Northern California Coast Research Articles

Sightings and Strandings of Guadalupe Fur Seals in Central and Northern California, 1988-1995

The Guadalupe fur seal ( Arctocephalus townsendi ) was hunted to near extinction before its natural history was well known. The last known population is currently centered on Guadalupe Island, Mexico, but in recent years northern extralimital records from California have become more frequent. We report 14 new records (3 adults, 11 juveniles) of Guadalupe fur seals stranded (nine) or sighted (five) along the central and northern coast of California. These northern records appear to correspond with El Nino events, seasonal currents in California, and to dispersal behavior in this species. Dietary items retrieved from stomachs and feces included otoliths from Citharichthys sordidus, Lampanyctus, Protomyctophum , and Scopelogadus , and beaks of the squids Loligo opalescens, Gonatopsis , and Onychoteuthis borealojaponica . Emaciation commonly was associated with stranding, but other findings included an umbilical hernia, septicemia, and bacterial pneumonia. Three of the stranded individuals had experienced entanglement in fishing gear or marine debris.

Induction and Termination of Winter Diapause in a Californian Strain of the Cabbage Maggot (Diptera: Anthomyiidae)

Populations of the cabbage maggot, Delia radicum (L.), occur in the field during all seasons in coastal northern California because the climate is mild, hosts are available, and a percentage of the population does not enter diapause. Laboratory experiments on this population of the cabbage maggot showed the following 6 results: (1) criteria for diapause vary with the conditions that induce diapause, (2) the proportion of larvae entering diapause is highest at low temperatures across all photoperiods and at short photoperiods across all temperatures, (3) developmental times of larvae producing diapause pupae were longer than for those producing nondiapause pupae, (4) rearing larvae at high temperatures and short photoperiods increased the diapause period for the pupal stage, (5) average pupal weights of diapause pupae (20.20 ± 2.27 mg) (mean ± SD) were higher than for nondiapause pupae (18.01 ± 3.31), and (6) fresh pupae weighing <15.5 mg did not complete diapause. The results support previous findings that field populations of D. radicum are induced into winter diapause mainly by short photoperiods, whereas temperature has a lesser effect.

Polarization Anomalies of Surface Waves Recorded by a Broadband Seismometer Network in Hokkaido, Japan.

Polarization anomalies of surface waves suggest the existence of lateral variations of isotropic and azimuthally anisotropic velocity structures in the upper mantle. We investigate the polarization anomalies of fundamental-mode Rayleigh and Love waves (37 earthquakes, 128 paths) at periods of 5-30 s as recorded by a local four-station network of broadband seismometers in Hokkaido, Japan. The network has been operated by the Research Center for Earthquake Prediction of Hokkaido University since December 1988. Rayleigh waves coming from many back-azimuthal ranges show three types of particle motion anomalies, which are usually called inclined, tilted, and sloping motions. The Rayleigh anomalies observed in the data for the Vanuatu region are mainly caused by the azimuthally anisotropic structure beneath the northwestern Pacific, because the effects of the lateral eterogeneities on the inclined motions are considered to be negligible. The Love waves coming from the earthquakes located near Oregon and California, USA, show anomalous waves in the vertical and radial components. It was expected that the waves were higher-mode Rayleigh waves. We calculate synthetic waveforms with normal modes for an oceanic spherically symmetric Earth model for the August 17, 1991, earthquake off the coast of northern California, which shows significant anomalous Love waves. A comparison of the synthetic and observed waveforms suggests that the anomalous waves are not higher-mode Rayleigh waves and require the Love to Rayleigh conversion. The conversion locations concentrate in and around the Kuril trench region. The Love wave anomalies may be caused by lateral variation in the isotropic or anisotropic structures beneath the Kuril trench region.

Polarimetric brightness temperatures of sea surfaces measured with aircraft K- and Ka-band radiometers

Dual-frequency (19 and 37 GHz), multi-incidence measurements of the Stokes parameters of sea surface microwave emission are reported. A series of aircraft polarimetric radiometer flights were carried out over the National Data Buoy Center (NDBC) moored buoys deployed off the northern California coast in July and August 1994. Measured radiometric temperatures showed a few Kelvin azimuth modulations in all Stokes parameters with respect to the wind direction. Wind directional signals observed in the 37-GHz channel were similar to those in the 19-GHz channel. This indicates that the wind direction signals in sea surface brightness temperatures have a weak frequency dependence in the range of 19-37 GHz. Harmonic coefficients of the wind direction signals were derived from experimental data versus incidence angle. It was found that the first harmonic coefficients, which are caused by the up and downwind asymmetric surface features, had a small increasing trend with the incidence angle. In contrast, the second harmonic coefficients, caused by the up and crosswind asymmetry, showed significant variations in T/sub v/ and U data, with a sign change when the incidence angle increased from 45/spl deg/ to 65/spl deg/. Besides the first three Stokes parameters, the fourth Stokes parameter, V, which had never been measured before for sea surfaces, was measured using our 19-GHz channel. The Stokes parameter V. Has an odd symmetry just like that of the third Stokes parameter U, and increases with increasing incidence angles. In summary, sea surface features created by surface winds are anisotropic in azimuth direction and modulate all Stokes parameters of sea surface microwave brightness temperatures by as large as a few Kelvin in the range of incidence angles from 45/spl deg/ to 65/spl deg/ applicable to spaceborne observations.

Acoustic thermometry of ocean climate. A description of the acoustic network

The ATOC acoustic feasibility network became functional in December 1995 following the installation of an acoustic source on Pioneer Seamount approximately 50 nm off the coast of Northern California. The current effort is part of the Marine Mammal Research Program Pilot Study. This paper describes the acoustic network of sources and receivers, including the augmentations to be made in summer 1996. The network was designed to take advantage of existing hydrophone arrays, while providing for maximum coverage of the North Pacific by the acoustic paths. The acoustical receptions currently being obtained are processed to obtain ‘‘dot plots’’ which show the arrival times and arrival angles of acoustical energy above a chosen signal-to-noise ratio. The ‘‘dot plot’’ histories demonstrate stable ray arrivals (albeit with significant amplitude fluctuations) for even the longest propagation ranges of 5 Mm. [Work supported by the Strategic Environmental Research and Development Program through ARPA.]

Constraints for upper mantle shear-wave models of the basin and range from surface-wave inversion

Abstract Several earthquakes in a limited region on the coast of Northern California and off the coast of Oregon have provided a set of broadband regional seismograms at Lajitas (LTX). The significant Love and Rayleigh waves contained in these waveforms have repetitively sampled the same source-receiver path within the Basin and Range province. Previous studies for this path (using a subset of these sources) of mantle S waves suggest a smoothly varying S velocity structure above 400 km followed by a strong gradient between 400 and 700 km. These data are unable to uniquely constrain the shear velocity at shallower depths. Surface-wave inversions are performed in order to refine the upper mantle S-wave model using group- and phase-velocity dispersion for periods between 10 and 100 sec. This period range gives good resolution for sub-Moho depths extending into the low-velocity zone. Group velocities are extracted by multiple filter analysis and show significant differences for events on- and off-shore at periods around 50 sec. This effect can be shown to be an interference pattern with the mantle S body-wave arrivals. As single-station data were used, phase velocities are estimated by phase-matched filtering. The recovered surface-wave dispersion data are used in an inversion procedure to recover a shear-wave structure for the Basin and Range path to LTX that consists of a relatively thin mantle lid underlain by a low-velocity channel extending to a depth of 200 km. Structure below 200 km is poorly resolved and trades off with shallower structure. The Rayleigh-wave group-velocity data favor shear-velocity models with a ridge within the low-velocity zone with velocities 0.05 to 0.2 km/sec higher than the background.

Acoustic remote sensing of benthic activity: A statistical approach

Acoustic backscatter at 40 kHz was recorded from a circular area of silt 75 m in radius every 0.1 d at a water depth of 91 m off the coast of northern California for 49 d in winter 1988–1989. Data were resolved into pixels that extended 7.5 m radially and 5° azimuthally. We analyzed the relatively small change in backscatter intensity and phase from a given pixel. In a time‐series analysis, this change in backscatter was decomposed into three components putatively due to large, rare, transient nekton and epibenthos; more abundant benthopelagic organisms that caused volume reverberation; and more sedentary benthos. Benthic change in backscatter was presumed due to movement of animals and other biogenic modifications of sound speed in the sediment‐water medium. Patterns of benthic activity and volume backscatter near the seabed changed abruptly twice, with the middle interval showing highest levels. During this middle interval, winter storms disturbed surficial sediments, offshore transport occurred near the seabed, and the benthic component was dominated by activity perfectly in phase with and linearly proportional to median, local, downwelling irradiance. We suspect that this circadian pattern was due to the burrowing urchin Brisaster latifrons that is known from previous studies at this site to emerge on the sediment surface at night when food resources are available there and to reburrow during the lighted part of the day. Extensive correlative physical data collected at the site as part of interdisciplinary studies (CODE and STRESS) allowed us to exclude other physical forcings as likely explanations for diurnal change in backscatter. In a spatial analysis, the transient component was removed explicitly pixel by pixel, and volume reverberation was removed implicitly to leave a benthic remainder that could be analyzed for spatial variation. Benthic activity showed distinct patchiness with coherence scales of roughly 5–10 m and negative spatial autocorrelation in activity levels near the largest spatial lag available (∼140 m). Patches did not move appreciably during the study.

Comments on “Structure of the Lower Atmosphere over the Northern California Coast during Winter”

Comments on “Structure of the Lower Atmosphere over the Northern California Coast during Winter”

Coastally Trapped Wind Reversals along the United States West Coast during the Warm Season. Part I: Climatology and Temporal Evolution

Abstract The northerly winds that predominate along the U.S. west coast during April–September are interrupted periodically by abrupt reversals to southerly flow. The climatology and composite temporal evolution of these reversals from Point Conception to the Canadian border are documented using hourly data from moored coastal buoys and Coastal-Marine Automated Network stations for the period 1981–91. The reversals are divided into two categories: coastally trapped reversals, in which the southerly flow is highly ageostrophic and restricted to the coastal zone, and synoptic reversals, which are associated with landfalling troughs or fronts. Coastally trapped events occur on average about 1.5 times per month along the central and northern California coast, about twice a month near the California–Oregon border, and about once a month near the Oregon–Washington border. The ratio of coastally trapped reversals to synoptic reversals is higher during July–September and lower during April–June, particularly in t...

Structure of the Lower Atmosphere over the Northern California Coast during Winter

Abstract The structure of the lower atmosphere over the northern California coastal ocean upwelling area was studied during the Shelf Mixed Layer Experiment in the winter of 1989. Surface data were collected at seven automated coastal stations and six buoys. Boundary layer soundings were made using balloons at the coast and a research aircraft over the ocean. The aircraft was also used to map the low-level (30 m) mean and flux fields over the 80 km × 120 km shelf area. The wintertime coastal weather conditions were more variable than in summer and were observed to fit into three categories: strong northerly (downcoast) winds, strong southerly (upcoast) winds, and weak winds. The variability was caused by the passage of wintertime cyclones interspersed with periods of small pressure gradients. The strong wind cases had small diurnal variations, whereas the diurnal variations were large for the weak wind case. The vertical structure of the coastal boundary layer was more uniform compared to that in summer, ...

Summary of aldicarb monitoring and research programs in the U.S.A.

Since 1979, over 130,000 soil and water samples have been collected and analyzed for aldicarb in monitoring and research programs conducted in the U.S.A. Comprehensive field research studies have been conducted on 40 plots located in 14 states and involving eight different crops. In addition, exploratory studies have been conducted in eight states including three in which field studies were not conducted at a later date. Drinking water samples have been collected in 39 states. Many laboratory studies have been performed to better define degradation mechanisms and rates. Modeling simulations have been performed to interpret field data and to properly apply the results to other situations. The movement and degradation of aldicarb residues in the unsaturated and saturated zone in a complex process affected by soil and hydrogeological properties, climatic conditions, and agricultural practices. These studies show that in most areas aldicarb residues degrade in the upper portion of the unsaturated zone. In the few areas where aldicarb residues reach groundwater, the combined effects of the primarily lateral movement of groundwater and the continuing degradation usually constrain aldicarb residues to shallow groundwater neat treated fields. Most of the cases where aldicarb residues in drinking water have occurred in excess of the EPA (and WHO) health advisory level of 10 μg L −1 (a MCL of 7 μg L −1 is being proposed by the EPA) resulted from applications made at planting to potatoes. Generally, these instances of drinking water residues have been in the Northeast and Wisconsin: however, above guideline residues in drinking water wells have occurred as result of applications to lily bulbs in northern coastal California, sugar beets in Wyoming and citrus in central Florida. Management practices have been implemented to eliminate the occurrence of aldicarb residues in drinking water wells from future applications. These management practices have consisted of changes in application timing, application rates, and restrictions on applications near shallow drinking water wells in areas with vulnerable soils and shallow water tables. Almost all of the residues in drinking water wells currently exceeding guidelines are the result of applications made prior to the adoption of these management practices.

Polarimetric measurements of sea surface brightness temperatures using an aircraft K-band radiometer

Presents the first experimental evidence that the polarimetric brightness temperatures of sea surfaces are sensitive to ocean wind direction in the incidence angle range of 30 to 50/spl deg/. The experimental data were collected by a K-band (19.35 GHz) polarimetric wind radiometer (WINDRAD) mounted on the NASA DC-8 aircraft. A set of aircraft radiometer flights was successfully completed in November 1993. The authors performed circle flights over National Data Buoy Center (NDBC) moored buoys deployed off the northern California coast, which provided ocean wind measurements. The results indicate that passive polarimetric radiometry has a strong potential for global ocean wind speed and direction measurements from space. >

The Role of Convective Geothermal Systems in the Generation, Migration, and Entrapment of Oil: ABSTRACT

Modern convective geothermal systems (for example, at Yellowstone National Park) and their fossil equivalents, epithermal mineral deposits (like McLaughlin, California) have traditionally been considered poor petroleum prospects. The concentrated heat which drives these systems is commonly viewed as a negative influence: in other words, any oil initially present in or generated by these systems is quickly degraded to a useless carbonaceous residue. This is true in extreme cases, but numerous examples from the Great Basin, the northern California Coast Ranges, and elsewhere suggest that under certain circumstances, geothermal systems can efficiently generate, transport, and entrap significant quantities of producible petroleum. B.R.T. Simoneit has shown that oil can be hydrothermally generated in an {open_quotes} instant{close_quotes} of geologic time. It follows, then, that away from geothermal systems` high-temperature centers (or in wholly moderate-temperature systems), the encompassing shallow thermal anomalies can distill large volumes of oil from otherwise immature hydrocarbon source rocks. Transport of this newly-generated oil is enhanced by the buoyant upwelling of heated aqueous fluid. Porosity for oil transport and storage is created or increased by hydrothermal dissolution of rock-forming or secondary silicates and carbonates. Finally, geothermal {open_quotes}self-sealing{close_quotes} -- the deposition of secondary minerals (especially silica and clay) at the marginsmore » of a system -- can provide a very effective hydrocarbon seal. Lee Allison has noted the coincidence of igneous intrusions and oil reservoirs in Nevada. It is suggested that here and elsewhere, both igneous-related and amagmatic geothermal systems in otherwise favorable settings should be viewed as prime petroleum exploration targets.« less

Effects of Aerosol Particles on the Microphysics of Coastal Stratiform Clouds

Aerosol particles can act as cloud condensation nuclei and thereby influence the number and size of droplets in clouds. Consequently, anthropogenic particles have the potential to influence global climate by increasing cloud albedo and decreasing precipitation efficiencies. Enhanced cloud reflectances associated with increases in panicle number have been observed, but our understanding of these interactions has been hindered by incomplete empirical studies and models of limited scope. In this study, aerosol and droplet size distributions were measured on 13 research flights in stratiform clouds within 300 km west of the northern California coast. The chemical composition of the droplet solute was also assessed. Microphysical and chemical properties indicated that most of the clouds were influenced by pollution from the North American continent, but pristine marine clouds were sampled on one flight during westerly flow conditions. Data from this flight and another, representing a pristine and polluted environment, were compared with high-resolution satellite observations. In the polluted case, particle and droplet number concentrations decreased, mean droplet size increased, and satellite-derived reflectance at 3.7 μm decreased with increasing distance from the northern California urban region. Relative to the unpolluted stratiform cloud, the polluted cloud had, on average, a sulfate concentration that was higher by an order of magnitude, droplet number concentrations higher by a factor of 6, droplet sizes smaller by a factor of 2, and 3.7-μm reflectance that was higher by a factor of 2. However, no significant difference in the visible reflectance was detected between the two cases, probably a result of differences in liquid water path.

Spatial structure of relaxation events and crab settlement in the northern California upwelling system

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 128:199-211 (1995) - doi:10.3354/meps128199 Spatial structure of relaxation events and crab settlement in the northern California upwelling system Wing SR, Botsford LW, Largier JL, Morgan LE During spring and summer 1993, we monitored settlement of crabs (primarily Cancer spp.) and sea urchins Strongylocentrotus spp. in conjunction with physical variables associated with coastal circulation to investigate how physical conditions influence the spatial distribution of recruitment along the coast. Observations were made along a 100 km stretch of the northern California coast (USA), from the Gulf of the Farallones north to Point Arena. Temperature, salinity and wind stress data indicated fluctuations in upwelling and provided evidence for the alongshore, northward flow of warm, low salinity water during upwelling relaxation events which typically lasted several days. On a weekly time scale, crab settlement was positively correlated with temperature, and negatively correlated with salinity, indicating that settlement occurred during relaxation events. Correlations were higher north of Point Reyes, where high settlement occurred only during relaxation, than south of Point Reyes, where settlement occurred both during relaxation events and to a lesser degree during upwelling. Overall crab settlement was higher south of Point Reyes. On a daily time scale, crab settlement north of Point Reyes was associated with the sharp increase in temperature observed as the relaxation current reached that point on the coast. This association suggested that crabs were transported northward alongshore in the thermal front which propagated northward during each relaxation event. This alongshore transport mechanism may be responsible for the predictable pattern of settlement variability within this system: with continuous, event-modulated settlement south of Point Reyes and episodic, event-dependent settlement to the north. Similar physical/biological interactions may occur at other points along this coast and along the midlatitude boundaries of other oceans. Settlement . Upwelling . Space Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 128. Publication date: November 23, 1995 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1995 Inter-Research.

The Kaneohe acoustic thermometry experiment and waves

A new parabolic approximation is derived and implemented that efficiently gives travel time predictions that are accurate to within a few milliseconds at a range of 1000 km and center frequency 75 Hz. Sensitivity of the full-wave travel time predictions to oceanographic and bathymetric inputs along a 3700-km track is studied by comparisons to acoustic data between a source at Kaneohe having center frequency 133 Hz and a bottom mounted receiver near the northern California coast. Path stability for a time interval of several years is also examined with the new broadband PE model, and full-wave generalizations of eigenrays, called eigentubes, are computed. [Work supported by SERDP, ARPA, and ONR.]

An introduction to the Sediment TRansport Events on Shelves and Slopes (STRESS) program

TRANSPORT of sediments on continental shelves involves several complex processes, including entrainment and deposition of particles at the sea floor, vertical transport of suspended particles by boundary layer turbulence, water-column evolution of particle size and density by floc aggregation and break-up, and advection of suspended particles by vertically non-uniform, unsteady, horizontal currents (Fig. 1). These processes lead to sediment dispersal and topographical evolution on a side range of spatial scales, which feed back to influence the various transport mechanisms. Shelf sediment transport influences, and is strongly influenced by, the activities of bottom-dwelling organisms, as well as by physical flow-particle and particle-particle interactions. The many processes involved in shelf sediment transport raise an intriguing array of scientific questions with applications related to evolution of bottom roughness and topography, development of stratigraphy, water clarity, and transport of contaminants attached to fine particles. The objective of the Sediment TRansport Events on Shelves and Slopes (STRESS) program (NoWELL et al. , 1987) was to understand the processes controlling sediment transport and microscale topography in the storm-dominated shelf setting, and to develop a tested capability to predict these processes. STRESS was primarily a field measurement program (Fig. 2) designed to provide comprehensive, high-quality measurements sufficient for critical evaluation and improvement of conceptual and mathematical models. The measurement program was a remarkably successful attempt to resolve the vertical distribution of velocity, temperature and salinity throughout the entire continental shelf bottom boundary layer, with corresponding indirect estimates of particle concentration, size and settling velocity, and accompanying observations of small-scale topography. This issue contains 10 articles describing initial results based on STRESS measurements. The first article (SHERWOOD et al . , 1994) provides a description and a classification of sediment transport events during fall and winter storms in the STRESS study area, off the coast of northern California (Fig. 2). A second group of articles addresses the difficult problem of obtaining time-series estimates of particle size and settling velocity, based on a novel laser diffraction device (AG~WAL and PO~SMITH, 1993), a more traditional optical settling tube (Hn~L et al. , 1994), and a combination of acoustical and optical backscatter

EVOLUTION OF THE PYGMY-FOREST EDAPHIC SUBSPECIES OFPINUS CONTORT AACROSS AN ECOLOGICAL STAIRCASE

Patterns of allozyme variation within and between two of the subspecies of Pinus contorta were examined for the evolutionary relationship between them. In coastal northern California, these subspecies are parapatric. Pinus contorta ssp. contorta occurs on grassy coastal bluffs on the lowest and youngest of a sequence of five marine terraces; P. contorta ssp. bolanderi is endemic to a pygmy forest ecosystem that occurs on the increasingly older and harsher soils of the third, fourth, and fifth terraces. The soils of the upper three terraces are characterized by extreme podzolization, low pH, low nutrient availability, summer drought (with periodic fires), and winter surface flooding above the hardpan. Dune and cliff soils support a tall redwood and Douglas-fir forest between the terraces. Analyses of seeds collected from 11 pygmy-forest and 6 coastal populations showed ssp. bolanderi to have significantly less allozyme variation than spp. contorta. The two subspecies did not show the phylogenetic dichotomy in allozyme allelic constitutions expected for subspecific classification. Within ssp. bolanderi, the pattern of genetic distances correlated better with edaphic differences among sites than with geographic distance. It appears that ssp. bolanderi is a recently evolved derivative of ssp. contorta, and that the low degree of allozyme differentiation among the bolanderi populations may be due to colonization of the sites by small numbers of individuals, or to hitchhiking of allozyme loci linked to loci undergoing strong selection imposed by the severe edaphic conditions typical of bolanderi sites.

Indentification and quantification of mono-, di- and trihydroxybenzenes (phenols) at trace concentrations in seawater by aqueous acetylation and gas chromatographic—mass spectrometric analysis

A method is described that uses aqueous acetylation with acetic anhydride, solid-phase extraction (SPE) and concentration, and gas chromatographic—mass spectrometric (GC-MS) analysis to identify and quantify mono-, di- and trihydroxybenzenes (phenols) at low concentrations in marine and waste waters. Phenolic compounds in water samples were buffered with NaHCO 3 and directly acetylated with acetic anhydride. Phenol acetates were then extracted using C 18 SPE columns. The columns were eluted and the phenol acetates concentrated and analyzed by GC-MS. Detection of phenols in the ng 1 −1 concentration range can be obtained with 500 ml of sample. A large volume extraction setup is described from which detection limits in the upper pg 1 −1 range may be obtained. The method was applicable to a wide range of phenolic compounds but was not suitable for nitrophenols. Water samples from several coastal environments and wastewater treatment facilities were analyzed for phenols using this method. Phenol, cresols and catechols were the most common phenolic compounds identified. Concentrations ranged from 2.5 to 370 ng 1 −1 for these phenols in seawater sampled in San Diego Bay, in the vicinity of White's Point outfall off San Pedro (Los Angeles area) and outfalls off the Northern coast of California near Eureka.

Coastal uplift associated with the 1992 Cape Mendocino earthquake, northern California

The April 25,1992, Cape Mendocino earthquake (Ms 7.1) uplifted ∼24 km of the northern California coast at the southern end of the Cascadia subduction zone, uplift which resulted in coastal emergence that caused extensive mortality of intertidal organisms between Cape Men docino and Punta Gorda. We estimated the amount of uplift by measuring the vertical extent of mortality of 14 sessile intertidal species on rocky sections of shore. The uplift profile along the coast is generally parallel to the strike of the earthquake focal mechanism and forms a broad, flat-topped arch ∼24 km long with a gentle south limb and a steeper north limb. The maximum uplift of 1.4 ±0.2 m is near the center of the profile. The profile is a manifestation of the more widespread domal upwarp produced by slip on an east-dipping buried thrust fault along or near the Cascadia megathrust. Small, new emergent terraces have formed where wave-cut intertidal platforms have been elevated. The new terraces resemble raised late Holocene benches that probably record paleoearthquakes similar to the 1992 event. However, several of the late Holocene terraces are broader and more continuous. These terraces, which extend several tens of kilometres north and south of the 1992 uplift, suggest that some paleoearthquakes were much larger than magnitude 7.