Lithologic and ground-water data for monitoring wells in the Santa Clara-Calleguas ground-water basin, Ventura County, California, 1989-95

Densmore, Jill N.

doi:10.3133/ofr96120

Cited by 7 publications

(7 citation statements)

References 5 publications

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“…In some localities, such as along the coast west of Los Angeles, boreholes can show seasonal variations in water level by tens of metres, typically with minima in October and maxima (which can exceed local ground surface level) in April-June (see, e.g., Densmore, 1996). It thus appears that seasonal recharge of the water table in this area is being fed by seasonal rainfall, presumably concentrated in adjacent coastal mountain ranges, and thus follows the seasonal rainfall pattern, albeit with some time lag.…”

Section: Late Spring Seismicity In Northern Japan Caused By Winter Snmentioning

confidence: 99%

“…It thus appears that seasonal recharge of the water table in this area is being fed by seasonal rainfall, presumably concentrated in adjacent coastal mountain ranges, and thus follows the seasonal rainfall pattern, albeit with some time lag. Conversely, in more inland areas, the water table may be >100 m below ground level, although well above sea-level, but shows only minimal seasonal variations (see, e.g., Densmore, 1996). It presumably provides the pressure head that drives subsurface flow towards the coastal areas.…”

Section: Late Spring Seismicity In Northern Japan Caused By Winter Snmentioning

confidence: 99%

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Investigation of coupling between surface processes and induced flow in the lower continental crust as a cause of intraplate seismicity

Westaway

2006

Earth Surf Processes Landf

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Many studies have highlighted the role of coupling between surface processes and flow in the lower continental crust in deforming the crust and creating topographic relief over Quaternary timescales. On the basis of the rheological knowledge gained, it is suggested that intraplate seismicity can also be caused by coupling between surface processes and flow in the lower continental crust. This view is shown to be a natural consequence of the modern idea that isostatic equilibrium is maintained by flow in the weak lower crust in response to erosion and sedimentation. It is supported by a general correlation between the vigour of surface processes and rates of intraplate seismicity, and by instances of seasonal seismicity that correlates with seasonal climate. Human interference in the environment can affect surface loading: for instance, deforestation for agriculture or urban development can cause increased erosion rates; global warming is expected to cause increased storminess (and thus increased erosion rates) and/or global sea-level rise. The possibility of increased rates of seismicity resulting from these processes should thus be considered in future hazard assessment.Surface processes as a cause of intraplate seismicity Figure 1. (a) Graph of estimated temperature T against depth z for the Palaeozoic continental crust beneath the Atlantic Coastal Plain (ACP) of South Carolina. Calculations use T , e.g., Lachenbruch, 1970), where T 0 is the mean surface temperature, K is the thermal conductivity of the crust, A 0 and D are the surface radiogenic heat production and its scale depth, and q 0 is the heat flow at the base of the lithosphere. T 0 is set to 20°C (cf. Bollinger et al., 1985). Values of K (3·29 W m −1°C−1 ) and A 0 (2·70 µW m −3 ) are from the borehole at Springfield, SC, ~150 km NW of Charleston. D = 8 km (typical for the ACP); q 0 is set to 48·5 mW m −2 (close to the 48·2 mW m −2 typical for the ACP) to give the observed surface heat flow at Springfield of 70·1 mW m −2 . All these geothermal data are from Costain et al. (1986). This calculated geotherm roughly matches the local ~15 km depth limit of seismicity (with 90 per cent of events shallower than 13 km), which is thought to represent thẽ 300°C isotherm (see, e.g., Bollinger et al., 1985), and indicates a Moho temperature (for 35 km depth) of 588°C. Extrapolated, it predicts the ~1400°C asthenosphere temperature at ~90 km depth, a conservative value given the ~80 km lithosphere thickness from seismic tomography (van der Lee, 2002). (b) Predicted variation of viscosity η with depth z across this lower crust, which from (a) is taken as spanning 15-35 km depth. η is calculated as η = η L exp(G/RT) (Westaway, 1998), where R is the molar gas constant (8·3143 J K −1 mol −1 ) and T(z) is the temperature predicted at each depth in (a). G (150 kJ mol −1 ) and η L (6·67 × 10 7 Pa s) parametrize the lower-crustal rheology (see Table I). Figure 2.Diagram illustrating an eroding region that provides the sediment source for an adjacent depocentre, with isost...

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Section: Late Spring Seismicity In Northern Japan Caused By Winter Snmentioning

confidence: 99%

Section: Late Spring Seismicity In Northern Japan Caused By Winter Snmentioning

confidence: 99%

Investigation of coupling between surface processes and induced flow in the lower continental crust as a cause of intraplate seismicity

Westaway

2006

Earth Surf Processes Landf

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“… 1 Electromagnetic flowmeter log. Production well–construction data from Pleasant Valley County Water District. Observation well–construction data from Densmore, 1996; —, no data; dates expressed as mm/yy or dd/mm/yy. Unless indicated flowmeter data were collected using an impeller‐type tool. …”

Section: Approachmentioning

confidence: 99%

Temporal Changes in the Vertical Distribution of Flow and Chloride in Deep Wells

Izbicki¹,

Christensen

Newhouse

et al. 2005

Groundwater

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The combination of flowmeter and depth-dependent water-quality data was used to evaluate the quantity and source of high-chloride water yielded from different depths to eight production wells in the Pleasant Valley area of southern California. The wells were screened from 117 to 437 m below land surface, and in most cases, flow from the aquifer into the wells was not uniformly distributed throughout the well screen. Wells having as little as 6 m of screen in the overlying upper aquifer system yielded as much as 50% of their water from the upper system during drought periods, while the deeper parts of the well screens yielded 15% or less of the total yield of the wells. Mixing of water within wells during pumping degraded higher-quality water with poorer-quality water from deeper depths, and in some cases with poorer-quality water from the overlying upper aquifer system. Changes in the mixture of water within a well, resulting from changes in the distribution of flow into the well, changed the quality of water from the surface discharge of wells over time. The combination of flowmeter and depth-dependent water quality data yielded information about sources of high-chloride water to wells that was not available on the basis of samples collected from nearby observation wells. Changing well design to eliminate small quantities of poor-quality water from deeper parts of the well may improve the quality of water from some wells without greatly reducing well yield.

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“…Results of water-quality analyses were presented by Izbicki and others (1995). Test-drilling, wellconstruction, and aquifer mineralogy data were presented by Densmore (1996). Additional data on aquifer mineralogy were presented by CH2M-Hill (1992).…”

Section: Data Collection and Approachmentioning

confidence: 99%

Use of isotopic data to evaluate recharge and geologic controls on the movement of ground water in Las Posas Valley, Ventura County, California

Izbicki¹,

Martin²

1997

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Injection, storage, and recovery of imported water is planned for aquifers underlying Las Posas Valley. To evaluate sources of groundwater recharge and the age of the water (time since recharge), and to identify barriers to groundwater flow prior to the injection of imported water, samples from wells and surface sources were collected and analyzed for chemical and isotopic composition. The delta oxygen-18 (818O) and delta deuterium (8D) composition in almost 50 samples from 32 wells ranged from-6.0 to-7.9 per mil, and-40 to-60 per mil, respectively; and in 13 samples of surface water at 6 sites the composition ranged from-6.2 to-9.4 per mil, and-42 to-71 per mil, respectively. Water from wells in the upper aquifer system near Arroyo Simi and Arroyo Las Posas (different reaches of the same stream) was isotopically lighter than water from other wells sampled and was similar in isotopic composition to water in the stream. Water in the stream is a mixture of local water and imported water from northern California that was discharged to the stream as treated municipal wastewater. Water from wells near the stream contained tritium and, therefore, was recharged less than 50 years ago. Water from wells in other parts of the valley was isotopically heavier, did not contain tritium, and, therefore, was recharged more than 50 years ago. Interpreted carbon-14 ages for water from wells along a flow path through the valley ranged from at least 800 to more than 8,000 years before present. There were large differences in the chemistry, isotopic composition, and interpreted age of water from wells between the eastern and western parts of Las Posas Valley. These changes are consistent with geologic and hydrologic data that suggest the presence of a barrier to groundwater flow between east and west Las Posas Valley.

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Lithologic and ground-water data for monitoring wells in the Santa Clara-Calleguas ground-water basin, Ventura County, California, 1989-95

Cited by 7 publications

References 5 publications

Investigation of coupling between surface processes and induced flow in the lower continental crust as a cause of intraplate seismicity

Investigation of coupling between surface processes and induced flow in the lower continental crust as a cause of intraplate seismicity

Temporal Changes in the Vertical Distribution of Flow and Chloride in Deep Wells

Use of isotopic data to evaluate recharge and geologic controls on the movement of ground water in Las Posas Valley, Ventura County, California

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