Long-term slip rate of the southern San Andreas Fault from10Be-26Al surface exposure dating of an offset alluvial fan

Four new latest Pleistocene slip rates from two sites along the northwestern half of the San Bernardino strand of the San Andreas fault suggest the slip rate decreases southeastward as slip transfers from the Mojave section of the San Andreas fault onto the northern San Jacinto fault zone. At Badger Canyon, offsets coupled with radiocarbon and optically stimulated luminescence (OSL) ages provide three independent slip rates (with 95% confidence intervals): (1) the apex of the oldest dated alluvial fan (ca. 30–28 ka) is right-laterally offset ~300–400 m yielding a slip rate of 13.5 +2.2/−2.5 mm/yr; (2) a terrace riser incised into the northwestern side of this alluvial fan is offset ~280–290 m and was abandoned ca. 23 ka, yielding a slip rate of 11.9 +0.9/−1.2 mm/yr; and (3) a younger alluvial fan (13–15 ka) has been offset 120–200 m from the same source canyon, yielding a slip rate of 11.8 +4.2/−3.5 mm/yr. These rates are all consistent and result in a preferred, time-averaged rate for the past ~28 k.y. of 12.8 +5.3/−4.7 mm/yr (95% confidence interval), with an 84% confidence interval of 10–16 mm/yr. At Matthews Ranch, in Pitman Canyon, ~13 km northwest of Badger Canyon, a landslide offset ~650 m with a 10Be age of ca. 47 ka yields a slip rate of 14.5 +9.9/−6.2 mm/yr (95% confidence interval). All of these slip rates for the San Bernardino strand are significantly slower than a previously published rate of 24.5 ± 3.5 mm/yr at the southern end of the Mojave section of the San Andreas fault (Weldon and Sieh, 1985), suggesting that ~12 mm/yr of slip transfers from the Mojave section of the San Andreas fault to the northern San Jacinto fault zone (and other faults) between Lone Pine Canyon and Badger Canyon, with most (if not all) of this slip transfer happening near Cajon Creek. This has been a consistent behavior of the fault for at least the past ~47 k.y.

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Identifying 2000 small and large creep events on the San Andreas Fault.

10.5194/egusphere-egu21-7452 ◽

2021 ◽

Author(s):

Daniel Gittins ◽

Jessica Hawthorne

Keyword(s):

Cross Correlation ◽

San Andreas Fault ◽

Slip Rate ◽

Automated Detection ◽

Seismogenic Zone ◽

Near Surface ◽

The North ◽

San Andreas ◽

Continuous Background

The San Andreas fault has been observed to creep at the surface along the 175km section between San Juan Bautista and Cholame (Titus et al., 2011). This section is known as the creeping section and accumulates slip in two modes: during continuous background slip at a long term slip rate and in accelerated slip bursts known as creep events (Gladwin et al., 1994). But the size and importance of creep events remain unclear. Some researchers treat them as small, ~100-m-wide near-surface events (Gladwin et al., 1994), but others suggest that many creep events reach 4 km depth, connecting the surface to the seismogenic zone (Bilham et al., 2016). So, in this study, we systematically characterize the along-strike rupture extents of creep events along the San Andreas Fault, to determine if these are small, localized phenomena or large, segment-rupturing events.We detect creep events and analyse their propagation using 18 USGS creepmeter records from the San Andreas Fault. Each creepmeter operated for at least 9 of the years between 1985 and 2020. To begin we systematically detect creep events using a cross-correlation approach. We identify periods that have significant slip and signals with high similarity to a template creep event. This automated detection allows us to produce a catalogue with 2000 creep events. The method detects at least 95% of the creep events identified by visual inspection.Once we have found creep events at each creepmeter, we examine how creep events propagate. We compare creep event detections between pairs of creepmeters to determine how many creep events propagate from one creepmeter to the other. At the northern end of the creeping section, we observe that 18-28% of the creep events found at Harris Ranch are also found at Cienega Winery within 24hrs. This coincident timing implies that 18-28% of creep events in the north have an along-strike length of at least 4 km. Many creep events at the southern end of the creeping section appear to be even larger. For instance, a few events appear to be at least 31 km long; 10-38% of creep events at Slacks Canyon also observed at Work Ranch (31 km away) within 24hrs. These large along-strike rupture extents imply that creep events connect the slip and stress field over large regions of the San Andreas Fault. These events may play an important role in the slip dynamics of the creeping section.

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Late Holocene Slip Rate of the Mojave Section of the San Andreas Fault near Palmdale, California

Bulletin of the Seismological Society of America ◽

10.1785/0120200278 ◽

2021 ◽

Author(s):

Elaine K. Young ◽

Eric Cowgill ◽

Katherine M. Scharer ◽

Emery O. Anderson-Merritt ◽

Amanda Keen-Zebert ◽

...

Keyword(s):

Late Holocene ◽

San Andreas Fault ◽

Slip Rate ◽

Earthquake Hazard ◽

Luminescence Dating ◽

Geologic Mapping ◽

Slip Rates ◽

San Andreas ◽

Aleatory Variability

ABSTRACT The geologic slip rate on the Mojave section of the San Andreas fault is poorly constrained, despite its importance for understanding earthquake hazard, apparent discrepancies between geologic and geodetic slip rates along this fault section, and long-term fault interactions in southern California. Here, we use surficial geologic mapping, excavations, and radiocarbon and luminescence dating to quantify the displacements and ages of late Holocene landforms offset by the fault at three sites. At the Ranch Center site, the slip rate is determined using the base of a fan marking incision and deflection of an ephemeral channel. At the adjacent Key Slide site, the margin of a landslide deposited on indigenous fire hearths provides a minimum rate. At the X-12 site, the slip rate is determined from a channel that incised into a broad fan surface, and is deflected and beheaded by the fault. We use maximum–minimum bounds on both the displacement and age of each offset feature to calculate slip rate for each site independently. Overlap of the three independent rate ranges yields a rate of 33–39 mm/yr over the last 3 ka, under the assumption that the sites share a common history, given their proximity. Considered in sequence, site-level epistemic uncertainties in the data permit but do not require a rate increase since ∼1200 cal B.P. Modest rate changes can be explained by aleatory variability in earthquake timing and magnitude; larger changes could suggest a shared regional variation with the Garlock and other faults. The new late Holocene slip rates are consistent with geodetic model estimates that include a viscoelastic crust and earthquake cycle effects. The geologic slip rates also provide average slip over dozens of earthquake cycles—a key constraint for long-term earthquake rupture forecasts.

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A revised position for the primary strand of the Pleistocene-Holocene San Andreas fault in southern California

Science Advances ◽

10.1126/sciadv.aaz5691 ◽

2021 ◽

Vol 7 (13) ◽

pp. eaaz5691

Author(s):

Kimberly Blisniuk ◽

Katherine Scharer ◽

Warren D. Sharp ◽

Roland Burgmann ◽

Colin Amos ◽

...

Keyword(s):

Los Angeles ◽

Southern California ◽

San Andreas Fault ◽

Slip Rate ◽

Large Magnitude ◽

Slip Rates ◽

San Andreas ◽

The Pacific ◽

Large Earthquakes ◽

Dependent Probability

The San Andreas fault has the highest calculated time-dependent probability for large-magnitude earthquakes in southern California. However, where the fault is multistranded east of the Los Angeles metropolitan area, it has been uncertain which strand has the fastest slip rate and, therefore, which has the highest probability of a destructive earthquake. Reconstruction of offset Pleistocene-Holocene landforms dated using the uranium-thorium soil carbonate and beryllium-10 surface exposure techniques indicates slip rates of 24.1 ± 3 millimeter per year for the San Andreas fault, with 21.6 ± 2 and 2.5 ± 1 millimeters per year for the Mission Creek and Banning strands, respectively. These data establish the Mission Creek strand as the primary fault bounding the Pacific and North American plates at this latitude and imply that 6 to 9 meters of elastic strain has accumulated along the fault since the most recent surface-rupturing earthquake, highlighting the potential for large earthquakes along this strand.

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Relation between effective friction and fault slip rate across the Northern San Andreas fault system

Geological Society London Special Publications ◽

10.1144/gsl.sp.2006.253.01.23 ◽

2006 ◽

Vol 253 (1) ◽

pp. 429-436 ◽

Cited By ~ 1

Author(s):

Ann-Sophie Provost ◽

Jean Chéry

Keyword(s):

San Andreas Fault ◽

Slip Rate ◽

Fault Slip ◽

Fault System ◽

San Andreas ◽

San Andreas Fault System ◽

Fault Slip Rate ◽

Effective Friction

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Reconstructing the Timing of Flash Floods Using 10Be Surface Exposure Dating at Leidy Creek Alluvial Fan and Valley, White Mountains, California–Nevada, USA

Quaternary Research ◽

10.1016/j.yqres.2014.08.006 ◽

2015 ◽

Vol 83 (1) ◽

pp. 178-186 ◽

Cited By ~ 4

Author(s):

Markus Fuchs ◽

Rebecca Reverman ◽

Lewis A. Owen ◽

Kurt L. Frankel

Keyword(s):

Flash Floods ◽

Alluvial Fan ◽

Optically Stimulated Luminescence ◽

Alluvial Fans ◽

White Mountains ◽

The Holocene ◽

Surface Exposure Dating ◽

Exposure Dating ◽

Outburst Floods ◽

Glacial Lake Outburst Floods

AbstractLarge alluvial fans characterize the piedmonts of the White Mountains, California–Nevada, USA, with large boulders strewn across their surfaces. The boulders are interpreted as flash floods deposits with an unclear trigger for the transport process. Several triggers are possible, including glacial lake outburst floods (GLOFs), thunderstorms or rainfall on snow cover. From a paleoenvironmental perspective, the origin of the flash floods is of fundamental importance. The alluvial fans that flank the White Mountains at Leidy Creek display particularly impressive examples of these deposits. The boulder deposits and the source catchment at Leidy Creek were examined using 10Be terrestrial cosmogenic nuclide (TCN) surface exposure dating to help elucidate their age and origin. All boulders dated on the alluvial fans date to the Holocene. This is in accordance with the geomorphic analyses of the Leidy Creek catchment and its terraces and sediment ridges, which were also dated to the Holocene using optically stimulated luminescence (OSL) and 10Be surface exposure. The results suggest that the boulders on the alluvial fan were deposited by flash floods during thunderstorm events affecting the catchment of the Leidy Creek valley. Paleomonsoonal-induced mid-Holocene flash floods are the most plausible explanation for the discharges needed for these boulder aggradations, but a regional dataset is needed to confirm this explanation.

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New geodetic constraints on southern San Andreas fault-slip rates, San Gorgonio Pass, California

Geosphere ◽

10.1130/ges02239.1 ◽

2020 ◽

Author(s):

Katherine A. Guns ◽

Richard A Bennett ◽

Joshua C. Spinler ◽

Sally F. McGill

Keyword(s):

Velocity Field ◽

Southern California ◽

San Andreas Fault ◽

Plate Boundary ◽

Slip Rate ◽

Fault Slip ◽

Slip Rates ◽

San Andreas ◽

Fault Slip Rates ◽

Gps Velocity Field

Assessing fault-slip rates in diffuse plate boundary systems such as the San Andreas fault in southern California is critical both to characterize seismic hazards and to understand how different fault strands work together to accommodate plate boundary motion. In places such as San Gorgonio Pass, the geometric complexity of numerous fault strands interacting in a small area adds an extra obstacle to understanding the rupture potential and behavior of each individual fault. To better understand partitioning of fault-slip rates in this region, we build a new set of elastic fault-block models that test 16 different model fault geometries for the area. These models build on previous studies by incorporating updated campaign GPS measurements from the San Bernardino Mountains and Eastern Transverse Ranges into a newly calculated GPS velocity field that has been removed of long- and short-term postseismic displacements from 12 past large-magnitude earthquakes to estimate model fault-slip rates. Using this postseismic-reduced GPS velocity field produces a best- fitting model geometry that resolves the long-standing geologic-geodetic slip-rate discrepancy in the Eastern California shear zone when off-fault deformation is taken into account, yielding a summed slip rate of 7.2 ± 2.8 mm/yr. Our models indicate that two active strands of the San Andreas system in San Gorgonio Pass are needed to produce sufficiently low geodetic dextral slip rates to match geologic observations. Lastly, results suggest that postseismic deformation may have more of a role to play in affecting the loading of faults in southern California than previously thought.

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