New Mapping of Creeping Faults 2009 2010 Bartlett

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

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

New Mapping of Creeping Faults Bartlett Springs Fault [2009] 170 -km long 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 !

Green Valley Fault, simple rupture model v. 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” NO N Northern GVF ER H RT Historical strike-slip ruptures 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 Southern GVF RN THE SOU Wesnousky (2008) W & A are terminal nodes

v. The northern GVF (Hunting Creek and Berryessa sections) also tends to rupture rarely (RI~1000+ yr) in large multisegment (M 6. 85 -6. 97), but more frequently in smaller (M 6. 2 -6. 6) single-segment ruptures HUNTING CREEK BERRY -ESSA v. The southern GVF (south of Berryessa) tends to rupture rarely (RI~1000+ yr) in large multisegment (M 6. 85 -6. 97), but more frequently in ~M 6. 7 single-segment ruptures CONCORDGREEN VALLEY Green Valley Fault, model results Simplifying assumptions: v 80% of ruptures unilateral (Mc. Guire et al. , 2002) v. Creep rate 3 mm/yr; long-term rate 6 mm/yr v 7. 5 km depth of creep using equations of Savage & Lisowski v 14 km rupture width (Waldhauser & Schaff, 2008) v. Mw-moment-area-slip: Hanks & Kanamori (1979), Wells and Coppersmith (1994) v. Ruptures nucleate at nodes i. e. , steps & bends (Oglesby, 2005)

UCERF 2 sources (BSF & GVF) revised sources Terminal Soft boundaries L ult Bartlett Springs fa P Huntin g Cr. B e rryessa W H S C Conc or Green d. Valley A

Green Valley Fault, new map & model v. Green Valley fault (GVF) zone length, ~130 km [Compared to WG 03 length, 56 km] v. 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) v. 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, 1 s) v. 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. v. The UCERF 2 sources for BSF and GVF can be greatly improved by including results of this new mapping