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A 250-km-long broadband and long-period (0.01–20,000 s periods) magnetotelluric (MT) line along latitude 40½°N spans from the California-Nevada border at longitude 120°W across the buried extension of the northern Sierra Nevada, the southern Cascades arc, and the subducting Gorda plate to longitude 123°W. The resulting resistivity cross section reveals conductors at the locations of dewatering of the subducting metasomatized crust at 100 km depth, partial melting of the mantle wedge at 40–60 km depth, and melting in the crust shallower than 40 km. The conductor at 100 km is too conductive (8 S/m) to result solely from magma; very conductive fluids must be present either separately or incorporated into hydrous melts. A melt fraction of 7% is estimated for the mantle wedge (average conductivity is 0.06 S/m). Sites of Pleistocene and Holocene volcanism at Lassen Peak, Hat Creek, and Poison Lake are closely associated with crustal conductors inferred to be shallow magma. The MT study also reveals presumably basaltic magma at 40–50 km depth in the upper mantle where the eastern end of the profile extends into the Basin and Range province.

A magnetotelluric profile consisting of 14 sites and spanning 240 km from the San Joaquin Valley to the Nevada border was installed across the central Sierra Nevada, through Yosemite National Park, in an effort to constrain the northward extent of lithospheric removal beneath the range. Broadband and long-period instruments from the EMSOC (Electromagnetic Studies of the Continents) consortium were used to record data with periods ranging from 0.01 to 20,000 s, allowing the conductivity structure beneath the Sierra to be imaged to a depth of 120 km. Two-dimensional models reveal that the batholith9s resistive root extends to a depth of just 30 km beneath the eastern Sierra and 45 km beneath the western Sierra. The batholith is separated by a thin conductive zone that coincides with the Moho from a resistive mantle structure at a depth of ∼55 km. We propose that this resistive structure is residual root. Deeper, a broad conductive feature dipping eastward at depths of 65–100 km below the range is upwelling asthenosphere containing 21% melt that originates from the extensional tectonic regime of the Basin and Range to the east.

The comment by Varotsos and Uyeda (2008) (VU hereafter) does not have much to do with our article, which reports electromagnetic data and their implications prior to, during, and following the 2004 M 6 Parkfield earthquake (EQ). In fact, our article did not include any extensive discussion of the possible flaws in the seismic electric signal (SES) approach to EQ prediction. The four main points VU discuss in their comment are from a summary sentence in the introduction that is preceded by the phrase “controversy about these (SES) results exists because (1), ... (2) ... (4),” where (1)–(4) are the specific points that VU list. We respond to each of these points in the following discussion. A final comment made by VU concerns our observation that SES-type signals are not seen in the data that we have. We could have provided more detailed evidence about the lack of SES in the months preceding the earthquake but see little point in including long data plots that show nothing. Note that all of these data are freely available from the Northern California Earthquake Data Center (NCEDC, www.ncedc.org, last accessed October 2007). In our article, we presented null results from sites above the Parkfield EQ rupture without extrapolating to the conclusion that SESs do not exist anywhere. In fact, Park et al. (2007) report additional data from 10–20 km lines over the entire region that also show no evidence for SES-type signals preceding the Parkfield EQ. Such signals were also not seen in 16 yr of previous monitoring with these lines (Park, 1991, 1997). Furthermore, no signals were seen in 2 yr of data on 10 km lines both along and within the fault and orthogonal to the fault a little farther to the north (Johnston, 1989). To suggest that all of these observations resulted from an …

An array designed to detect changes of resistivity in the upper 10 km of the crust has been in continuous operation since 1988. Long period ( T =300–7200 s) telluric signals are recorded digitally on 5–16 km long dipoles. Telluric transfer functions are computed between field dipoles and two reference dipoles and then decomposed to examine daily fluctuations of those functions. Based on analysis of these daily fluctuations, stabilities of 0.1–0.3% are achieved. No intermediate term resistivity changes are seen associated with any of the 5 M b >4.0 earthquakes that have occurred since 1989. Short term fluctuations are seen associated with most of these earthquakes, however. Minimum bounds on resistivity changes that could have caused the fluctuations in the telluric responses range from 1.7 to 13.0%. While these are within the ranges seen in other field studies, the statistical significance of these fluctuations is low because they also occur at many times that cannot be correlated to earthquakes. Comparison of the one potential resistivity change associated with a strain change results in a strain sensitivity that is unrealistically high. This possible resistivity change coincides spatially with a temporary variation in seismic travel time in May–June 1989, however. It is likely that many of the fluctuations in the telluric responses are random variations except for the one in 1989, and recording through the next M∼6 earthquake will be needed in order to detect a statistically significant resistivity change.

Within the syntaxial bends of the India-Asia collision the Himalaya terminate abruptly in a pair of metamorphic massifs. Nanga Parbat in the west and Namche Barwa in the east are actively deforming antiformal domes which expose Quaternary metamorphic rocks and granites. The massifs are transected by major Himalayan rivers (Indus and Tsangpo) and are loci of deep and rapid exhumation. On the basis of velocity and attenuation tomography and microseismic, magnetotelluric, geochronological, petrological, structural, and geomorphic data we have collected at Nanga Parbat we propose a model in which this intense metamorphic and structural reworking of crustal lithosphere is a consequence of strain focusing caused by significant erosion within deep gorges cut by the Indus and Tsangpo as these rivers turn sharply toward the foreland and exit their host syntaxes. The localization of this phenomenon at the terminations of the Himalayan arc owes its origin to both regional and local feedbacks between erosion and tectonics.

Petrographic studies of peridotitic xenoliths entrained in late Quaternary basalts from beneath the southern Sierra Nevada have revealed the presence of accessory sulfide minerals along grain boundaries and fractures. Equilibration temperatures from the xenoliths are sufficiently high that the molten sulfides coexist with the basaltic melt. Sulfides are extremely conductive relative to the solid matrix or the basaltic melt, so a small fraction can increase the bulk conductivity of the mantle appreciably. Previous estimates of 2–5% partial melt from magnetotelluric measurements can be plausibly reduced to less than 1%. Such low melt percentages have longer residence times in the mantle and are more consistent with the volumetrically minor late Quaternary basalt flows and the primitive basalt compositions.

Conductivity models beneath the Nanga Parbat Haramosh Massif (NPHM) derived from magnetotelluric soundings reveal that there is no widespread, interconnected, conductive aqueous fluid to minimum depths of 40 km below sea level. Given the continuing tectonic denudation, young granitic and migmatitic bodies indicating partial melt at shallow crustal depths, and active seismicity, this result is surprising in light of similar studies in active tectonic regimes elsewhere. Away from the NPHM, models reveal the usual conductive lower crust. We propose that deep magmatic and metamorphic fluids are produced beneath NPHM in isolated zones but that the active deformation permits their escape through the brittle–ductile transition. A magnetotelluric survey in an area as complicated as Nanga Parbat required the development of methodologies for utilizing standard two-dimensional inversions in a three-dimensional environment. We show here how to identify which parts of the magnetotelluric responses are adequately represented with two-dimensional approximations. Unlike previous efforts, we do not attempt to create a set of generic rules that may be applicable to all geologic environments. Instead, a procedure is outlined that can be tailored to each interpretation. One important result of this work is that magnetotelluric data along a profile can be used to constrain structure off the ends of the profile.

A new model of the average shear-wave velocity in the uppermost 30 m has been generated by extrapolation of discrete velocity profiles using surface geology at several scales. Statistical methods have been applied to create a map that is no more complicated than is supported by the velocity data; several geologic units with similar responses are grouped together. The resulting map is simpler than previous ones and yet fits the observed velocity profiles better than earlier, more complicated maps. Analysis within a geographic information system will permit updates and modification of the map as new velocity data are added.

The movement of a small plume of fresh water through the vadose zone was monitored using surface resistivity tomography and pole‐pole potential measurements. Sets of potential measurements on a square grid at several times throughout the experiment show gradual, progressive, and systematic development of low‐resistivity zones that are inferred to be loci of fluid concentration. A procedure for inverting percentage changes in potentials is developed here and used to map maximum potential changes of 13% into resistivity decreases of up to 40% through 3-D resistivity inversion. The resulting patterns are complex, with both resistivity increases and decreases needed to match the observed data. The resistivity reductions show a spatial connection to the plume’s source and are suggestive of the fluid migration. Resistivity increases generally appear to form rims surrounding the decreases and may be artifacts of the inversion process. However, some isolated increases in the surface layer may be caused by evaporation of fluid from previous precipitation events. Interpretation of the complex patterns may limit the usefulness of this method for monitoring fluid migration. Nonetheless, the resulting pattern of resistivity reductions may show details of fluid migration that are unavailable with more conventional monitoring techniques. In this experiment, comparison of the volume with reduced resistivity with the volume of injected water predicts only a 0.5% increase in saturated porosity, demonstrating that fluid flow in the vadose zone was most likely controlled by the distribution of fine‐grained clays and silts and occurred by capillary action.

Continuous electric field measurements from 1988–1995 with a telluric array straddling the San Andreas fault in Parkfield, California have been analyzed for changes in electrical resistivity associated with the four largest (Mb>4.0) local earthquakes and three larger but more distant California earthquakes (1989 Loma Prieta, 1992 Landers, 1994 Northridge). Treatment of the propagation of errors through the analysis process yields formal estimates of the uncertainties in the results and thus a definition of anomalous variations based on statistical confidence. Statistically significant variations of the telluric coefficients were associated with none of the four local earthquakes and none of the California earthquakes. An obvious, but mistaken, conclusion from this disappointing result is that resistivity changes do not occur prior to earthquakes; previous observations in both the field and laboratory have shown that they do occur. A more likely explanation of the current result is that the telluric array is not sufficiently sensitive to resistivity changes associated with such small earthquakes. The next Parkfield earthquake, while overdue, should be of sufficient magnitude to test this explanation. Results from this experiment have shown the need for continuous, redundant measurements in precursory monitoring studies.

A magnetotelluric survey in northern Pakistan contains effects from both 2-D and 3-D structure. Identification of the effects of the sediments along the Indus River valley using 3-D modeling permitted the selection of modes that could be accurately inverted with 2-D inversions. The resulting 2-D model reveals generally resistive (> 500 ohm-m) upper crust (0–8 km), a more conductive (30–50 ohm-m) middle to lower crust (8–40 km), and a resistive (> 300 ohm-m) upper mantle. Shallow crustal (< 10 km) conductors correlate with a hydrothermally altered fault zone and/or carbonaceous metamorphic rocks near the Raikot fault. A prominent midcrustal conductor located beneath Nanga Parbat is required to fit the data, but its depth, dimensions, and conductivity are poorly constrained by existing data.

Frequency domain experiments (FDEs) were introduced to perform system sensitivity analysis for factor screening in complex simulations. Since then, FDEs have been used in simulation optimization, gradient estimation and several other research areas. Central to all FDEs is the Fourier analysis of a sampled data sequence. The choice of an appropriate oscillation index and associated sampling index for the sampled data sequence has been a much researched topic now known in the FDE literature as the indexing problem. In this paper we address the indexing problem by providing some general guidelines on the selection of the oscillation index and considering the implementation of two different indices: the continuous global simulation clock time and an inherently discrete index such as the job index in a simple queuing system. We show that the choice of a discrete oscillation index has to be made in an application-dependent manner and does not generalize well to different discrete-event simulation scenarios. In contrast, because the notion of time underlies all discrete-event simulations, the global simulation clock time is a natural choice for an FDE indexing scheme. Two different schemes for the global simulation clock time are presented. The results are illustrated via different scenarios commonly found in simulations of queuing networks and manufacturing systems.

Image restoration of forward-looking infrared (FLIR) imagery has the potential to significantly improve the quality of image used by an automatic target recognizer (ATR) or human observer. This study investigates the feasibility of real-time image restoration algorithms and the problem of measuring image quality as it relates to target acquisition performance. This paper describes a technique for deriving small kernel filters that efficiently restore and reconstruct. Subject to implementation constraints associated with efficient application, the filters optimize image fidelity to an ‘ideal’ close-range image. The paper describes simulation experiments employing an end-to-end imaging system model, experiments with actual images using a model-based characterization of an actual imaging system, and simulation experiments that illustrate the utility of the system model and filtering in FLIR imaging system design.

The San Jacinto Basin is a northwest‐trending, pull‐apart basin in the San Jacinto fault zone of the San Andreas fault system in southern California. About 24 km long and 2 to 4 km wide, the basin sits on a graben bounded by two strands of the San Jacinto fault zone: the Claremont Fault on the northeast and the Casa Loma Fault on the southwest. We present a case study of shallow structure (less than 1 km) in the central basin. A 2.75-km refraction line running from the northeast to southwest across the regional structural trend reveals a groundwater barrier (Offset I). Another line, bent southward and continued for 1.65-km, shows a crystalline basement offset (Offset III) near an inferred trace of the Casa Loma Fault. Although a basement refractor was not observed along the 2.75-km line, a mismatch between the estimate of its minimum depth and the basement depth determined for the 1.65-km line suggests that an offset in the basement (greater than 260 m) exists around the junction of the two refraction lines (Offset II). By revealing more faults and subtle sedimentary structures, the reflection stack sections confirm the two refraction offsets as faults. Offsets I and III each separate sediments of contrasting structures and, in addition, Offset III disrupts an unconformity. However, the sense and amount of the offset across Offset III contradict what may be expected across the Casa Loma Fault, which has its basinward basement down‐thrown to about 2.5 km in the better defined southeastern part of the graben. The Casa Loma Fault trace has been mislinked in the existing geological maps and the trace should be remapped to Offset II where the reflector disruptions spread over a 400-m wide zone. Our Offset III is an unnamed, concealed fault.

Band-limited magnetotelluric measurements were collected at several sites across a wide area in the California Basin and Range and northern Mojave Desert from early 1988 until March 1989. Due to the large spacing between sites and the limited frequency range of the data, there are limits to what the data can resolve. However, a three-dimensional (3-D) magnetotelluric modeling study and sensitivity analysis of a subset of the data support the following conclusions. (1) Electrical currents from the Pacific Ocean are channelled across the western Mojave Desert and into the southern Basin and Range. (2) The 3-D geometry of the basins significantly influences the fit to the data mode aligned along the strike of the basins (transverse electric mode). (3) The lower crust in the California Basin and Range is more conductive than the lower crust under the Mojave Desert and Pacific Ocean. The resistivity values we modeled for the lower crust in the California Basin and Range, though inconsistent with mineral semiconduction, can be explained by electrical conduction through small amounts of saline fluids.

A wideband (0.01–1000 s) magnetotelluric survey across the southern Sierra Nevada has identified zones of enhanced conductivity in the lower crust and upper mantle that underlie the resistive batholithic rocks at depths greater than 10–20 km. The eastern zone underlies the highest topography of the range and extends eastward. This eastern conductive zone extends to depths in excess of 100 km, based on model sensitivities, and lies well below the Moho depth of 32–38 km from seismological studies. Therefore the enhanced conductivity in the mantle cannot be attributed to conventional explanations for conductive continental crust and is instead likely due to partial melt. Such an interpretation is consistent with gravitational, seismological, and geologic evidence. Estimates of the partial melt fraction range from 2 to 5% at depths of 40–70 km, which are consistent with fractions of melt inclusions observed in xenoliths from the eastern Sierra Nevada. This partial melt accounts for approximately one third of the density decrease required in the mantle for support of the present high elevations. The other two thirds of the density decrease could be due to thermal expansion of the upper mantle or due to mineralogical changes. The western conductive zone also straddles the Moho and extends into the mantle beneath western foothills of the Sierra Nevada and the Great Valley sediments to the west. However, xenoliths from this region indicate high-velocity crustal rocks to depths in excess of 60 km, and we therefore attribute the enhanced conductivity to graphitic metasediments and/or dehydration of metaserpentinite emplaced by downward return flow of the host rocks during intrusion of the Sierran plutons.

Field measurements in the past several years have documented electromagnetic signals which are attributed to precursory stress and strain changes which were followed ultimately by earthquakes. Precursory electric field changes observed in Greece on multiple dipoles have been used to issue earthquake predictions. While the source of these signals is still unknown, a sufficient number of predictions has been issued to allow some, but not all, statistical analyses to show this method is better than randomly sampling the earthquake catalog. Ongoing efforts to identify the sources of both these signals and the magnetic field variations prior to the Loma Prieta earthquake are focusing on electrokinetic coupling of fluid flow and transient electric fields. A mechanism related to local fluid flow appears to be best suited at this time of explaining the variety of purported precursors. However, much more work is needed to improve the observations and refine the models of precursor generation. Efforts to monitor magnetotelluric transfer functions at longer periods (T>10s) have been hampered by variability of the functions. The use of modern noise reduction techniques such as remote referencing should reduce this variability, but may not reduce errors to a level needed for monitoring. Monitoring of high frequency (81 kHz) seismoelectric emissions may be promising, but lack of simultaneous observations on multiple instruments hinders the utility of this technique.

A statistical test of the VAN method compares its prediction rate (number of successful predictions divided by the total number of predictions issued) between 1987 and 1989 to that from randomly sampling the earthquake catalog. Unlike previous tests, this one samples distributions derived from the historic spatial and magnitude distribution between 1960 and 1985. The VAN method yields a prediction rate of 67.9% at a time delay of 22 days, which is achievable in less than 0.06% (P-value ≤ 0.06%) of the realizations in randomly sampling the full NEIC catalog (37.2% mean prediction rate). VAN's prediction rate drops to 66.7% with aftershocks removed from the catalog and prediction list, which is still significant at a p-value of less than 0.1%. With an alternate aftershock model, the prediction rate drops to 48.0%. This latter value is significant only for P-values less than 7.96%. We conclude from these tests that the VAN method is formally significant at a time lag of 22 days.

Active and passive seismic experiments show that the southern Sierra, despite standing 1.8 to 2.8 kilometers above its surroundings, is underlain by crust of similar seismic thickness, about 30 to 40 kilometers. Thermobarometry of xenolith suites and magnetotelluric profiles indicate that the upper mantle is eclogitic to depths of 60 kilometers beneath the western and central parts of the range, but little subcrustal lithosphere is present beneath the eastern High Sierra and adjacent Basin and Range. These and other data imply the crust of both the High Sierra and Basin and Range thinned by a factor of 2 since 20 million years ago, at odds with purported late Cenozoic regional uplift of some 2 kilometers.

Three high-resolution seismic reflection lines were acquired in the northern part of the San Jacinto graben. The graben, a pull-apart basin formed by a dilational right step of the San Jacinto fault zone, has been previously interpreted as a simple rhombochasm. The reflection survey located at least one significant and previously unidentified intrabasin fault, referred to here as the Farm Road strand. This fault lies approximately halfway between the Claremont and Casa Loma strands of the San Jacinto fault zone. At the north end of the basin, the southwestern boundary of the graben is interpreted to be the newly identified Farm Road strand and not the Casa Loma strand as was previously thought. The identification of this intrabasin fault allows us to infer that the San Jacinto basin comprises coalescing subbasins and is not a simple pull-apart basin with an unusually large length:width ratio. The distances between the en echelon Casa Loma, Farm Road, and Claremont strands are between 1 and 2 km. This close spacing would likely permit an earthquake rupture to jump between strands and thus propagate through the San Jacinto basin.

Despite over 2 decades of international and national monitoring of electrical signals with the hope of detecting precursors to earthquakes, the scientific community is no closer to understanding why precursors are observed only in some cases. Laboratory measurements have demonstrated conclusively that self potentials develop owing to fluid flow and that both resistivity and magnetization change when rocks are stressed. However, field experiments have had much less success. Many purported observations of low-frequency electrical precursors are much larger than expectations based on laboratory results. In some cases, no precursors occurred prior to earthquakes, or precursory signals were reported with no corresponding coseismic signals. Nonetheless, the field experiments are in approximate agreement with laboratory measurements. Maximum resistivity changes of a few percent have been observed prior to some earthquakes in China, but the mechanism causing those changes is still unknown. Anomalous electric and magnetic fields associated with fluid flow prior to earthquakes may have been observed. Finally, piezomagnetic signals associated with stress release in earthquakes have been documented in measurements of magnetic fields.

This paper is a 1-D analysis of the degradation caused by image sampling and interpolative reconstruction. The analysis includes the sample-scene phase as an explicit random parameter and provides a complete characterization of this image degradation as the sum of two terms: one term accounts for the mean effect of undersampling (aliasing) and nonideal reconstruction averaged over all sample-scene phases; the other term accounts for variations about this mean. The results of this paper have application to the design and performance analysis of image scanning, sampling, and reconstruction systems.

The quality of image reconstructions from discrete data suffers not only from the blurring of spatial detail caused by limitations in the spatial frequency response of electrooptical systems, but also from the aliasing generated if spatial detail has been undersampled. P. Mertz and F. Grey [Bell Syst. Tech. J. 13, 464 (1934)] and O. H. Schade [J. Soc. Motion Pict. Telev. Eng. 56, 131 (1955); 58, 181 (1952); 61, 97 (1953); 64, 593 (1955)] have observed that reasonable spot intensity profiles and photosensor aperture shapes of equivalent size result in about equal blurring but that some profiles and shapes suppress aliasing better than others. This paper presents quantitative results of the magnitude of aliasing and blurring as a function of random radiancefields typical for natural scenes and of spatial responses and sampling intervals typical for TV cameras and optical-mechanical scanners. These results indicate that aliasing may often be a larger source of degradation than either blurring or electronic noise.

A technique is presented for estimating spectral reflectance curves from multispectral image data even if the spectral samples are obtained from channels whose spectral responsivity is not narrowband. It is demonstrated that these reflectance estimates can be written as a linear combination of the spectral samples and that, analogous to Shannon's sampling theorem, if the spectral reflectance is a natural cubic spline, it can be estimated exactly provided the number of spectral channels is sufficiently large. Simulation results suggest that the accuracy of the spectral reflectance estimates is quite good and very insensitive to the spectral responsivity shapes.

A magnetotelluric traverse of the Peninsular Ranges in southern California has revealed a pervasive zone of lower resistivity beginning at a uniform depth of 10 km and extending to depths of 60–90 km. Resistivities above 10 km depth are similar to those found in batholiths; very high values correspond to outcrops of crystalline basement. Because seismicity below 11–12 km is sparse, others have concluded that the brittle-ductile transition is shallow beneath the range. The zone of low resistivity in the lower crust corresponds well to the ductile region, and we conclude that the lower values are caused by fluids trapped below the transition. Because the range has experienced vertical uplifts during the Pliocene era and the top of the low resistivity zone is flat, the present brittle-ductile transition must have been formed in the last 5 M.y. A possible source for the fluids is the rift to the east in the Salton Trough.

SYNOPTIC ABSTRACTWe develop a simulation-based network model to demonstrate the inconsistencies that can arise when a steady-state average response time model is used to determine the home location of mobile servers in a congested network. In addition, we discuss the importance of the transient behavior of a congested network and the need to acctoount for non-homogeneities in the arrival process.

A telluric array has been designed to monitor long-period changes of resistivity in Parkfield prior to the next characteristic earthquake there. The array straddles the San Andreas fault and utilizes dipoles which range from 5 to 18 km long. A method of data analysis using robust processing in the time domain and singular value decomposition yields daily estimates of telluric coefficients which are stable to within 1 %. The array has detected several fluctuations above the noise level of the measurements. Most of these fluctuations are uncorrelated with bursts of seismic activity, changes in water levels, anomalous strain and creep, or magnetic storms. However, the largest fluctuation in 2 years coincided with a tensor strain anomaly, and both of these preceded a M=3.7 earthquake by approximately 1 month. This is the largest earthquake to occur in Parkfield since the array was installed.

Two common methods for detecting leaks from storage ponds are detection of contaminants in monitoring wells and use of two asphaltic liners with a seep collection system between them. However, significant quantities of the impounded fluid may have leaked by the time contaminants are detected in the wells. Double liners have the advantage that leaks are detected before the fluid escapes into the environment, but they are expensive. An alternative approach is to use electrical resistivity methods to detect leaks. Several studies have mapped conductive zones with electrical methods and have inferred the presence of contaminated groundwater (e.g., Greenhouse and Harris, 1983). A fundamental ambiguity in any such survey is that the subsurface may contain conductive sediments (such as clay or silt) that may be mistaken for contaminated water, however. Parra (1988) proposed an alternative method that detects holes in a liner by mapping the electrical response due to a short circuit across an insulating liner which results from conductive fluid in a hole. An important result is that the electrical response of the leak is detectable only within a few meters with this method.

We have developed a practical algorithm for inverting gridded resistivity data for three‐dimensional structure and applied it to data from an experiment designed to detect leaks from ponds. This method yields relatively accurate reconstructions of structure when applied to synthetic data, but lateral contrasts in resistivity are mapped much more accurately than are vertical contrasts. The best results are obtained when transmitting electrodes are located directly above the suspected leak. Application to real data yields results which are consistent with well data and an adjacent Schlumberger sounding.

Vertical electrical soundings were used to map the presence or absence of an aquitard separating a shallow, contaminated aquifer from a deeper, uncontaminated one in San Bernardino Valley, California. Correlation of vertical electrical soundings with lithologie logs from adjacent wells allowed us to also map local variations in the elevation of the water table Comparison of known waste sites, the distribution of the aquitard, and elevation of the water table yielded probable directions of contaminant transport. We conclude that there is a significant hazard to municipal water wells due to possible transport of contaminants between the shallow and deeper aquifers.

An algorithm is developed for computing the mean-square-optimal values for small, image-restoration kernels. The algorithm is based on a comprehensive, end-to-end imaging system model that accounts for the important components of the imaging process: the statistics of the scene, the point-spread function of the image-gathering device, sampling effects, noise, and display reconstruction. Subject to constraints on the spatial support of the kernel, the algorithm generates the kernel values that restore the image with maximum fidelity, that is, the kernel minimizes the expected mean-square restoration error. The algorithm is consistent with the derivation of the spatially unconstrained Wiener filter, but leads to a small, spatially constrained kernel that, unlike the unconstrained filter, can be efficiently implemented by convolution. Simulation experiments demonstrate that for a wide range of imaging systems these small kernels can restore images with fidelity comparable to images restored with the unconstrained Wiener filter. >

DC resistivity methods were used to confirm the existence of the Bryn Mawr fault and to evaluate its efficacy as a barrier to ground water in the Bunker Hill basin beneath the San Bernardino valley, California. Vertical electrical sounding indicates layering and vertical offsets across the fault. Dipole-dipole measurements located the fault and determined its attitude. Our modeling indicates that the fault gouge has decreasing resistivity with depth. The resistivity trend is likely caused by increasing clay content. If the interpretation is correct, the ability of the fault to impede ground-water flow will increase with declining water levels. This theory is supported by greater offset of water levels across the fault when the levels were deeper. DC resistivity methods independently yield models which are consistent with known hydrogeological conditions, and can be used to predict them.