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USGS1991

An analysis of a seismic reflection from the base of a gas hydrate zone, offshore Peru

Seismic reflection data recorded near ODP Site 688, offshore Peru, exhibit a persistent bottom-simulating reflector (BSR) from a depth corresponding to the theoretical base of the gas hydrate stability field. Although gas hydrate has been recovered in cores from scientific drilling in both the Pacific and the Atlantic, drilling in areas exhibiting a BSR has usually been avoided because of the perceived risk of releasing free gas trapped beneath the hydrated sediments. To carry out a quantitative analysis of the BSR, the seismic data were reprocessed using signature deconvolution and true amplitude recovery techniques. Synthetic seismograms that were created using acoustic parameters extracted from the seismic data and physical properties from Site 688 borehole measurement were compared to the observed seismic data to estimate the thickness of the free-gas zone. Results indicate the BSR is discontinuous laterally. Where the BSR is of high amplitude, free gas in a zone 5.5-17 m thick beneath the hydrated sediments provides the observed waveform; where the BSR amplitude is low, the free-gas zone is much thinner than 5.5 m or is entirely absent.

American Association of Petroleum Geologists Bulle↗

USGS1976

Landslides - Cause and effect

Landslides can cause seismic disturbances; landslides can also result from seismic disturbances, and earthquake-induced slides have caused loss of life in many countries. Slides can cause disastrous flooding, particularly when landslide dams across streams are breached, and flooding may trigger slides. Slope movement in general is a major process of the geologic environment that places constraints on engineering development. In order to understand and foresee both the causes and effects of slope movement, studies must be made on a regional scale, at individual sites, and in the laboratory. Areal studies — some embracing entire countries — have shown that certain geologic conditions on slopes facilitate landsliding; these conditions include intensely sheared rocks; poorly consolidated, fine-grained clastic rocks; hard fractured rocks underlain by less resistant rocks; or loose accumulations of fine-grained surface debris. Field investigations as well as mathematical- and physical-model studies are increasing our understanding of the mechanism of slope movement in fractured rock, and assist in arriving at practical solutions to landslide problems related to all kinds of land development for human use. Progressive failure of slopes has been studied in both soil and rock mechanics. New procedures have been developed to evaluate earthquake response of embankments and slopes. The finite element method of analysis is being extensively used in the calculation of slope stability in rock broken by joints, faults, and other discontinuities.

Bulletin of the International Association of Engin↗

USGS2004

Geophysical and isotopic mapping of preexisting crustal structures that influenced the location and development of the San Jacinto fault zone, southern California

We examine the role of preexisting crustal structure within the Peninsular Ranges batholith on determining the location of the San Jacinto fault zone by analysis of geophysical anomalies and initial strontium ratio data. A 1000-km-long boundary within the Peninsular Ranges batholith, separating relatively mafic, dense, and magnetic rocks of the western Peninsular Ranges batholith from the more felsic, less dense, and weakly magnetic rocks of the eastern Peninsular Ranges batholith, strikes north-northwest toward the San Jacinto fault zone. Modeling of the gravity and magnetic field anomalies caused by this boundary indicates that it extends to depths of at least 20 km. The anomalies do not cross the San Jacinto fault zone, but instead trend northwesterly and coincide with the fault zone. A 75-km-long gradient in initial strontium ratios (Sri) in the eastern Peninsular Ranges batholith coincides with the San Jacinto fault zone. Here rocks east of the fault are characterized by Sri greater than 0.706, indicating a source of largely continental crust, sedimentary materials, or different lithosphere. We argue that the physical property contrast produced by the Peninsular Ranges batholith boundary provided a mechanically favorable path for the San Jacinto fault zone, bypassing the San Gorgonio structural knot as slip was transferred from the San Andreas fault 1.0-1.5 Ma. Two historical M6.7 earthquakes may have nucleated along the Peninsular Ranges batholith discontinuity in San Jacinto Valley, suggesting that Peninsular Ranges batholith crustal structure may continue to affect how strain is accommodated along the San Jacinto fault zone. ?? 2004 Geological Society of America.

Geological Society of America Bulletin↗

USGS1956

Geophysical abstracts 165, April-June 1956

Geophysical Abstracts includes abstracts of technical papers and books on the physics of the solid earth, the application of physical methods and techniques to geologic problems, and geophysical exploration. The table of contents, which is alphabetically arranged, shows the material covered. Abstracts are prepared only of material that is believed to be generally available. Ordinarily abstracts are not published of material with limited circulation (such as dissertations, open-file reports, or memoranda) or of other papers presented orally at meetings unless summaries of substantial length are published. Abstracts of papers in Japanese and Chinese are based on abstracts or summaries in a western language accompanying the paper.

Bulletin↗

USGS1956

Geophysical abstracts 166, July-September 1956

Bulletin↗

USGS2022

Getting ahead of flash drought: From early warning to early action

Flash droughts, characterized by their unusually rapid intensification, have garnered increasing attention within the weather, climate, agriculture, and ecological communities in recent years due to their large environmental and socioeconomic impacts. Because flash droughts intensify quickly, they require different early warning capabilities and management approaches than are typically used for slower-developing “conventional” droughts. In this essay, we describe an integrated research-and-applications agenda that emphasizes the need to reconceptualize our understanding of flash drought within existing drought early warning systems by focusing on opportunities to improve monitoring and prediction. We illustrate the need for engagement among physical scientists, social scientists, operational monitoring and forecast centers, practitioners, and policy-makers to inform how they view, monitor, predict, plan for, and respond to flash drought. We discuss five related topics that together constitute the pillars of a robust flash drought early warning system, including the development of 1) a physically based identification framework, 2) comprehensive drought monitoring capabilities, and 3) improved prediction over various time scales that together 4) aid impact assessments and 5) guide decision-making and policy. We provide specific recommendations to illustrate how this fivefold approach could be used to enhance decision-making capabilities of practitioners, develop new areas of research, and provide guidance to policy-makers attempting to account for flash drought in drought preparedness and response plans.

Bulletin of American Meteorological Society (BAMS)↗

USGS2009

Suggested notation conventions for rotational seismology

We note substantial inconsistency among authors discussing rotational motions observed with inertial seismic sensors (and much more so in the broader topic of rotational phenomena). Working from physics and other precedents, we propose standard terminology and a preferred reference frame for inertial sensors (Fig. 1) that may be consistently used in discussions of both finite and infinitesimal observed rotational and translational motions in seismology and earthquake engineering. The scope of this article is limited to observations because there are significant differences in the analysis of finite and infinitesimal rotations, though such discussions should remain compatible with those presented here where possible. We recommend the general use of the notation conventions presented in this tutorial, and we recommend that any deviations or alternatives be explicitly defined.

Bulletin of the Seismological Society of America↗

USGS1980

Sir Harold Jeffreys

Sir Harold Jeffreys is a world authority in theoretical geophyiscs. hew as born in Northumbria (northeast of England) and educated at Armstrong College (now the University of Newcastle-upon-Tyne) and Cambridge University. He is now a Senior Fellow of St.John's College, Cambridge. He has published over 300 scientific papers and is the author of 7 books, including Theory of Probability and Mathematical Physics (with his wife, Lady Bertha Swirles Jeffreys) . Sir Harold has made innumerable theoretical contributions to seismology. Many of these are documented in his book The Earth , which has been published in six editions. His papers have recently been collated by Gordon and Breach (Publishers) into six volumes, Collected Papers on Sir Harold Jeffreys on Geophyiscs and other Sciences. Some idea of the breadth of this research can be seen from the individual volume titles: "Theoretical and Observational Seismology," "Observational Seismology," "Gravity," "Dissipation of Energy and Thermal History," "Astronomy and Geophysics," and "Matematics, Probability and Miscellaneious Other Sciences."

Earthquake Information Bulletin (USGS)↗

USGS1956

Geophysical abstracts 164, January-March 1956

Geophysical Abstracts includes abstracts of technical papers and books on the physics of the solid earth, the application of physical methods and techniques to geologic problems, and geophysical exploration. A new table of contents, alphabetically arranged, has been adapted to show more clearly the material covered. Abstracts are prepared only of material that is believed to be generally available. Ordinarily abstracts are not published of material with limited circulation (such as dissertations, open-file reports, or memoranda) or of papers presented orally at meetings unless summaries of substantial length are published. Abstracts of papers in Japanese and Chinese are based on abstracts or summaries in a western language accompanying the paper.

Bulletin↗

USGS2007

The rate and pattern of bed incision and bank adjustment on the Colorado River in Glen Canyon downstream from Glen Canyon Dam, 1956-2000

Closure of Glen Canyon Dam in 1963 transformed the Colorado River by reducing the magnitude and duration of spring floods, increasing the magnitude of base flows, and trapping fine sediment delivered from the upper watershed. These changes caused the channel downstream in Glen Canyon to incise, armor, and narrow. This study synthesizes over 45 yr of channel-change measurements and demonstrates that the rate and style of channel adjustment are directly related to both natural processes associated with sediment deficit and human decisions about dam operations. Although bed lowering in lower Glen Canyon began when the first cofferdam was installed in 1959, most incision occurred in 1965 in conjunction with 14 pulsed high flows that scoured an average of 2.6 m of sediment from the center of the channel. The average grain size of bed material has increased from 0.25 mm in 1956 to over 20 mm in 1999. The magnitude of incision at riffles decreases with distance downstream from the dam, while the magnitude of sediment evacuation from pools is spatially variable and extends farther downstream. Analysis of bed-material mobility indicates that the increase in bed-material grain size and reduction in reach-average gradient are consistent with the transformation of an adjustable-bed alluvial river to a channel with a stable bed that is rarely mobilized. Decreased magnitude of peak discharges in the post-dam regime coupled with channel incision and the associated downward shifts of stage-discharge relations have caused sandbar and terrace erosion and the transformation of previously active sandbars and gravel bars to abandoned deposits that are no longer inundated. Erosion has been concentrated in a few pre-dam terraces that eroded rapidly for brief periods and have since stabilized. The abundance of abandoned deposits decreases downstream in conjunction with decreasing magnitude of shift in the stage-discharge relations. In the downstream part of the study area where riffles controlling channel elevation have not incised, channel narrowing has resulted from decreased magnitude of peak discharges and minor post-dam deposition. These physical changes to the aquatic and riparian systems have supported the establishment and success of an artifact ecosystem dominated by non-native species. Models for the channel response downstream from large dams typically consider factors such as the degree of sediment deficit, the pre-dam surface and subsurface grain size, and the magnitude of post-dam average flows. These results suggest that it is also necessary to consider (1) the possibility of variable responses among different channel elements and (2) the potential importance of exceptional flows resulting from management decisions. ?? 2007 Geological Society of America.

Geological Society of America Bulletin↗

USGS2026

Action in uncertainty: Data-driven decisions that acknowledge emotional responses and transcendental connections

The increasing uncertainty with global change often stifles action and results in calls for more data before moving beyond status quo environmental decisions (Mahapatra & Ratha 2017; Ripple et al. 2017; Montefalcone et al. 2025). Advancing science and collecting more data is crucial; however, science alone (i.e., “western” or “positivist” science, as described in Fuller, 2001; Reid et al. 2020) may be insufficient to reduce uncertainty to a comfortable level for decision making. Therefore, increasing personal and collective capacity to make proactive decisions may require decision makers to recognize that their own understanding of the world, and therefore interpretation of scientific data, is influenced by all Four Realms of human perception: Physical, Mental, Emotional, and Transcendental (Wolf 2017; Dukes et al. 2021; Clifford et al. 2022). In the ESA Special Session, Action in Uncertainty, we introduced four questions to help participants increase cognitive awareness of how all Four Realms may affect their understanding in uncertain environmental decision contexts: 1. Physical: How do I observe uncertainty through the five senses (feel, see, hear, taste, smell)? The physical realm is what people observe, including ecological data observations and experimentation. 2. Mental: How do I think about uncertainty using logic, reason, and language-based understanding? The mental realm is how people think about the world, including scientific theory, modeling, and decision frameworks. 3. Emotional: How do I feel in uncertainty? The emotional realm is a person’s subjective emotional state, such as fear, curiosity, defensiveness, and awe. 4. Transcendental: How do I connect to something greater than myself in uncertainty? The transcendental realm includes people’s sense of purpose, responsibility for others, or moral code.

ESA Bulletin↗

USGS2001

Relocation of Wyoming mine production blasts using calibration explosions

An important requirement for a comprehensive seismic monitoring system is the capability to accurately locate small seismic events worldwide. Accurate event location can improve the probability of determining whether or not a small event, recorded predominantly by local and regional stations, is a nuclear explosion. For those portions of the earth where crustal velocities are not well established, reference event calibration techniques offer a method of increased locational accuracy and reduced locational bias. In this study, data from a set of mining events with good ground-truth data in the Powder River Basin region of eastern Wyoming are used to investigate the potential of event calibration techniques in the area. Results of this study are compared with locations published in the prototype International Data Center’s Reviewed Event Bulletin (REB). A Joint Hypocenter Determination (JHD) method was applied to a set of 23 events. Four of those events with superior ground-truth control (mining company report or Global Positioning System data) were used as JHD reference events, Nineteen (83%) of the solutions converged and the resulting set of station-phase travel-time corrections from the JHD results was then tested. When those travel-time corrections were applied individually to the four events with good ground-truth control, the average locational error reduced the original REB location error from 16.1 km to 5.7 km (65% improvement). The JHD locations indicated reduced locational bias and all of the individual error ellipses enclosed the actual known event locations. Given a set of well-recorded calibration events, it appears that the JHD methodology is a viable technique for improving locational accuracy of future small events where the location depends on arrival times from predominantly local and/or regional stations. In this specific case, the International Association of Seismology and the Physics of the Earth’s Interior (IASPEI) travel-time tables, coupled with JHDderived travel-time corrections, may obviate the need for an accurately known regional velocity structure in the Powder River Basin region.

Montana, Wyoming↗

USGS2015

Computing elastic‐rebound‐motivated rarthquake probabilities in unsegmented fault models: a new methodology supported by physics‐based simulators

A methodology is presented for computing elastic‐rebound‐based probabilities in an unsegmented fault or fault system, which involves computing along‐fault averages of renewal‐model parameters. The approach is less biased and more self‐consistent than a logical extension of that applied most recently for multisegment ruptures in California. It also enables the application of magnitude‐dependent aperiodicity values, which the previous approach does not. Monte Carlo simulations are used to analyze long‐term system behavior, which is generally found to be consistent with that of physics‐based earthquake simulators. Results cast doubt that recurrence‐interval distributions at points on faults look anything like traditionally applied renewal models, a fact that should be considered when interpreting paleoseismic data. We avoid such assumptions by changing the "probability of what" question (from offset at a point to the occurrence of a rupture, assuming it is the next event to occur). The new methodology is simple, although not perfect in terms of recovering long‐term rates in Monte Carlo simulations. It represents a reasonable, improved way to represent first‐order elastic‐rebound predictability, assuming it is there in the first place, and for a system that clearly exhibits other unmodeled complexities, such as aftershock triggering.

Bulletin of the Seismological Society of America↗

USGS2025

Earthquake stress drop, source spectra from laboratory experiments, and the apparent unsteadiness of frictional slip

Over a range of co-seismic total energy release, high sample rate slip, stress, and slip velocity measurements were made during frictional failure to determine seismic source properties. The near-field measurements were used to estimate stress drops using spectral approaches that are analogous to the standard seismological moment-corner determined Δσ and acceleration amplitude Δσ arms stress drops. Rapid frictional sliding produces slip velocity amplitude spectra that vary with frequency -1 so long as the energy dissipated by friction approaches the total energy release. Under these conditions Δσ and Δσ arms are similar in size. Since these are nearly direct measurements of fault slip velocity and because they produce flat acceleration spectra between the corner and an apparent fmax, friction in these experiments seems to produce dynamic acceleration and deceleration at all resolved frequencies. The physical origin of this unsteady motion is not known exactly but likely reflects rapid dynamic variations in fault strength or applied stress. On the other hand, when the total energy stored prior to failure is artificially made somewhat larger relative to that which can be dissipated by friction the velocity spectra vary with frequency -2 immediately below the corner. At these conditions Δσ and Δσ arms diverge. The excess stored energy is preferentially partitioned into radiated energy upon failure. Collectively the experiments imply that to produce unsteady, white noise accelerations that are observed for natural earthquakes, requires that at least 95% of the energy released does not escape the source region to be radiated to the far-field.

Bulletin of the Seismological Society of America↗

USGS2021

Current activity on the Martian surface: A key subject for future exploration

One of the fundamental discoveries in Mars science in the last decade has been the extent and importance of current surface activity. Recent results have shifted our view of Mars from a world where the most interesting geologic events were in the distant past (similar to the Moon) to a world that undergoes active evolution and one where understanding the present is key to deciphering the planet’s history. When input was requested for the last Planetary Science Decadal Survey, some observations of surface changes had been published, but the number of detections was small and their significance not fully appreciated. Since that time, detections have proliferated, driven primarily by the long-term operation of the Mars Reconnaissance Orbiter (MRO) and the High Resolution Imaging Science Experiment (HiRISE) as well as landed observations of aeolian activity. In addition to observed changes, theory suggests that additional important surface processes are likely active but not yet observed because orbital data are limited in space and time and landed studies are rare. Understanding current Martian surface processes is a fundamental science question in itself, as it provides a test for physical and terrestrial analog-based models of specific geological processes acting under non-Earth planetary and environmental conditions. It is also an essential step for reading Mars’ geologic history and providing input to climate models: without understanding current dynamic processes, we cannot understand how they have varied during recent climate cycles, nor how they are reflected in ancient rock or modern ice records. Understanding the rates and types of current surface activity is also highly relevant to selecting geological samples, setting Planetary Protection rules, and understanding the hazards and environment that would be experienced by future human explorers.

Bulletin of the AAS↗

USGS2004

Chapter G: Tentative Correlation Between CIPW Normin pl (Total Plagioclase) and Los Angeles Wear in Precambrian Midcontinental Granites-Examples from Missouri and Oklahoma, with Applications and Limitations for Use

The normative chemical classification of Cross, Iddings, Pirsson, and Washington (CIPW) is commonly used in igneous petrology to distinguish igneous rocks by comparing their magmatic chemistries for similar and dissimilar components. A potential use for this classification other than in petrologic studies is in the rapid assessment of aggregate sources, possibly leading to an economic advantage for an aggregate producer or user, by providing the opportunity to determine whether further physical testing of an aggregate is warranted before its use in asphalt or concrete pavement. However, the CIPW classification currently should not be substituted for the physical testing required in specifications by State departments of transportation. Demands for physical testing of aggregates have increased nationally as users seek to maximize the quality of the aggregate they purchase for their pavements. Concrete pavements are being laid with increased thicknesses to withstand increasing highway loads. New pavement mixes, most notably Superior Performance Asphalt Pavement ('Superpave'), are designed for additional service life. For both concrete and asphalt, the intent is to generate a durable pavement with a longer service life that should decrease overall life-cycle costs. Numerous aggregate producers possess chemical-composition data available for examination to answer questions from the potential user. State geological surveys also possess chemical-composition data for stone sources. Paired with the results of physical testing, chemical- composition data provide indicative information about stone durability and aggregate strength. The Missouri Department of Transportation has noted a possible relation among coarse-grained Precambrian granites of the midcontinental region, correlating the results of abrasion testing with the contents of normative minerals, also known as normins, calculated from chemical composition data. Thus, normin pl ( total plagioclase) can predict, by way of simple regression, the Los Angeles wear for granite samples collected in Missouri. The results of this abrasion testing were extended to another granite in Oklahoma where normin pl predicted Los Angeles wear to within 0.6 percent. This relation may also exist for granitic rocks outside the Oklahoma-Missouri region, as well as for other igneous-rock types.

Bulletin↗

USGS2014

Pyroclast/snow interactions and thermally driven slurry formation. Part 1: Theory for monodisperse grain beds

Lahars are often produced as pyroclastic flows move over snow. This phenomenon involves a complicated interplay of mechanical and thermal processes that need to be separated to get at the fundamental physics. The thermal physics of pyroclast/snow interactions form the focus of this paper. A theoretical model is developed of heat- and mass transfer at the interface between a layer of uniformly sized pyroclasts and an underlying bed of snow, for the case in which there is no relative shear motion between pyroclasts and snow. A microscale view of the interface is required to properly specify boundary conditions. The physical model leads to the prediction that the upward flux of water vapor - which depends upon emplacement temperature, pyroclast grain size, pyroclast-layer thickness, and snow permeability - is sometimes sufficient to fluidize the pyroclasts. Uniform fluidization is usually unstable to bubble formation, which leads to vigorous convection of the pyroclasts themselves. Thus, predicted threshold conditions for fluidization are tantamount to predicted thresholds for particle convection. Such predictions are quantitatively in good agreement with results of experiments described in part 2 of this paper. Because particle convection commonly causes scour of the snow bed and transformation of the pyroclast layer to a slurry, there exists a 'thermal scour' process for generating lahars from pyroclastic flows moving over snow regardless of the possible role of mechanical scour.

Bulletin of Volcanology↗

USGS2015

Nearshore dynamics of artificial sand and oil agglomerates

Weathered oil can mix with sediment to form heavier-than-water sand and oil agglomerates (SOAs) that can cause beach re-oiling for years after a spill. Few studies have focused on the physical dynamics of SOAs. In this study, artificial SOAs (aSOAs) were created and deployed in the nearshore, and shear stress-based mobility formulations were assessed to predict SOA response. Prediction sensitivity to uncertainty in hydrodynamic conditions and shear stress parameterizations were explored. Critical stress estimates accounting for large particle exposure in a mixed bed gave the best predictions of mobility under shoaling and breaking waves. In the surf zone, the 10-cm aSOA was immobile and began to bury in the seafloor while smaller size classes dispersed alongshore. aSOAs up to 5 cm in diameter were frequently mobilized in the swash zone. The uncertainty in predicting aSOA dynamics reflects a broader uncertainty in applying mobility and transport formulations to cm-sized particles.

Marine Pollution Bulletin↗