Faults with Quaternary displacement, northwestern San Francisco Bay region, California
No abstract available.
California↗
Geology topics
Research about San Francisco Bay
Source-linked reports with geographic coverage including San Francisco Bay.
Map showing faults with Quaternary displacement, northeastern San Francisco Bay region, California
This map shows faults with Quaternary displacement in the northeast San Francisco Bay region of California. Faults that have been historically active or that show evidence of movement during approximately the last 2 million years (the Quaternary Period) are delineated and are classified according to the age of their last surface displacement. The map is designed to provide a synopsis of Quaternary faulting in the northeast San Francisco Bay area contributing toward an understanding of neotectonic crustal deformation in the central Coast Range of California. Future crustal movement will most likely occur along these fault breaks.
California↗
Paleomagnetic investigation of late Quaternary sediments of south San Francisco Bay, California
Paleomagnetic inclinations of the Late Quaternary sediments of South San Francisco Bay were determined from bore hole samples collected near Dumbarton Bridge. The sediments consist of estuarine muds and nonmarine sand deposits, floored by bedrock of the Mesozoic Franciscan Formation. - Beneath Dumbarton Bridge the entire sedimentary fill is normally polarized; therefore, the fill postdates the Brunhes-Matayama polarity reversal (700,000 y. B.P.). Magnetic time lines such as the Mono Lake excursion (24,000 y. B.P.) and the reversed Blake event (110,000 y B.P.) were not found in this bore hole. In addition to Holocene and modern deposits of San Francisco Bay, an older estuarine unit occurs in the stratigraphic section. The older unit was deposited during a period of high sea level, tentatively correlated with the Sangamon interglacial period. Because evidence of the Blake event is not present in the older estuarine unit, the proposed age of this unit could not be confirmed. Although the Holocene estuarine deposits of South San Francisco Bay carry stable remanent magnetization, a reliable record of geomagnetic secular variation could not be recovered because the water-saturated sdiment was deformed by drilling.
California↗
In-situ measurements of seismic velocities in the San Francisco Bay Region; part III
Seismic wave velocities (compressional and shear) are important parameters for estimating the seismic response characteristics of various geologic units when subjected to strong earthquake ground shaking. Seismic velocities of various units often show a strong correlation with the amounts of damage following large earthquakes and have been used as a basis for certain types of seismic zonation studies. In the current program seismic velocities have been measured at 59 locations 1n the San Francisco Bay Region. This report is the third in a series of Open-File Reports and describes the in-situ velocity measurements at locations 35-59. At each location seismic travel times are measured in drill holes, normally at 2.5-m intervals to a depth of 30 m. Geologic logs are determined from drill cuttings, undisturbed (cored) samples, and penetrometer samples. The data provide a detailed comparison of geologic and seismic characteristics and provide parameters for estimating strong earthquake ground motions quantitatively at each of the sites. A major emphasis of this program is to obtain a detailed comparison of geologic and seismic data on a regional scale for use in seismic zonation. There is a variety of geologic and seismic data available in the San Francisco Bay Region for use 1n developing the general zoning techniques which can then be applied to other areas. Shear wave velocities 1n near-surface geologic materials are of especial interest for engineering seismology and seismic zonation studies, yet in general, they are difficult to measure because of contamination by compressional waves. A comparison of various in-situ techniques by Warrick (1974) establishes the reliability of the method utilizing a "horizontal traction" source for sites underlain by bay mud and alluvium. Gibbs, and others (1975a) present data from 12 holes and establishes the reliability of the method for sites underlain by a variety of different rock units and suggest extending the measurements to a large number of sites. Data collected from the first 12 holes also provide an opportunity for developing a routine and efficient procedure for collection and reduction of the data. Gibbs and others (1975b) report preliminary comparisons of the data with the amplification data recorded from nuclear explosions, and the intensity data for the 1906 earthquake. These comparisons show that correlations exist between the three data sets. Average shear wave velocity in each geologic unit form the basis for the preliminary correlations, however, some of the geologic units (that is, granite and Franciscan Formation) exhibit a wide range of shear wave velocity. It is apparent that other factors must be considered in these units, perhaps near surface weathering or fracture spacing. Work is continuing in this area.
California↗
Late Quaternary depositional history, Holocene sea-level changes, and vertical crustal movement, southern San Francisco Bay, California
Sediments collected for bridge foundation studies at southern San Francisco Bay, Calif., record estuaries that formed during Sangamon (100,000 years ago) and post-Wisconsin (less than 10,000 years ago) high stands of sea level. The estuarine deposits of Sangamon and post-Wisconsin ages are separated by alluvial and eolian deposits and by erosional unconformities and surfaces of nondeposition, features that indicate lowered base levels and oceanward migrations of the shoreline accompanying low stands of the sea. Estuarine deposits of mid-Wisconsin age appear to be absent, suggesting that sea level was not near its present height 30,000–40,000 years ago in central California. Holocene sea-level changes are measured from the elevations and apparent 14 C ages of plant remains from 13 core samples. Uncertainties of ±2 to ±4 m in the elevations of the dated sea levels represent the sum of errors in determination of (1) sample elevation relative to present sea level, (2) sample elevation relative to sea level at the time of accumulation of the dated material, and (3) postdepositional subsidence of the sample due to compaction of underlying sediments. Sea level in the vicinity of southern San Francisco Bay rose about 2 cm/yr from 9,500 to 8,000 years ago. The rate of relative sea-level rise then declined about tenfold from 8,000 to 6,000 years ago, and it has averaged 0.1–0.2 cm/yr from 6,000 years ago to the present. This submergence history indicates that the rising sea entered the Golden Gate 10,000–11,000 years ago and spread across land areas as rapidly as 30 m/yr until 8,000 years ago. Subsequent shoreline changes were more gradual because of the decrease in rate of sea-level rise. Some of the sediments under southern San Francisco Bay appear to be below the level at which they initially accumulated. The vertical crustal movement suggested by these sediments may be summarized as follows: (1) Some Quaternary(?) sediments have sustained at least 100 m of tectonic subsidence in less than 1.5 million years (<0.07 mm/yr) relative to the likely elevation of the lowest Pleistocene land surface; (2) the deepest Sangamon estuarine deposits subsided tectonically about 20–40 m in about 0.1 million years (0.2±0.1–0.4±0.1 mm/yr) relative to the assumed initial elevations of the thalwegs buried by these sediments; and (3) Holocene salt-marsh deposits have undergone about 5 m of tectonic and possibly isostatic subsidence in about 6,000 years (0.8±.0.7 mm/yr) relative to elevations which might be expected from eustatic sea-level changes alone.
California↗
Breeding avifauna of the south San Francisco Bay estuary
San Francisco Bay represents one of the largest estuarine areas on the Pacific Coast of North America. Its open waters, tidal flats, tidal marshes and solar evaporation ponds provide critical foraging, resting and breeding habitat for migratory and resident birds. The avifauna of San Francisco Bay has received considerable attention; however, little of it has been directed toward assessing the overall importance of the Bay as a nesting area. Works by Grinnell and Wythe (1927), Grinnell and Miller (1944) and Sibley (1952) are the only comprehensive studies of San Francisco Bay avifauna. These studies, while major contributions, are broad in scope as they relate to the breeding avifauna of the Bay's estuarine areas. Several studies by Johnston (1955, 1956a, b), Marshall (1948a, b), DeGroot (1927, 1931) and Zucca (1954) have concentrated on the breeding biology of individual species; however, much of the marsh reclamation and Bay fill has occurred since. The present breeding status of many resident and migratory birds is poorly known for San Francisco Bay. Included among these are three rare or endangered forms: California Black Rail, California Clapper Rail and California Least Tern. In addition, some species now found in the area represent recent breeding range extensions. This study, undertaken from March to September 1971 and including a few more recent data, presents a quantitative assessment of the present breeding bird populations in the South San Francisco Bay area.
California↗
Effects of local geological conditions in the San Francisco Bay region on ground motions and the intensities of the 1906 earthquake
Measurements of ground motion generated by nuclear explosions in Nevada have been completed for 99 locations in the San Francisco Bay region, California. The recordings show marked amplitude variations in the frequency band 0.25 to 3.0 Hz that are consistently related to the local geological conditions of the recording site. The average spectral amplifications observed for vertical and horizontal ground motions are, respectively: (1, 1) for granite, (1.5, 1.6) for the Franciscan Formation, (3.0, 2.7) for the Santa Clara Formation, (3.3, 4.4) for alluvium, and (3.7, 11.3) for bay mud. Spectral amplification curves define predominant ground frequencies in the band 0.25 to 3.0 E for bay mud sites and for some alluvial sites. Amplitude spectra computed from recordings of seismic background noise at 50 sites do not generally define predominant ground frequencies. The intensities ascribed to various sites in the San Francisco Bay region for the California earthquake of April 18, 1906, are strongly dependent on distance from the zone of surface faulting and the geological character of the ground. Considering only those sites (approximately one square city block in size) for which there is good evidence for the degree of ascribed intensity, the intensities for 917 sites on Franciscan rocks generally decrease with the logarithm of distance as Intensity = 2.69 - 1.90 log (Distance in kilometers). (1) For sites on other geological units, intensity increments, derived from this empirical relation, correlate strongly with the Average Horizontal Spectral Amplifications (AHSA) according to the empirical relation Intensity Increment = 0.27 + 2.70 log (AHSA). (2) Average intensity increments predicted for the various geological units are −0.3 for granite, 0.2 for the Franciscan Formation, 0.6 for the Great Valley sequence, 0.8 for the Santa Clara Formation, 1.3 for alluvium, and 2.4 for bay mud. The maximum intensity map predicted on the basis of these data delineates areas in the San Francisco Bay region of potentially high intensity for large earthquakes on either the San Andreas fault or the Hayward fault. The map provides a crude form of seismic zonation for the region and may be useful for certain general types of land-use zonation.
California↗
Location of the non-tidal current null zone in northern San Francisco Bay
Variations in Sacramento-San Joaquin River discharge into northern San Francisco Bay causes shifts in location of the bottom density current null zone. At a river flow of 2000 m 3 /s this null zone is approximately 20 km from the seaward end of the estuary, whereas at a river flow of 100 m 3 /s it is 80 km from the seaward end; the corresponding distances of salinity penetration are approximately 40 and 90 km from the seaward end. Seaward of the null zone, during low (summer) river discharge conditions, the inward-flowing bottom density current appears typically strong (5–15 cm/s) relative to the outward-flowing river current (river discharge per unit cross-channel area) of <2 cm/s. Landward from this null zone the average river current increases with decreasing cross-channel area. This circulation implies that during the summer water within the null zone has the longest average advective replacement time relative to water seaward or landward of the null zone.
California↗
Distribution and cost of landslides that have damaged manmade structures during the rainy season of 1972-1973 in the San Francisco Bay region, California
This report presents data on the location and cost of damage related to landslides in the San Francisco Bay region during the rainy season of 1972-73 (figs. 1 and 2). By showing the general location of landslides that caused damage during that season, the report also shows which parts of the region have the most severe problems. These data supplement earlier reports by the U.S . Geological Survey on the damage caused by landsliding throughout the bay region during the rainy season of 1968-69 (Taylor and Brabb, 1972), in Contra Costa County from 1950 to 1971 (Nilsen and Turner, 1975), in Alameda County from 1940 to 1971 (Nilsen and others, 1975), and in the northeastern part of the city of San Jose from 1967 to 1971 (Nilsen and Brabb, 1972). The nine San Francisco Bay region counties are included in this investigation: Alameda, Contra Costa, Marin, Napa, San ,Francisco, San Mateo, Santa Clara, Solano, and Sonoma. Landslide costs for these counties during the 1972-73 rainy season (table 1) were at least \$9,716,284. Of this total, $3,284,918 was direct loss of or damage to private property, mainly by lowering the property market value, and \$6,431,366 was for public property, chiefly for repair or relocation of roads. The data used to compile these costs are incomplete, thus the total cost could be significantly greater.
California↗
Selected chlorinated hydrocarbons in bottom material from streams tributary to San Francisco Bay
As part of a study of the environmental quality of San Francisco Bay, bottom material from 26 streams tributary to the Bay were analyzed for chlordane, DDD, DDE, DDT, and PCB residues. These compounds were present in essentially all streams tested. Chlordane proved to be ubiquitous, with a concentration range similar to that of the other compounds. Noteworthy was the occurrence in one stream of polychlorinated naphthalene residues. Compounds occurring in concentrations above 20 μg/kg were identified in most instances by combined gas chromatography/mass spectrometry.
California↗
Map showing areas bordering the southern part of San Francisco Bay where a high water table may adversely affect land use
No abstract available.
California↗
Review of wastewater problems and wastewater-management planning in the San Francisco Bay region, California
The San Francisco Bay region has suffered adverse environmental effects related to the discharge of municipal-, industrial-, and agricultural- wastewater and storm-water runoff. Specific pollutional properties of theses discharges are not well understood in all cases although the toxic materials and aquatic-plant nutrients (biostimulants) found in municipal and industrial waterwater are considered to be a major cause of regional water-quality problems. Other water-quality problems in the region are commonly attributed to pesticides found in agricultural wastewater and potentially pathogenic bacteria in municipal-wastewater discharges and in storm-water runoff. The geographical distribution and magnitude of wastewater discharges in the bay region, particularly those from municipalities and industries, is largely a function of population, economic growth, and urban development. As might be expected, the total volume of wastewater has increased in a trend paralleling this growth and development. More significant, perhaps, is the fact that the total volume parameters such as BOD (biochemical oxygen demand), biostimulant concentrations, and toxicity, has increased despite large expenditures on new and improved municipal- and industrial-wastewater-treatment plants. Also, pollutant loadings from other major source, such as agriculture and storm-water runoff, have increased. At the time of writing (1972), many Federal, State, regional, and local agencies are engaged in a comprehensive wastewater-management-planning effort for the entire bay region. Initial objectives of this planning effort are: (1) the consolidation and coordination of loosely integrated wastewater-management facilities and (2) the elimination of wastewater discharges to ecologically sensitive areas, such as fresh-water streams and shallow extremities of San Francisco Bay. There has been some investigation of potential long-range wastewater-management alternatives based upon disposal in deep water in the bay, in the Pacific Ocean, or on land. Also, wastewater-reclamation and water-reuse concepts seem to be growing in favor with the public and should become and important part of future wastewater-management plans. Because most wastewater-reclamation and water-reuse systems would involve the use of land (that is agricultural irrigation, ground-water recharge, recreational reservoirs) local and regional lang-use planners can ass much to wastewater-management planning by identifying local and subregional waterwater-reclamation and water-reuse possibilities within their jurisdictions and integrating them with future land-use plans. The timely participation of planner is essential because Federal and State planning and funding deadlines for a regional wastewater-management system become effective in July 1973 and 1974, respectively.
California↗
Liquefaction potential of unconsolidated sediments in the southern San Francisco Bay Region, California
A preliminary map of liquefaction potential of unconsolidated sediments has been made for the southern part of the San Francisco Bay region. Map zones are established on the basis of recent detailed geologic mapping. Liquefaction potential for each zone is estimated from an analysis of lithologic, water-table and standard penetration test data. Due to empirical aspects of the evaluation method, approximations in establishing parameters and the generalizations of limited test data to entire map zones, the liquefaction potential map must be considered as~preliminary and approximate. Nevertheless, the map should serve the intended purpose of generally delineating areas where the probability for liquefaction during a major earthquake is greatest and, hence, areas where special attention should be given to the possibility of liquefaction. Sediments with the highest potential for liquefaction are clean granular layers within the younger bay sediments. These layers are not everywhere present but commonly occur locally near present and former stream channels. Clean granular beds and layers immediately beneath the younger bay sediments generally have a lesser but significant potential for liquefaction. Younger (Holocene) alluvial deposits have an even lower potential, however, the potential can be locally high in recent channel and overbank deposits. Part of the Holocene unit is normally above water-table and thus would have only a seasonal potential for liquefaction. Older (Pleistocene) alluvial fan deposits have a generally low liquefaction potential. Lateral spreading landslides are commonly associated with liquefaction beneath gentle slopes. Thus. during a major earthquake. slides of this type would probably be the most pervasive damaging effect of liquefaction on the broad alluvial plain surrounding San Francisco Bay.
California↗
Map showing areas serviced by municipal and private sewerage agencies, San Francisco Bay region, California, 1970
No abstract available.
California↗
A summary view of water supply and demand in the San Francisco Bay Region, California
This report presents a summary view of the water-supply situation in the nine counties that comprise the San Francisco Bay region, California, and thereby provides water data, based on 1970 conditions, that are needed for regional planning. For the purpose of this study the nine-county region has been divided into 15 subregions on the basis of hydrologic and economic considerations. Firm water supply is tabulated for each subregion by source--ground water, surface water, and imported water. Water demand in 1970 is tabulated for each subregion by type of use or demand--public supply, rural self-supply, irrigation, self-supplied industrial water and thermoelectric power generation. The San Francisco Bay region is dependent to a large degree on imported water. Under 1970 conditions of development, the firm water supply is 2.2 million acre-feet per year; of that quantity, almost 1 million acre-feet per year is imported water. The water demand in 1970 was 1.9 million acre-feet, about half of which was consumed. Under 1970 conditions of water development and use, a series of dry years would probably necessitate some curtailment of irrigation activities in four of the subregions, where the bulk of the demands i for irrigation water. Under those same conditions there is generally ample water for municipal and industrial use throughout the region, except in eastern Marin County where the firm municipal supple does not exceed the 1970 demand for municipal and industrial water. Although the firm water supply of the San Francisco Bay region, including imported water, is generally adequate to meet present needs, supplemental supply will be required to meet increased demand in the future. The expansion of existing surface-water facilities and the construction of new surface-water projects, now considered feasible, could provide a combined firm supplemental yield of slightly more than 1 million acre-feet per year, almost three-fourths of which would be available for import by those subregions that might experience a water deficient in the future. However, any supplemental water that might be developed by such alternative methods as desalination of brackish or salt water, weather modification, and various conservation measure, will correspondingly reduce requirement for supplemental water from the more conventional sources. The aspect of water quality is not discussed in this paper. Because of the present availability of imported water of good or acceptable quality, water quality, as it affects the supply, is not a serious problem at this time, except perhaps in local areas adjacent to San Francisco Bay and in the Sacramento-San Joaquin Delta. In those areas ground water has been degraded by salinity intrusion. Although the prediction of future trends in population, land use, and water demand is beyond the scope of this report, there is not doubt that vigilance and careful planning will be required to prevent serious future deterioration of the quality of the water supply.
California↗
The earthquake sequence near Danville, California, 1970
Several thousand small earthquakes, with magnitudes ranging up to 4, occurred near Danville, California, during May, June, and July 1970. Seven temporary seismographs were installed near the epicentral region to augment an existing telemetered network within 1 day after the first felt earthquake. The dense concentration of 10 seismographs within 12 km of the seismic activity and the existence of a reversed seismic-refraction profile through the region permitted a very detailed study of this earthquake sequence. Over 400 events with magnitude greater than 0.5 were located with an average accuracy of ±1 km. The main earthquake region was approximately spherical: 1 km in radius, 6 km deep, and centered about 5 km southeast of Danville, 40 km east of San Francisco. Fault-plane solutions indicate that faulting associated with the earthquakes was of the right-lateral strike-slip type, with a strike of N 35°W.
California↗