bluuebunny/crossref_metadata_2025_split huggingface dataset:
Automatic time-domain calculation of source parameters for the analysis of induced seismicity
Authors: Urbancic T. I. , Trifu C.-I. , Mercer R. A. , Feustel A. J. , Alexander J. A. G. 
Published: July 2023

Abstract
A time-domain methodology for the automatic (on-line) calculation of source parameters is introduced. The method is based on applying Parseval's theorem to the spectral equations proposed by Andrews (1986). The appropriateness of the technique for the analysis of induced seismicity was tested by comparing on-line values of seismic moment, seismic energy, and static stress drop with those obtained in the frequency domain (off-line) for an aftershock sequence of events recorded underground at Creighton mine, Ontario. Our analysis shows that the calculated on-line and off-line source parameters are in good agreement, with an average slope offset of 4% from the 1:1 line, suggesting that the proposed method is reliable. Additionally, by applying empirical on-line attenuation corrections (coda Q), similar results are obtained to those calculated using off-line corrections (spectral decay), improving the average slope offset to 1%.
On the coherence of ground motion in the San Fernando Valley
Authors: Hough S.  E. , Field E.  H. 
Published: July 2023

Abstract
We present an analysis of the coherence of seismic ground motion recorded on alluvial sediments in the San Fernando Valley, California. Using aftershocks of the 17 January 1994 Mw6.7 earthquake recorded at a quasi-dense array of portable stations, we analyze the coherence of three well-recorded magnitude 3.7 to 4.0 events over the frequency range 0.5 to 15 Hz and a distance range of 0.5 to 5.3 km. All stations are located at sites with broadly similar near-site geology, characterized by medium to fine-grain Quaternary alluvial sediments. On average, relatively high values of coherence are observed for distances up to 3 to 4 km and frequencies up to 2 to 3 Hz; coherence drops sharply at frequencies near and above 3 Hz. Although average coherence functions are described reasonably well by a log-linear relationship with frequency, the curves at all distances exhibit a flattening at low frequencies that is not consistent with previous observations of coherence at hardrock sites. The distance decay of coherence is also markedly less strong, with high coherence values observed over station separations corresponding to multiple wavelengths. This may reflect fundamental differences in shallow-wave propagation in the two environments, with high-frequency scattering relatively more dominant in regions of hard-rock near-surface geology. Within a sedimentary basin or valley, the site response itself generally reflects a resonance phenomenon that may tend to give rise to more uniform ground motions. However, previous studies have demonstrated the existence of pathological focusing and amplification effects within complex sedimentary basin environments such as the greater Los Angeles region; our results undoubtedly do not quantify the full range of ground-motion variability at all sites, but rather represent the level of that variability that can be expected, and quantified, for typical source/receiver paths.
Control of strong motion by the upper 30 meters
Authors: Anderson John  G. , Lee Yajie , Zeng Yuehua , Day Steven 
Published: July 2023

Abstract
Local site effects have an enormous influence on the character of ground motions. Currently, soil categories and site factors used in building codes for seismic design are generally based on, or at least correlated with, the seismic velocity of the surface layer. We note, however, that the upper 30 m (a typical depth of investigation) would almost never represent more than 1% of the distance from the source; 0.1% to 0.2% would be more typical of situations where motion is damaging. We investigate the influence of this thin skin on the high-frequency properties of seismograms. We examine properties of seismograms consisting of vertically propagating S waves through an arbitrarily complex stack of flat, solid, elastic layers, where the properties of the lowermost layer (taken at 5 km depth) and a surface layer (thickness 30 m) are constrained. Input at the bottom of the stack is an impulse. We find that the character of the seismograms, and the peak spectral frequencies, are strongly influenced by the properties of the intervening layers. However, for infinite Q, the integral of amplitude squared at the surface (which determines energy if the input and output are regarded as velocity, or Arias intensity if the input and output are regarded as acceleration) is independent of the intervening layers. Also, the peak amplitude of the seismogram at the surface is relatively independent of the intervening properties. For finite, frequency-independent Q, the integral of amplitude squared and peak amplitude decrease as t* increases. There is some scatter that depends on the intervening layers, but it is surprisingly small.
These calculations suggest that the surficial geology has a greater influence on ground motions than might be expected based on its thickness alone. They suggest that variable influences of Q along the entire path have a comparable importance for predictions of ground motions. Finally, they suggest that detailed characterization of deeper velocity structure in regions where a 1D model is appropriate gives only a limited amount of added information. Based on our 1D numerical results, we propose a new method to characterize these properties as site factors that could be used in building codes. Full three-dimensional synthetics are tested and give a similar conclusion.
A neotectonic study of the San Miguel-Vallecitos fault, Baja California, Mexico
Authors: Hirabayashi C.  Kenji , Rockwell Thomas  K. , Wesnousky Steven  G. , Stirling Mark  W. , Suarez-Vidal Francisco 
Published: July 2023

Abstract
The San Miguel strand of the San Miguel-Vallecitos fault zone displaces an alluvial ridge 23+5/−10 m in the vicinity of Dolores Mountain. The same section of fault produced surface rupture during the M6.8 earthquake of 1956. We estimate a minimum age of the ridge at between 110+150/−60 ka by comparing soil development on the offset ridge to two soil chronosequences in southern California. Dividing the measured offset by the age of the ridge places a maximum range on the fault slip rate of 0.2+0.35/−0.15 mm/yr. Excavations along and across the fault at the same site revealed at least 80 cm and probably 115 cm of right-lateral offset of a now-buried stream channel deposit. We attribute the 115-cm offset to the 1956 M6.8 earthquake, a displacement that is slightly larger than previously reported for this earthquake. Dividing the 80 to 115 cm of displacement by the calculated fault slip rate yields an estimated return time for similar-sized events of about 5.8+17/−4.3 ka. Similarly, dividing the slip expected for rupture of the entire 160-km length of the San Miguel-Vallecitos fault zone by the fault slip rate yields an estimate of return time of Mw7.8 earthquakes of about 80 ka. The slip rate determined from this study is at least an order of magnitude less than that contributed by the Agua Blanca fault and indicates that the San Miguel fault zone transfers less than about 1% of the plate motions.
The San Miguel fault shows a complex fault trace and registers a small value of cumulative geologic offset (maximum of 0.6 km). When combining the geological estimates of magnitude and return time of the largest earthquakes with magnitude-frequency data recorded along the San Miguel fault by the RESNOR seismic network during the period 1976 to 1991, we observe that the shape of the magnitude-frequency distribution along the fault may be described by the Gutenberg-Richter relationship Log n = a − bM. In contrast, along-strike-slip faults in southern California that are characterized by orders of magnitude more cumulative offset and less complex fault traces, we observe that extrapolation of earthquake frequency statistics from the instrumental record of seismicity severely underestimates the rate of occurrence of maximum expected events. We speculate that the relatively high productivity of small earthquakes along the San Miguel fault reflects a more heterogeneous stress field associated with the incipient and complex nature of the fault trace.
Geomorphic evidence for Holocene earthquakes in the Olinghouse fault zone, western Nevada
Authors: Sanders Christopher O. , Slemmons D. Burton 
Published: July 2023

AbstractMapping and morphologic analysis of young fault scarps in the Olinghouse fault zone of western Nevada yields information about the ages and magnitudes of Holocene-late Pleistocene surface-rupturing earthquakes. Twenty profiles of single-event scarps in the eastern third of the fault zone yield ages that average 4.5 ± 2.0 ka. Ages were determined assuming linear diffusion of scarp material, with the diffusion coefficient as a function of scarp offset determined from profiles of Lake Lahontan high-stand shorelines located nearby. The mid-Holocene age is consistent with the observation that the scarps are cutting alluvial material that buries the 15.4-ka shorelines. The minimum length of faulting during this earthquake was 8 km, and the maximum normal fault offset was about 1 m, suggesting an earthquake of about M 6.7. Several older scarp segments have cumulative normal offsets of 2.5 to 4.8 m and one or two crest bevels above the most recent scarp slope, suggesting that two to three earthquakes have formed these scarps. The average diffusion age of five multiple-event scarp profiles is about 13 ka. If this represents a weighted average of the ages of the earthquakes that formed the scarps, then two or three large earthquakes have occurred since about 21 ka, which gives a speculative average recurrence period of 8 to 16 kyr. Historical accounts and geomorphic evidence of young left-slip offsets of up to 3.6 m (M 7.1) at the western end of the Olinghouse fault zone suggest that it may have ruptured historically. Thus, the potential exists for large earthquake generation all along the 20+ km length of the fault zone.
Rare, large earthquakes at the Laramide deformation front—Colorado (1882) and Wyoming (1984)
Authors: Spence William , Langer C.  J. , Choy George  L. 
Published: July 2023

Abstract
The largest historical earthquake known in Colorado occurred on 7 November 1882. Knowledge of its size, location, and specific tectonic environment is important for the design of critical structures in the rapidly growing region of the Southern Rocky Mountains. More than one century later, on 18 October 1984, an mb 5.3 earthquake occurred in the Laramie Mountains, Wyoming. By studying the 1984 earthquake, we are able to provide constraints on the location and size of the 1882 earthquake. Analysis of broadband seismic data shows the 1984 mainshock to have nucleated at a depth of 27.5 ± 1.0 km and to have ruptured ‖ 2.7 km updip, with a corresponding average displacement of about 48 cm and average stress drop of about 180 bars. This high stress drop may explain why the earthquake was felt over an area about 3.5 times that expected for a shallow earthquake of the same magnitude in this region. A microearthquake survey shows aftershocks to be just above the mainshock's rupture, mostly in a volume measuring 3 to 4 km across. Focal mechanisms for the mainshock and aftershocks have NE-SW-trending T axes, a feature shared by most earthquakes in western Colorado and by the induced Denver earthquakes of 1967.
The only data for the 1882 earthquake were intensity reports from a heterogeneously distributed population. Interpretation of these reports also might be affected by ground-motion amplification from fluvial deposits and possible significant focal depth for the mainshock. The primary aftershock of the 1882 earthquake was felt most strongly in the northern Front Range, leading Kirkham and Rogers (1985) to locate the epicenters of the aftershock and mainshock there. The Front Range is a geomorphic extension of the Laramie Mountains. Both features are part of the eastern deformation front of the Laramide orogeny. Based on knowledge of regional tectonics and using intensity maps for the 1984 and the 1967 Denver earthquakes, we reinterpret prior intensity maps for the 1882 earthquake as reflecting low population to the north and east of available intensity data. We estimate that, had there been a more evenly distributed population, the 1882 earthquake would have been felt over an area of about 850,000 km2, with a corresponding moment magnitude (Mw) of 6.6 ± 0.6. Our study, in the context of regional tectonics, implies that rare earthquakes of magnitude up to Mw 6.6 ± 0.6, at depths from shallow to mid-crustal, are possible throughout the Laramie Mountains and the Front Range, approximately from Casper, Wyoming, to Pueblo, Colorado.
Characteristics of short-period wave propagation in regions of Fennoscandia, with emphasis on Lg
Authors: Vogfjörd Kristín  S. , Langston Charles  A. 
Published: July 2023

Abstract
Wave propagation of crustal phases, in particular Lg, near the ARCESS array in northern Norway is examined and compared to propagation characteristics near the NORESS array in southern Norway. Relying on array analysis, we show that ray-theory explanations of arrivals in local and regional seismograms are very useful in deducing the composition of the crustal wave trains. Frequency-wavenumber analysis is applied to the array data to identify the arrivals; then a composite of array beams is used to approximate each event. Record sections of composite seismograms are constructed for different directions from ARCESS to study propagational characteristics with distance and azimuth and then compared to composite-seismogram record sections from NORESS to study different regional characteristics. To model the observed character of Lg and Rg, synthetic record sections are constructed by wavenumber integration in velocity models representative of structure in the different regions. The results show that Rg propagation distance varies significantly between regions and that the velocity gradient in the lower crust is the dominant factor in specifying Lg characteristics in the Baltic shield region. Lg is dominated by several discrete arrivals representing multiple Moho reflections, or by multiple Moho reflections and turning waves, with each multiple confined to a small distance range so that only one multiple set dominates at each distance. Furthermore, we demonstrate that incomplete knowledge of the propagation characteristics leads to mislocations of local and regional events and inhibits source-depth discrimination of events. We identify three earthquakes in the ARCESS data set based on source depths. These are constrained by phase velocities and depth phases, none of which were properly identified by the automatic array-detection software.
Seismic radiation from explosively loaded cavities in isotropic and transversely isotropic media
Authors: Gibson R.  L. , Toksöz M.  N. , Dong W. 
Published: July 2023

Abstract
We analyze the influence of cavity shape on far-field seismic-wave radiation from small explosion sources in isotropic and transversely isotropic media using the indirect boundary-element method (BEM). The analysis utilizes two possible mathematical models for the pressure fields generated by the explosion in the acoustic medium inside the cavity. One simple model for the source is a volume injection (explosion) point source inside the cavity, which generates a pressure field that arrives approximately instantaneously at each point on the cavity wall. The amplitude of the field decays at a rate inversely proportional to propagation distance. We use this model to compare results with finite-difference solutions, and the test confirms the accuracy of the BEM implementation. Strong compressional and shear signals propagate into the far-field from the source cavity, and the compressional-wave amplitude depends strongly on direction of propagation. The behavior is similar at frequencies up to 200 Hz, including those typical of regional seismic-wave propagation (1 to 10 Hz).
A second model of the source, one that has been applied in previous analytical and numerical work, is to assume that the explosion will instantaneously and uniformly pressurize the source cavity. This approach yields a radiation pattern that is very different from the point source model. The compressional-wave radiation patterns have a large variation in signal strength and very strong shear waves when frequencies up to 200 Hz are included, but seismograms computed for frequency ranges of interest in regional wave propagation (around 1 Hz) have a nearly isotropic compressional-wave radiation pattern and a much smaller shear wave. This shear wave is largest for long, tunnel-like cavities or short, disklike cavities. When the cavity is located in a transversely isotropic medium, quasi-shear waves are generated, but, for the media we consider, their magnitude decreases for long, tunnel-like cavities and is larger for more equidimensional cavities. These somewhat counterintuitive results show that anisotropy can actually cause a radiation pattern to appear more isotropic than the corresponding wave fields in an isotropic medium.
On the probability of mistaking an earthquake for an explosion using the simplicity of P
Authors: Bowers David 
Published: July 2023

Abstract
The observation that P waves from an earthquake are generally more complex than those from an underground explosion was first noted in the 1960s. This difference in P-wave character may still be the only way of identifying small earthquakes close to the detection threshold of a given station network. However, there are certain earthquakes that produce simple seismograms. The frequency at which such earthquakes are mistaken for explosions, using the complexity criterion, is known as the false alarm rate. A simple seismogram can be defined as having only one large-amplitude phase that can be caused by several mechanisms. We examine the proportion of simple seismograms produced by a randomly oriented double-couple source buried in three different crustal structures, observed at a single station at a range of epicentral distances. The model predicts that if the hypocenter of a small earthquake (near the detection threshold) is in a region with thick sediments, then the false alarm rate at a single station can be as high as 50% in the teleseismic distance range (30° to 90°). The results suggest that the false alarm rate is minimized if (1) array stations are used, (2) the station is at a large epicentral distance, (3) the source region structure has few layers, or (4) the disturbance is recorded at more than one station.
On the variation of slip direction during earthquake rupture: Supporting and conflicting evidence from the 1989 Loma Prieta earthquake
Authors: Guatteri Mariagiovanna , Cocco Massimo 
Published: July 2023

AbstractThe direction of the slip can change during a rupture episode as a function of time and/or of the position on the fault plane. In this work, we focus on the spatial variations of slip direction during an earthquake. Theoretically, the spatial variations of rake are caused by changes in the direction of the static and dynamic traction. The 1989 Loma Prieta earthquake provides one of the most striking examples of slip direction rotation during the coseismic rupture. All the source models obtained by using different inversion procedures show strong spatial partitioning of slip into strike-slip motion SE of the epicenter and dip-slip motion in the NW section. In this study, we perform both forward waveform modeling and waveform inversion tests to check if the previously observed variations of rake are constrained by seismological data. We use the isochrone approach and a tomographic back-projection algorithm to solve the forward modeling and the inverse problem, respectively. Results show that observed ground velocities can be well reproduced by source models having spatial slip distribution similar to the Beroza's (1991) inversion solution, but having constant rake. Synthetic inversion tests point out that the inversion procedure does not constrain the slip direction. We have analyzed the S-wave polarization in order to constrain the direction of slip along the fault. This analysis confirms that a predominant strike component (rake ∼ 160°) characterizes the slip direction in the southeastern section, while an increase of the reverse component in the northwest section of the fault allows one to explain the observed polarization well. An oblique mechanism is consistent with the fault-plane solution, confirming a spatial variation of the slip direction during the earthquake. If the rake actually varied, then a nonuniform prestress condition (due to a change in fault geometry or to a redistribution of static stress) or a spatially inhomogeneous stress release should be proposed in order to explain the observed changes of slip direction. We conclude that a nonuniform prestress is a likely explanation for the inferred rake rotations. These variations of the direction of slip involve a low value of the initial stress.
Macroseismic study of shallow earthquakes in the central and eastern parts of the trans-Mexican volcanic belt, Mexico
Authors: Suter Max , Carrillo-Martínez Miguel , Quintero-Legorreta Odranoel 
Published: July 2023

Abstract
We present isoseismal maps for eight shallow earthquakes (1887 Pinal de Amoles, 1912 Acambay, 1920 Jalapa, 1950 Ixmiquilpan, 1976 Cardonal, 1979 Maravatío, 1987 Actopan, and 1989 Landa; 4.1 ≦ mb ≦ 6.9) that occurred in the central and eastern parts of the trans-Mexican volcanic belt. Based on their intensity distributions, we can relate several of these earthquakes to east-west striking Quaternary normal faults known from geological observations. Furthermore, we derive for these events, by empirical curve fitting, linear relations between the magnitude calculated from the instrumental record, the intensity distribution, and the maximum intensity. The comparison of these relations with equations from the literature suggests that the area shaken with a certain intensity by an earthquake in the trans-Mexican volcanic belt is approximately 10 times smaller than the area shaken by a shallow earthquake of the same magnitude in the intracratonic part of North America. Moreover, we use the derived relationships between magnitude, isoseismal area, and maximum intensity to estimate the intensity magnitude Mi of the 1887 Pinal de Amoles earthquake as 5.3 ± 0.5.
Earth-flattening transformation for P-SV waves
Authors: Bhattacharya S.  N. 
Published: July 2023

Abstract
We consider a layered nongravitating spherical Earth where in each layer P- and S-wave velocities are proportional to r and Lame's elastic parameters λ and μ are proportional to rp, where r is the radial distance and p is an arbitrary constant. In this article, the solutions of equations of motion in each layer are obtained in terms of exponential functions, and the expression for the stress-displacement matrix becomes similar to that for a flat-layered Earth. Thus, widely used formulations of a flat-layered Earth can be applied to study P-SV waves in a spherical-layered Earth through the transformation proposed here. When p = −2, explicit expressions are obtained for eigenvalues appearing in the solutions, and this makes the transformation further simplified. The transformation is applied, as an example, to find (1) the roots of the secular function and (2) eigenfunctions of Rayleigh waves in a spherical Earth through available formulations for a flat Earth.