Aspects of Pn and Pg propagation at regional distances

1982 ◽  
Vol 72 (2) ◽  
pp. 457-471
Author(s):  
Charles A. Langston
Keyword(s):  
United States ◽  
Moment Tensor ◽  
High Amplitude ◽  
Western United States ◽  
Horizontal Distance ◽  
Ray Theory ◽  
Eastern United States ◽  
Crustal Layer ◽  
Head Waves ◽  
Earth Structures

Abstract Generalized ray theory models are calculated for a moment tensor point source in two idealized structure models appropriate for the Eastern United States to study the wave propagation of regional Pn and Pg. The models are analyzed to determine useful discriminants between earthquakes and explosions. Pg is composed of multiply reflected postcritical rays trapped in the upper crustal layer. The amplitude decay with distance of Pg is found to be source dependent and may be useful as a discriminant in well-calibrated earth structures. Pg waves from dip-slip sources fall off r-0.5 to r-0.9 faster than those from isotropic and vertical strike-slip sources, where r is the horizontal distance. In conjunction with previously published refraction results and magnitude studies, it is shown that regional Pn along many profiles in eastern North America consists principally of high-amplitude turning rays rather than head waves as observed in the Western United States. These turning rays are as large or larger than the Pg phase explaining why Pg is not as commonly observed as a distinct phase in the east as compared with observations in the Western United States.

A comparison of earthquake damage areas as a function of magnitude across the United States

1993 ◽  
Vol 83 (4) ◽  
pp. 1064-1080 ◽  
Author(s):  
G. A. Bollinger ◽  
M. C. Chapman ◽  
M. S. Sibol
Keyword(s):  
United States ◽  
North America ◽  
Ground Motion ◽  
Epicentral Distance ◽  
The United States ◽  
Western United States ◽  
Eastern North America ◽  
Similar Response ◽  
Eastern United States ◽  
The West

Abstract This study investigates the relationship between earthquake magnitude and the size of damage areas in the eastern and western United States. To quantify damage area as a function of moment magnitude (M), 149 MMI VI and VII areas for 109 earthquakes (88 in the western United States, 21 in the eastern United States and Canada) were measured. Regression of isoseismal areas versus M indicated that areas in the East were larger than those in the West, at both intensity levels, by an average 5 × in the M 4.5 to 7.5 range. In terms of radii for circles of equivalent area, these results indicate that damaging ground motion from shocks of the same magnitude extend 2 × the epicentral distance in eastern North America compared to the West. To determine source and site parameters consistent with the above results, response spectral levels for eastern North America were stochastically simulated and compared with response spectral ordinates derived from recorded strong ground motion data in the western United States. Stress-drop values of 200 bars, combined with a surficial 2-km-thick low velocity “sedimentary” layer over rock basement, produced results that are compatible with the intensity observations, i.e., similar response spectral levels in the east at approximately twice their epicentral distance in the western U.S. distance. These results suggest that ground motion modeling in eastern North America may need to incorporate source and site parameters different from those presently in general use. The results are also of importance to eastern U.S. hazard assessments as they require allowance for the larger damage areas in preparedness and mitigation programs.

scholarly journals Contrasting Patterns of Genetic Diversity and Population Structure of Armillaria mellea sensu stricto in the Eastern and Western United States

2010 ◽  
Vol 100 (7) ◽  
pp. 708-718 ◽  
Author(s):  
Kendra Baumgartner ◽  
Renaud Travadon ◽  
Johann Bruhn ◽  
Sarah E. Bergemann
Keyword(s):  
United States ◽  
Genetic Diversity ◽  
Population Structure ◽  
Los Angeles ◽  
The United States ◽  
Sensu Stricto ◽  
Western United States ◽  
Eastern United States ◽  
Armillaria Mellea ◽  
Genetic Pools

Armillaria mellea infects hundreds of plant species in natural and managed ecosystems throughout the Northern hemisphere. Previously reported nuclear genetic divergence between eastern and western U.S. isolates is consistent with the disjunct range of A. mellea in North America, which is restricted mainly to both coasts of the United States. We investigated patterns of population structure and genetic diversity of the eastern (northern and southern Appalachians, Ozarks, and western Great Lakes) and western (Berkeley, Los Angeles, St. Helena, and San Jose, CA) regions of the United States. In total, 156 diploid isolates were genotyped using 12 microsatellite loci. Absence of genetic differentiation within either eastern subpopulations (θST = –0.002, P = 0.5 ) or western subpopulations (θST = 0.004, P = 0.3 ) suggests that spore dispersal within each region is sufficient to prevent geographic differentiation. In contrast to the western United States, our finding of more than one genetic cluster of isolates within the eastern United States (K = 3), revealed by Bayesian assignment of multilocus genotypes in STRUCTURE and confirmed by genetic multivariate analyses, suggests that eastern subpopulations are derived from multiple founder sources. The existence of amplifiable and nonamplifiable loci and contrasting patterns of genetic diversity between the two regions demonstrate that there are two geographically isolated, divergent genetic pools of A. mellea in the United States.

scholarly journals Clustering CAMELS using hydrological signatures with high spatial predictability

2019 ◽  
Author(s):  
Florian Ulrich Jehn ◽  
Konrad Bestian ◽  
Lutz Breuer ◽  
Philipp Kraft ◽  
Tobias Houska
Keyword(s):  
United States ◽  
Western United States ◽  
Hydrological Models ◽  
Eastern United States ◽  
Quadratic Regression ◽  
Discharge Characteristics ◽  
The Mean ◽  
Hydrological Signatures ◽  
High Spatial Variability

Abstract. The behavior of every catchment is unique. Still, we need ways to classify them as this helps to improve hydrological theories. Usually catchments are classified along either their attributes classes (e.g. climate, topography) or their discharge characteristics, which is often captured in hydrological signatures. However, recent studies have shown that many hydrological signatures have a low predictability in space and therefore only dubious hydrological meaning. Therefore, this study uses hydrological signatures with the highest predictability in space to cluster 643 catchments from the continental United States (CAMELS (Catchment Attributes and MEteorology for Large-Sample Studies) dataset) into ten groups. We then evaluated the connection between catchment attributes with the hydrological signatures with quadratic regression, both in the overall CAMELS dataset and the ten clusters. In the overall dataset, aridity had the strongest connection to the hydrological signatures, especially in the eastern United States. However, the clusters in the western United States showed a more heterogeneous pattern with a larger influence of forest fraction, the mean elevation or the snow fraction. From this, we conclude that catchment behavior can be mainly attributed to climate in regions with homogenous topography. In regions with a heterogeneous topography, there is no clear pattern of the catchment behavior, as catchments show high spatial variability in their attributes. The classification of the CAMELS dataset with the hydrological signatures allows testing hydrological models in contrasting environments.

Magnitude determination at regional and near-regional distances in the United States

1967 ◽  
Vol 57 (4) ◽  
pp. 591-639
Author(s):  
J. F. Evernden
Keyword(s):  
United States ◽  
Velocity Structure ◽  
The United States ◽  
Western United States ◽  
Eastern United States ◽  
Origin Time ◽  
Distance Data ◽  
Chemical Explosions ◽  
Low Amplitude ◽  
Magnitude Determination

abstract This report deals with the problems of variation of Pn amplitudes in the regional and near-regional distance ranges (200-2100 kilometers). The data used were recorded by Long Range Seismic Measurement vans of the VELA Seismological Center as a result of earthquakes throughout the United States and numberous nuclear and chemical explosions in the same region. It is shown that the patterns of Pn amplitudes versus Δ in Western United States and Eastern United States are markedly different and that these differences are related to different velocity structures in the two regions. These differences extend to at least 150 kilometers depth. Neither the Western United States nor Eastern United States amplitude patterns conform even approximately to that predicted or suggested by Gutenberg and Richter in the 1000-2000 kilometer range. The predicted zone of low-amplitude signals in that distance range does not exist and overestimation of magnitude by as much as 1.5 magnitude units is frequently done because of failure to properly understand the patterns of radiation. By proper calibration of the Western United States by use of numerous events, it is now possible to make consistent estimates of magnitude at all distance ranges for most explosions and earthquakes. Obtaining consistent estimates of amplitude as a function of distance for a particular event requires a knowledge of the energy distribution between the several refracted phases used between 200 and 2500 kilometers distance. Data on hand show that the energy partition function is reasonably uniform throughout the regions investigated but that locally it may vary radically, resulting in a ten-fold change in relative excitation of two refracted phases. Patterns of energy radiation and decay are probably approximately determinable from knowledge of velocity structure and vice versa. Both are best determinable from explosion data where origin time and focus are accurately known.

An analysis of the travel times of S waves to North American stations in the distance range 28° to 82°

1967 ◽  
Vol 57 (4) ◽  
pp. 761-771 ◽  
Author(s):  
H. A. Doyle ◽  
A. L. Hales
Keyword(s):  
United States ◽  
Upper Mantle ◽  
Univariate Analysis ◽  
Western United States ◽  
Travel Times ◽  
Eastern United States ◽  
S Waves ◽  
Distance Range ◽  
Time Term ◽  
Mantle Velocity

abstract The travel times of S waves from 20 earthquakes to stations in North America in the distance range 28° to 82° have been studied. The deviations from J-B times were analyzed into station, source and distance components using the least-squares time-term approach of Cleary and Hales. Station anomalies had a range of about eight seconds, as compared to three seconds for the P anomalies, and are believed to be caused largely by variations in the upper mantle velocity distribution. S residuals, like the P residuals, were generally positive in the western United States, and negative in the central and eastern United States. P and S residuals at the same station correlated with a coefficient of 0.75, the slope of the regression of S anomaly on P anomaly being 3.72. Corrections to J-B times for S were of the order of the standard errors of the determinations. Within the distance range of 28° to 82° large changes of the S travel times, such as were required by the lower mantle velocities proposed by MacDonald and Ness (1961), are not permitted by the present data. The analysis was checked by carrying out a univariate analysis of variance of the same data.

scholarly journals Discrimination of Small Earthquakes and Buried Single-Fired Chemical Explosions at Local Distances (<150  km) in the Western United States from Comparison of Local Magnitude (ML) and Coda Duration Magnitude (MC)

2020 ◽  
Author(s):  
Keith D. Koper ◽  
Monique M. Holt ◽  
Jonathan R. Voyles ◽  
Relu Burlacu ◽  
Moira L. Pyle ◽  
...  
Keyword(s):  
United States ◽  
High Frequency ◽  
Characteristic Curve ◽  
Moment Tensor ◽  
Western United States ◽  
Local Magnitude ◽  
Underground Nuclear Explosions ◽  
Nuclear Explosions ◽  
Duration Magnitude ◽  
Chemical Explosions

ABSTRACT Seismologists distinguish underground nuclear explosions from more commonly occurring earthquakes using moment tensor inversion, high-frequency P/S amplitude ratios, mb:Ms comparisons, and P-pP differential travel times. These methods are generally successful for large seismic events (M&gt;3–4) well recorded at regional-to-teleseismic distances (&gt;150  km); however, it is unclear whether they can be modified to work for small events (M&lt;3) well recorded only at local distances (&lt;150  km). Here, we evaluate a recently proposed, local-distance seismic source discriminant—the difference between local magnitude (ML) and coda duration magnitude (MC)—using seismograms of earthquakes and buried, single-fired chemical explosions recorded in three regions of the western United States. The quantity ML–MC was previously found to be sensitive to source depth, effectively discriminating mine blasts, induced earthquakes, and very shallow tectonic earthquakes from deeper crustal earthquakes. In this study, we report the first evaluation of ML–MC as a depth discriminant using data from buried, single-fired explosions that, unlike the seismic sources studied earlier, are good analogs for underground nuclear explosions. We find that even when using generic, uncalibrated methods of assigning magnitudes, ML–MC separates single-fired explosions and earthquakes. The area under the receiver operating characteristic curve is 0.92 for 19 explosions and 14 earthquakes in Washington, 0.90 for 22 explosions and 90 earthquakes in Wyoming, and 0.99 for three explosions and 149 earthquakes in Nevada. ML:MC comparisons have the potential to enhance discrimination based on high-frequency P/S amplitudes ratios—which perform less well at local than regional distances—because the two metrics have complementary sensitivities.

The lasting impact of N.M. Fenneman’s works physiography of the western and eastern United States

2021 ◽  
pp. 030913332110129
Author(s):  
Carol F Sawyer
Keyword(s):  
United States ◽  
The United States ◽  
Western United States ◽  
Eastern United States ◽  
Continued Use ◽  
Physiographic Regions

The publication of Fenneman’s two volumes on physiography: The Physiography of Western United States and the Physiography of Eastern United States, was the culmination of over 20 years of work toward formalization of the physiographic regions in the United States. This paper details the relevant works that predate these volumes, the two volumes themselves, as well as briefly describing Fenneman’s career and the continued use of the works 80 plus years post-publication.

scholarly journals Recent Changes in United States Extreme 3-Day Precipitation Using the R-CAT Scale

2020 ◽  
Vol 21 (6) ◽  
pp. 1207-1221 ◽  
Author(s):  
Maryam A. Lamjiri ◽  
F. Martin Ralph ◽  
Michael D. Dettinger
Keyword(s):  
United States ◽  
East Coast ◽  
The United States ◽  
Western United States ◽  
Eastern United States ◽  
Atmospheric Rivers ◽  
The Past ◽  
Extreme Precipitation Events ◽  
Precipitation Total ◽  
Precipitation Events

AbstractExtraordinary precipitation events have impacted the United States recently, including Hurricanes Harvey (2017) and Florence (2018), with 3-day precipitation totals larger than any others reported in the United States during the past 70 years. The rainfall category (R-CAT) scaling method is used here to document extreme precipitation events and test for trends nationally. The R-CAT scale uses thresholds of 3-day precipitation total in 100-mm increments (starting with 200 mm) that do not vary temporally or geographically, allowing for simple, intuitive comparisons of extremes over space and time. The paper that introduced the scale only required levels 1–4 to represent historical extremes, finding that R-CATs 3–4 strike the conterminous United States about as frequently as EF 4–5 tornadoes or category 3–5 hurricanes. Remarkably, Florence and Harvey require extending the scale to R-CAT 7 and 9, respectively. Trend analyses of annual maximum 3-day totals (1950–2019) here identify significant increases in the eastern United States, along with declines in Northern California and Oregon. Consistent with these results, R-CAT storms have been more frequent in the eastern, and less frequent in western, United States during the past decade compared to 1950–2008. Tropical storms dominate R-CAT events along the southeastern coast and East Coast with surprising contributions from atmospheric rivers, while atmospheric rivers completely dominate along the West Coast.

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