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Research about San Francisco, California

Source-linked reports with geographic coverage including San Francisco, California.

At least 19 recordsLinked to original sources
USGS2026

Assessment of extreme subsurface hydrologic conditions captured during atmospheric river storms in the San Francisco Bay area (California, USA) with applications to shallow landslide early warning

An increase in soil pore water pressure is the typical trigger for the majority of landslides caused by rainfall. Atmospheric river storms, common to the west coast of North America during the winter season, can deliver landslide triggering rainfall resulting in severe impacts to coastal communities. Using a network of hydrologic monitoring stations situated within landslide-prone terrain in the San Francisco Bay area of California (USA), we assess the meteorologic conditions and resulting hydrologic and landslide response resulting from eight consecutive storm events that caused thousands of shallow landslides during the winter of 2022–2023. We find disparate hydrological responses and resultant degrees of observed landsliding ranging from < 1 landslide/km2 to 18 landslides/km2 at the monitoring sites that reflect the interplay and differences between rainfall delivery, subsurface hydrological characteristics, and geotechnical properties at each site. Antecedent soil moisture from both early season rainfall and the first storm in the sequence played a critical role in setting up some hillslopes for failure. Subsequent storms then generated elevated pore water pressures for several hours with associated landsliding. However, we find that the occurrence of widespread landsliding required not only sufficient pore water pressure magnitude in susceptible hillslopes, but also full and prolonged effective soil saturation throughout hillslope profiles. Landslides may still occur at lower values and durations of effective saturation but are likely to be less extensive regionally. We present these findings within the context of research directions and improvements to landslide early warning systems first suggested by researchers 40 years ago.

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USGS2025

Relationship between peak and cumulative ground motions from 49 Mw 3-6 earthquakes in the San Francisco Bay Area

We examine the relationship between peak ground velocity (PGV) and cumulative absolute displacement (CAD) for 49 M w 3 – 6 earthquakes in the San Francisco Bay Area (SFBA) and gain insight into the spatiotemporal partitioning of seismic energy in ground motion records with respect to source, path, and site effects. PGV and CAD are positively correlated, but there can be large deviations from the average trend. For example, ground motion records with either very long duration resonance or short pulse-like motions will have higher or lower CAD, respectively, but could have very similar PGV. We perform principal component analysis (PCA) on PGV-CAD for >7000 records in the SFBA with the goal of investigating what influences positive or negative anomalies in cumulative motions. PCA rotates the PGV-CAD datapoints into two principal components, where the one with the larger variance, which we call the “primary intensity” represents mostly the distance-dependence of ground motion amplitudes. The other principal component, which we call the “excess motion”, represents the deviation from cumulative motions that would be typical for a ground motion record with a given PGV. The excess motion will be positive in the case of records with long duration ringing and will be negative for short duration pulse-like ground motions. We find that excess motion is generally positive at sites in sedimentary basins and in soft sediments around the SF Bay. Excess motion is generally negative in the very near field, as well as at sites on hard bedrock. We discuss the findings here in terms of implications for seismic hazard applications and other wave propagation phenomena.

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USGS2021

The potential of satellite remote sensing time series to uncover wetland phenology under unique challenges of tidal setting

While growth history of vegetation within upland systems is well studied, plant phenology within coastal tidal systems is less understood. Landscape-scale, satellite-derived indicators of plant greenness may not adequately represent seasonality of vegetation biomass and productivity within tidal wetlands due to limitations of cloud cover, satellite temporal frequency and attenu-ation of plant signals by tidal flooding. However, understanding plant phenology is necessary to gain insight into aboveground biomass, photosynthetic activity, and carbon sequestration. In this study we use a modeling approach to estimate plant greenness throughout a year in tidal wet-lands located within the San Francisco Bay Area, USA. We used variables such as EVI history, temperature, and elevation to predict plant greenness on a 14-day timestep. We found this ap-proach accurately estimated plant greenness, with larger error observed within more dynamic restored wetlands, particularly at early post-restoration stages. We also found modeled EVI can be used as an input variable into greenhouse gas models, allowing for an estimate of carbon se-questration and gross primary production. Our strategy can be further developed in future re-search by assessing restoration and management effects on wetland phenological dynamics and through incorporating the entire Sentinel-2 time-series once it becomes available within Google Earth Engine.

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USGS2021

A geology and geodesy based model of dynamic earthquake rupture on the Rodgers Creek‐Hayward‐Calaveras Fault System, California

The Hayward fault in California's San Francisco Bay area produces large earthquakes, with the last occurring in 1868. We examine how physics‐based dynamic rupture modeling can be used to numerically simulate large earthquakes on not only the Hayward fault, but also its connected companions to the north and south, the Rodgers Creek and Calaveras faults. Equipped with a wealth of images of this fault system, including those of its 3D geology and 3D geometry, in addition to inferences about its interseismic creep‐rate pattern and rock‐friction behavior, we use a finite‐element computer code to perform 3D dynamic earthquake rupture simulations. We find that the rock properties affect the locations and amount of slip produced in our simulated large earthquakes. Crucial factors that control rupture behavior in our modeling are the earthquake nucleation locations, the fault geometry, and the data that reveal where the fault system is creeping or locked. Our findings suggest that large Rodgers Creek‐Hayward‐Calaveras‐Northern Calaveras (RC‐H‐C‐NC) fault‐system earthquakes may result from dynamic rupture that starts in a locked part of the fault system, but is then stopped by the creeping parts, leading to high‐magnitude‐6 earthquakes; or, from dynamic rupture that starts in a locked part of the fault system, then cascades through some of the creeping parts, leading to magnitude‐7 earthquakes.

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USGS2021

Seasonal impoundment alters patterns of tidal wetland plant diversity across spatial scales

Understanding patterns of biodiversity is a key goal of ecology and is especially pressing in the current human‐caused biodiversity crisis. In wetland ecosystems, human impacts are centered around hydrologic manipulation including the common practice of wetland diking and impoundment. Constraining how wetland management influences plant biodiversity patterns across spatial scales will provide information on how best to modify actions to preserve biodiversity and ecosystem function in managed wetlands. Here, we compare patterns of plant diversity and species presence, abundance, and community composition at several spatial scales among tidal wetlands along an estuarine salinity gradient and managed wetlands that were formerly tidal. Managed impounded wetlands had decreased alpha and gamma diversity of rare species, with less than 60% of the species richness found in tidal brackish wetlands at several spatial scales. There was little change in the overall pattern of alpha, beta, and gamma diversity for common species in impounded wetlands; however, dominant tidal brackish species, primarily perennial rhizomatous graminoids, were replaced with management target plants and non‐native annual grasses in impounded wetlands. This species replacement led to over 60% of impounded sites being classified as containing novel plant assemblages. An additional 25% of impounded sites were classified as containing tidal saline plant assemblages, suggesting potential soil salinization. Along the estuarine gradient, patchiness and codominance of common plant species drove high diversity and turnover in tidal brackish wetlands, while it remains unclear whether tidal fresh or brackish wetlands maximize rare plant diversity. With reduced species richness, altered functional dominants, and novel or saline assemblages, impounded brackish wetlands may require careful water management to balance native plant biodiversity, associated ecosystem processes, and waterfowl requirements.

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USGS2020

Salinity and inundation effects on productivity of brackish tidal marsh plants in the San Francisco Bay-Delta Estuary

Plant productivity is central to numerous ecosystem functions in tidal wetlands. We examined how productivity of brackish marsh plants in northern California responded to abiotic stress gradients of inundation and salinity using two experimental approaches. In a greenhouse study with varying salinity, shoot production and biomass of Juncus balticus , Schoenoplectus acutus and S. americanus all declined monotonically with higher salinity, with evidence of differences in sensitivity among species by their varied functional responses. Salinity also negatively affected fecundity for the one species ( S. americanus ) that produced enough inflorescences during the experiment for analysis. In a field manipulation of inundation and initial pore water salinity, total end-of-season biomass and other metrics of growth in the high marsh species, J. balticus , had unimodal relationships with inundation. Root production tended to be greater strongly impacted by greater inundation than shoot production. The salinity treatment quickly dissipated for treatments that were flooded more frequently but persisted at a higher marsh elevation where it suppressed plant growth. These results suggest that both increased flooding and salinity associated with climate change and sea-level rise may negatively impact productivity of brackish marsh species, but with variable effects by species and stressor.

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USGS2020

Production of the copepod Pseudodiaptomus forbesi is not enhanced by ingestion of the diatom Aulacoseira granulata during a bloom

In 2016, a massive bloom of the chain-forming diatom Aulacoseira granulata occurred in the upper San Francisco Estuary, California, with chlorophyll concentrations up to 75 μg Chl L −1 . In this study, quantitative PCR was used to investigate consumption of the bloom organism by the numerically dominant zooplankter Pseudodiaptomus forbesi (Copepoda: Calanoida) and to estimate the contribution of the bloom to egg production. Copepods were collected on four transects during May and June 2016; egg production rates were somewhat elevated above previous rates measured in the estuary. Ingestion of A. granulata was highest on the first sampling day, just after the peak of the bloom, ranging from 175 to 945 cells copepod −1 day −1 . One month later ingestion rates dropped to 0–130 cells copepod −1 day −1 , despite continued dominance of A. granulata in the plankton. Ingestion of A. granulata provided from 0 to 21% (median 1%) of the estimated daily carbon required for growth and reproduction of P. forbesi . Although the copepods probably obtained nutrition from a microbial food web stimulated by the bloom, monitoring data showed little demographic response to this bloom. Thus, a massive diatom bloom in an unproductive estuary provided only a minor stimulus through an abundant consumer to the pelagic food web.

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USGS2020

Brackish tidal marsh management and the ecology of a declining freshwater turtle

Water management practices in tidal marshes of the San Francisco Bay Estuary, California are often aimed at increasing suitable habitat for threatened fish species and sport fishes. However, little is known about how best to manage habitat for other sensitive status species like the semiaquatic freshwater Western Pond Turtle (Actinemys marmorata) that is declining throughout much of its range. Here, we examined the basking activity, abundance, survival, and growth of Western Pond Turtles at two brackish water study sites in Suisun Marsh, California that differed in how they were managed, with one having passive management (i.e., no active water regulation) and another having active management (i.e., water regulated for seasonal hunting). Our results revealed that basking activity was greatest when salinity, water stage, and air temperatures were low, shortwave radiation was high, and wind levels were intermediate. These preferred habitat characteristics often reflected conditions that were naturally maintained at the passively managed, muted tidal site. We also found that turtles were more abundant and had higher survival rates in the passively managed habitat compared to the actively managed habitat (201-323 turtles/km 2 and 96% survival versus 11-135 turtles/km 2 and 77% survival, respectively). Finally, characteristic growth constants from von Bertalanffy models showed that turtles grew more quickly in passively managed habitat compared to the actively managed habitat. Our results suggest that management strategies for this sensitive status species may be more effective if they protect passively managed muted tidal systems that limit or delay extreme cycles of salinity and water levels and conserve elevated terrestrial buffer zones adjacent to muted and full tidal systems.

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USGS2020

Use of the smeltCam as an efficient fish sampling alternative within the San Francisco Estuary

Resource managers often rely on long-term monitoring surveys to detect trends in biological data. However, no survey gear is 100% efficient, and many sources of bias can be responsible for detecting or not detecting biological trends. The SmeltCam is an imaging apparatus developed as a potential sampling alternative to long-term trawling gear surveys within the San Francisco Estuary, California, to reduce handling stress on sensitive species like the Delta Smelt ( Hypomesus transpacificus ). Although believed to be a reliable alternative to closed cod-end trawling surveys, no formal test of sampling efficiency has been implemented using the SmeltCam. We used a paired deployment of the SmeltCam and a conventional closed cod-end trawl within the Napa River and San Pablo Bay, a Bayesian binomial N -mixture model, and data simulations to determine the sampling efficiency of both deployed gear types to capture a Delta Smelt surrogate (Northern Anchovy, Engraulis mordax ) and to test potential bias in our modeling framework. We found that retention efficiency—a component of detection efficiency that estimates the probability a fish is retained by the gear, conditional on gear contact—was slightly higher using the SmeltCam (mean = 0.58) than the conventional trawl (mean = 0.47, Probability SmeltCam retention efficiency > trawl retention efficiency = 94%). We also found turbidity did not affect the SmeltCam’s retention efficiency, although total fish density during an individual tow improved the trawl’s retention efficiency. Simulations also showed the binomial model was accurate when model assumptions were met. Collectively, our results suggest the SmeltCam to be a reliable alternative to sampling with conventional trawling gear, but future tests are needed to confirm whether the SmeltCam is as reliable when applied to taxa other than Northern Anchovy over a greater range of conditions.

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USGS2019

Joint system-input identification of bridge structures

This paper presents a novel framework for system identification of bridge structures using recorded earthquake data. Bridge structures are prone to spatial variability of ground motions because they extend over relatively long distances. So, input motion measurement is a challenging task, especially for long bridges with multiple piers. Moreover, direct measurement of the bridge Foundation Input Motions (FIMs) may not be possible due to both inertial and kinematic Soil-Structure Interaction (SSI) effects. In this study, we propose a joint system-input identification solution using sparsely measured earthquake-induced responses. We verify this method and its applicability for real scale problems using simulated data obtained from the Golden Gate Bridge.

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USGS2019

The behavior of the Salesforce Tower, the tallest building in San Francisco, California inferred from earthquake and ambient shaking

The newly constructed tallest building designed in conformance with performance-based design procedure in San Francisco, California is a 61-story building equipped with an accelerometric array that recorded the January 4, 2018 M4.4 Berkeley earthquake. The building is designed with concrete core shear walls and perimeter gravity steel columns. The earthquake records as well as on-demand recorded ambient responses of the building are studied to determine its dynamic characteristics and building-specific behavior. At the level of shaking of either the earthquake or ambient excitation, the frequencies and low modal damping ratios (<2%) are similar. The building exhibits torsional behavior most likely due to abrupt asymmetrical changes in the size of the core shear wall. The translational and torsional modes during the earthquake are closely coupled, which leads to a beating effect, the period of which is calculable. Due to the relatively low-amplitude shaking during the earthquake, the drift ratios were small and did not cause any damage. It is expected that during stronger shaking levels, these characteristics may change.

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USGS2018

The influence of neap-spring tidal variation and wave energy on sediment flux in salt marsh tidal creeks

Sediment flux in marsh tidal creeks is commonly used to gage sediment supply to marshes. We conducted a field investigation of temporal variability in sediment flux in tidal creeks in the accreting tidal marsh at China Camp State Park adjacent to northern San Francisco Bay. Suspended-sediment concentration (SSC), velocity, and depth were measured near the mouths of two tidal creeks during three six-to-ten-week deployments: two in winter and one in summer. Currents, wave properties and SSC were measured in the adjacent shallows. All deployments spanned the largest spring tides of the season. Results show that tidally-averaged suspended-sediment flux (SSF) in the tidal creeks decreased with increasing tidal energy, and SSF was negative (bayward) for tidal cycles with maximum water surface elevation above the marsh plain. Export during the largest spring tides dominated the cumulative SSF measured during the deployments. During ebb tides following the highest tides, velocities exceeded 1 m/s in the narrow tidal creeks, resulting in negative tidally-averaged water flux, and mobilizing sediment from the creek banks or bed. Storm surge also produced negative SSF. Tidally-averaged SSF was positive in wavey conditions with moderate tides. Spring-tide sediment export was about 50% less at a station 130 m further up the tidal creek than at the creek mouth. The negative tidally-averaged water flux near the creek mouth during spring tides indicates that in the lower marsh, some of the water flooding directly across the bay--marsh interface drains through the tidal creeks, and suggests that this interface may be a pathway for sediment supply to the lower marsh as well.

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USGS2018

Geology and geologic history: Overview of the geology of the San Francisco Bay region

The geology of San Francisco and the surrounding northern and central California area has played a pivotal role in the development of our understanding of Earth processes, especially the process of tectonic accretion at a continental margin and the development of transform plate margins. The Franciscan Complex, which underlies most (or perhaps all) of the City and County of San Francisco, is widely considered the "type" accretionary complex. More regionally, the Sierra Nevada, Great Valley, and Coast Ranges are often used as an illustration of the arc-forearc-accretionary prism geometry of a continental convergent margin, and the San Andreas Fault, just offshore to the west of San Francisco, serves as the prototype transform plate margin, although as illustrated below the actual geometry and geologic history is more complicated.

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USGS2017

What determines water temperature dynamics in the San Francisco Bay-Delta system?

Water temperature is an important factor determining estuarine species habitat conditions. Water temperature is mainly governed by advection (e.g., from rivers) and atmospheric exchange processes varying strongly over time (day-night, seasonally) and the spatial domain. On a long time scale, climate change will impact water temperature in estuarine systems due to changes in river flow regimes, air temperature, and sea level rise. To determine which factors govern estuarine water temperature and its sensitivity to changes in its forcing, we developed a process-based numerical model (Delft3D Flexible Mesh) and applied it to a well-monitored estuarine system (the San Francisco Estuary) for validation. The process-based approach allows for detailed process description and a physics-based analysis of governing processes. The model was calibrated for water year 2011 and incorporated 3-D hydrodynamics, salinity intrusion, water temperature dynamics, and atmospheric coupling. Results show significant skill in reproducing temperature observations on daily, seasonal, and yearly time scales. In North San Francisco Bay, thermal stratification is present, enhanced by salinity stratification. The temperature of the upstream, fresh water Delta area is captured well in 2-D mode, although locally—on a small scale—vertical processes (e.g., stratification) may be important. The impact of upstream river temperature and discharge and atmospheric forcing on water temperatures differs throughout the Delta, possibly depending on dispersion and residence times. Our modeling effort provides a sound basis for future modeling studies including climate change impact on water temperature and associated ecological modeling, e.g., clam and fish habitat and phytoplankton dynamics.

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USGS2017

Conceptual model for invasive bivalve control on wetland productivity

Tidal wetlands were the historically dominant features of many coastal regions around the world, including the San Francisco Estuary (Callaway et al. 2011; Whipple et al. 2012). These mosaics of varied interconnected habitats (Mitsch and Gosselink 1993) provide a host of ecosystem services, including biodiversity maintenance, fish and wildlife habitat, water quality improvement, flood abatement, and carbon sequestration (Rabenhorst 1995; Costanza et al. 1997; Bottom et al. 2005; Zedler and Kercher 2005; Barbier et al. 2010). They also support human activities and values such as recreation and aesthetic appreciation (Barbier et al. 2010; Milligan and Kraus-Polk 2016). Despite their critical functions, many wetland landscapes have been destroyed or irreparably altered, either incidentally or intentionally, by human activities (Holland et al. 2004; Zedler and Kercher 2005; Callaway et al. 2011; Cloern and Jassby 2012; Whipple et al. 2012; Schile et al. 2014). San Francisco Estuary (SFE) (see Figure 1) tidal wetlands were largely converted to other land uses in the late 1800s and early 1900s, with the extent of loss and new use varying by region. Wetland losses in the North, Central, and South San Francisco bays and Suisun Bay ranged from 70 percent to 93 percent to accommodate agricultural uses, salt production, managed waterfowl habitat, and urban development (Callaway et al. 2011). Landscape transformation within the most inland portion of the SFE, the Sacramento-San Joaquin Delta (Delta), was even more dramatic. Overall, today’s Delta contains 97 percent less freshwater tidal wetland than its historical state and nearly double the open water area (Whipple et al. 2012). The majority of the modern Delta consists of agricultural tracts protected from tidal waters by human-made dikes or levees, which are commonly armored with riprap. The de-watered, rich peat soils of these created islands have supported abundant agricultural production, but have oxidized, compacted, and blown away in the process, causing significant subsidence (Deverel and Leighton 2010). Occasional levee failures turn islands into lakes; a few large shallow lakes remain after accidental levee breaches were not repaired (Whipple et al. 2012).

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USGS2017

Responses of a 64-story unique San Francisco, CA. building to four earthquakes and ambient motions

We analyze the ambient and earthquake responses of a 64-story, instrumented, concrete core shear wall building in San Francisco, Calif. equipped with tuned sloshing liquid dampers (TSDs) and buckling restraining braces (BRBs). In an earlier paper [1], only ambient data were used to identify dynamic characteristics. Recently, the 72-channel instrumental array of the building recorded the 24 August 2014 Mw6.0 South Napa and three other earthquakes – allowing comparison of the dynamic characteristics using ambient and earthquake data. Peak accelerations of ambient and the larger South Napa EQ responses at the basement are 0.12 and 5.2 cm/s/s, respectively – a factor of ~ 42 and, at the 61st level, are 0.30 and 16.8 cm/s/s, respectively –a factor of ~56. Fundamental frequencies determined from spectral ratios for the NS (~0.3Hz), EW (0.27Hz) and torsional accelerations for the earthquake response vary within an insignificant frequency band of ~ 0.02-0.03 Hz as compared to those determined from ambient data. At the level of shaking, BRBs or TSDs are not effective enough to alter dynamic characteristics (frequency or damping). Under future stronger (e.g. design level) shaking of the building, the nonlinearities caused by actions of TSDs and BRBs can substantially shift the dynamic characteristics of the building.

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USGS2016

Island characteristics within wetlands influence waterbird nest success and abundance

Coastal waterbird populations are threatened by habitat loss and degradation from urban and agricultural development and forecasted sea level rise associated with climate change. Remaining wetlands often must be managed to ensure that waterbird habitat needs, and other ecosystem functions, are met. For many waterbirds, the availability of island nesting habitat is important for conserving breeding populations. We used linear mixed models to investigate the influence of pond and island landscape characteristics on nest abundance and nest success of American avocets ( Recurvirostra americana ), black-necked stilts ( Himantopus mexicanus ), and Forster's terns ( Sterna forsteri ) in San Francisco Bay, California, USA, based on a 9-year dataset that included >9,000 nests. Nest abundance and nest success were greatest within ponds and on individual islands located either <1&thinsp;km or >4&thinsp;km from San Francisco Bay. Further, nest abundance was greater within ponds with relatively few islands, and on linear-shaped, highly elongated islands compared to more rounded islands. Nest success was greater on islands located away from the nearest surrounding pond levee. Compared to more rounded islands, linear islands contained more near-water habitat preferred by many nesting waterbirds. Islands located away from pond levees may provide greater protection from terrestrial egg and chick predators. Our results indicate that creating and maintaining a few, relatively small, highly elongated and narrow islands away from mainland levees, in as many wetland ponds as possible would be effective at providing waterbirds with preferred nesting habitat.

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