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A response by R. D. Catchings and colleagues to a comment about their article "Near-Surface Location, Geometry and Velocities of the Santa Monica Fault Zone, Los Angeles, California," published in a 2008 issue is presented. The researchers contend that their study is not a duplicate of a previous study also conducted on the Santa Monica fault in Los Angeles, California. They stress that two near-surface strands exist in the Wadsworth Veterans Administration Hospital (WVAH). They conclude that the objections to their study that were raised are not valid.

The Mission Creek and Banning faults are two of the principal strands of the San Andreas fault zone in the northern Coachella Valley of southern California. Structural characteristics of the faults affect both regional earthquake hazards and local groundwater resources. We use seismic, gravity, and geological data to characterize the San Andreas fault zone in the vicinity of Desert Hot Springs. Seismic images of the upper 500 m of the Mission Creek fault at Desert Hot Springs show multiple fault strands distributed over a 500 m wide zone, with concentrated faulting within a central 200 m wide area of the fault zone. High-velocity (up to 5000 m/sec) rocks on the northeast side of the fault are juxtaposed against a low-velocity (< 2000 m/sec) basin on the southwest side within the upper few hundred meters. Near-surface strands of the Mission Creek fault dip steeply southwestward and northeastward and merge at depth to form a narrower, steeply southwestward-dipping or near-vertical (80° to 90°) fault zone. The Banning fault, in contrast, dips northeastward (45° to 70°) toward the Mission Creek fault, and the two faults likely merge into a single San Andreas fault zone at depth, indicating a transtensional fault system. Mainshock hypocenters for two of the historically largest (M > 6.0) earthquakes in the area (in 1948 and 1986) occurred at or near the depths (~10 to 12 km) of the merged (San Andreas) fault. Large-magnitude earthquakes that nucleate at or below the merged fault will likely generate strong shaking from guided waves along both fault zones and from amplified seismic waves in the low-velocity basin between the two fault zones. The Mission Creek fault zone is a groundwater barrier with the top of the water table varying by 60 m in depth and the aquifer varying by about 50 m in thickness across a 200 m wide zone of concentrated faulting. [ABSTRACT FROM AUTHOR]

To better understand the structure of the San Andreas fault (SAF) at Burro Flats in southern California, we acquired a three-dimensional combined set of seismic reflection and refraction profiles centered on the main active trace at Burro Flats. In this article, we discuss the variation in shallow-depth velocities along each seismic profile, with special emphasis on the 1500 m/sec P-wave velocity contour, which can be an indicator of shallow-depth water-saturated unconsolidated sediments. Along the four seismic profiles, minimum depths of the groundwater table, as inferred from 1500 m=sec velocity contour, range from 10 to about 20 m. The largest variations in depth to the top of the groundwater table occur in areas near mapped faults, suggesting that the groundwater flow in Burro Flats is strongly affected by the locations of fault traces. We also used the seismic data to develop seismic reflection images that show multiple strands of the SAF in the upper 60 m. Reflectors above the 10 m depth probably correspond to Holocene alluvial deposits; reflectors below the 15 m depth probably arise from velocity or density variations within the Precambrian gneiss complex, likely due to weathering. Apparent vertical offsets of reflectors are observed along profiles (lines 1 and 2) that are normal to the SAF, indicating minor apparent vertical offsets on the SAF at shallow depths. Along line 2, the apparently vertically offset reflectors correlate with zones of relatively low P-wave velocity. Along the central part of lines 1 and 2, the faults form a flower structure, which is typical of strike-slip faults such as the SAF. [ABSTRACT FROM AUTHOR]

High-resolution seismic-reflection and seismic-refraction imaging, combined with existing borehole, earthquake, and paleoseismic trenching data, suggest that the Santa Monica fault zone in Los Angeles consists of multiple strands from several kilometers depth to the near surface. We interpret our seismic data as showing two shallow-depth low-angle fault strands and multiple near-vertical (~85°) faults in the upper 100 m. One of the low-angle faults dips northward at about 28° and approaches the surface at the base of a topographic scarp on the grounds of the Wadsworth VA Hospital (WVAH). The other principal low-angle fault dips northward at about 20° and projects toward the surface about 200 m south of the topographic scarp, near the northernmost areas of the Los Angeles Basin that experienced strong shaking during the 1994 Northridge earthquake. The 20° north-dipping low-angle fault is also apparent on a previously published seismic-reflection image by Pratt et al. (1998) and appears to extend northward to at least Wilshire Boulevard, where the fault may be about 450 m below the surface. Slip rates determined at the WVAH site could be significantly underestimated if it is assumed that slip occurs only on a single strand of the Santa Monica fault or if it is assumed that the near-surface faults dip at angles greater than 20-28°. At the WVAH, tomographic velocity modeling shows a significant decrease in velocity across near-surface strands of the Santa Monica fault. P-wave velocities range from about 500 m/sec at the surface to about 4500 m/sec within the upper 50 m on the north side of the fault zone at WVAH, but maximum measured velocities on the south side of the low-angle fault zone at WVAH are about 3500 m/sec. These refraction velocities compare favorably with velocities measured in nearby boreholes by Gibbs et al. (2000). This study illustrates the utility of combined seismic-reflection and seismic-refraction methods, which allow more accurate reflection imaging and compositional estimations across areas with highly variable velocities, a property that is characteristic of most fault zones. [ABSTRACT FROM AUTHOR]

Competing Interests: The authors have declared that no competing interests exist.

This article focuses on the value and benefit of a Breast Center to an organization by identifying the best ways to maximize their contribution in order to create and sustain a financially viable, clinically respected and community-oriented Breast Center. The goal of the Breast Center is to ultimately benefit the community and the hospital's Comprehensive Cancer Program as a whole. The value propositions are divided into three areas that have positive impacts to the program and hospital, collectively. These value propositions are: 1. Financial Value e identified values of the Breast Center that contribute to the bottom line - or Return on Investment (ROI) - of the Cancer Program. 2. Clinical Quality Values - identified values of the Breast Center that improve the quality of care and outcomes of the patients. 3. Intangibles Values - identified values of the Breast Center that connect to the community and women that is invaluable to the Cancer Program., (2010 Elsevier Ltd. All rights reserved.)