scholarly journals Tectonic controls on Quaternary landscape evolution in the Ventura basin, southern California, USA, quantified using cosmogenic isotopes and topographic analyses

2022 ◽  
Author(s):  
A. Hughes ◽  
D.H. Rood ◽  
D.E. DeVecchio ◽  
A.C. Whittaker ◽  
R.E. Bell ◽  
...  
Keyword(s):  
Southern California ◽  
Response Times ◽  
Tectonic Uplift ◽  
Reverse Fault ◽  
Slip Rates ◽  
Oak Ridge ◽  
Erosion Rates ◽  
Exposure Dating ◽  
Ventura Basin ◽  
Mountain Belts

The quantification of rates for the competing forces of tectonic uplift and erosion has important implications for understanding topographic evolution. Here, we quantify the complex interplay between tectonic uplift, topographic development, and erosion recorded in the hanging walls of several active reverse faults in the Ventura basin, southern California, USA. We use cosmogenic 26Al/10Be isochron burial dating and 10Be surface exposure dating to construct a basin-wide geochronology, which includes burial dating of the Saugus Formation: an important, but poorly dated, regional Quaternary strain marker. Our ages for the top of the exposed Saugus Formation range from 0.36 +0.18/−0.22 Ma to 1.06 +0.23/−0.26 Ma, and our burial ages near the base of shallow marine deposits, which underlie the Saugus Formation, increase eastward from 0.60 +0.05/−0.06 Ma to 3.30 +0.30/−0.41 Ma. Our geochronology is used to calculate rapid long-term reverse fault slip rates of 8.6−12.6 mm yr−1 since ca. 1.0 Ma for the San Cayetano fault and 1.3−3.0 mm yr−1 since ca. 1.0 Ma for the Oak Ridge fault, which are both broadly consistent with contemporary reverse slip rates derived from mechanical models driven by global positioning system (GPS) data. We also calculate terrestrial cosmogenic nuclide (TCN)-derived, catchment-averaged erosion rates that range from 0.05−1.14 mm yr−1 and discuss the applicability of TCN-derived, catchment-averaged erosion rates in rapidly uplifting, landslide-prone landscapes. We compare patterns in erosion rates and tectonic rates to fluvial response times and geomorphic landscape parameters to show that in young, rapidly uplifting mountain belts, catchments may attain a quasi-steady-state on timescales of <105 years even if catchment-averaged erosion rates are still adjusting to tectonic forcing.

10Be exposure dating of river terraces at the southern mountain front of the Dzungarian Alatau (SE Kazakhstan) reveals rate of thrust faulting over the past ~ 400 ka

2014 ◽  
Vol 81 (1) ◽  
pp. 168-178 ◽  
Author(s):  
Anja Cording ◽  
Ralf Hetzel ◽  
Martin Kober ◽  
Jonas Kley
Keyword(s):  
Slip Rate ◽  
Thrust Fault ◽  
Tien Shan ◽  
Slip Rates ◽  
Exposure Dating ◽  
River Terraces ◽  
Mountain Front ◽  
Mountain Belts ◽  
10Be Exposure Dating ◽  
Age Constraints

AbstractThe mountain belts of the Dzungarian Alatau (SE Kazakhstan) and the Tien Shan are part of the actively deforming India–Asia collision zone but how the strain is partitioned on individual faults remains poorly known. Here we use terrace mapping, topographic profiling, and 10Be exposure dating to constrain the slip rate of the 160-km-long Usek thrust fault, which defines the southern front of the Dzungarian Alatau. In the eastern part of the fault, where the Usek River has formed five terraces (T1–T5), the Usek thrust fault has vertically displaced terrace T4 by 132 ± 10 m. At two sites on T4, exposure dating of boulders, amalgamated quartz pebbles, and sand from a depth profile yielded 10Be ages of 366 ± 60 ka and 360 + 77/− 48 ka (both calculated for an erosion rate of 0.5 mm/ka). Combined with the vertical offset and a 45–70° dip of the Usek fault, these age constraints result in vertical and horizontal slip rates of ~ 0.4 and ~ 0.25 mm/a, respectively. These rates are below the current resolution of GPS measurements and highlight the importance of determining slip rates for individual faults by dating deformed landforms to resolve the pattern of strain distribution across intracontinental mountain belts.

Tectonically-dominated Quaternary landscape evolution of the Ventura basin, southern California, quantified using cosmogenic isotopes and topographic analyses

2020 ◽  
Author(s):  
Dylan Rood ◽  
Alex Hughes ◽  
Alex Whittaker ◽  
Rebecca Bell ◽  
Klaus Wilcken ◽  
...  
Keyword(s):  
Southern California ◽  
Landscape Evolution ◽  
Sedimentary Basins ◽  
Temporal Variations ◽  
Channel Morphology ◽  
Primary Control ◽  
Fault Activity ◽  
Erosion Rates ◽  
Ventura Basin ◽  
Channel Steepness

<p>Spatial and temporal variations in fault activity informs models of seismic hazards and can affect local patterns of relief generation and channel morphology. Therefore, the quantification of rates of fault activity has important applications for understanding natural hazards and landscape evolution. Here, we quantify the complex interplay among tectonic uplift, topographic development, and channel erosion recorded in the hanging walls of several seismically-active reverse faults in the Ventura basin, southern California, USA. We use cosmogenic <sup>26</sup>Al/<sup>10</sup>Be isochron burial dating to construct a basin-wide geochronology for the Saugus Formation: an important, but poorly dated, regional Quaternary strain marker. Our geochronology of the Saugus Formation is used to calculate tectonically-driven rock uplift rates and reduce uncertainties in fault-slip rates. In addition, we calculate <sup>10</sup>Be catchment-averaged erosion rates, characterise patterns of catchment relief and channel steepness indices, and analyse river long-profiles in fault hanging walls to compare with patterns of fault displacement rates averaged over various temporal scales.</p><p> </p><p>The results of the burial dating confirm that the Saugus Formation is time-transgressive with ages for the top of the exposed Saugus Formation of ~0.4 Ma in the western Ventura basin and ~2.5 Ma in the eastern Ventura basin. The burial ages for the base of shallow marine sands, which underlie the Saugus Formation throughout the basin, are ~0.6 Ma in the western Ventura basin and ~3.3 Ma in the eastern Ventura basin. The results of the landscape analysis indicate that relief, channel steepness, and erosion rates are still adjusting to tectonic boundary conditions imposed by different tectonic perturbations that have occurred at various times since ~1.5 Ma, which include fault initiation and fault linkage. The data presented here suggest that, for transient landscapes in sedimentary basins up to 2500 km<sup>2</sup>, where climate can be considered uniform, fault activity is the primary control on patterns of relief generation and channel morphology over periods of 10<sup>4 </sup>to 10<sup>6 </sup>years.</p>

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

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.

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

Geosphere ◽  
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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