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At least 91 records · Page 5Linked to original sources
USGS2000

Accounting for site effects in probabilistic seismic hazard analyses of southern California: Overview of the SCEC Phase III Report

This article presents an overview of the Southern California Earthquake Center (SCEC) Phase-III effort to determine the extent to which probabilistic seismic hazard analysis (PSHA) can be improved by accounting for site effects. The contributions made in this endeavor are represented in the various articles that compose this special issue of BSSA. Given the somewhat arbitrary nature of the site-effect distinction, it must be carefully defined in any given context. With respect to PSHA, we define the site effect as the response, relative to an attenuation relationship, averaged over all damaging earthquakes in the region. A diligent effort has been made to identify any attributes that predispose a site to greater or lower levels of shaking. The most detailed maps of Quaternary geology are not found to be helpful; either they are overly detailed in terms of distinguishing different amplification factors or present southern California strong-motion observations are inadequate to reveal their superiority. A map based on the average shear-wave velocity in the upper 30 m, however, is found to delineate significantly different amplification factors. A correlation of amplification with basin depth is also found to be significant, implying up to a factor of two difference between the shallowest and deepest parts of the Los Angeles basin. In fact, for peak acceleration the basin-depth correction is more influential than the 30-m shear-wave velocity. Questions remain, however, as to whether basin depth is a proxy for some other site attribute. In spite of these significant and important site effects, the standard deviation of an attenuation relationship (the prediction error) is not significantly reduced by making such corrections. That is, given the influence of basin-edge-induced waves, subsurface focusing, and scattering in general, any model that attempts to predict ground motion with only a few parameters will have a substantial intrinsic variability. Our best hope for reducing such uncertainties is via waveform modeling based on first principals of physics. Finally, questions remain with respect to the overall reliability of attenuation relationships at large magnitudes and short distances. Current discrepancies between viable models produce up to a factor of 3 difference among predicted 10% in 50-yr exceedance levels, part of which results from the uncertain influence of sediment nonlinearity.

California↗
USGS2003

An empirical model for earthquake probabilities in the San Francisco Bay region, California, 2002-2031

The moment magnitude M 7.8 earthquake in 1906 profoundly changed the rate of seismic activity over much of northern California. The low rate of seismic activity in the San Francisco Bay region (SFBR) since 1906, relative to that of the preceding 55 yr, is often explained as a stress-shadow effect of the 1906 earthquake. However, existing elastic and visco-elastic models of stress change fail to fully account for the duration of the lowered rate of earthquake activity. We use variations in the rate of earthquakes as a basis for a simple empirical model for estimating the probability of M ≥6.7 earthquakes in the SFBR. The model preserves the relative magnitude distribution of sources predicted by the Working Group on California Earthquake Probabilities' ( WGCEP, 1999 ; WGCEP, 2002 ) model of characterized ruptures on SFBR faults and is consistent with the occurrence of the four M ≥6.7 earthquakes in the region since 1838. When the empirical model is extrapolated 30 yr forward from 2002, it gives a probability of 0.42 for one or more M ≥6.7 in the SFBR. This result is lower than the probability of 0.5 estimated by WGCEP ( 1988 ), lower than the 30-yr Poisson probability of 0.60 obtained by WGCEP ( 1999 ) and WGCEP ( 2002 ), and lower than the 30-yr time-dependent probabilities of 0.67, 0.70, and 0.63 obtained by WGCEP ( 1990 ), WGCEP ( 1999 ), and WGCEP ( 2002 ), respectively, for the occurrence of one or more large earthquakes. This lower probability is consistent with the lack of adequate accounting for the 1906 stress-shadow in these earlier reports. The empirical model represents one possible approach toward accounting for the stress-shadow effect of the 1906 earthquake. However, the discrepancy between our result and those obtained with other modeling methods underscores the fact that the physics controlling the timing of earthquakes is not well understood. Hence, we advise against using the empirical model alone (or any other single probability model) for estimating the earthquake hazard and endorse the use of all credible earthquake probability models for the region, including the empirical model, with appropriate weighting, as was done in WGCEP ( 2002 ).

California↗
USGS1979

The Survey’s first venture into seismology

The occurrence of two small but widely felt earthquakes in the Eastern United States in 1884 led an editor of the research journal Science to suggest, in the October 3 issue of the magazine, that an "earthquake club" be formed. Its purpose was so that observers and students of "this branch of physical geography" could become acquainted with each other and thus insure the proper collection and collation of their observations. Because this was its intent, he though the club should be "unembarrassed by formal regulations"; consequently, there is no record of whether such an organziation ever existed. But the other suggestion, thata of collecting earthquake records was acted on promptly.

Earthquake Information Bulletin (USGS)↗
USGS1990

Diurnal time-activity budgets of wintering canvasbacks in Louisiana

We determined diurnal time-activity budgets of Canvasbacks ( Aythya valisineria ) at Catahoula Lake and at the Mississippi River Delta, Louisiana, from December 1987 to March 1988. Canvasback feeding, resting, locomotory, and comfort activities varied by month and location with a month-location interaction. Moreover, the percentage of time spent feeding varied by sex with a month-sex interaction. Study site differences in the time- activity budgets of wintering Canvasbacks may be related to characteristics of their foods, foraging mode, disturbance level, and physical features of habitats at the two study sites. Canvasbacks wintering in Louisiana generally spent less time feeding and more time resting during the day than they did in Mississippi or coastal South Carolina. Levels of agonistic behavior were lower than those observed in South Carolina. We found no evidence of male dominance of female Canvasbacks in Louisiana.

Louisiana↗
USGS2026

Temporal and spatial changes in seismic attenuation associated with inferred fluid migration in the 2016 central Apennines earthquake sequence

Prior work suggests that high‐frequency seismic attenuation acts as a highly sensitive proxy for crustal permeability and fluid mobility in fractured media. We test the hypothesis that the fault system responsible for the 2016–2017 Amatrice–Visso–Norcia–Capitignano sequence acted as an impermeable seal, compartmentalizing pressurized fluids until dynamic rupture triggered widespread fluid diffusion. By tracking across the sequence the spatiotemporal evolution of the S ‐wave anelastic attenuation parameter, we identify large, positive low‐frequency attenuation anomalies emerging within the hanging wall following the Amatrice mainshock and strictly preceding subsequent large ruptures. Conversely, we observe weaker, negative anomalies in the footwall, anticorrelated in time with those of the hanging wall, revealing a massive asymmetry in fluid redistribution and permeability evolution across the fault system. Furthermore, aftershock migration rates reveal distinct linear alignments in a distance‐reduced time space, allowing us to explicitly track and quantify episodes of lateral and upward fluid migration. These physically consistent patterns suggest that stress‐driven fluid diffusion directly weakens adjacent fault patches, dictating the spatiotemporal migration of seismicity. We conclude that near‐real‐time monitoring of seismic attenuation may help detect fluid redistribution in active fault systems and may provide useful information for time‐dependent seismic hazard assessment.

central Apennines↗
USGS2024

Real-time lava flow forecasting during the 2022 Mauna Loa eruption response

On November 27, 2022, Mauna Loa (Hawai‘i) erupted for the first time in 38 years, initially producing lava flows that covered the floor of its summit caldera, Moku‘āweoweo. Over the first 12 h following the summit eruption, four main fissures opened on Mauna Loa’s Northeast Rift Zone, with “fissure 3” quickly becoming the dominant source of lava flows. For the next 12 days, fissure 3 produced a 19-km-long lava flow to the north, crossing the Mauna Loa Weather Observatory access road and coming within 2.8 km of inundating the Daniel K. Inouye Highway (Saddle Road). Within 40 min of fissure 3 opening, inundation modeling efforts had begun. For the duration of the eruption, the computational fluid dynamics model Lava2d was run in real time, using flow front locations and other field observations to make sequential forecast improvements, eventually producing a set of models which accurately predicted the routing and arrival times of lava from fissure 3. These models were used to inform timing estimates of possible future inundation of the Saddle Road. As the eruption progressed, almost 4000 Lava2d models were made using high-performance computing resources, providing critical information on uncertainty in multi-week forecasts. To our knowledge, this was the first ever real-time physics-based ensemble lava flow modeling and forecasting effort. Here, we present a chronology of these real-time efforts, focusing on the successes and limitations of this approach.

Hawaii↗
USGS2013

Techniques for capturing bighorn sheep lambs

Low lamb recruitment is a major challenge facing managers attempting to mitigate the decline of bighorn sheep ( Ovis canadensis ), and investigations into the underlying mechanisms are limited because of the inability to readily capture and monitor bighorn sheep lambs. We evaluated 4 capture techniques for bighorn sheep lambs: 1) hand-capture of lambs from radiocollared adult females fitted with vaginal implant transmitters (VITs), 2) hand-capture of lambs of intensively monitored radiocollared adult females, 3) helicopter net-gunning, and 4) hand-capture of lambs from helicopters. During 2010–2012, we successfully captured 90% of lambs from females that retained VITs to ≤1 day of parturition, although we noted differences in capture rates between an area of high road density in the Black Hills (92–100%) of South Dakota, USA, and less accessible areas of New Mexico (71%), USA. Retention of VITs was 78% with pre-partum expulsion the main cause of failure. We were less likely to capture lambs from females that expelled VITs ≥1 day of parturition (range = 80–83%) or females that were collared without VITs (range = 60–78%). We used helicopter net-gunning at several sites in 1999, 2001–2002, and 2011, and it proved a useful technique; however, at one site, attempts to capture lambs led to lamb predation by golden eagles ( Aquila chrysaetos ). We attempted helicopter hand-captures at one site in 1999, and they also were successful in certain circumstances and avoided risk of physical trauma from net-gunning; however, application was limited. In areas of low accessibility or if personnel lack the ability to monitor females and/or VITs for extended periods, helicopter capture may provide a viable option for lamb capture.

Colorado;New Mexico;South Dakota↗
USGS1980

An economical educational seismic system

There is a considerable interest in seismology from the nonprofessional or amateur standpoint. The operation of a seismic system can be satisfying and educational, especially when you have built and operated the system yourself. A long-period indoor-type sensor and recording system that works extremely well has been developed in the James Madison University Physics Deparment. The system can be built quite economically, and any educational institution that cannot commit themselves to a professional installation need not be without first-hand seismic information. The system design approach has been selected by college students working a project or senior thesis, several elementary and secondary science teachers, as well as the more ambitious tinkerer or hobbyist at home

Earthquake Information Bulletin (USGS)↗
USGS2018

Review: Past and future fault rupture lengths in seismic source characterization—The long and short of it

The potential rupture length of an active fault is primary input, and an uncertainty, in source characterization for seismic hazard analysis. The past several decades have seen source models in which faults are divided into potential rupture segments based on fault‐specific behavioral and geometric observations. These models (prescribed segmentation) produced single and multisegment ruptures for use in earthquake probability and regional ground‐motion estimates. The 2013 Uniform California Earthquake Rupture Forecast, Version 3 (UCERF3), relaxed segmentation through modeling of fault‐to‐fault jumps that result in ruptures along the San Andreas fault system as long as 1200 km. Principle controls of UCERF3 rupture length are the stepover distance between different faults or fault sections, and their orientation relative to modeled coulomb stress changes. Observations of surface faulting worldwide since the mid‐1800s in shallow continental crust show that only 30 of the reported ruptures, about 12% of the reported examples, have been longer than 100 km; only 6 have been longer than 300 km and none has exceeded 500 km. A review of characteristics of long ruptures shows that, in general, they occur along essentially continuous traces with limited stepping or branching from one fault to another as opposed to rupture propagation on linkages of different faults with highly variable physical characteristics. These commonly occupy from 10% to 70% of the total host fault length. Neither segmented nor relaxed models of rupture length have been tested by the occurrence of actual ruptures. There is no reason why segmentation models incorporating timing, dynamic, and rheological factors cannot provide reasonable approximations of future rupture length. For many faults of concern worldwide, this may be the most effective approach.

California↗
USGS1998

Exchanges of sediment between the flood plain and channel of the Amazon River in Brazil

Sediment transport through the Brazilian sector of the Amazon River valley, a distance of 2010 km, involves exchanges between the channel and the flood plain that in each direction exceed the annual flux of sediment out of the river at Óbidos (∼1200 Mt yr −1 ). The exchanges occur through bank erosion, bar deposition, settling from diffuse overbank flow, and sedimentation in flood-plain channels. We estimated the magnitude of these exchanges for each of 10 reaches of the valley, and combined them with calculations of sediment transport into and out of the reaches based on sediment sampling and flow records to define a sediment budget for each reach. Residuals in the sediment budget of a reach include errors of estimation and erosion or deposition within the channel. The annual supply of sediment entering the channel from bank erosion was estimated to average 1570 Mt yr −1 (1.3 × the Óbidos flux) and the amount transferred from channel transport to the bars (380 Mt yr −1 ) and the flood plain (460 Mt yr −1 in channelized flow; 1230 Mt yr −1 in diffuse overbank flow) totaled 2070 Mt yr −1 (1.7 × the Óbidos flux). Thus, deposition on the bars and flood plain exceeded bank erosion by 500 Mt yr −1 over a 10–16 yr period. Sampling and calculation of sediment loads in the channel indicate a net accumulation in the valley floor of approximately 200 Mt yr −1 over 16 yr, crudely validating the process-based calculations of the sediment budget, which in turn illuminate the physical controls on each exchange process. Another 300–400 Mt yr −1 are deposited in a delta plain downstream of Óbidos. The components of the sediment budget reflect hydrologic characteristics of the valley floor and geomorphic characteristics of the channel and flood plain, which in turn are influenced by tectonic features of the Amazon structural trough.

Geological Society of America Bulletin↗
USGS2012

Extraordinary distance limits of landslides triggered by the 2011 Mineral, Virginia, earthquake

The 23 August 2011 Mineral, Virginia, earthquake (M w 5.8) was the largest to strike the eastern U.S. since 1897 and was felt over an extraordinarily large area. Although no large landslides occurred, the shaking did trigger many rock and soil falls from steep river banks and natural cliffs in the epicentral area and from steep road cuts along, and northwest of, the Blue Ridge Parkway. We mapped the occurrence of rock falls to determine distance limits that could be compared with those from other documented earthquakes. Studies of previous earthquakes indicated a maximum epicentral distance limit for landsliding of ~60 km for an M 5.8 earthquake; the maximum distance limit for the 2011 earthquake was 245 km, the largest exceedance of the historical limit ever recorded. Likewise, the previous maximum area affected by landslides for this magnitude was 1500 km 2 ; the area affected by landslides in the 2011 earthquake was 33,400 km 2 . These observations provide physical evidence that attenuation of strong shaking for eastern U.S. earthquakes is significantly lower than for plate‐boundary earthquakes. Also, distance limits parallel to the regional structural trend are greater than those that transect the structure, which suggests anisotropic attenuation related to the regional geologic structure. Peak ground acceleration (PGA) at the landslide distance limits is estimated to have been about 0.02–0.04g.

Virginia↗
USGS2025

Near-real-time geochemical monitoring of Hawaiian volcanoes using energy dispersive X-ray fluorescence (EDXRF)

Syn-eruption geochemical monitoring during volcanic activity is an important component of integrated volcanic monitoring. Volcanoes on the Island of Hawai‘i are primarily monitored by the U.S. Geological Survey’s Hawaiian Volcano Observatory using instrumental networks, field surveys, satellite observations, and petrologic monitoring. In collaboration with the University of Hawaiʻi at Hilo, an important component of this monitoring is near-real-time (generally within 24 h of sample collection) bulk-rock geochemistry using benchtop energy-dispersive X-ray fluorescence (EDXRF). Bulk-rock geochemistry, coupled with additional petrologic and geophysical analyses, are used to track eruption dynamics to help facilitate identification and understanding of changes that signal the onset of potentially hazardous activity. In this paper, we present EDXRF methodology for bulk-rock analysis used to evaluate the 2018 Kīlauea and 2022 Mauna Loa eruptions and compare this technique to other geochemical methods. Syn-eruption geochemical monitoring using EDXRF provides reliable quantitative data that is important for understanding eruption dynamics. Critical to this process are calibrating the instrument for analysis over the same range of compositions expected during volcanic activity, compiling a relevant database from past eruptions on the same instrument for comparison, and having the physical infrastructure and trained personnel to complete the analyses in a timely fashion. In addition to the scientific goals of petrologic monitoring, near-real-time geochemical analysis in Hawaii provides important information about the nature of on-going eruptions and informs decision-makers and the public about associated evolving hazards.

Hawaii↗
USGS1971

Results from the apollo-12 passive seismic experiment

The objective of the passive seismic experiment is to measure vibrations of the lunar surface produced by all natural and artificial sources of seismic energy and to use these data to deduce the internal structure and composition of the moon, the nature of forces which may cause deformation of the moon and moonquakes, and the numbers and masses of meteoroids striking the lunar surface. The ALSEP* seismometers can magnify lunar surface vibrations 10 million times. No instrument can operate on earth with this sensitivity, because weather and man produce too much seismic noise. To obtain answers to the above questions, seismic data must be combined with data from laboratory measurements of the physical and chemical properties of surface rocks, and many other geophyiscal and geochemical measurements. Thus far, we have had the opportunity to record data from two lunar seismic stations which were installed by the astronauts during Apollo misions and 12. The combined recording time from the stations is presently over 12 months, but there was no overlap to permit recording of the same event at two stations.

Earthquake Information Bulletin (USGS)↗
USGS2010

A multiscale and multidisciplinary investigation of ecosystem-atmosphere CO 2 exchange over the rocky mountains of colorado

A field study combined with modeling investigation demonstrated that the organization of CO2 transport by mountain terrain strongly affects the regional CO2 budget. Atmospheric dynamics can lead to complicated flows generated by inhomogeneous landscapes, topography or synoptic weather systems. The field campaign conducted of a ground deployment, the Carbon in the Mountain Experiment (CME04), and an aircraft deployment of the national Center for Atmospheric Research (NCAR) C-130, the Airborne Carbon in the Mountains Experiment (ACME04) over the period of spring to fall of 2004 to cover the seasonal variation of ecosystem-atmosphere carbon exchange. The role of the mountain circulation in CO2 transport can be played over seemingly flat terrain by mesoscale flows generated by various physical processes. The three dimensional observation strategy considered can also be applied over flat terrain.

Bulletin of the American Meteorological Society↗
USGS1970

Petrogenesis of mylonites of high metamorphic grade in the Peninsular Ranges of southern California

A fairly continuous, narrow belt of mylonite gneisses extends approximately 60 miles across southern California and crops out prominently at Coyote Mountain, near Borrego Springs, San Diego County. At Coyote Mountain, both prebatholithic rocks and igneous rocks lithologically similar to rocks from the nearby southern California batholith have been deformed in the mylonite zone—a deformation that is the last plutonic event recorded in the rocks. Petrographic evidence within these mylonites at Coyote Mountain indicates that sillimamte-K feldspar-muscovite-quartz assemblages remained stable or recrystallized (or both) during mylonitization. In addition, a maximum “set” temperature of 580° C, inferred from the MgCO 3 content of calcite in deformed dolomite marbles, was determined. The physical conditions probable at the metamorphic peak accompanying mylonitization are: P-T conditions inferred from experimentally studied systems, T = 580° to 660° C and Pxotai = PH, O( ? ) = 3.4 to 7.0 kb; high H 2 O activity, as indicated by the continued stability of muscovite at such high temperatures. Mylonitization within this belt may be related to a rise of magma to higher crustal levels from within the southern California batholith.

California↗
USGS2009

Water, something peculiar

Some chemical and physical properties of water are discussed and compared with those of other fluids. For instance, the boiling point is much higher than one would expect considering the molecular weight of water. The heat capacity is also much higher but the viscosity is not. The dielectric constant is exceptionally high. These and other properties of water can be explained by the geometry of the water molecule and the structure of water or ice.

Hydrological Sciences Bulletin↗
USGS1990

Relationship between strong-motion array parameters and the accuracy of source inversion and physical waves

We develop general rules for a strong-motion array layout on the basis of our method of applying a prediction analysis to a source inversion scheme. A systematic analysis is done to obtain a relationship between fault-array parameters and the accuracy of a source inversion. An overdetermined least-squares inversion scheme is used, where the spatial resolution is predetermined by the subfault size and the model variance is used as the accuracy of the source inversion. The accuracy of source inversion is efficiently estimated by using Wolberg's prediction analysis.

Bulletin of the Seismological Society of America↗
USGS2022

Noninvasive sampling of mountain lion hair using modified foothold traps

Genetic analysis of non-invasively obtained samples is an increasingly affordable option for many wildlife studies, but it has remained difficult to obtain high-quality samples from many species. We modified 8” Belisle foot snares (Belisle Enterprises, Quebec, Canada) to non-invasively obtain mountain lion ( Puma concolor ) hair samples in unbaited trail sets. We deployed 22 hair traps, monitored by remote cameras, at 66 locations for 1618 active trap nights ( x̄ = 24.5 nights, SD = 7.2 nights). Photos indicated 20 instances of mountain lions passing within 2 m of a hair trap and we collected 7 mountain lion hair samples, which averaged >20 hairs/sample. All samples contained hair with visible roots and were identifiable to species; 6 of the 7 (85.7%) yielded sufficient DNA for individual identification. We attributed failure to obtain samples to 3 primary causes: individual trap saturation (2 instances), trap failure (2 instances), and non-trigger events (9 instances). Black bears ( Ursus americanus ) and heavy rains were the primary sources of disturbance to hair trap sets, contributing to individual trap saturation and trap failure. We speculate that low trigger rates were associated with pan tension having been set too high in the first month of the study, as well as disturbance of hair traps or leading foot placements by nontarget species. We discuss strategies to increase hair sample collection rates, including seasonal use of hair traps, more selective placement on the landscape, and altering physical attributes of the hair traps. Taking these strategies and the quality of hair samples collected into account, we believe hair traps are a viable tool for noninvasively collecting genetic material for individual identification of mountain lions and other elusive species. These data can be applied to studies of habitat connectivity, breeding success and relatedness, population density, metapopulation structure, or any others in which a bank of individual genotypes are useful.

New Mexico↗