Geology topics

Research about Palmdale, California

Source-linked reports with geographic coverage including Palmdale, California.

6 recordsLinked to original sources

USGS2021

Late Holocene slip rate of the Mojave section of the San Andreas Fault near Palmdale, California

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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USGS2015

Feasibility and potential effects of the proposed Amargosa Creek Recharge Project, Palmdale, California

Historically, the city of Palmdale and vicinity have relied on groundwater as the primary source of water, owing, in large part, to the scarcity of surface water in the region. Despite recent importing of surface water, groundwater withdrawal for municipal, industrial, and agricultural use has resulted in groundwater-level declines near the city of Palmdale in excess of 200 feet since the early 1900s. To meet the growing water demand in the area, the city of Palmdale has proposed the Amargosa Creek Recharge Project (ACRP), which has a footprint of about 150 acres along the Amargosa Creek 2 miles west of Palmdale, California. The objective of this study was to evaluate the long-term feasibility of recharging the Antelope Valley aquifer system by using infiltration of imported surface water from the California State Water Project in percolation basins at the ACRP. Three monitoring sites were constructed, and geophysical surveys (gravity, seismic, and resistivity) were completed to define the thickness of valley-fill deposits, depth to water, and location of faults that could influence groundwater flow. Data collected at the monitoring sites, and results from the geophysical surveys, were used to identify three northwest-southeast trending faults in the vicinity of the proposed recharge facility; these faults are probably related to the nearby San Andreas fault zone. Water levels collected from wells at the monitoring sites showed water-level altitude differences as much as 230 feet between the upgradient and downgradient sides of the faults, indicating that these faults are barriers to groundwater flow. Lithologic and geophysical logs indicated the presence of a coarse gravel and sand unit extending from land surface to about 150 feet below land surface that did not appear to be disrupted by faulting. Water samples collected from the monitoring wells were analyzed for major ions, nutrients, trace elements, dissolved organic carbon, volatile organic compounds, stable isotopes of oxygen (oxygen-18) and hydrogen (hydrogen-2, or deuterium), and the radioactive isotopes of hydrogen (hydrogen-3, or tritium) and carbon (carbon-14, or 14 C) to determine the water quality of the aquifer system and to help determine the source and age of the groundwater. Results of the water-quality analysis indicated that the source of natural recharge is Amargosa Creek near the ACRP, but that the creek does not provide modern-day recharge downstream of the ACRP. Potential effects of artificial recharge at the ACRP were evaluated by using a local-scale model of groundwater flow. On the basis of geologic samples collected during drilling, the hydraulic conductivity of the sand and gravel unit in the upper 150 feet was assumed to range from 10 to 100 feet per day. To address the goal of minimizing the potential for liquefaction during an earthquake from water-table rise associated with groundwater recharge at the ACRP, simulated water levels were constrained to remain at least 50 feet below land surface, except beneath the proposed artificial-recharge facility. The hydraulic conductivities of faults were estimated on the basis of water-level data and an estimate of natural recharge along Amargosa Creek. With assumed horizontal hydraulic conductivities of 10 and 100 feet per day in the upper 150 feet, the simulated maximum artificial recharge rates to the regional flow system at the ACRP were 3,400 and 9,400 acre-feet per year, respectively. These maximum recharge rates were limited primarily by the horizontal hydraulic conductivity in the upper 150 feet and by the liquefaction constraint. Future monitoring of water-level and soil-water content changes during the proposed project would allow improved estimation of aquifer hydraulic properties, the effect of the faults on groundwater movement, and the overall recharge capacity of the ACRP.

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USGS1982

Observations of strain accumulation across the San Andreas fault near Palmdale, California, with a two-color geodimeter

Two-color laser ranging measurements during a 15-month period over a geodetic network spanning the San Andreas fault near Palmdale, California, indicate that the crust expands and contracts aseismically in episodes as short as 2 weeks. Shear strain parallel to the fault has accumulated monotonically since November 1980, but at a variable rate. Improvements in measurement precision and temporal resolution over those of previous geodetic studies near Palmdale have resulted in the definition of a time history of crustal deformation that is much more complex than formerly realized.

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USGS1981

Strain on the San Andreas fault near Palmdale, California: Rapid, aseismic change

Frequently repeated strain measurements near Palmdale, California, during the period from 1971 through 1980 indicate that, in addition to a uniform accumulation of right-lateral shear strain (engineering shear, 0.35 microradian per year) across the San Andreas fault, a 1-microstrain contraction perpendicular to the fault that accumulated gradually during the interval 1974 through 1978 was aseismically released between February and November 1979. Subsequently (November 1979 to March 1980), about half of the contraction was recovered. This sequence of strain changes can be explained in terms of south-southwestward migration of a slip event consisting of the south-southwestward movement of the upper crust on a horizontal detachment surface at a depth of 10 to 30 kilometers. The large strain change in 1979 corresponds to the passage of the slip event beneath the San Andreas fault.

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USGS1979

Magnitude of shear stress on the San Andreas fault: Implications of a stress measurement profile at shallow depth

A profile of measurements of shear stress perpendicular to the San Andreas fault near Palmdale, California, shows a marked increase in stress with distance from the fault. The pattern suggests that shear stress on the fault increases slowly with depth and reaches a value on the order of the average stress released during earthquakes. This result has important implications for both long- and short-term prediction of large earthquakes.

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USGS1978

Earthquake swarm along the San Andreas fault near Palmdale, Southern California, 1976 to 1977

Between November 1976 and November 1977 a swarm of small earthquakes (local magnitude ≤ 3) occurred on or near the San Andreas fault near Palmdale, California. This swarm was the first observed along this section of the San Andreas since cataloging of instrumental data began in 1932. The activity followed partial subsidence of the 35-centimeter vertical crustal uplift known as the Palmdale bulge along this "locked" section of the San Andreas, which last broke in the great (surface-wave magnitude = 8¼;+) 1857 Fort Tejon earthquake. The swarm events exhibit characteristics previously observed for some foreshock sequences, such as tight clustering of hypocenters and time-dependent rotations of stress axes inferred from focal mechanisms. However, because of our present lack of understanding of the processes that precede earthquake faulting, the implications of the swarm for future large earthquakes on the San Andreas fault are unknown.

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