Fine-grained Units Research Articles

Evaluation of a Process by which Individual Interest Supports Learning within a Formal Middle School Classroom Context.

The affective domain and its impact on science achievement has been studied with increasing attention over the past decade. However, there has been little empirical work on how individual interest, and facilitation of situational interest in the classroom, facilitates learning of concepts within fine-grained units of instruction. Drawing upon previous theoretical and empirical work, we test the hypothesis that individual interest facilitates situational interest, and that this in turn facilitates content learning, with respect to a 10-day health education intervention focused on teaching middle school students about light, color and vision. We found that individual interest in science facilitates situational interest in the classroom activities and the teacher's instruction, and that situational interest has a positive and significant effect on learning concepts related to light and vision. Our data suggest that facilitating situational interest is a requirement if individual interest and prior knowledge are to be effective scaffolds for conceptual learning. However, targeting of other affective traits like motivation and engagement or cognitive processes like goal setting may be necessary to fully harness students' interest toward effective scaffolding of learning.

Large Holocene tsunamis in the northern Arabian Sea

Tsunamis have repeatedly hit the shores of Oman (Northern Arabian Sea) in historical times (e.g. 1945, 2013). These events had small (< 3 m) wave heights and short inundation distances, but it is unclear if much stronger events can affect the area. Boulder deposits and fine-grained sediments are described from the north coast of Oman, which are interpreted as evidence for much larger pre-historic tsunami events. No systematic dating was available, which hampers interpretation. In this paper we report radiocarbon dating results for marine organisms in these deposits and present luminescence dating of fine-grained units. We document new sedimentological and archaeological evidence for past tsunamis and describe new data on the impact of the 1945 Makran tsunami in Oman. Since the coast of Oman is prone to tropical storms, we discuss the possibility of sediment transport by cyclones and we compare our findings with recent evidence of boulder transport by storms worldwide. We argue that our results favor an interpretation as tsunamites based on sedimentological, archaeological, and spatial criteria. The dating results allow us to show that a tsunami hit the northern coast of Oman around 1000 years ago. A comparison with historical tsunami impact indicates that this palaeo-event exceeded in size all modern examples in the study area. We speculate that only a large earthquake at the Makran Subduction Zone can produce a tsunami of this size. In that case, the earthquake might have at least partially ruptured the western Makran, which would imply that the western Makran is not completely unlocked. Hazard scenarios based on historical data underestimate the tsunami threat in the Northern Arabian Sea.

Sedimentary and diapiric mélanges in the Skrzydlna area (Outer Carpathians of Poland) as indicators of basinal and structural evolution

The Dukla Nappe in the Skrzydlna area exposes two types of mélange reflecting two different phases of basinal and tectonic evolution of the Outer West Carpathian orogen in its Polish sector. The Oligocene-age sedimentary mélange (olistostrome) is related to growth of the accretionary wedge, whereas the Miocene-age diapiric mélange postdates the orogenic thrusting. Textural and structural features of the very coarse-grained sedimentary mélange suggest non-cohesive debris flows and high-density turbidity currents as predominant emplacement mechanisms. Growth strata, associated with progressive unconformities, and facies contrast between the underlying fine-grained unit and the overlying olistostrome reflect a considerable uplift of the source area and rotation of the adjacent part of the basin floor. The olistostrome and the overlying turbidite succession form a retrogressive sequence interpreted as a submarine canyon infill grading to a small submarine fan. The diapiric mélange, injected into the Oligocene-age succession of the Dukla Nappe, contains the Early and Late Cretaceous-age blocks and matrix derived from the underlying Silesian Nappe. The features reflecting diapiric emplacement include matrix proportion increase and block content decrease towards the mélange margins, scaly fabric and shear zones. Both mélanges, interpreted in the past as chaotic bodies, upon detailed examination reveal genesis-related subtle internal organization.

Organizing Health Data Standards Based on Knowledge Map.

To facilitate easy use of health data standards, we collected health data standards and parsed them into more fine-grained knowledge units. Reference and inclusion relations among these standards were constructed into knowledge map. Until now there are 156 standards collected and 4796 reference relations linked within those standards. Besides, an interface was built to enable users to easily get one standard's main information without referring to numerous PDF documents.

Litho-structural controls on Quaternary landslide distribution in the Rangitikei hill country, North Island, New Zealand

ABSTRACTThe aim of this research is to investigate the influence of stratigraphy and structure on the development of present-day topography in the Rangitikei hill country. This is achieved by (1) comparing a new inventory of deep-seated Late Quaternary relict landslide zones to the hydraulic, physical and structural properties of the Whanganui Basin fill, (2) analysing the proximity of landslides to structures and rivers, and (3) exploring the relationships between geology and slope morphology. Analysis suggests postglacial incision and daylighting of the Whanganui Basin fill is a primary control on landslide distribution, providing the necessary conditions upon which a range of triggering mechanisms operate. Faults display a clear relationship to landslide frequency, suggesting earthquakes are possibly an important triggering mechanism. Landscape evolution involves inversion and denudation of alternating coarse and fine-grained sedimentary units. Frequent, shallow landslides dominate on steep, northern scarp slopes, and deep-seated rock planar slides dominate on gentle, southern dip slopes.

Grain size effects in rime judgment across literacy development in German

AbstractPhonological similarity effects are biases to judge words as phonologically similar (i.e., rhyming), even if they are not. First found in rime awareness tasks in preliterates, these biases have recently also been found in proficient adult readers. In this study, we evaluated underlying phonological processing in rime judgment longitudinally, across literacy development. To this end, we created a new rime judgment task (rime; i.e., /t∙aɪ̯∙l/ - /z∙aɪ̯∙l/) with two distractor conditions that varied in size of phonological overlap (body; i.e., /t∙aɪ̯∙l/ - /t∙aɪ̯ ç/; nucleus; i.e., /t∙aɪ̯∙l/ - /r∙aɪ̯∙s/). The task was administered to a group of 61 German-speaking children at four time points across school entry and to 21 adults. Accuracy and latency responses were recorded. Results indicated that children and adults showed phonological similarity effects but the effect decreased gradually over time. However, preliterate children were more sensitive to large compared to small phonological overlap, while the same effect was significantly smaller in literate children and adults. Results suggest that preliterate children are more sensitive to larger grain sizes and become more sensitive to fine-grained units across literacy development. The findings are in line with the assumptions of the psycholinguistic grain size theory.

Preservation of local high-resolution data in a regional low-resolution dataset: A ‘nested’ 3D modeling approach using an example from a Quaternary glacial stratigraphy (Ontario, Canada)

Regional scale 3D models provide insight into general unit geometries and stratigraphic relationships; however, potentially significant local scale data and unit geometries are rarely preserved. Accurate modeling of local scale unit geometries and stratigraphic relationships is important for understanding aquifer-aquitard connectivity, estimation of aquifer volume, and prediction of contaminant migration pathways; this is particularly important in previously glaciated areas because of the high degree of lithological heterogeneity and stratigraphic variation in glaciogenic deposits. This study presents a case study (Ontario, Canada) that explores the impacts of an optimized model (in which high-resolution data are preserved in local scale models as ‘golden blocks’) and non-optimized regional scale 3D models on the predicted geometries and stratigraphic relationships of coarse- and fine-grained units (lithofacies associations) within a Quaternary stratigraphy. Each of the regional scale models include high quality data (outcrop and cored borehole logs) and low quality data (water well lithology logs); however, the optimized model was constructed by seamlessly integrating the golden blocks into the regional scale model using an algorithm (producing a ‘nested’ model), whereas the non-optimized model was built using a global modeling approach. By way of comparison to unit geometries previously delineated in outcrops and surficial geology maps and hydraulic responses from pumping tests, the results of this study indicate that coarse-grained units, which host significant municipal aquifers, and fine-grained units were more realistically and accurately represented in the optimized model as a result of the nested 3D modeling approach. This case study demonstrates a relatively simple and effective method for preserving high quality data in a regional scale 3D model without sacrificing model accuracy in key areas of interest (e.g. aquifer well fields).

Multiple meltwater discharge and ice rafting events recorded in the deglacial sediments along the Beaufort Margin, Arctic Ocean

The first regional model for the deglacial history of the Beaufort margin slope, in the western Arctic, is presented. The conceptual model was developed using new high-resolution CHIRP seismic reflection, multibeam bathymetry, and sediment core data acquired along the margin. This synthesis provides important constraints on sediment source and dispersal patterns for the last deglaciation. The continental slope from Barrow Canyon to the Mackenzie Trough is characterized by thick Holocene sediments mostly sourced from Barrow Canyon and continental discharge. This acoustically transparent, fine-grained unit overlies acoustically laminated sediments sourced from the Mackenzie River and ice rafting. The deglacial history of the margin from Mackenzie Trough to the Amundsen Gulf is characterized by many ice rafting and meltwater discharge events. Ice rafted debris layers were deposited around ∼14.6 ka and ∼14.1 ka and likely document enhanced ice shedding events from the Amundsen and M'Clure ice streams as they retreated. There are three inferred meltwater discharge events, all sourced from the Mackenzie region. The oldest discharge event had two phases, one sometime between ∼14.5 ka and ∼14.2 ka and another between ∼14.0 ka and ∼13.0 ka. This discharge deposited finely laminated sediments more than 7 m thick sourced from proglacial lakes in the area. Following this was a flood event starting at ∼12.94 ka, which generated high amplitude reflectors, deposited coarse debris, and caused a lowering in the δ18O record. This is possibly a major outburst flood from glacial Lake Agassiz with an additional component of Agassiz meltwater that was diverted from its southern drainage pathway down the Mississippi to the Gulf of Mexico. Finally, a third discharge event was initiated by ∼11.3 ka, which deposited coarse laminated sediments focused in the Mackenzie Trough. Timing of these second and third events correlates with the onset of the Younger Dryas cold period and the preBoreal oscillation event, respectively, suggesting that fresh water discharge may have reached a tipping point, leading to those climate events.

A high expansion implicit finite-element prestack reverse time migration method

Building on the concepts of cohesion degree and local relaxation, we propose an integrated hierarchical equilibrium parallel finite-element reverse time migration (HEP-FE-RTM) algorithm, which is a fine-grained central processing unit (CPU) parallel computation method in two-level host-sub-processors mode. A single master process is responsible for data reading and controlling the progress of the calculation, while each subordinate process deals with a part of the depth domain space. This algorithm is able to achieve single source forward-modelling and inversion calculation using more than 2000 CPUs. On the premise of controlling iteration times for convergence, sub-module/processors only communicate with their adjacent counterparts and the host processor, so the level of data exchange is proportional to cohesion degree. This HEP-FE-RTM algorithm has the distinct advantage that parallel efficiency does not decrease as the number of processors increases. In two-level host-sub-processors mode, more than 2000 processors are used and one billion unknowns are solved. By combining the finite-element implicit dynamic Newmark integral scheme, this approach achieves a prestack reverse time migration (RTM) with high expansion. Making full use of the characteristics of high accuracy and strong boundary adaptability of the finite-element method, through the optimisation of finite-element solving, the HEP-FE-RTM algorithm improved the efficiency of parallel computing and achieved RTM implementation using finite element. Model tests show that this method has a significant effect on both imaging efficiency and accuracy.

Tc(VII) and Cr(VI) Interaction with Naturally Reduced Ferruginous Smectite from a Redox Transition Zone.

Fe(II)-rich clay minerals found in subsurface redox transition zones (RTZs) can serve as important sources of electron equivalents limiting the transport of redox-active contaminants. While most laboratory reactivity studies are based on reduced model clays, the reactivity of naturally reduced field samples remains poorly explored. Characterization of the clay size fraction of a fine-grained unit from the RTZ interface at the Hanford site, Washington, including mineralogy, crystal chemistry, and Fe(II)/(III) content, indicates that ferruginous montmorillonite is the dominant mineralogical component. Oxic and anoxic fractions differ significantly in Fe(II) natural content, but FeTOTAL remains constant, demonstrating no Fe loss during its reduction-oxidation cyclings. At native pH of 8.6, the anoxic fraction, despite its significant Fe(II), ∼23% of FeTOTAL, exhibits minimal reactivity with TcO4- and CrO42- and much slower reaction kinetics than those measured in studies with biologically/chemically reduced model clays. Reduction capacity is enhanced by added/sorbed Fe(II) (if Fe(II)SORBED > 8% clay Fe(II)LABILE); however, the kinetics of this conceptually surface-mediated reaction remain sluggish. Surface-sensitive Fe L-edge X-ray absorption spectroscopy shows that Fe(II)SORBED and the resulting reducing equivalents are not available in the outermost few nanometers of clay surfaces. Slow kinetics thus appear related to diffusion-limited access to electron equivalents retained within the clay mineral structure.

Gas hydrate reservoirs and gas migration mechanisms in the Terrebonne Basin, Gulf of Mexico

The interactions of microbial methane generation in fine-grained clay-rich sediments, methane migration, and gas hydrate accumulation in coarse-grained, sand-rich sediments are not yet fully understood. The Terrebonne Basin in the northern Gulf of Mexico provides an ideal setting to investigate the migration of methane resulting in the formation of hydrate in thin sand units interbedded with fractured muds.Using 3D seismic and well log data, we have identified several previously unidentified hydrate bearing units in the Terrebonne Basin. Two units are >100 m-thick fine-grained clay-rich units where gas hydrate occurs in near-vertical fractures. In some locations, these fine-grained units lack fracture features, and they contain 1–4-m thick hydrate bearing-sands. In addition, several other thin sand units were identified that contain gas hydrate, including one sand that was intersected by a well at the location of a discontinuous bottom-simulating reflector. Using correlation of well log data to seismic data, we have mapped and described these new units in detail across the extent of the available data, allowing us to determine the variation of seismic amplitudes and investigate the distribution of free gas and/or hydrate.We present several potential source-reservoir scenarios between the thick fractured mud units and thin hydrate bearing sands. We observe that hydrate preferentially forms within thin sand layers rather than fractures when sands are present in larger marine mud units. Based on regional mapping showing the patchy lateral extent of the thin sand layers, we propose that diffusive methane migration or short-migration of microbially generated methane from the marine mud units led to the formation of hydrate in these thin sands, as discontinuous sands would not be conducive to long-range migration of methane from deeper reservoirs.

High-resolution seismic characterization of the gas and gas hydrate system at Green Canyon 955, Gulf of Mexico, USA

The Pliocene and Pleistocene sediments at lease block Green Canyon 955 (GC955) in the Gulf of Mexico include sand-rich strata with high saturations of gas hydrate; these gas hydrate accumulations and the associated geology have been characterized over the past decade using conventional industry three-dimensional (3D) seismic data and dedicated logging-while-drilling (LWD) borehole data. To improve structural and stratigraphic characterization and to address questions of gas flow and reservoir properties, in 2013 the U.S. Geological Survey acquired high-resolution two-dimensional (2D) seismic data at GC955. Combined analysis of all available data improves our understanding of the geological evolution of the study area, which includes basin-scale migration of the Mississippi River sediment influx as well as local-scale shifting of sedimentary channels at GC955 in response to salt-driven uplift, structural deformation associated with the salt uplift, and upward gas migration from deeper sediments that charges the main gas hydrate reservoir and shallower strata. The 2D data confirm that the sand-rich reservoir is composed principally of sediments deposited in a proximal levee setting and that episodes of channel scour, interspersed with levee deposition, have resulted in an assemblage of many individual proximal levee deposit “pods” each with horizontal extent up to several hundred meters. Joint analysis of the 2D and 3D data reveals new detail of a complex fault network that controls the fluid-flow system; large east-west trending normal faults allow fluid flow through the reservoir-sealing fine-grained unit, and smaller north-south oriented faults provide focused fluid-flow pathways (chimneys) through the shallower sediments. This system has enabled the flow of gas from the main reservoir to the seafloor throughout the recent history at GC955, and its intricacies help explain the distributed occurrences of gas hydrate in the intervening strata.

Spatial scale and measuring segregation: illustrated by the formation of Chicago’s ghetto

Few studies of residential segregation in cities have directly addressed the issue of spatial scale, apart from noting that the traditional indices of segregation tend to be larger when calculated for small rather than large spatial units. That observation however ignores Duncan et al.’s (Statistical geography: problems in analyzing areal data. Free Press, Glencoe, 1961) explication that any measure of segregation at a fine-grained scale necessarily incorporates, to an unknown extent, segregation at a larger scale within which the finer-grained units are nested. To avoid that problem, a multi-level modelling perspective is introduced that identifies the intensity of segregation at each scale net of its intensity at any larger scale included in the analysis. It is applied to an analysis of the emergence of Chicago’s Black ghetto over the twentieth century’s first three decades, using data at the ward and ED scales. It shows that across Chicago as a whole segregation was equally as intense at the two scales, with statistically significant increases in that intensity at both scales across the three decades. At the finer scale, however, segregation was much more intense across the EDs within those wards that formed the core of the emerging ghetto than it was in the remainder of the city.

Transport of Solute from a Fine-Grained Unit to a Coarse-Grained Host Under Pulsed-Pumping Fluid Dynamics: An Experimental Investigation

Pulsed pumping has the potential to be an effective alternative to continuous pumping pump-and-treat remediation techniques in porous media that exhibit a sharp material interface and tailing phenomenon is observed. Solute transport experiments performed in a soil column filled with a uniform coarse sand containing a uniform silt cylinder were conducted. Concentration measurements using saltwater as a tracer were taken employing time-domain reflectometry probes located throughout the column. The laboratory trials employed continuous pumping, 24-h periods of pumping followed by 24-h periods of no pumping, and 4-h periods of pumping followed by 24-h periods of no pumping. The experimental results suggest that pulsed pumping can achieve similar contaminant removal for a given amount of time as continuous pumping while pumping less water.

Fluvial Facies Architecture and Sequence Stratigraphy of the Tertiary Duchesne River Formation, Uinta Basin, Utah, U.S.A.

Continental sequence stratigraphy in upstream fluvial environments can be complex due to the interplay of source tectonics, local and global climate change, and topography. The Tertiary Duchesne River Formation, Utah, U.S.A., represents the last stage of intermontane basin fill in the Uinta Basin. It is surrounded by sediment source mountain ranges of the Uinta Mountains to the north and the Sevier Fold-Thrust Belt (FTB) to the west. Excellent basin-scale exposure of the Duchesne River Formation allows the vertical and lateral characterization of facies architectures in the upstream environments. The four members of the Duchesne River Formation are distinctive lithological units. The lower three members comprise a typical upward-fining unconformity-bounded fluvial sequence from the basal coarse-grained unit into the overlying fine-grained units. The fourth uppermost coarse-grained member records the onset of another upward-fining cycle. The sequence stratigraphy of these unconformity-bounded upward-fining cycle(s) was primarily tectonics-driven due to uplift of the Uinta Mountains. The Duchesne River Formation records a distinct change in fluvial–lacustrine styles between the western and eastern part of the basin, demonstrating the variable allogenic controls of tectonic subsidence and discharge related to the local climate and source-terrain input within the basin. Specifically, the western degradational fluvial system with a high net-sandstone-to-gross-thickness ratio of the basal member was controlled by high discharge due to a wet climate and two source-terrain inputs (i.e., Uinta Mountains and Sevier Fold-Thrust Belt), whereas the eastern aggradational fluvial system with a low net-sandstone-to-gross-thickness ratio was controlled by low discharge due to a dry climate and single source terrain input (i.e., Uinta Mountains). The development of local lacustrine environments on the alluvial plain of the third member, present in the western Uinta Basin, was controlled by differential tectonic subsidence in the basin. The Duchesne River Formation preserves a valuable example of an upstream fluvial sequence, and demonstrates how internal facies architectures at the basin scale were dictated by allogenic controls.

Palaeoenvironment of braided fluvial systems in different tectonic realms of the Triassic Sherwood Sandstone Group, UK

Fluvial successions comprising the fills of sedimentary basins occur in a variety of tectonic realms related to extensional, compressional and strike-slip settings, as well as on slowly subsiding, passive basin margins. A major rifting phase affected NW Europe during the Triassic and resulted in the generation of numerous sedimentary basins. In the UK, much of the fill of these basins is represented by fluvial and aeolian successions of the Sherwood Sandstone Group. Additionally, regions that experienced slow rates of Mesozoic subsidence unrelated to Triassic rifting also acted as sites of accumulation of the Sherwood Sandstone Group, one well-exposed example being the eastern England Shelf. The fluvial depositional architecture of deposits of the Sherwood Sandstone Group of the eastern England Shelf (a shelf-edge basin) is compared with similar fluvial deposits of the St Bees Sandstone Formation, eastern Irish Sea Basin (a half-graben). The two studied successions represent the preserved deposits of braided fluvial systems that were influenced by common allogenic factors (climate, sediment source, delivery style); differences in preserved sedimentary style principally reflect their different tectonics settings. Analysis of lithofacies and architectural elements demonstrates that both studied successions are characterized by amalgamated channel-fill elements that are recorded predominantly by downstream-accreting sandy barforms. The different tectonic settings in which the two braided-fluvial systems accumulated exerted a dominant control on preserved sedimentary style and long-term preservation potential. On the eastern England Shelf, the vertical stacking of pebbly units and the general absence of fine-grained units reflect a slow rate of sediment accommodation generation (18–19.4m/Myr). In this shelf-edge basin, successive fluvial cycles repeatedly reworked the uppermost parts of earlier fluvial deposits such that only the lowermost channel lags tend to be preserved. By contrast, in the eastern Irish Sea Basin of west Cumbria, the rate of sediment accommodation generation was substantially greater (119m/Myr) such that space was available to preserve complete fluvial cycles, including silty drape units that cap the channelized deposits.

Identifying functional subdivisions in the human brain using meta-analytic activation modeling-based parcellation

Parcellation of the human brain into fine-grained units by grouping voxels into distinct clusters has been an effective approach for delineating specific brain regions and their subregions. Published neuroimaging studies employing coordinate-based meta-analyses have shown that the activation foci and their corresponding behavioral categories may contain useful information about the anatomical–functional organization of brain regions. Inspired by these developments, we proposed a new parcellation scheme called meta-analytic activation modeling-based parcellation (MAMP) that uses meta-analytically obtained information. The raw meta data, including the experiments and the reported activation coordinates related to a brain region of interest, were acquired from the Brainmap database. Using this data, we first obtained the “modeled activation” pattern by modeling the voxel-wise activation probability given spatial uncertainty for each experiment that featured at least one focus within the region of interest. Then, we processed these “modeled activation” patterns across the experiments with a K-means clustering algorithm to group the voxels into different subregions. In order to verify the reliability of the method, we employed our method to parcellate the amygdala and the left Brodmann area 44 (BA44). The parcellation results were quite consistent with previous cytoarchitectonic and in vivo neuroimaging findings. Therefore, the MAMP proposed in the current study could be a useful complement to other methods for uncovering the functional organization of the human brain.

One minute of grief: emotional processing in short-term dynamic psychotherapy for adjustment disorder.

Depth of emotional processing has shown to be related to outcome across approaches to psychotherapy. Moreover, a specific emotional sequence has been postulated and tested in several studies on experiential psychotherapy (Pascual-Leone & Greenberg, 2007). This process-outcome study aims at reproducing the sequential model of emotional processing in psychodynamic psychotherapy for adjustment disorder and linking these variables with ultimate therapeutic outcome. In this study, 32 patients underwent short-term dynamic psychotherapy. On the basis of reliable clinical change statistics, a subgroup (n = 16) presented with good outcome and another subgroup (n = 16) had a poor outcome in the end of treatment. The strongest alliance session of each case was rated using the observer-rated system Classification of Affective Meaning States. Reliability coefficients for the measure were excellent (κ = .82). Using 1 min as the fine-grained unit of analysis, results showed that the experience of fundamentally adaptive grief was more common in the in-session process of patients with good outcome, compared with those with poor outcomes (χ2 = 6.56, p = .01, d = 1.23). This variable alone predicted 19% of the change in depressive symptoms as measured by the Beck Depression Inventory at the end of treatment. Moreover, sequences of the original model were supported and related to outcome. These results are discussed within the framework of the sequential model of emotional processing and its possible relevance for psychodynamic psychotherapy.

A quasi-elastic aquifer deformational behavior: Madrid aquifer case study

Summary The purpose of this paper is to analyze the quasi-elastic deformational behavior that has been induced by groundwater withdrawal of the Tertiary detrital aquifer of Madrid (Spain). The spatial and temporal evolution of ground surface displacement was estimated by processing two datasets of radar satellite images (SAR) using Persistent Scatterer Interferometry (PSI). The first SAR dataset was acquired between April 1992 and November 2000 by ERS-1 and ERS-2 satellites, and the second one by the ENVISAT satellite between August 2002 and September 2010. The spatial distribution of PSI measurements reveals that the magnitude of the displacement increases gradually towards the center of the well field area, where approximately 80 mm of maximum cumulated displacement is registered. The correlation analysis made between displacement and piezometric time series provides a correlation coefficient greater than 85% for all the wells. The elastic and inelastic components of measured displacements were separated, observing that the elastic component is, on average, more than 4 times the inelastic component for the studied period. Moreover, the hysteresis loops on the stress–strain plots indicate that the response is in the elastic range. These results demonstrate the quasi-elastic behavior of the aquifer. During the aquifer recovery phase ground surface uplift almost recovers from the subsidence experienced during the preceding extraction phase. Taking into account this unique aquifer system, a one dimensional elastic model was calibrated in the period 1997–2000. Subsequently, the model was used to predict the ground surface movements during the period 1992–2010. Modeled displacements were validated with PSI displacement measurements, exhibiting an error of 13% on average, related with the inelastic component of deformation occurring as a long-term trend in low permeability fine-grained units. This result further demonstrates the quasi-elastic deformational behavior of this unique aquifer system.

Bedrock geology of the San Francisco Bay Area: A local sediment source for bay and coastal systems

Abstract Local watersheds may contribute over half of the sediment load coming into San Francisco Bay today. The bedrock underlying these watersheds is the ultimate source for most of this sediment. This paper outlines the geologic history of this bedrock, which records the complex tectonic history of the San Francisco Bay Area over the last 200 Ma. The Jurassic to Eocene Franciscan Complex in the Bay Area is the most widespread bedrock. The local Franciscan can be broken into nine tectonic terranes that represent pieces of seafloor that were accreted to the North American margin in over a 100 Myr period of subduction. Each terrane has a unique age range, sequence of seafloor rocks, and metamorphic history. The Franciscan rocks were thrust eastward under the Great Valley Complex. The Great Valley Complex reflects a forearc basin comprised of Jurassic ocean crust—the Coast Range ophiolite—and overlying Jurassic and Cretaceous turbidite-dominated sedimentary rocks of the Great Valley Group. By the beginning of the Cenozoic Era, shallowing of the angle of subduction along the continental margin led to uplift and infilling of the forearc basin to shelf depth. Recorded at this time are sedimentary sequences governed by eustatic sealevel changes and evidence of the first unroofing of Franciscan rocks. Marine sedimentary rocks dominate the region through the Miocene and unconformities within the Early Tertiary sedimentary record reflect periods of tectonic activity and uplift. Middle to late Miocene sedimentary rocks are extensively deposited throughout the Bay Area. In the late Miocene, the Mendocino triple junction passed northward through the area and transform tectonism commenced. A slab window developed behind the triple junction resulted in volcanic activity that produced the Sonoma Volcanics in the North Bay and volcanics of the East Bay Hills. By Pliocene time, terrestrial sedimentary rocks were being deposited in many parts of the Bay Area. Faulting associated with the San Andreas system led to the development of small basins, the displacement of local bedrock blocks, and the transport of the Salinian Complex from the southern Sierra to the western margin of the Bay Area. The modern topography of the region started emerging by about 6 Ma to 4 Ma, when compression across the San Andreas system increased and uplift of the Coast Ranges began. The first estuarine influence in San Francisco Bay is recorded in ~ 600 ka rocks, about the same time as the modern Sacramento River system started flowing through the San Francisco estuary/valley. Today's local San Francisco Bay watershed is comprised of numerous small stream systems around the Bay with headwaters in the surrounding hills and mountains. Active tectonism produces relief in these watersheds of typically 500 m or more, with the ridgelines typically supported by more resistant bedrock units. Steep topography leads to rapid bedrock erosion, particularly of the finer-grained sedimentary rocks. Landslides provide a significant portion of the sediment carried by the streams and several of the bedrock units are more prone to landslides, particularly the Central and Novato Quarry terranes of the Franciscan Complex, and finer-grained units of both the Great Valley Group and Tertiary rocks. Many of the larger streams have dammed reservoirs that trap much of their sediment load before it can reach the bay.