Northern California Coast Research Articles

Joint determination of seismic velocity ratios: Theory and application to an aftershock sequence

abstract Two different approaches are considered to the problem of determining seismic velocity ratios from P and S arrival data from a group of earthquakes. Each method arises naturally from a different assumption about the sources of error. If the S reading error is the predominant source of error, S versus P regression, an extension of the Wadati Plot method to pooled data, should be used. If, however, S reading errors do not dominate, a symmetric regression should be used. A natural extension of the latter method allows the determination of station-by-station variation of α/β . The methods are illustrated with data from an aftershock sequence which occurred off the coast of northern California. The average velocity ratio is not as well determined as the station-by-station variation about the average. However, the results show that the method has some utility in the study of regional variation of seismic velocities.

Some examples of detection of oceanic mesoscale eddies by the SEASAT synthetic‐aperture radar

This note presents images of three dynamically different regions in the ocean to demonstrate the variety of mesoscale variabilities detected by the SEASAT synthetic‐aperture radar (SAR). South of the Grand Banks of Newfoundland, a cold eddy is observed to form as the result of the southward intrusion of Labrador Sea water, perhaps having led to the birth of a Gulf Stream extension ring. Off the northern coast of California, features resulting from the offshore intrusions of cold upwelling water are observed. Two topographically generated eddies are detected near Misteriosa Bank on the Cayman Ridge in the northwestern Caribbean. Comparisons are made with concurrent NOAA‐5 infrared images whenever the eddies have thermal signatures.

Sediment Failure on Continental Shelf: Response to 1980 Earthquake off Northern California: ABSTRACT

On November 8, 1980, a large magnitude earthquake (M ~ 7) occurred 60 km (37 mi) off the coast of northern California. Damage was minimal onshore, but extensive changes to the sea floor were reported from the area of the Klamath River delta. Data from three successive surveys conducted in the area at intervals of 1, 6, and 11 months after the shock demonstrate the extent and type of sea floor failure. Side-scan sonar and high-resolution seismic reflection profiles, together with sea floor photographs and video images, define a thin (< 15 m, 49 ft) failure zone that measures 1 × 20 km (0.6 × 12.5 mi) and trends parallel to the shoreline on the shallow (~ 60 m, 200 ft) and nearly flat (~ 0.25°) surface of the Klamath River delta. The failure zone is charac erized by a very flat (~ 0.02°) terrace that is mantled by silty sand and is bounded to seaward by an irregular 1 to 2 m (3 to 6.5 ft) high scarp. Sonographs and bottom photographs provide evidence that failure occurred by liquefaction, lateral spreading, and sediment flow, producing various sediment patterns and relief features on the sea floor. The modes of failure with their corresponding features are: (1) liquefaction--identified from side-scan sonographs showing sand boils 5 to 25 m (16 to 82 ft) in diameter; (2) lateral spreading--identified from photographs and sonographs showing a prominent, nearly continuous, blocky, chaotic scarp at the seaward terminus of the failure zone and belts of small (10 m long, 0.5 m high; 33 ft long, 20 in. high) pressure ridges seaward of the scarp; and (3) sediment flow--identified from sonographs showing both (a) overlapping rhythmic flow deposits that become more irregular in a seaward di ection as flow became progressively less mobile, and (b) flow windows, or voids, left by highly viscous, dewatered flows. In addition to these large- and small-scale changes to the morphology of the sea floor on the Klamath River delta, the sediment failure resulted in several distinctive phenomena. These phenomena include a net seaward translation of sand, a reported temporary decrease in the abundance of Dungeness crabs, and plumes of gas venting into the water column that were still evident 11 months after the earthquake. End_of_Article - Last_Page 460------------

Temperature and Precipitation Estimates Through the Last Glacial Cycle from Clear Lake, California, Pollen Data

Modern pollen surface samples from six lake and marsh sites in the northern California Coast Ranges establish a linear relation between elevation and the oakl(oak + pine) pollen ratio. Modern temperature and precipitation lapse rates were used to convert variations in the pollen ratio into temperature and precipitation changes. Pollen data from two cores from Clear Lake, Lake County, California, spanning the past 40,000 and 130,000 years were used to estimate temperature and precipitation changes through the last full glacial cycle. The maximum glacial cooling is estimated to be 7 degrees to 8 degrees C; the last full interglacial period was about 1.5 degrees C warmer than the Holocene, and a mid-Holocene interval was warmer than the present. The estimated precipitation changes are probably less reliable than the estimated temperature changes.

Earthquake-induced sediment failures on a 0.25° slope, Klamath River delta, California

On November 8, 1980, a major earthquake (magnitude 6.5 to 7.2) occurred 60 km off the coast of northern California. A survey of the area using high-resolution seismic-reflection and side-scan sonar equipment revealed the presence of extensive sediment failure and flows in a zone about 1 km wide and 20 km long that trends parallel to the shelf on the very gently sloping ( c and a prominent 1- to 2-m high, seaward-facing toe scarp on the outer margin of the terrace. This toe scarp is sinuous, appears to be nearly continuous for a distance of 20 km, and closely parallels the 60-m isobath. Evidence indicates that the toe scarp is the terminus of lateral spreads and lobes of sediment flows. Side-scan sonar records show evidence of gas vents and small (10 × 3 × 0.5 m high) pressure ridges formed seaward of and parallel to the sediment flow scarp. Indicators of liquefaction (sand boils and collapse craters) are present on the sediment flow terrace. Extensive sediment failure occurred on a sea-floor slope of less than 0.25°, and we can unequivocally pinpoint the cause as an earthquake of known location, magnitude, and time.

Maritime Fiasco on the Northern California Coast

Maritime Fiasco on the Northern California Coast

Behavioral responses of seven species of asteroids to the asteroid predator, Solaster dawsoni (responses of asteroids to the predator Solaster dawsoni).

Seven asteroid species common to the northern California coast were studied for their defensive responses to the predator Solaster dawsoni. The presence or absence of an escape response was used to predict whether or not these species were susceptible to predation from Solaster. Strong escape responses were displayed by Patiria miniata, Henricia leviuscula, Leptasterias hexactis, Pycnopodia helianthoides, and small Pisaster ochraceus. Subsequent capture and consumption of Patiria, Henricia, Leptasterias and small P. ochraceus were observed. Solaster attacked all Pisaster spp. tested, but Pisaster brevispinus and larger P. ochraceus protected themselves from predation by utilizing their pedicellariae against Solaster whenever contact occurred. Dermasterias imbricata appeared to be immune to predation by Solaster. Contact between these two asteroids failed to elicit a defensive response in the former or an attack by the latter asteroid.

COASTAL ECOSYSTEM STUDIES AND THEIR APPLICATION TO OIL SPILL RESPONSE

ABSTRACT Because of increased energy demands, the coastal areas of the United States have been subject to rather severe land-use and water-use conflicts. One of the results has been the alteration of coastal habitats that support valuable fish and wildlife resources. Because of threats of further alteration, the U.S. Fish and Wildlife Service (FWS) has conducted several studies about coastal environments and environmental problems. Since 1975, nine coastal ecological studies have been completed; others are being negotiated. Study areas have included the coast of Maine, and central and northern California. Each of these studies provides an information base, a data analysis, and habitat maps. An ecological inventory of the Atlantic Coast has been completed and other inventories are contemplated for the Gulf of Mexico, the West coast of the United States, Alaska, and Hawaii. The ecological inventories mainly are maps showing types of land use and coastal fish and wildlife resources and their habitats. Other more site-specific or species-specific studies also have been published. These various reports about coastal ecology should be useful to national, regional, and field spill response teams for understanding environmental concerns more fully, planning regional oil spill responses, making on-site decisions, and planning post-spill environmental damage studies.

Sedimentary Facies Within Coastal Belt Franciscan Complex, Garberville Quadrangle, Northern California: ABSTRACT

Mildly deformed shale and sandstone, exposed along the South Fork of the Eel River in the Garberville Quadrangle (northern California Coast Ranges), are thought to represent a distinct lithofacies of the coastal belt Franciscan complex. These rocks have been correlated with the so-called Yager Formation, exposed farther to the north. Near Garberville, the folded sandy turbidites and shales are probably Eocene or younger in age, and are in contact with three other tectonostratigraphic units: (1) melange of the Franciscan central belt; (2) deformed sedimentary rocks of the coastal belt and King Range, exposed to the west; and (3) younger (Miocene-Pliocene) shelf deposits, which resemble the Wildcat Group of the Eel River basin. Regional mapping of turbidite facies (using the Ricci-Lucchi scheme) shows that a high percentage of the section consists of hemipelagic mudstone and shale; these facies G deposits are commonly interbedded with thin facies E silty turbidites. Locally, the fine-grained strata pass abruptly into sequences of thick-bedded to massive facies B sandstone and associated facies C turbidites. At one locality, thinner facies D turbidites are abundant within a thickening-upward and coarsening-upward sequence that is over 100 m thick. Small-scale thinning-upward cycles within this mega-sequence suggest localized channel migration and abandonment. The measured orientations of flute casts indicate that paleocurrents radiated toward the west and southwest, apparently at a high angle to the continent l margin. Together, these data suggest that sediments exposed in the Garberville area were probably deposited within continental slope and restricted basin settings. If the general model associating the Franciscan complex with a Mesozoic-Cenozoic trench wedge is followed, then these strata can be interpreted as sediments deposited on the trench slope and within small trench slope basins above the deformed accretionary prism represented by much of the rest of the Franciscan. End_of_Article - Last_Page 1003------------

Confirmation of Imbricate Thrusting in California Coast Ranges: Geology of Mysterious Valley Area, Napa County

End_Page 970------------------------------Most of the structural relief in the northern California Coast Ranges is generated by imbricate thrust faulting, although the region is undergoing major strike-slip deformation. In the Napa County Coast Ranges, the presence of subequal outcrop areas of Franciscan rocks and of Great Valley Sequence sediments and their underlying ultramafic basement, highlights the regional structures. The area is characterized by plunging folds which show relay patterns, by windows and klippen, and by vertical and lateral repetition of the stratigraphic section. Flat-lying faults are common. Individually these structures are best explained by thrust faulting; as an ensemble they are characteristic of the imbricate overthrust belts of compressional orogenes. Construction of a series of retrodeformable (balanced) cross sections, using a quantitative geometric theory of fault-bend folding, reveals a limited range of possible solutions to the regional deep structure. The structures include thrust faults rotated to high angles, anticlines formed by repeated small-scale imbrication, and regional back thrusts. The cross sections are characterized by thrust faults which rise southwestward cross strike and southeastward along strike from the Franciscan into the serpentinite and then into the Great Valley Sequence. Decollement horizons are recognizable in all three lithologies. The concept of imbricate thrusting provides a single unifying hypothesis with significant predictive ability which explains much of the map pattern and illuminates the three-dimensional structure of the eastern half of the Santa Rosa 1:250,000 map sheet. End_of_Article - Last_Page 971------------

Mineral paragenesis in Franciscan metagraywackes of the Nacimiento Block, a subduction complex of the Southern California Coast Ranges

Geologic‐petrographic reconnaissance of Franciscan metagraywackes from the Nacimiento block of the southern California Coast Ranges has demonstrated a perceptible eastward increase in metamorphic grade. Most feebly recrystallized zone I metaclastic rocks bordering the Pacific Ocean are rich in calcite veins and patches and contain no new Ca‐Al hydrous silicates; abundant unstable detritus includes lithic fragments, biotite flakes, and epidote granules. Metasedimentary rocks of medial zone II are characterized by fine‐grained intergrowths of pumpellyite ±5 minor regenerated epidote‐clinozoisite. Easternmost zone III metasandstones contain lawsonite, rarely aragonite and/or jadeitic pyroxene. In general, proportions of calcite, rock fragments, epidote, and biotite decrease eastward, and white mica, chlorite, and stilpnomelane increase. On the basis of experimental phase equilibrium data, temperatures of 150±50°C are estimated to have attended recrystallization, with lithostatic pressures increasing eastward from about 2–3 kbar on the west to approximately 5 kbar, and locally approaching 8 kbar, on the east. Absence of zeolites in the lowest grade zone I metagraywackes may indicate dilution of the aqueous fluid phase by CO2 during the metamorphism. In combination with the northwest tectonic ‘grain’ of the Nacimiento block and its inferred imbricate structure, the assemblage of rock types, the general north‐eastward dip of bedding, and predominantly right‐side‐up nature of the section, this continental margin deposit is thought to have been recrystallized during a period of relatively rapid (and perhaps brief) Late Cretaceous plate convergence. The lack of eclogite and amphibolite as tectonic blocks may indicate less profound depths of recovered subduction compared to Franciscan basement lying northeast of the San Andreas fault. Metamorphosed Nacimiento lithic belts evidently were assembled over a brief period of subduction offscraping at the western edge of the American lithospheric plate and seem to mirror events which unfolded over a longer time interval in Franciscan rocks of the northern California Coast Ranges.

Sources, Dispersal, and Clay Mineral Composition of Fine-Grained Sediment off Central and Northern California

Fine-grained sediment delivered to the continental margin of central and northern California is dominated by input from coastal rivers. Suspended sediment from northern California rivers (the Eel, Klamath-Trinity, Mad, Smith, and Mattole Rivers, and Redwood Creek) amounts to 81% of the sediment produced between Point Conception and the Oregon border. Steep and uns Table hillslopes combined with high rainfall and land use alterations produce average annual sediment yields up to nearly . Offshore circulation during periods of peak sediment discharge is dominated by the northerly flowing Davidson Current. LANDS AT imagery reveals large clockwise gyres that transport suspended sediment at least 100 km offshore in surface waters. Along the central coast the regional sediment yields are less than those along the northern California coast by an order of magnitude. Lower precipitation and numerous impoundments and diversions reduce sediment discharge. The Russian, Sacramento and San Joaquin Rivers do discharge significant volumes of suspended sediment, however. From Monterey Bay to Point Conception the climate is even drier, and sediment input declines further. Distinct sediment plumes on LANDS AT imagery, however, often extend offshore from Monterey Bay and also along the coast north of Point Conception. Based on the clay mineral composition of sediment samples from the continental margin, five distinct provinces were delineated. The composite clay mineral composition of the sediments taken from rivers draining into the individual provinces in general agree reasonably well with offshore compositions. Compositional differences existing off the central coast, however, are believed to be a result of relict Pleistocene sediments on the shelf which have not yet been covered by post-glacial sediment input.

Hydrocarbons reported off northern California coast

The USGS reports finding the first concentrations of hydrocarbons off the northern California coast in a sea floor sample taken about 40 km. east of Eureka. Analyzed aboard RV Sea Sounder, the 1.6‐m gravity core was found to contain anomalously high amounts of natural gases, ranging from methane to butane.The sample was collected and examined by Michael E. Field, Keith A. Kvenvolden, and Samuel H. Clarke, Jr. It was taken in November from a small pond of sediment near the crest of a knoll about 500 m below the sea surface on the Eel Plateau. The knoll, say the scientists, is a diapir‐like structure similar in some respects to the salt domes in the petroleum regions of Texas and the Gulf of Mexico.

Sediment Sources and Clay Mineral Distributions Off the Oregon Coast

ABSTRACT Results of clay mineral analyses of surface sediments from the Oregon continental margin are combined with estimates of continental sediment influx to determine the relations between major source regions and dominant dispersal pathways of fine grained sediment in offshore areas. Both the clay assemblages and the sediment supply estimates indicate that the rivers of the northern California Coast Range, the Klamath Mountains and the Columbia Watershed are the principal sediment suppliers, providing over 90 percent of the silts and clays to the Oregon margin and Cascadia Basin. In order of importance, the major sediment sources appear to be, in l06 tonnes/year, the Eel (24.8), Columbia (14.3), Klamath (10.9), Rogue (4.7 estimated), Umpqua (3.2) and Mad (2.5) rivers. Trends in the clay mineral distributions suggest that deposition of fine grained sediments on the Oregon continental shelf is controlled by seasonal meteorological and oceanic factors such as periodic peak river discharges, winter storms and summer coastal upwelling. A lobe of montmorillonite-rich clays on the northern Oregon shelf may be caused either by southward extension of the Columbia River Plume in May-June, or more likely, from discharges of local Coast Range streams and northward transport during the winter months. Montmorillonite-rich clays found in submarine canyons and channel systems suggest that much of the Columbia load is channelled to abyssal fans off Washington and northern Oregon. On the continental slope, clays relatively rich in chlorite indicate that a portion of the massive influx from the northern California and southern Oregon coastal streams is carried northward, probably via the California Undercurrent. The imprint of this poleward flow can be traced to marginal areas off the Washington coast. Clays in the Cascadia Basin appear to be a mixture of Columbia River and Klamath/California Coast Range type sediments, suggesting that the northward flow may not be confined to the continental slope.

A sediment budget and an analysis of geomorphic process in the Van Duzen River basin, north coastal California, 1941–1975: Summary

The coastal river basins of the northern California Coast Ranges have the highest sediment discharge of basins of comparable size with the United States (Judson and Ritter, 1964; Brown and Ritter, 1971; Knott, 1971; Janda, 1975; Brown, 1975). The high erosion rates in this region are caused by the unique combination of tectonic setting, geology, land use, and climate. This rapidly eroding region is located adjacent to the seismically active triple junction of three crustal plates near Cape Mendocino, California; late Tertiary and Quaternary underthrusting along the continental margin has caused recent (post-mid-Miocene) uplift (Silver, 1971). The area is underlain by the Mesozoic and early Cenozoic Franciscan assemblage, which is a deformed, faulted, locally sheared, and in part metamorphosed accumulation of continental-margin deposits. These deposits consist of intermixed units of melange and more coherent sandstones. The melange consists of an intensely sheared matrix of siltstone or sandy siltstone in which are dispersed large blocks and smaller boulders of sandstone, metasandstone, greenstone, chert, blueschist, and greenschist. Before European settlement, the area was vegetated with redwood (Sequoia sempervirens) , Douglas fir (Pseudotsuga menziesii) , and interior expanses of grassland and grass-oak woodland. Since 1870, the region has undergone progressively more intensive land use. Cattle and sheep grazing on the prairies became widespread by the 18709s, and harvesting of redwood in the lower basin started in the late 18809s. Extensive harvesting of Douglas fir commenced on private lands in the middle and upper portions of the basin after World War II and continued until the mid-sixties. The region has high annual rainfall (125 to 300 cm) that occurs almost entirely between October and April. Between two and six intense rainstorms each winter furnish the streamflows that transport the majority of the annual sediment yield. An important climatic feature is the occurrence at intervals of 100 to 500 yr of storms of extreme intensity and duration that may be responsible for much of the erosion in the region. One such storm occurred in December of 1964. All of the above features, the climate, tectonic setting, geology, vegetation, and land-use history, probably contribute to the high erosion rate of the region. In order to reach some understanding of the relative contributions of these factors and of how sediment moves through the watershed in this region, a detailed analysis was undertaken of the processes and distribution of erosion and deposition in the upper 575 km 2 of the 1,111-km 2 Van Duzen River basin (Kelsey, 1977). The Van Duzen is the northernmost tributary of the Eel River in north coastal California, and flows into the Eel 22 km upstream of its mouth (Fig. 1). Field work for the study took place in 1973–1976. In addition, six sets of aerial photos covering the basin from 1941 through 1975 are available, and stream-gaging records for a U.S. Geological Survey gaging station at the downstream end of the study area near Bridgeville, California, have been available since 1951. A study of changes recognizable in the aerial photographs and interpretation of stream-gaging data for 1940–1975 and sediment discharge data for the periods 1956–1967 and 1975–1976 make possible an analysis of erosion and sedimentation for the 35-yr period, 1941–1975. Surveying records going back to 1869, plus datable trees buried by flood deposits, make it possible to extend some aspects of the record to the last century.

The Fort Ross earthquake sequence, March and April, 1978

abstract On March 31, 1978, an earthquake of coda magnitude 3.3 (ML = 3.7 BRK) occurred 5 km off the coast of northern California near Fort Ross. A single foreshock preceded the earthquake and approximately 60 aftershocks followed. Locations based on P- and S-wave arrival times indicate that the earthquakes occurred offshore, west of the San Andreas fault in the vicinity of a fault that is visible on acoustic reflection profiles. All earthquakes had hypocentral depths less than 8 km. A fault-plane solution from P-wave first motions suggests that the focal mechanism of the main shock consisted of nearly equal components of dextral and vertical movement on a plane striking northwest. Other events in this sequence had first-motion patterns strikingly different than the main shock, indicating that more than one type of faulting occurred during the sequence. Seismic moments computed for three aftershocks ranged from 3.8 × 1019 to 1.1 × 1019 dyne-cm.

Geologic mapping for coastal zone planning in California—Background and examples

With increasing pressure for development on one of California's greatest natural resources, her coastline, comprehensive land-use planning becomes a necessity. One aspect of land-use planning is effective geologic mapping for the delineation of geologic hazards. Geologists from the California Division of Mines and Geology undertook an evaluation of the feasibility of local government implementation of the geologic policies in the 1975 California Coastal Plan, a plan designed to facilitate and direct comprehensive coastal land-use planning. Operating under restrictions similar to those that would be encountered by local agencies attempting to implement the policies, the Division of Mines and Geology personnel applied the geologic guidelines to two areas in Mendocino County on the northern coast of California. Using limited data and reconnaissance mapping techniques, reports and maps were prepared which delineated the geologic hazards that should be considered in coastal land-use planning. It was apparent from the two studies that the types and detail of data required for the implementation of the geologic policies of the Coastal Plan could be developed by local agencies only by augmenting their staffs to include trained geologists or by using the services of outside consultant geologists.

Technological Innovation: Capital and Labour

Two case histories are provided as accounts of technological innovation in a particular industry, i.e. bulk cargo handling and containerisation in the Port Industry. The geographical setting is the Pacific Coast of Northern California, more precisely at Sacramento and at San Francisco. The information was gathered during October and November 1975, from local sources through personal interviews, with key people and literature relating directly to the two ports. An additional source was the unpublished Masters Degree thesis of Andrea Mohn, ‘Economic Impact of the Port of Sacramento: Its Sources and Results’, of California State University, Sacramento. The report as a whole identifies certain key motifs:

Earthflows in Franciscan melange, Van Duzen River basin, California

Large earthflows are a significant source of sediment in the highly sheared and easily eroded Franciscan melange of the northern California Coast Ranges. They are active during the winter wet season, and their movement averages 2.4 to 4.0 m/yr. Fluvial sediment yield from the gullied and broken earthflow surface is about equal to sediment yield by mass movement. Indirect evidence suggests that changes in vegetation cover due to grazing beginning in the nineteenth century may have increased the rate of earthflow movement.

The Summertime Stratus over the Offshore Waters of California

Abstract Satellite pictures have been used to investigate the distribution of stratus clouds over the Pacific Ocean near California during one summer. A north-south oriented line of minimum cloudiness, which was particularly well-defined in July, was found off the northern and central California coast. The characteristic is believed to be caused by strong divergence of the surface winds. The clouds east of this minimum cloudiness line are generally “smooth-topped” stratus that form in air which is cooled by the upwelled water adjacent to the coast; in contrast, those to the west of the line are mainly stratocumulus, formed in air streaming southward over warmer water. A strong diurnal variation in low cloudiness was noted: over 18% of the clouds present at 0745 PST dissipated (in the mean) by 1345 PST. The maximum cloud cover occurred near sunrise and the minimum in the late afternoon, suggesting that the net radiative flux by clouds is primarily responsible for the diurnal variation. Divergence and advec...