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At least 1,513 records · Page 84Linked to original sources
USGS1982

Paleomagnetic study of some Cretaceous and Tertiary sedimentary rocks of the Klamath Mountains province, California

Paleomagnetic investigation of Cretaceous outliers and Tertiary sedimentary strata of the Klamath Mountains province, and of onlapping Cretaceous strata, has shown the rocks to be largely remagnetized. Samples studied are from the Upper Jurassic to Upper Cretaceous Great Valley sequence, Upper Cretaceous Hornbrook Formation, Eocene Montgomery Creek Formation, and Oligocene(?) Weaverville Formation. Cretaceous samples that survived the remagnetization have a mean remanence direction that is very close to the expected direction of the Cretaceous magnetic field at the locality of the Klamath Mountains. Data from both primary and remagnetized samples suggest the possibility of 11.5° ± 15.8° of post-Cretaceous clockwise rotation of the Klamath Mountains province. None of the data from either the primary or remagnetized samples shows evidence of the large amounts (∼ 70°) of clockwise rotation that other workers have measured for the lower Tertiary of the Oregon Coast Range. Our data indicate that the Oregon Coast Range and Klamath Mountains province did not behave as a single rigid block during the early Tertiary. They also suggest that any post-Oligocene rotation of the Klamath Mountains province is less than the approximately 30° post-Oligocene rotation recently proposed for a combined Oregon Coast Range–Klamath Mountains–Cascade Range block.

California↗
USGS2017

Geomorphology, denudation rates, and stream channel profiles reveal patterns of mountain building adjacent to the San Andreas fault in northern California, USA

Relative horizontal motion along strike-slip faults can build mountains when motion is oblique to the trend of the strike-slip boundary. The resulting contraction and uplift pose off-fault seismic hazards, which are often difficult to detect because of the poor vertical resolution of satellite geodesy and difficulty of locating offset datable landforms in active mountain ranges. Sparse geomorphic markers, topographic analyses, and measurement of denudation allow us to map spatiotemporal patterns of uplift along the northern San Andreas fault. Between Jenner and Mendocino, California, emergent marine terraces found southwest of the San Andreas fault record late Pleistocene uplift rates between 0.20 and 0.45 mm yr –1 along much of the coast. However, on the northeast side of the San Andreas fault, a zone of rapid uplift (0.6–1.0 mm yr –1 ) exists adjacent to the San Andreas fault, but rates decay northeastward as the coast becomes more distant from the San Andreas fault. A newly dated 4.5 Ma shallow-marine deposit located at ∼500 m above sea level (masl) adjacent to the San Andreas fault is warped down to just 150 masl 15 km northeast of the San Andreas fault, and it is exposed at just 60–110 masl to the west of the fault. Landscape denudation rates calculated from abundance of cosmogenic radionuclides in fluvial sediment northeast of, and adjacent to, the San Andreas fault are 0.16–0.29 mm yr –1 , but they are only 0.03–0.07 mm yr –1 west of the fault. Basin-average channel steepness and the denudation rates can be used to infer the erosive properties of the underlying bedrock. Calibrated erosion rates can then be estimated across the entire landscape using the spatial distribution of channel steepness with these erosive properties. The lower-elevation areas of this landscape that show high channel steepness (and hence calibrated erosion rate) are distinct from higher-elevation areas with systematically lower channel steepness and denudation rates. These two areas do not appear to be coincident with lithologic contacts. Assuming that changes in rock uplift rates are manifest in channel steepness values as an upstream-propagating kinematic wave that separates high and low channel steepness values, the distance that this transition has migrated vertically provides an estimate of the timing of rock uplift rate increase. This analysis suggests that rock uplift rates along the coast changed from 0.3 to 0.75 mm yr –1 between 450 and 350 ka. This zone of recent, relatively rapid crustal deformation along the plate boundary may be a result of the impingement of relatively strong crust underlying the Gualala block into the thinner, weaker oceanic crust left at the western margin of the North American plate by the westward migration of the subduction zone prior to establishment of the current transform plate boundary. The warped Pliocene marine deposits and the presence of a topographic ridge support the patterns indicated by the channel steepness analyses, and further indicate that the zone of rapid uplift may herald elevated off-fault seismic hazard if this uplift is created by periodic stick-slip motion on contractional structures.

California↗
USGS1979

Petrology, composition, and age of intrusive rocks associated with the Quartz Hill molybdenite deposit, southeastern Alaska

A large porphyry molybdenum deposit (Quartz Hill deposit) was recently discovered in the heart of the Coast Range batholithic complex about 70 km east of Ketchikan, southeastern Alaska. Intrusive rocks associated with the mineral deposit form two composite epizonal to hypabyssal stocks and many dikes in country rocks. The stocks are characterized by a variety of textural rock types varying from equigranular or weakly seriate biotite granite to porphyries with aphanitic or very fine grained and aplitic groundmasses. These rocks contain about equal amounts of quartz, albitic plagioclase, and microperthitic microcline and less than 2.5% biotite. Unaltered rocks contain between 0.2 and 1% CaO, less than 1.7% combined Fe 2 O 3 , FeO, and MgO, and 74.4 to 77.7% SiO 2 . Total alkalis are between 8 and 9%, and K 2 O/Na 2 O is about 1.1. The range of major-oxide variation is small, but it is systematically related to lithology. Many trace-elements, including B, Pb, Sn, and Li have low concentrations. Intrusive rocks associated with the Quartz Hill deposit are more albitic and possibly trace-element depleted compared to some other rocks associated with porphyry molybdenum deposits.All observed metallization and alteration is within the Quartz Hill stock. Molybdenite forms fracture coatings and occurs in veins with quartz. Alteration is widespread and includes development of secondary quartz, pyrite, K-feldspar, biotite, white mica, chlorite, and zeolite. Field relations indicate that the stocks were emplaced after regional uplift and erosion of the Coast Range batholithic complex, and K–Ar data show that intrusion and alteration took place in late Oligocene time, about 27 to 30 Ma ago. Data from the Ketchikan quadrangle indicate that porphyry molybdenum metallization in the Coast Range batholithic complex is associated with regionally extensive but spotty, middle Tertiary or younger, felsic magmatism.

Alaska↗
USGS2011

A 4-year study of invasive and native spider populations in Maine

Invasive spiders pose potential threats to native spiders. In 2002, the European spider Linyphia triangularis (Clerck, 1757) (Araneae: Linyphiidae) was discovered in all but one county in Maine. At Acadia National Park, we conducted a 4-year study of L. triangularis and three native linyphiid species of a similar size ( Frontinella communis (Hentz, 1850), Pityohyphantes subarcticus Chamberlin and Ivie, 1943, and Neriene radiata (Walckenaer, 1842)). Using line-transect surveys, we measured population densities in coastal and forest habitat. The density of L. triangularis varied across years but was always significantly higher on the coast than in the forest. In contrast, only one native species was present on the coast and at very low numbers. Coastal L. triangularis were larger and in better condition than those in the forest, and numbers and biomass of insect prey were also higher on the coast. In 2 years, we also conducted transects at a second coastal location in Maine where the invader was at low density. At that site, native densities were substantially higher than at either Acadia site. Our data are consistent with the hypothesis that L. triangularis is reducing populations of native spiders. Companion studies suggest that L. triangularis negatively impacts natives by usurping both web sites and webs.

Maine↗
USGS2023

Barrier islands and spits of northern Alaska: Decadal scale morphological change

Arctic barrier islands and spits are dynamic features influenced by a variety of oceanographic, geologic, and environmental factors. Many serve as habitat and protection for native species and shelter the coast from waves and storms that can flood and erode the adjacent mainland. This paper summarizes results of a study documenting changes to barrier morphology along the North Slope coast of Alaska between the United States-Canadian border and Cape Beaufort, from 1947 to 2020. Changes considered include number of barriers, area and perimeter, shoreline length, barrier sinuosity and width, presence and number of relict terminus features, presence and coverage of tundra vegetation, barrier orientation, termini migration rates, and elevation metrics. Wave conditions are also summarized and related to changes in barrier morphology. The results of this study help to better predict future barrier evolution and prevalence along Alaska’s coast by increasing our understanding of Arctic barrier development, migration, and degradation via the evaluation of historical morphometrics.

Alaska↗
USGS2023

Multiscale assessment of shoreline evolution in the US Pacific Northwest via a process-based model

Prediction of shoreline evolution in coastal environments is critical to aid adaptation strategy planning for coastal communities. To perform reliable predictions, process-based shoreline change models have recently gained popularity in many applications. The study region here, Tillamook County, Oregon, on the US Pacific Northwest coast, has recently been experiencing elevated shoreline erosion rates. The inherent uncertainties driving coastal change, e.g., sea-level rise and changing patterns of storminess, emphasize the need for robust shoreline evolution predictions in this region. To this end, we applied CoSMoS-COAST, an ensemble data-assimilated shoreline model that simulates short- and long-term shoreline change processes. We calibrated and validated the model using the hindcasted wave time series and observed shoreline positions and found a strong correlation between the number of observed shoreline positions and the model’s hindcasting skill. Moreover, results revealed an alongshore close-to-uniform shoreline change rate in the past several years, mainly driven by short-term, wave-driven processes. So far CoSMoS-COAST has performed satisfactorily with the spatially sparse supply of quality historical shoreline positions in our application. Moreover, this model resolves various components (e.g., short- and long-term processes) in the shoreline change sufficiently. This study represents a starting point in the long-term projection of shoreline evolution throughout the entire PNW (Oregon and Washington) coastline since Tillamook County features the majority of the coastal settings present in other coastal regions in the PNW.

Oregon↗
USGS2012

Hurricanes, sea level rise, and coastal change

Sixteen hurricanes have made landfall along the U.S. east and Gulf coasts over the past decade. For most of these storms, the USGS with our partners in NASA and the U.S. Army Corps of Engineers have flown before and after lidar missions to detect changes in beaches and dunes. The most dramatic changes occurred when the coasts were completely submerged in an inundation regime. Where this occurred locally, a new breach was cut, like during Hurricane Isabel in North Carolina. Where surge inundated an entire island, the sand was stripped off leaving marshy outcrops behind, like during Hurricane Katrina in Louisiana. Sea level rise together with sand starvation and repeated hurricane impacts could increase the probabilities of inundation and degrade coasts more than sea level rise alone.

Conference Paper↗
USGS2000

Vertical accretion versus elevational adjustment in UK saltmarshes: An evaluation of alternative methodologies

Simultaneous measurements of vertical accretion from marker horizons and marsh-elevation change from sedimentation-erosion tables (SET) were made in selected marshes along the East Anglian coast of the UK in order to address the following objectives: to ascertain the validity of treating accretion measurements obtained within tidally dominated, minerogenic saltmarshes as equivalent to surface elevation changes; to explore the implications, in terms of physical and biological processes, of discrepancies between separately measured vertical accretion and elevation change within contrasting marsh types. Data were collected from several marsh environments at Scolt Head Island and Stiffkey on the North Norfolk coast and at an experimental managed realignment project near Tollesbury, Essex. Scolt Head Island was selected for its long-term datasets of marsh accretion, Stiffkey for its contrasting open coast-back barrier settings, and Tollesbury for its experimental management, in order to illustrate the potential application of the SET method and evaluate the relationship between vertical accretion and elevation change in a variety of marsh settings. The relationship between vertical accretion and elevation change varied widely among marsh settings of different age and height (within the tidal frame) at Scolt Head Island and Stiffkey. Rates of vertical accretion and elevation change were similar in the older and mid-height settings on Scolt Head Island, indicating control of elevation change by surface accretionary processes (e.g. sediment deposition). However, subsurface processes controlled elevation at three of the marsh sites. Spartina Marsh, the youngest and lowest of the back barrier settings at Scolt Head Island, exhibited continuous shallow subsidence (vertical accretion greater than elevation change) over a 4-year period, implying that compaction controls elevation change. In the upper part of Hut Marsh and the interior of the Stiffkey marshes, elevation change exceeded vertical accretion suggesting that subsurface processes (e.g. organic accumulation) controlled elevation in these settings. Surface accretionary processes control elevation change in both the highly dynamic, outer marsh at Stiffkey and the low, restored marsh at Tollesbury. Despite the occurrence of shallow subsidence, all sites gained elevation at an annual rate comparable to that of sea-level rise. In summary, the SET provides the means to critically evaluate the influence of vertical accretion measures on elevation and represents an improved method by which to evaluate the vulnerability of a marsh to sea-level rise.

Scolt Head Island Marsh, Stiffkey Marsh, Tollesbur↗
USGS2006

Alongshore wind forcing of coastal sea level as a function of frequency

The amplitude of the frequency response function between coastal alongshore wind stress and adjusted sea level anomalies along the west coast of the United States increases linearly as a function of the logarithm (log10) of the period for time scales up to at least 60, and possibly 100, days. The amplitude of the frequency response function increases even more rapidly at longer periods out to at least 5 yr. At the shortest periods, the amplitude of the frequency response function is small because sea level is forced only by the local component of the wind field. The regional wind field, which controls the wind-forced response in sea level for periods between 20 and 100 days, not only has much broader spatial scales than the local wind, but also propagates along the coast in the same direction as continental shelf waves. Hence, it has a stronger coupling to and an increased frequency response for sea level. At periods of a year or more, observed coastal sea level fluctuations are not only forced by the regional winds, but also by joint correlations among the larger-scale climatic patterns associated with El Nin??o. Therefore, the amplitude of the frequency response function is large, despite the fact that the energy in the coastal wind field is relatively small. These data show that the coastal sea level response to wind stress forcing along the west coast of the United States changes in a consistent and predictable pattern over a very broad range of frequencies with time scales from a few days to several years.

Journal of Physical Oceanography↗
USGS1968

Geologic implications of aeromagnetic data for the eastern continental margin of the United States

An aeromagnetic survey extending from the Gulf of Maine to the tip of Florida was conducted by the U. S. Naval Oceanographic Office between 1964 and 1966. Flight traverses were flown in a northwesterly direction at right angles to the geologic grain. The flight lines were approximately 800 km long and had an 8-km separation. The survey traversed part of the New England, Piedmont, and Coastal Plain provinces and extended some 320 km beyond the continental shelf into the Atlantic Ocean. Despite the wide flight-line spacing, numerous geological and structural features became apparent from this survey. Interpretation of these features was aided by using the available gravity and seismic data in addition to the State and Provincial geologic maps. The residual aeromagnetic map shows a continuous magnetic high on or near the continental slope as far south as the 31st parallel. At about the 36th parallel, this east-coast magnetic anomaly splits into two branches, and both of them parallel the 850-fathom contour. At the 31st parallel, the outer branch of the anomaly swings westward and crosses the coastline near Brunswick, Georgia. This continuous magnetic anomaly may result from an igneous intrusive body that parallels the edge of the pre-Paleozoic continental landmass. These magnetic data suggest that Florida and part of Georgia were added to the paleo-continent in pre-Paleozoic time. Landward from the east-coast anomaly, the magnetic field is quite variable, whereas oceanward it has an extremely small gradient. The absence of magnetic anomalies east of the continental slope suggests that in this region layer 2 may be composed of metamorphosed basalt. The characteristic magnetic patterns observed over the Piedmont and New England provinces extend oceanward to the east-coast anomaly.

Eastern United States↗
USGS1971

An aeromagnetic and aeroradioactivity survey of Liberia, West Africa

A 140,000 km aeromagnetic and total-count gamma radiometric survey was made over Liberia in 1967-68 along north-south lines spaced 0.8 km over land and 4 km over the continental shelf. The data approximately delineate the boundary between the Liberian (ca. 2700 m.y.) age province in the northwestern two-thirds of the country, and the Pan-African (ca. 550 m.y.) age province in the coastal area of the northwestern two-thirds of the country, as well as a boundary marking the northwest extent of the isoclinally folded paragneisses and migmatites deformed within the Eburnean (ca. 2000 m.y.) age province in the southeast one-third. A zone of diabase dikes about 90 km inland can be traced, parallel to the coast from Sierra Leone to Ivory Coast on the basis of the magnetic data. Another zone of diabase dikes about 185 m.y. old is located along the coastal area and beneath the continental shelf parallel to the coast northwest of Greenville. Intrusion of these dikes probably coincides with the separation of Africa from North and South America. The magnetic data suggest basins of sedimentary rocks possibly 5 km thick on the continental shelf. The map indicates high-amplitude magnetic anomalies greater than 600 gammas; some reach amplitudes as great as 18,000 gammas over iron formation and about 1800 gammas over mafic and ultramafic intrusive bodies. The radioactivity data have a background level less than 100 counts per second (cps) over mafic granulite-facies rocks and unmetamorphosed sedimentary rocks in the coastal area. Granitic rocks have the greatest variation. The central area of the country has the highest background radiation level with large areas above 250 cps; the level in the eastern one-third of the country is low. These data are proving quite useful in reconnaissance geologic mapping. All anomalies over 500 cps are shown; some reach amplitudes over 750 cps. Total-count radiation levels have a significant correlation with percent K 2 O in bedrock analyses, but anomalous amounts of Th and U must be present to account for the highest amplitude anomalies. A few specific anomalies have been correlated with concentrations of monazite and zircon in bedrock as well as in beach deposits.

Geophysics↗
USGS2009

Geoengineering and seismological aspects of the Niigata-Ken Chuetsu-Oki earthquake of 16 July 2007

The M6.6 Niigata-Ken Chuetsu-Oki earthquake of 16 July 2007 occurred off the west coast of Japan with a focal depth of 10 km, immediately west of Kashiwazaki City and Kariwa Village in southern Niigata Prefecture. Peak horizontal ground accelerations of 0.68 g were measured in Kashiwazaki City, as well as at the reactor floor level of the world's largest nuclear reactor, located on the coast at Kariwa Village. Liquefaction of historic and modern river deposits, aeolian dune sand, and manmade fill was widespread in the coastal region nearest the epicenter and caused ground deformations that damaged bridges, embankments, roadways, buildings, ports, railways and utilities. Landslides along the coast of southern Niigata Prefecture and in mountainous regions inland of Kashiwazaki were also widespread affecting transportation infrastructure. Liquefaction and a landslide also damaged the nuclear power plant sites. This paper, along with a companion digital map database available at http://walrus.wr.usgs.gOv/infobank/n/nii07jp/html/n-ii-07-jp.sites.kmz, describes the seismological and geo-engineering aspects of the event. ?? 2009, Earthquake Engineering Research Institute.

Earthquake Spectra↗
USGS2009

Spatial habitat use patterns of sea otters in coastal washington

Sea otter (Enhydra lutris kenyoni) movements, home range, and activity budgets were described from data collected during very-high-frequency radiotelemetry studies of 75 individuals on the outer coast of Washington State between 1992 and 1999. Sea otters were located at least once per week from 22 accessible sites along the coast. Over the 7-year study period, range expansion occurred from the core range north and east into the Strait of Juan de Fuca (SJF) as well as southward on the outer coast. Forty-three percent of the sea otters moved into the SJF at least once, most often in winter, using habitat that had not been occupied by sea otters since their extirpation 100 years ago. All sea otters spent portions of their time in the vicinity of Cape Alava, and many animals demonstrated consistent periodic seasonal shifts between specific portions of the coastline over several years. Ninety-five percent annual linear home ranges differed between sex and age classes. Adult males used the largest amount of coastline (50 km ?? 9 5D) and subadult females used the least (24 ?? 9 km). Both adult males and females demonstrated high seasonal periodicity in range use in summer and winter. Twenty-four-hour time budgets in the core portion of the range revealed on average sea otters spent 41% ?? 14% SD of the time foraging and 45% ?? 13% of the time resting (age and sex classes pooled). Adult and subadult female sea otters were most frequently found resting and foraging close to shore (< 1,000 m) and in shallow water (0-10 m), whereas adult and subadult males rested and foraged > 1,000 m offshore and at depths between 10 and 30 m. Given current rates of population growth and observed mobility, sea otters in Washington have high potential for range expansion into unoccupied habitat such as Grays Harbor, Willapa Bay, the SJF, or along Vancouver Island. ?? 2009 American Society of Mammalogists.

Journal of Mammalogy↗
USGS2009

Migration patterns and wintering range of common loons breeding in the Northeastern United States

A study, using satellite telemetry, was conducted to determine the precise migration patterns and wintering locations of Common Loons (Gavia immer) breeding in the northeastern United States. Transmitters were implanted in 17 loons (16 adults and one juvenile) that were captured on breeding lakes in New York, New Hampshire, and Maine during the summers of 2003, 2004, and 2005. Transmitters from ten of the birds provided adequate location data to document movement to wintering areas. Most adult loons appeared to travel non-stop from breeding lakes, or neighboring lakes (within 15 km), to the Atlantic coast. Adult loons marked in New Hampshire and Maine wintered 152 to 239 km from breeding lakes, along the Maine coast. Adult loons marked in the Adirondack Park of New York wintered along the coasts of Massachusetts (414 km from breeding lake), Rhode Island (362 km), and southern New Jersey (527 km). Most of the loons remained relatively stationary throughout the winter, but the size of individual wintering areas of adult loons ranged from 43 to 1,159 km 2 , based on a 95% fixed kernel utilization distribution probability. A juvenile bird from New York made a number of stops at lakes and reservoirs en route to Long Island Sound (325 km from breeding lake). Maximum functional life of transmitters was about 12 months, providing an opportunity to document spring migration movements as well. This work provides essential information for development and implementation of regional Common Loon conservation strategies in the Northeastern U.S.

Waterbirds↗
USGS2014

Modeling the effects of source and path heterogeneity on ground motions of great earthquakes on the Cascadia Subduction Zone Using 3D simulations

We ran finite‐difference earthquake simulations for great subduction zone earthquakes in Cascadia to model the effects of source and path heterogeneity for the purpose of improving strong‐motion predictions. We developed a rupture model for large subduction zone earthquakes based on a k −2 slip spectrum and scale‐dependent rise times by representing the slip distribution as the sum of normal modes of a vibrating membrane. Finite source and path effects were important in determining the distribution of strong motions through the locations of the hypocenter, subevents, and crustal structures like sedimentary basins. Some regions in Cascadia appear to be at greater risk than others during an event due to the geometry of the Cascadia fault zone relative to the coast and populated regions. The southern Oregon coast appears to have increased risk because it is closer to the locked zone of the Cascadia fault than other coastal areas and is also in the path of directivity amplification from any rupture propagating north to south in that part of the subduction zone, and the basins in the Puget Sound area are efficiently amplified by both north and south propagating ruptures off the coast of western Washington. We find that the median spectral accelerations at 5 s period from the simulations are similar to that of the Zhao et al. (2006) ground‐motion prediction equation, although our simulations predict higher amplitudes near the region of greatest slip and in the sedimentary basins, such as the Seattle basin.

Bulletin of the Seismological Society of America↗
USGS2017

An updated geospatial liquefaction model for global application

We present an updated geospatial approach to estimation of earthquake-induced liquefaction from globally available geospatial proxies. Our previous iteration of the geospatial liquefaction model was based on mapped liquefaction surface effects from four earthquakes in Christchurch, New Zealand, and Kobe, Japan, paired with geospatial explanatory variables including slope-derived VS30, compound topographic index, and magnitude-adjusted peak ground acceleration from ShakeMap. The updated geospatial liquefaction model presented herein improves the performance and the generality of the model. The updates include (1) expanding the liquefaction database to 27 earthquake events across 6 countries, (2) addressing the sampling of nonliquefaction for incomplete liquefaction inventories, (3) testing interaction effects between explanatory variables, and (4) overall improving model performance. While we test 14 geospatial proxies for soil density and soil saturation, the most promising geospatial parameters are slope-derived VS30, modeled water table depth, distance to coast, distance to river, distance to closest water body, and precipitation. We found that peak ground velocity (PGV) performs better than peak ground acceleration (PGA) as the shaking intensity parameter. We present two models which offer improved performance over prior models. We evaluate model performance using the area under the curve under the Receiver Operating Characteristic (ROC) curve (AUC) and the Brier score. The best-performing model in a coastal setting uses distance to coast but is problematic for regions away from the coast. The second best model, using PGV, VS30, water table depth, distance to closest water body, and precipitation, performs better in noncoastal regions and thus is the model we recommend for global implementation.

Christchurch, Kobe↗
USGS2021

Survey of fragile geologic features and their quasi-static earthquake ground-motion constraints, southern Oregon

Fragile geologic features (FGFs), which are extant on the landscape but vulnerable to earthquake ground shaking, may provide geological constraints on the intensity of prior shaking. These empirical constraints are particularly important in regions such as the Pacific Northwest that have not experienced a megathrust earthquake in written history. Here, we describe our field survey of FGFs in southern Oregon. We documented 58 features with fragile geometric characteristics, as determined from field measurements of size and strength, historical photographs, and light detection and ranging point clouds. Among the surveyed FGFs, sea stacks have particular advantages for use as ground‐motion constraints: (1) they are frequently tall and thin; (2) they are widely distributed parallel to the coast, proximal to the trench and the likely megathrust rupture surface; and (3) they are formed by sea cliff retreat, meaning that their ages may be coarsely estimated as a function of distance from the coast. About 40% of the surveyed sea stacks appear to have survived multiple Cascadia megathrust earthquakes. Using a quasi‐static analysis, we estimate the minimum horizontal ground accelerations that could fracture the rock pillars. We provide context for the quasi‐static results by comparing them with predictions from kinematic simulations and ground‐motion prediction equations. Among the sea stacks old enough to have survived multiple megathrust earthquakes ( n = 16), eight yield breaking accelerations lower than the predictions, although they generally overlap within uncertainty. FGFs with the lowest breaking accelerations are distributed uniformly over 130 km of coastline. Results for inland features, such as speleothems, are in close agreement with the predictions. We conclude that FGFs show promise for investigating both past earthquake shaking and its spatial variability along the coasts of Oregon and Washington, where sea stacks are often prevalent. Future work can refine our understanding of FGF age and evolution.

Oregon↗
USGS2013

Per capita invasion probabilities: an empirical model to predict rates of invasion via ballast water

Ballast water discharges are a major source of species introductions into marine and estuarine ecosystems. To mitigate the introduction of new invaders into these ecosystems, many agencies are proposing standards that establish upper concentration limits for organisms in ballast discharge. Ideally, ballast discharge standards will be biologically defensible and adequately protective of the marine environment. We propose a new technique, the per capita invasion probability (PCIP), for managers to quantitatively evaluate the relative risk of different concentration-based ballast water discharge standards. PCIP represents the likelihood that a single discharged organism will become established as a new nonindigenous species. This value is calculated by dividing the total number of ballast water invaders per year by the total number of organisms discharged from ballast. Analysis was done at the coast-wide scale for the Atlantic, Gulf, and Pacific coasts, as well as the Great Lakes, to reduce uncertainty due to secondary invasions between estuaries on a single coast. The PCIP metric is then used to predict the rate of new ballast-associated invasions given various regulatory scenarios. Depending upon the assumptions used in the risk analysis, this approach predicts that approximately one new species will invade every 10–100 years with the International Maritime Organization (IMO) discharge standard of <10 organisms with body size >50 μm per m 3 of ballast. This approach resolves many of the limitations associated with other methods of establishing ecologically sound discharge standards, and it allows policy makers to use risk-based methodologies to establish biologically defensible discharge standards.

Ecological Applications↗