SEARCH · USGS Science

Results for “Energy”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,117 records · Page 62Linked to original sources

USGS2022

Analog field-scale acoustic study of volcanic eruption directivity using a tiltable liquid nitrogen-charged water cannon

Laterally directed explosive eruptions are responsible for multiple fatalities over the past decade and are an increasingly important volcanology problem. To understand the energy dynamics for these events, we collected field-scale explosion data from nine acoustic sensors surrounding a tiltable cannon as part of an exploratory experimental design. For each cannon discharge, the blast direction was varied systematically at 0°, 12°, and 24° from vertical, capturing acoustic wavefield directivity related to the tilt angle. While each event was similar in energy discharge potential, the resulting acoustic signal features were variable event-to-event, producing non-repetitious waveforms and spectra. Systematic features were observed in a subset of individual events for vertical and lateral discharges. For vertical discharges, the acoustic energy had a uniform radiation pattern. The lateral discharges showed an asymmetric radiation pattern with higher frequencies in the direction of the blast and depletion of those frequencies behind the cannon. Results suggest that, in natural volcanic systems, near-field blast directionality may be elucidated from acoustic sensors in absence of visual data, with implications for volcano monitoring and hazard assessment.

Earth, Planets and Space↗

USGS2015

Summer of Applied Geophysical Experience (SAGE): Training for our future geoscientists

Energy and natural resources are crucial to the sustainability of worldwide economies, security, and overall well-being. However, the future workforce in the energy and natural-resources sector is at risk, and meeting the challenges of this dwindling workforce requires well-educated geoscientists in exploration and applied geophysics and related geoscience and technology disciplines. Programs such as geophysical field courses that are supported by SEG and industry, in partnership with academic institutions and government laboratories, are important approaches to maintaining and enhancing expertise in exploration geophysics. One example of a geophysical field course devoted to educating our future workforce is the Summer of Applied Geophysical Experience (SAGE), a four-week program based in Santa Fe, New Mexico, designed to actively engage students in all phases of applied geophysical research. SAGE is a unique educational experience that combines teaching and research as a partnership among universities, industry, government agencies, and professional societies. SAGE teaches the principles and applications of refraction and reflection seismology, magnetics, gravity, GPS, heat flow, several electromagnetic (EM) methods, and ground-penetrating radar (GPR) in a field-based, hands-on setting. More than 850 students and qualified professionals have attended SAGE, many of whom have gone on to become leaders in academia, industry, and government. SAGE students are exposed to the exciting challenges that face earth scientists today, and they develop skills that are necessary to address the world's growing energy demands. Examples of SAGE research projects include mapping archaeological sites and tectonic structure and investigating water and geothermal resources in the Rio Grande rift.

Leading Edge (Tulsa, OK)↗

USGS1980

Paleoenvironment of the New Albany Shale Group ( Devonian- Mississippian) of Illinois

The distribution of lithofacies in the New Albany Shale Group of Illinois was determined by wave energy, bottom oxygenation, and bottom topography in a deep water stratified anoxic basin. A transect from the margin to the center of the Illinois Basin reveals a complete transition from high energy, aerobic, shallow-water environments to quiet, anaerobic, deep-water environments. Shallow areas at the margin of the basin are characterized by rapid facies transitions over short distances. High energy, very shallow conditions are recorded by oolitic-skeletal grainstones and packstones with abundant brachiopods, crinoids, trilobites, and other calcified marine invertebrates. Bioturbation did not destroy primary sedimentary structures in these facies. Offshore, less agitated areas are represented by highly bioturbated carbonate wackestones, argillaceous quartz siltstones, and greenish-gray mudstones. Calcified invertebrates are generally rare in these facies, indicating deposition in dysaerobic conditions. Basinward, slope areas are characterized by olive-gray to black, weakly bioturbated shales commonly interbedded with thickly laminated black shales. Trace fossils, including Zoophycos, Chondrites , and Planolites , are abundant along the bases of the olive-gray beds. In areas where the anaerobic/dysaerobic boundary intersected the bottom slope, slight fluctuations of the position of the boundary resulted in thin interbedding of olive-gray and black shales and laterally persistent interfingering of the two lithologies. Anaerobic conditions prevailed during most of New Albany time in the deepest areas of the basin, and finely laminated, undisturbed, pelagic black shales were deposited.

Journal of Sedimentary Petrology↗

USGS1987

A Pennsylvanian-age terrestrial storm deposit: using plant fossils to characterize the history and process of sediment accumulation

A thin black shale overlying the B-coal underclay (in the Middle Pennsylvanian post-Pottsville strata of the Bernice Basin) contains a compression flora composed of large, prostrate, unidirectionally oriented lycopod trunks and randomly oriented pteridosperm stems. Analyses of modern log accumulations indicate that unidirectional trunk orientations can be produced by riverflood currents, volcanic blasts, and most high-energy windstorms. Since there are neither fluvial sediments nor ash deposits associated with the Bernice assemblage, this deposit is believed to have been formed by high-energy winds. Furthermore, this deposit is interpreted to be in situ because storm winds (and volcanic blasts) rarely have sufficient energy for the physical transport of large, intact tree trunks. The sedimentary history of the B-coal underclay can be determined from the successional changes in the species and plant part compositions (leaves, seeds, branches, trunks, etc.) of the preserved plant material. The underclay is an accretionary floodplain soil which accumulated as discrete increments during episodic floods. The sediments deposited with each flood incorporated the litter layer of the lycopod-pteridosperm forest which occupied this site. Ordinarily, the flood water would recede, and renewed root growth would destroy the primary sedimentary structures and the newly incorporated organic material. Because the bedding and forest litter are preserved in the top 5 cm of the underclay, root growth and silt deposition must have been terminated by the last flooding event. The site eventually became permanently inundated, and an organic-rich mud began to accumulate in the resulting floodplain lake. The lycopod-pteridosperm forest drowned and, at some later time, was blown down into the lake. The trunks are preserved on a single bedding plane in a 2-cm-thick, organic-rich lacustrine black shale. Continued organic accumulation in the lake resulted in the accumulation of a hypautochthonous peat which eventually was colonized by a peat-forming flora.

Journal of Sedimentary Petrology↗

USGS2014

Land cover and topography affect the land transformation caused by wind facilities

Land transformation (ha of surface disturbance/MW) associated with wind facilities shows wide variation in its reported values. In addition, no studies have attempted to explain the variation across facilities. We digitized land transformation at 39 wind facilities using high resolution aerial imagery. We then modeled the effects of turbine size, configuration, land cover, and topography on the levels of land transformation at three spatial scales. The scales included strings (turbines with intervening roads only), sites (strings with roads connecting them, buried cables and other infrastructure), and entire facilities (sites and the roads or transmission lines connecting them to existing infrastructure). An information theoretic modeling approach indicated land cover and topography were well-supported variables affecting land transformation, but not turbine size or configuration. Tilled landscapes, despite larger distances between turbines, had lower average land transformation, while facilities in forested landscapes generally had the highest land transformation. At site and string scales, flat topographies had the lowest land transformation, while facilities on mesas had the largest. The results indicate the landscape in which the facilities are placed affects the levels of land transformation associated with wind energy. This creates opportunities for optimizing wind energy production while minimizing land cover change. In addition, the results indicate forecasting the impacts of wind energy on land transformation should include the geographic variables affecting land transformation reported here.

PLoS ONE↗

USGS2020

Shifting food web structure during dam removal—Disturbance and recovery during a major restoration action

We measured food availability and diet composition of juvenile salmonids over multiple years and seasons before and during the world’s largest dam removal on the Elwha River, Washington State. We conducted these measurements over three sediment-impacted sections (the estuary and two sections of the river downstream of each dam) and compared these to data collected from mainstem tributaries not directly affected by the massive amount of sediment released from the reservoirs. We found that sediment impacts from dam removal significantly reduced invertebrate prey availability, but juvenile salmon adjusted their foraging so that the amount of energy in diets was similar before and during dam removal. This general pattern was seen in both river and estuary habitats, although the mechanisms driving the change and the response differed between habitats. In the estuary, the dietary shifts were related to changes in invertebrate assemblages following a hydrological transition from brackish to freshwater caused by sediment deposition at the river’s mouth. The loss of brackish invertebrate species caused fish to increase piscivory and rely on new prey sources such as plankton. In the river, energy provided to fish by Ephemeroptera, Plecoptera, and Trichoptera taxa before dam removal was replaced first by terrestrial invertebrates, and then by sediment-tolerant taxa such as Chironomidae. The results of our study are consistent with many others that have shown sharp declines in invertebrate density during dam removal. Our study further shows how those changes can move through the food web and affect fish diet composition, selectivity, and energy availability. As we move further along the dam removal response trajectory, we hypothesize that food web complexity will continue to increase as annual sediment load now approaches natural background levels, anadromous fish have recolonized the majority of the watershed between and above the former dams, and revegetation and microhabitats continue to develop in the estuary.

Washington↗

USGS1991

Response of rainbow trout to soy lecithin, choline and autoclaved isolated soy protein

Fry of rainbow trout ( Oncorhynchus mykiss ) were fed, from first feeding (mean weight, 0.12 g), basal diets containing either a nonautoclaved (raw) sodium proteinate form of isolated soy protein (ISP) or the same ISP autoclaved at 0.56 kg/cm 2 and l 10°C for 30 min. In the three‐way factorial, 16‐week study, I measured the effects of autoclaving ISP on the growth, survival, and chemical composition of rainbow trout at three levels of soy lecithin (0, 4, and 8%) and two levels of choline (0 and 0.3%). Fish fed raw ISP grew no faster with or without choline than did those fed the basal diet, but those fed heated ISP with choline showed a quantitatively small but significant advantage in weight gain. Whereas fish fed 4% lecithin with raw ISP more than tripled weight gain compared with fish fed the basal diets, fish fed 4% lecithin with heated ISP grew seven times as fast as those fed no lecithin or choline. Rainbow trout fed choline and 4% lecithin with heated ISP (but not raw ISP) grew significantly faster than those fed heated ISP and 4% lecithin alone. The higher level (8%) of lecithin promoted no more growth than the 4% lecithin with either raw or heated ISP. Among rainbow trout fed heated ISP, 4 and 8% supplemental lecithin – either with or without choline – reduced mortality to the same level, but 8% lecithin was the only concentration that significantly reduced the mortality of fish fed raw ISP. The results of calorimetry and determination of nitrogen with larger (235–375 g) rainbow trout individually held in metabolism chambers indicated that autoclaved ISP enhanced the growth and survival responses offish to lecithin by increasing digestible protein and energy and metabolizable energy. This higher amount of bioavailable energy and protein increased the deposition of body fat.

Progressive Fish-Culturist↗

USGS2000

Hurricanes, coral reefs and rainforests: resistance, ruin and recovery in the Caribbean

The coexistence of hurricanes, coral reefs, and rainforests in the Caribbean demonstrates that highly structured ecosystems with great diversity can flourish in spite of recurring exposure to intense destructive energy. Coral reefs develop in response to wave energy and resist hurricanes largely by virtue of their structural strength. Limited fetch also protects some reefs from fully developed hurricane waves. While storms may produce dramatic local reef damage, they appear to have little impact on the ability of coral reefs to provide food or habitat for fish and other animals. Rainforests experience an enormous increase in wind energy during hurricanes with dramatic structural changes in the vegetation. The resulting changes in forest microclimate are larger than those on reefs and the loss of fruit, leaves, cover, and microclimate has a great impact on animal populations. Recovery of many aspects of rainforest structure and function is rapid, though there may be long-term changes in species composition. While resistance and repair have maintained reefs and rainforests in the past, human impacts may threaten their ability to survive.

Ambio↗

USGS2018

Using automated radio telemetry to quantify activity patterns of songbirds during stopover

During migration, birds require stopover habitat to rest and refuel before resuming flight. While long-distance migratory flights represent a large energy investment, stopover accounts for roughly two-thirds of a bird's total energy expenditure during migration. Therefore, birds should minimize energy expenditure while also minimizing time and predation risk during stopover. To understand activity during migration, we recorded activity patterns (i.e. fine-scale movements associated with a range of behaviors) of 3 species, Red-eyed Vireo ( Vireo olivaceus ), Swainson's Thrush ( Catharus ustulatus ), and Wood Thrush ( Hylocichla mustelina ), at a stopover site along the northern coast of the Gulf of Mexico during autumn migration using automated radio telemetry. We found Red-eyed Vireos to be the most active and Swainson's Thrushes the least active. For each species, we used boosted regression trees to investigate associations between activity and factors known to influence bird behavior during stopover. While species differed, day of year and temperature were important predictors of activity for all species. Vireos were active early in the season, under light winds and warmer temperatures, and on evenings when winds were more favorable. Thrushes were more active as the season progressed and when temperatures were cooler. Thrush activity also differed between years, although thrushes increased activity later in the season during all years. Our results illustrate automated radio telemetry as a unique and valuable tool for understanding fine-scale behaviors of birds during stopover.

Alabama↗

USGS2005

Insectivory versus piscivory in Black Terns: Implications for food provisioning and growth of chicks

The Black Tern (Chlidonias niger) is known for insectivory in their breeding range, but they are piscivorous in winter and feed some fish to chicks. Fish have potentially high value for chick provisioning because of their larger mass, but the relative value of fish and insect diets for chick growth is unknown. In 1999-2000, we documented use of fish and insects for provisioning chicks at four Black Tern colonies in Maine and examined chick growth rates at two colonies (Douglas Pond and Carlton Pond) that differed in fish and insect use. Deliveries of fish and insects to broods were documented using video cameras and observations from blinds, while concurrently measuring chick growth in nest enclosures. Fish use was substantial (>25% of deliveries) at three of four colonies. Fish comprised 29% of items and 56% of metabolizable energy delivered to chicks at Douglas Pond compared to 13% of items and 22% of metabolizeable energy at Carlton Pond. Food delivery rate was inversely related to the proportion of large fish. In brood diets at Douglas and Carlton Ponds and increased with brood age at Carlton Pond only, apparently due to high insect use. Chick growth rate did not vary with respect to fish and insect composition of diets. It is concluded that adults were able to raise chicks through age 12 d at comparable growth rates with insect-or fish-dominated diets. Use of fish may be more energy efficient for adults, and the capability to use both fish and insects may reduce potential variability in food availability during the breeding season.

Waterbirds↗

USGS2004

The effect of bandwidth limitations on the inference of earthquake slip-weakening distance from seismograms

Numerous researchers have obtained estimates of slip-weakening distance, Dc, and fracture energy for recent earthquakes. Dc, is often observed to be a significant fraction of the total slip and tends to correlate with total slip. Although these observations may well be true of real earthquakes, we show that low-pass filtering of strong-motion seismograms can also produce some of these effects in inverted rupture models. We test the accuracy of Dc, estimates by calculating them in low-pass-filtered versions of models A and B of Guatteri and Spudich (2000). Models A and B are two different rupture models for a hypothetical M 6.5 earthquake, and they have nearly identical rupture time, slip, and stress-drop distributions, and nearly identical predicted seismograms, but Dc, for model B is about twice that for model A. By low-pass filtering slip models A and B at 1.0 Hz, we simulate the blurring effects of band-limited waveform inversions on these slip models. At each point on a fault, D???c is defined to be the slip at the time of the peak slip speed at that point. Low-pass filtering the slip models causes an upward bias in Dc inferred from stress-slip curves, and it causes an artificial correlation between D???c and the total slip. Low-pass filtering might also bias fracture energy high and radiated energy low. These biases should be considered when interpreting Dc derived from band-limited slip models of real earthquakes.

Bulletin of the Seismological Society of America↗

USGS2005

Moment tensor inversion of ground motion from mining-induced earthquakes, Trail Mountain, Utah

A seismic network was operated in the vicinity of the Trail Mountain mine, central Utah, from the summer of 2000 to the spring of 2001 to investigate the seismic hazard to a local dam from mining-induced events that we expect to be triggered by future coal mining in this area. In support of efforts to develop groundmotion prediction relations for this situation, we inverted ground-motion recordings for six mining-induced events to determine seismic moment tensors and then to estimate moment magnitudes M for comparison with the network coda magnitudes Mc. Six components of the tensor were determined, for an assumed point source, following the inversion method of McGarr (1992a), which uses key measurements of amplitude from obvious features of the displacement waveforms. When the resulting moment tensors were decomposed into implosive and deviatoric components, we found that four of the six events showed a substantial volume reduction, presumably due to coseismic closure of the adjacent mine openings. For these four events, the volume reduction ranges from 27% to 55% of the shear component (fault area times average slip). Radiated seismic energy, computed from attenuation-corrected body-wave spectra, ranged from 2.4 ?? 105 to 2.4 ?? 106 J for events with M from 1.3 to 1.8, yielding apparent stresses from 0.02 to 0.06 MPa. The energy released for each event, approximated as the product of volume reduction and overburden stress, when compared with the corresponding seismic energies, revealed seismic efficiencies ranging from 0.5% to 7%. The low apparent stresses are consistent with the shallow focal depths of 0.2 to 0.6 km and rupture in a low stress/low strength regime compared with typical earthquake source regions at midcrustal depths.

Bulletin of the Seismological Society of America↗

USGS2004

Rupture process of the M 7.9 Denali fault, Alaska, earthquake: Subevents, directivity, and scaling of high-frequency ground motions

Displacement waveforms and high-frequency acceleration envelopes from stations at distances of 3-300 km were inverted to determine the source process of the M 7.9 Denali fault earthquake. Fitting the initial portion of the displacement waveforms indicates that the earthquake started with an oblique thrust subevent (subevent # 1) with an east-west-striking, north-dipping nodal plane consistent with the observed surface rupture on the Susitna Glacier fault. Inversion of the remainder of the waveforms (0.02-0.5 Hz) for moment release along the Denali and Totschunda faults shows that rupture proceeded eastward on the Denali fault, with two strike-slip subevents (numbers 2 and 3) centered about 90 and 210 km east of the hypocenter. Subevent 2 was located across from the station at PS 10 (Trans-Alaska Pipeline Pump Station #10) and was very localized in space and time. Subevent 3 extended from 160 to 230 km east of the hypocenter and had the largest moment of the subevents. Based on the timing between subevent 2 and the east end of subevent 3, an average rupture velocity of 3.5 km/sec, close to the shear wave velocity at the average rupture depth, was found. However, the portion of the rupture 130-220 km east of the epicenter appears to have an effective rupture velocity of about 5.0 km/ sec, which is supershear. These two subevents correspond approximately to areas of large surface offsets observed after the earthquake. Using waveforms of the M 6.7 Nenana Mountain earthquake as empirical Green's functions, the high-frequency (1-10 Hz) envelopes of the M 7.9 earthquake were inverted to determine the location of high-frequency energy release along the faults. The initial thrust subevent produced the largest high-frequency energy release per unit fault length. The high-frequency envelopes and acceleration spectra (>0.5 Hz) of the M 7.9 earthquake can be simulated by chaining together rupture zones of the M 6.7 earthquake over distances from 30 to 180 km east of the hypocenter. However, the inversion indicates that there was relatively little high-frequency energy generated along the 60-km portion of the Totschunda fault on the east end of the rupture.

Alaska↗

USGS2015

Interpretation of S waves generated by near-surface chemical explosions at SAFOD

A series of near-surface chemical explosions conducted at the San Andreas Fault Observatory at Depth (SAFOD) were recorded by high-frequency downhole receiver arrays in separate experiments in November 2003 and May 2005. The 2003 experiment involved &sim;100  kg shots detonated along a 46-km-long line (Hole–Ryberg line) centered on SAFOD and recorded by 32 three-component geophones in the pilot hole between 0.8 and 2.0 km depth. The 2005 experiment involved &sim;36  kg shots detonated at Parkfield Area Seismic Observatory (PASO) stations (at &sim;1–8  km offset) recorded by 80 three-component geophones in the main hole between the surface and 2.4 km depth. These data sample the downgoing seismic wavefield and constrain the shallow velocity and attenuation structure, as well as the first-order characteristics of the source. Using forward modeling on a velocity structure designed for the near field, both observed P - and S -wave energy for the PASO shots are identified with the travel times expected for direct and/or reflected phases. Larger-offset recordings from shots along the Hole–Ryberg line reveal substantial SV and SH energy, especially southwest of SAFOD from the source as indicated by P -to- S amplitude ratios. The generated SV energy is interpreted to arise chiefly from P -to- S conversions at subhorizontal discontinuities. This provides a simple mechanism for often-observed low P -to- S amplitude ratios from nuclear explosions in the far field, as originating from strong near-field wave conversions.

Bulletin of the Seismological Society of America↗

USGS1989

An exact anelastic model for the free-surface reflection of P and S-I waves

Exact anelastic solutions incorporating inhomogeneous waves are used to model numerically S -I and P waves incident on the free surface of a low-loss anelastic half-space. Anelastic free-surface reflection coefficients are computed for the volumetric strain and displacement components of inhomogeneous wave fields. For the problem of an incident homogeneous S -I wave in Pierre shale, the largest strain and displacement amplitudes for the reflected P wave occur at angles of incidence for which the particle motion for the reflected inhomogeneous P wave is elliptical (minor/major axis = 0.6), the specific absorption ( Q P −1 ) is greater (300 per cent) and the velocity is less (25 per cent) than those for a corresponding homogeneous P wave, the direction of phase propagation is not parallel to the free surface, and the amplitude of the wave shows a significant increase with depth (6 per cent in one wavelength). Energy reflection coefficients computed for this low-loss anelastic model show that energy flow due to interaction of the incident and reflected waves reach maxima (30 per cent of the incident energy) near large but nongrazing angles of incidence. For the problem of an incident homogeneous P wave in Pierre shale, the inhomogeneity of the reflected S wave is shown not to contribute to significant variations in wave field characteristics over those that would be expected for a homogeneous wave.

Bulletin of the Seismological Society of America↗

USGS1989

On the use of volumetric strain meters to infer additional characteristics of short-period seismic radiation

Volumetric strain meters (Sacks-Evertson design) are installed at 15 sites along the San Andreas fault system, to monitor long-term strain changes for earthquake prediction. Deployment of portable broadband, high-resolution digital recorders (GEOS) at several of the sites extends the detection band for volumetric strain to periods shorter than 5 × 10 −2 sec and permits the simultaneous observation of seismic radiation fields using conventional short-period pendulum seismometers. Simultaneous observations establish that the strain detection bandwidth extends from periods greater than 10 7 seconds to periods near 5 × 10 −2 sec with a dynamic range exceeding 140 dB. Measurements of earth-strain noise for the period band, 10 7 to 10 −2 sec, show that ground noise, not instrument noise, currently limits the measurement of strain over a bandwidth of more than eight orders of magnitude in period. Comparison of the short-period portion of earth-strain, noise spectra (20 to 5 × 10 −2 sec) with average spectra determined from pendulum seismometers, suggest that observed noise is predominantly dilatational energy. Recordings of local and regional earthquakes indicate that dilatometers respond to P energy but not direct shear energy and that straingrams can be used to resolve superimposed reflected P and S waves for inference of wave characteristics not permitted by either sensor alone. Simultaneous measurements of incident P - and S -wave amplitudes are used to introduce a technique for single-station estimates of wave field inhomogeneity, free-surface reflection coefficients and local material P velocity. Estimates of these parameters derived for the North Palm Springs earthquake ( M w 5.9) respectively for an incident P wave of 29° are −85°, 1.71, 2.9 km/sec, and for an incident S wave of 17° are 79°, 0.85, 2.9 km/sec. The empirical estimates of reflection coefficients are consistent with model estimates derived using an anelastic half-space model with incident inhomogeneous wave fields.

California↗

USGS1994

Local observations of the onset of a large earthquake: 28 June 1992 Landers, California

The Landers earthquake ( M W 7.3) of 28 June 1992 had a very emergent onset. The first large amplitude arrivals are delayed by about 3 sec with respect to the origin time, and are preceded by smaller-scale slip. Other large earthquakes have been observed to have similar emergent onsets, but the Landers event is one of the first to be well recorded on nearby stations. We used these recordings to investigate the spatial relationship between the hypocenter and the onset of the large energy release, and to determine the slip function of the 3-sec nucleation process. Relative location of the onset of the large energy release with respect to the initial hypocenter indicates its source was between 1 and 4 km north of the hypocenter and delayed by approximately 2.5 sec. Three-station array analysis of the P wave shows that the large amplitude onset arrives with a faster apparent velocity compared to the first arrivals, indicating that the large amplitude source was several kilometers deeper than the initial onset. An M L 2.8 foreshock, located close to the hypocenter, was used as an empirical Green's function to correct for path and site effects from the first 3 sec of the mainshock seismogram. The resultant deconvolution produced a slip function that showed two subevents preceding the main energy release, an M W 4.4 followed by an M W 5.6. These subevents do not appear anomalous in comparison to simple moderate-sized earthquakes, suggesting that they were normal events which just triggered or grew into a much larger earthquake. If small and moderate-sized earthquakes commonly “detonate” much larger events, this implies that the dynamic stresses during earthquake rupture are at least as important as long-term static stresses in causing earthquakes, and the prospects of reliable earthquake prediction from premonitory phenomena are not improved.

California↗

USGS1992

Holocene coastal development on the Florida peninsula

The Florida peninsula contains five distinct coastal sections, each resulting from its own spectrum of coastal processes and sediment availability during a slowly rising, late Holocene sea level. The east coast barrier system is wave-dominated and has a large cuspate foreland (Cape Canaveral) near its middle. The Florida Keys and reef tract represent the only coastal carbonate system in the continental United States. An open-marine mangrove coast characterizes the low-energy, tide-dominated southwest part of the State. The central Gulf barrier system displays a mixed-energy morphology in a microtidal, low-energy setting. The open-coast marsh system of the Big Bend area that is north of the barrier system is also tide dominated, and is developed on a sediment-starved carbonate platform. The oldest preserved coastal Holocene section is the Florida Keys area where, at about 6 to 8 ka, sequences accumulated during the Holocene. Most of the remainder of the peninsular coast is characterized by terrigenous sequences less than 3 ka. The younger sequences accumulated almost exclusively from reworking of older strata without benefit of additional sediment supply from land.

Florida↗