~130 km) ruptures are possible, creep and geometrical discontinuities tend to limit actual rupture lengths. GVF and Bartlett Springs fault (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) • 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 agrees with our millennial paleoseismic record on GVF (199 ± 82 yr, 1s) • However, on the much shorter Berryessa and Hunting Creek sections, our model suggests such large events are probably much less frequent, ~650 yr and ~1400 yr estimated recurrence intervals, respectively. • The UCERF2 sources for BSF and GVF can be greatly improved by including results of this new mapping Green Valley Fault, new map & model