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Research about Northern California

Source-linked reports with geographic coverage including Northern California.

9 recordsLinked to original sources
USGS2026

Constraining source and path effects of large magnitude earthquakes using ground motion simulations

The purpose of this study is to use ground‐motion simulations to investigate ways in which source and path effects for large‐magnitude earthquakes can be represented in nonergodic ground‐motion models (GMMs). To achieve this, we designed a ground‐motion study in the San Francisco Bay Area that includes earthquakes with a broad range of magnitudes distributed uniformly on a fault plane, and sites covering a large range of rupture distances and azimuths. After running a large suite of kinematic simulations (magnitude 4–7), we then develop a nonergodic GMM with the simulated data. We find that trends in the within‐site residuals are affected significantly by the earthquake radiation pattern, rupture directivity, and slip patterns. Next, we modify an existing rupture directivity model to fit and remove the observed radiation pattern and rupture directivity from the residuals. We also minimize the contributions of slip patterns by averaging the within‐site residuals among multiple source realizations. Finally, after removing the source effects from the within‐site residuals, we compare the path effects computed with different magnitude groups using two approaches. The first approach only considers the small events that have the same shortest path to a site as the large events, whereas the second approach considers all small events on the fault plane. The results indicate that it is difficult to satisfactorily approximate the path effects of large events with those of small events using either approach, at least in the case of simulations.

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USGS2020

Simultaneous Middle Pleistocene eruption of three widespread tholeiitic basalts in northern California (USA): Insights into crustal magma transport in an actively extending back arc

Mapping and chronology are central to understanding spatiotemporal volcanic trends in diverse tectonic settings. The Cascades back arc in northern California (USA) hosts abundant lava flows and normal faults, but tholeiitic basalts older than 200 ka are difficult to discriminate by classic mapping methods. Paleomagnetism and chemistry offer independent means of correlating basalts, including the Tennant, Dry Lake, and Hammond Crossing basalt fields. Paleomagnetic analysis of these chemically similar basalts yield notable overlap, with statistical analysis yielding 7 chances in 1,000,000 that their similar mean remanent directions are random. These basalts also have overlapping 40 Ar/ 39 Ar ages of 272.5 ± 30.6 ka (Tennant), 305.8 ± 23.9 ka (Dry Lake), and 300.4 ± 15.2 and 322.6 ± 17.4 ka (Hammond Crossing). Chemical and paleomagnetic analyses indicate that these spatially distributed basalts represent simultaneous (<100 yr uncertainty) eruptions, and thus we use 305.5 ± 9.8 ka (weighted mean) as the eruption age. Their vents align on a N25°W trend over a distance of 39 km. Tennant erupted the largest volume (3.55 ± 0.75 km 3 ) at the highest elevation; both factors decay to the south-southeast at Dry Lake (0.75 ± 0.15 km 3 ) and Hammond Crossing (0.15 ± 0.05 km 3 ). We propose vertical magma ascent beneath the Tennant vent area, where the most evolved, high-SiO 2 magma erupted, with lateral dike propagation in the brittle crust. Propagation was near orthogonal to east-west extension (0.3–0.6 mm/yr) along north-northwest–trending normal faults.

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USGS2020

Virome of bat guano from nine northern California roosts

Bats are hosts to a large variety of viruses, including many capable of cross species transmissions to other mammals or humans. We characterized the virome in guano from five common bat species in 9 Northern California roosts and a pool of 5 individual bats. Genomes belonging to 14 viral families known to infect mammals and 17 viral families infecting insects or of unknown tropism were detected. Near or complete genomes of a novel parvovirus, astrovirus, nodavirus, CRESS-DNA viruses and densoviruses and more partial genomes of a novel alphacoronavirus, and bunyavirus were characterized. Lower numbers of reads with >90% amino acid identity to previously described calicivirus, circovirus, adenoviruses, hepatovirus, bocaparvoviruses, and polyomavirus in other bat species were also found likely reflecting their wide distribution among different bats. Unexpectedly a few sequence reads of canine parvovirus 2 and the recently described mouse kidney parvovirus were also detected and their presence confirmed by PCR possibly originating from guano contamination by carnivores and rodents. The majority of eukaryotic viral reads were highly divergent indicating that numerous viruses still remain to be characterized even from such a heavily investigated order as Chiroptera.

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USGS2019

Eruption age and duration of the ~9 km3 Burney Mountain dacite dome complex, northern California

At ~9 km3, the six dacite domes of Burney Mountain (db1–db6) constitute the most voluminous Quaternary dome complex in the Cascades volcanic arc. Whole-rock geochemistry, electron microprobe, and petrographic data indicate that the domes are magmatically related, which, when integrated with geomorphology and stratigraphy, indicate early (db1, db2, db3) and late (db4, db5, db6) erupted groups. We present 40Ar/39Ar ages of 271.9±4.6 ka (db1), 280.8±8.2 and 281.7±6.8 ka (db2), and 290.2±6.0 ka (db3) along with a previous age of 280±12 ka (db1). These ages scatter over 20 kyr, whereas remanent magnetic directions are similar between 53.3–59.0° inclination and 352.7–355.9° declination. The latter dataset indicates that the dacite domes were emplaced over a geologically brief time interval; not thousands of years. Crystal-size distribution patterns of plagioclase were used to calculate residence times, which we use to infer the duration over which the eruptions likely occurred. Three slopes represent three populations of plagioclase crystals (fine-grained groundmass, coarse-grained groundmass, phenocrysts). A commonly used growth rate for plagioclase in dacitic magmas (10-10 mm/s) yields 9–10 years of growth for the coarse-grained groundmass (early erupted domes of db1, db2, db3), whereas plagioclase in the fine-grained groundmass (late erupted domes of db4, db5, db6) grew over 4–5 years. All plagioclase phenocrysts have apparent residence times of 26–36 years; however, they contain high An>70 resorbed cores with sieve textures, which have euhedral, lower An<65 overgrowth rims. Similarities in chemistry between groundmass plagioclase and phenocryst overgrowth rims indicate that they grew concurrently, and we therefore propose that both have similar residence times. Thus, the Burney Mountain dacite dome complex was emplaced during a single eruptive episode over the course of years to decades at 281.1±4.8 ka (weighted mean age).

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USGS2011

Effect of dietary salt on migration and survival of yearling steelhead produced at Iron Gate Hatchery, Klamath River, 2009

We surgically implanted radio transmitters into 30 hatchery yearling steelhead (Oncorhynchus mykiss) released from Iron Gate Hatchery during the spring of 2009 to improve our understanding of the effect of dietary salt on their out-migration and survival. Steelhead yearlings were divided into two feed treatments to test the efficacy of a salt-enriched feed in promoting out-migration. Fish were fed either their regular diet (control treatment) or a salt-enriched diet (test treatment) for 38 d prior to their release. We implanted 15 fish of each treatment with radio transmitters for a total of 30 tagged individuals. Nine of the radio-tagged steelhead (four of the control treatment; five of the test treatment) completed their downstream migration to the estuary within the 60-d operational period of the tags. Tagged fish migrated from the hatchery release site to the estuary in an average of 45 d. Neither migration nor survival differed between diet treatments, but small sample size and the relatively short duration of this study limit the conclusiveness of our findings.

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USGS1986

Long-term on-site and off-site effects of logging and erosion in the Redwood Creek basin, northern California

For nearly 15 years, the Redwood Creek Watershed in north coastal California has been the focus of both U.S. Geological Survey (USGS) and National Park Service (NPS) studies designed to document and quantify the nature of erosion, sedimentation and sediment transport processes active in the basin. While none of these studies were specifically designed to assess possible cumulative effects resulting from land use, we can demonstrate, by synthesizing a number of study findings throughout the watershed, that some land use practices do result in long-term and persistent changes to hillslopes and stream channels. For this discussion, "Cumulative Effects" are viewed as multiple, persistent impacts which are separated in either space or time from the original land use disturbance. Although each incremental disturbance may have an insignificant effect when viewed alone, the impacts may become cumulatively significant when seen in aggregate or when multiple erosion sources are triggered simultaneously by a large storm. For example, an undersized culvert which becomes plugged of whose capacity is exceeded by storm runoff can cause erosion at the site where it is installed as all or part of the fill crossing is washed out. In addition, streamflow can be diverted from the channel and cause considerable erosion in downslope areas where gullies will form, and in far removed fish-bearing streams where the sediment is finally deposited. In addition to being spatially displaced from its source, the effect may also be delayed in time. The undersized culvert may not plug or its capacity be exceeded for many years, and the resultant erosion and sedimentation may not occur for decades after the original disturbance. An entire road network, which is not being permanently maintained or whose culverts have been underdesigned, may not reveal significant erosional impacts from road construction until a major storm cause widespread culvert failure, stream crossing erosion and stream diversions. The effects of land use are then additive, occur essentially instantaneously over large areas, and are displaced both spatially and temporally from their source and time of initiation. The objective of this brief report is to describe how specific land use practices can cause multiple on-site and off-site geomorphic impacts which may become obvious only years following the land use disturbance. Additionally, we will briefly outline how a large percentage of these persistent effects can be avoided entirely by minor changes in road construction techniques.

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USGS1984

Correlation of the middle eocene Kellogg Shale of northern California

The Kellogg Shale of northern California has traditionally been considered to be late Eocene in age on the basis of benthic foraminifer, radiolarian, and diatom correlations. The 30-m-thick Kellogg section exposed west of Byron, California, however, contains middle Eocene planktonic foraminifers (Zone P12), coccoliths (Subzones CP13c and CP14a), silicoflagellates (Dictyocha hexacantha Zone), and diatoms. Quantitative studies of the silicoflagellates and diatoms show a general cooling trend through the section which is consistent with paleoclimatic trends for this part of the middle Eocene (ca. 42-45 Ma) from elsewhere in the world. Seven new silicoflagellate taxa (Corbisema angularis, C. exilis, C. hastata miranda, C. inermis ballantina, C. regina, Dictyocha byronalis, Naviculopsis americana) and one new coccolithophorid species (Helicosphaera neolophota) are described.

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USGS1979

Trees as indicators of past movements on the San Andreas Fault

Trees are sources of information about fault movements that have occurred before the earliest historical reports. This kind of evidence can be used to improve estimates of when earthquakes will recur on faults known to be seismically active and to identify active faults that have no record of movement during recent history. The approach is not new. Robert Page of the U.S Geological Survey described the effects of the 1958 earthquake on trees along the Fairweather fault in Alaska. He showed that tree rings methods could have been used to identify and to closely date this event. We undertook a similar study of the northern part of the San Andreas fault, in part because there are no historic records prior to 1906 along this segment. Earthquakes and surface rupture along faults affect trees in several different ways. Direct effects include fracturing, twisting, and tilting of trees that grown on the surface of the break. In a much wider zone along the fault, trees may be felled or topped as a result of ground motion. Among the indirect effects are tilting, felling, or burial of trees in earthquake-triggered landslides. Long-term effects may include changes in growth rate due to local hydrologic and topographic changes as well as to biological effects such as the death of neighboring trees. Under favoralbe circumstances these can be dated by tree ring methods.

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