bluuebunny/crossref_metadata_2025_split huggingface dataset:
Observed effects of topography on ground motion
Authors: Davis Lawrence L. , West Lewis R. 
Published: September 2021

abstract
Field experiments were performed to obtain data needed for studying the effects of topography on seismic motion. L-7 instruments deployed at the crest and base of Kagel Mountain and Josephine Peak, California, recorded several aftershocks of the February 9, 1971, San Fernando earthquake. L-7 instruments deployed at the crest, middle, and base of Butler Mountain near Tonopah, Nevada, recorded the seismic signal generated by the cavity collapse following the Nevada Test Site detonation, ALGODONES. Frequency-dependent amplification of the motion at the crest relative to the motion at the base was observed at all three mountains. Factors as large as 30 in the frequency domain were seen at Kagel Mountain with lesser amounts at the other two locations. The three mountains are similar in shape, but different in size. The effect of shape is not clear. The smallest mountain amplified the motion in a narrow range of periods (peaking around 0.3 to 0.5 sec), the medium-size mountain showed amplification over a slightly broader range (peaking at periods of 0.4 to 0.5 sec), whereas the largest mountain showed less amplification, but it occurred over a broader range of periods. Effects in the time domain are generally comparable to, or less than, the effects in the frequency domain. The ratios of peak amplitudes (crest to base) are usually less than the spectral ratios. It is concluded that topography plays a significant role and is an important consideration in determining the seismic motion that a particular site receives.
A note on discrepancies between local magnitude (ML) and microearthquake magnitude scales
Authors: Thatcher Wayne 
Published: September 2021

abstract
A necessary correction for relating local network magnitude scales to Richter's local magnitude (ML) involves accounting for the shape of the far-field body-wave spectrum of the phases used for determining magnitude. When not corrected for, this effect causes errors of about one magnitude unit at ML ∼ 3 for some southern California earthquakes. The discrepancy should be comparable for ML &gt; 3, but at smaller magnitudes will decrease with decreasing ML. It may be corrected for either by direct comparison of network scales with magnitudes determined from Wood-Anderson seismograms, or by spectrum measurements over a range of magnitudes. The nature of the discrepancy and the corrections required to account for it are demonstrated by an example, the aftershocks of the 1968 Borrego Mountain, California earthquake.
A portable multi-channel seismic recorder and a data processing system
Authors: Green R. 
Published: September 2021

abstract
A portable seismograph utilizing a magnetic tape recorder and capable of recording both long- and short-period seismic information is described. The field system which is housed in two weatherproof steel containers is completely self-contained and incorporates both a radio and an internal clock for timing. Eight data channels can record in either AM or FM mode which allows a frequency range from dc to 200 Hz. A feature of the field system is that it incorporates a test panel that enables a check to be kept on all of the recording functions. The field system power consumption is less than 7.5 watts and two 6-volt batteries power the system for up to 12 days. The replay electronics are primarily designed to digitize the analog tapes and the process utilizes an “aspect clock” dividing system that links the recorded clock time to the digitization time.
Body waves as normal and leaking modes: Dispersion and excitation on the (+ −) sheet
Authors: Stalmach D. M. , De Bremaecker J. Cl. 
Published: September 2021

abstract
Leaking modes are little influenced by the presence of a low α layer. The lattice-like structure of the phase-velocity curves occurs for a two-layer model as well as for a six-layer one. The excitation tends to be high where phase-velocity curves cross (or approach) each other. Both normally and inversely dispersed wave trains are predicted; the agreement with the observations varies from fair to good.
A variational method for love waves in nonhorizontally layered structures
Authors: Gjevik B. 
Published: September 2021

abstract
A variational principle for Love waves propagating in a layer with varying thickness overlying a half-space is formulated. By an averaging procedure, the wave modulation due to gradual variation of the thickness of the upper layer is found. The case of long-period Love waves is particularly examined and the wave number and amplitude modulation both for a monochromatic wave and for a transient wave train due to an impulsive source are determined. Moreover, the travel time for a certain phase in the wave train is determined. It is found that for well-dispersed wave trains the travel time is given by the phase velocity corresponding to the mean depth of the upper layer.
Coupled torsional dynamic analysis of a multistory building
Authors: Douglas Bruce M. , Trabert Thomas E. 
Published: September 2021

abstract
The coupled bending and torsional vibrations of a relatively symmetric 22-story reinforced concrete building in Reno, Nevada are studied. Analytical results are compared with observations obtained during the nuclear explosion FAULTLESS and to ambient vibration data. The fundamental periods of vibration observed during FAULTLESS were (TNS = 1.42, TEW = 1.81, TTORSION = 1.12 sec), and the calculated periods were (TNS = 2.14, TEW = 2.07, TTORSION = 1.90 sec). It was estimated that between 25 and 45 per cent of the total available nonstructural stiffness was required to explain the differences in the observed and calculated fundamental periods.
Each floor diaphragm in the system was allowed three degrees of freedom-two translations and a rotation. It was found that coupled torsional motions can influence the response of structural elements near the periphery of the structure. Strong-motion structural response calculations comparing the simultaneous use of both components of horizontal ground motion to a single component analysis showed that the simultaneous application of both components of ground motion can significantly alter the response of lateral load-carrying elements. Differences of the order of 45 per cent were observed in the frames near the ends of the structure. Also, it was shown that the overall response of tall buildings is sensitive not only to the choice of input ground motion but also to the orientation of the structure with respect to the seismic waves.
Comparison of earthquake and microtremor ground motions in El Centro, California
Authors: Udwadia F. E. , Trifunac M. D. 
Published: September 2021

abstract
Strong earthquake ground shaking has been investigated by the study of 15 events recorded in El Centro, California. The strong-motion records analyzed show that no simple features (e.g., local site conditions) govern the details of local ground shaking. Any effects of local subsoil conditions at this site appear to be overshadowed by the source mechanism and the transmission path, there being no distinctly identifiable site periodicities.
Microtremor measurements have been taken in the area surrounding the strong-motion site. The objective was an investigation of possible correlations with strong ground motions and the analysis of site-response characteristics. Basic difficulties in ascertaining local site conditions through such low-amplitude ground motions are illustrated. It has been found that in this area microtremor and earthquake processes are widely different in character, there being little to no correlation between the ground's response to earthquakes and to microtremor excitations. Microtremors have been found to be nonstationary over periods of about a day or so, introducing further uncertainties into inferences from such measurements.
Stress drop and aftershocks
Authors: Gibowicz S. J. 
Published: September 2021

abstract
Eighteen aftershock sequences, nine from California and nine from New Zealand, are studied. It is found that a general relationship exists between the local magnitude ML and the stress drop in the main shock. The stress drop in the main earthquake determines the principal characteristics of the aftershock sequences. A low stress drop leads to a low value of the coefficient b, high magnitude of the largest aftershock, and short duration, and conversely. A sequence is arbitrarily considered to be over when the rate of aftershock occurrence falls to a value of one shock per day. The duration depends on the area of fault surface and the stress drop in the main shock. For an average stress drop, the coefficient b has a value of 0.8 to 0.9, and the difference in magnitude between the main shock and the largest aftershock is 1.2, a relation often called Båth's law.
The calculation of horizontal accelerations from seismoscope records
Authors: Scott Ronald F. 
Published: September 2021

abstract
The seismoscope is a simple instrument designed originally to give a largely qualitative indication of the strong ground motions produced by an earthquake. It consists of a smoked watch glass attached to a two-degree-of-freedom pendulum with a period of 34 sec and damping about 10 per cent of critical; a pen records the pendulum motions on the watch glass. One point on the displacement spectrum of the recorded ground motion at this period and damping is obtained from the measurement of the maximum pendulum excursion.
An examination of the seismoscope record obtained on the east abutment of the failed Lower San Fernando dam during the 1971 San Fernando earthquake showed a high-frequency vibration superimposed on the general oscillations. It did not seem likely that this was solely an earthquake vibration component, and shaking table tests of seismoscopes revealed the presence of a seismoscope vibration mode at frequencies of 15 to 18 Hz depending on the instrument. The oscillations due to this mode on the abutment seismocope record have, therefore, been used as timing marks, to enable the seismoscope equation to be solved for the input acceleration components. The results of the calculations are presented along with analyses of the seismoscope response to indicate the range of applicability. One other record, obtained on a seismoscope alongside a strong-motion accelerograph, was also analyzed for comparison with the recorded accelerations, to demonstrate the validity of the technique. The timing vibration appears on a number of seismoscope records.
Reflection, refraction and mode conversion of long-period surface waves and the measurement of Q−1 for free oscillations
Authors: Reiter Leon 
Published: September 2021

abstract
Filtered time series of Rayleigh waves from 4 events recorded on the quartz accelerometer at the IGPP, Camp Elliott Station, were analyzed. Attenuation (Q−1) was computed for spheroidal fundamental modes (oS19 to oS24) from several sequences of time-lapsed records for each event. A five-fold variation in measured Q−1 (and some variations in peak frequency) was assumed to be the result of lateral inhomogeneities in earth structure. Utilizing the duality between Rayleigh waves and fundamental-mode spheroidal oscillations, model power spectra were computed by summing the simulated Fourier transforms of dispersed wave trains. The effect of lateral variations in earth structure resulting in reflection, refraction and mode conversion of fundamental-mode surface waves was simulated by changes in amplitude, phase angle, and group and component travel times. Assuming an anelastic 10,000/Q of 33.3 (Q = 300), the observed range of measured Q−1 (and peak frequency) variations was duplicated by models with up to 5 per cent of the fundamental-mode Rayleigh-wave energy being “scattered”, i.e., reflected, refracted or converted to higher modes. In the real Earth, this would call for lateral variations in velocity structure well below the upper few hundred kilometers of the mantle. Recent seismological investigations have suggested lateral variations at these depths.
Detection and analysis of multiple seismic events
Authors: Flinn E. A. , Cohen T. J. , McCowan D. W. 
Published: September 2021

Abstract
We compare several methods of analyzing short-period seismic records with the purpose of detecting multiple events. The data used were from a pair of chemical explosions at a dam site near Alma Ata, recorded at the seismic observatory at Mould Bay, Canada. The methods evaluated include visual analysis of the array-beam sums, multichannel matched filtering, autocorrelation analysis, and cepstral analysis. For matched filtering we used the recorded wave forms from a seismic event which occurred reasonably close to the Alma Ata site. Measurements using the spectra or the cepstra appear to be most accurate in determining the delay time between the two events. The analysis methods discussed here generally give results which are in good agreement with the announced time between the explosion and announced yield ratio.
Probabilistic seismic hazard analysis and design earthquakes: Closing the loop
Authors: McGuire Robin K. 
Published: September 2021

Abstract
Probabilistic seismic hazard analysis (PSHA) is conducted because there is a perceived earthquake threat: active seismic sources in the region may produce a moderate-to-large earthquake. The analysis considers a multitude of earthquake occurrences and ground motions, and produces an integrated description of seismic hazard representing all events. For design, analysis, retrofit, or other seismic risk decisions a single “design earthquake” is often desired wherein the earthquake threat is characterized by a single magnitude, distance, and perhaps other parameters. This allows additional characteristics of the ground shaking to be modeled, such as duration, nonstationarity of motion, and critical pulses. This study describes a method wherein a design earthquake can be obtained that accurately represents the uniform hazard spectrum from a PSHA. There are two key steps in the derivation. First, the contribution to hazard by magnitude M, distance R, and ɛ must be maintained separately for each attenuation equation used in the analysis. Here, ɛ is the number of standard deviations that the target ground motion is above or below the median predicted motion for that equation. Second, the hazard for two natural frequencies (herein taken to be 10 and 1 Hz) must be examined by seismic source to see if one source dominates the hazard at both frequencies. This allows us to determine whether it is reasonable to represent the hazard with a single design earthquake, and if so to select the most-likely combination of M, R, and ɛ (herein called the “beta earthquake”) to accurately replicate the uniform hazard spectrum. This closes the loop between the original perception of the earthquake threat, the consideration of all possible seismic events that might contribute to that threat, and the representation of the threat with a single (or few) set of parameters for design or analysis.
Attenuation of earthquake ground motion in Japan including deep focus events
Authors: Molas Gilbert L. , Yamazaki Fumio 
Published: September 2021

Abstract
New attenuation equations for peak ground acceleration and velocity for Japan are developed. The equations are derived using extensive data recorded by the new JMA-87-type accelerometers, which do not require instrumental corrections that the older SMAC-type accelerometers do. Earthquakes with depths up to 200 km are used to make the equation applicable to subduction zone regions, which are common in Japan. Effects of depth and local site on the attenuation are considered simultaneously with the distance dependence and magnitude dependence using a two-stage regression procedure to separate the magnitude dependence from the distance dependence. Since the resulting normal equations become singular, an iterative partial regression algorithm is proposed. It is found that for the same magnitude and distance, peak ground motion increases as depth increases. The variation of the station coefficients with respect to the corresponding soil-type classification is quite wide. The station coefficients for the peak ground acceleration are found to be weakly correlated with the general soil classification, while a stronger correlation was found for the peak ground velocity. The resulting attenuation relations are given by log10PGA=0.206+0.477MJ−log10r−0.00144r−0.00144r+0.00311h+cia,log10PGV=−1.769+0.628MJ−log10r−0.00130r−0.00144r+0.00222h+civ, where PGA (cm/sec2) and PGV (cm/sec) are the larger of the peak accelerations and velocities from two horizontal components, MJ is the JMA magnitude, r is the closest distance to the fault rupture, h is the depth, and ci is the station coefficient of the recording station. The mean of the coefficients of the JMA stations is given by ci = 0.
Application of bandlimited anelastic models to wave propagation in highly attenuative media
Authors: Liu Hsi-Ping 
Published: September 2021

Abstract
Because of its simple form, a bandlimited, four-parameter anelastic model that yields nearly constant midband Q for low-loss materials is often used for calculating synthetic seismograms. The four parameters used in the literature to characterize anelastic behavior are τ1, τ2, Qm, and MR in the relaxation-function approach (s1 = 1/τ1 and s2 = 1/τ2 are angular frequencies defining the bandwidth, MR is the relaxed modulus, and Qm is approximately the midband quality factor when Qm ≫ 1); or τ1, τ2, Qm, and MR in the creep-function approach (s1 = 1/τ1 and s2 = 1/τ2 are angular frequencies defining the bandwidth, and Qm is approximately the midband quality factor when Qm ≫ 1). In practice, it is often the case that, for a particular medium, the quality factor Q(ω0) and phase velocity c(ω0) at an angular frequency ω0 (s1 &lt; ω0 &lt; s2; s1 &lt; ω0 &lt; s2) are known from field measurements. If values are assigned to τ1 and τ2 (τ2 &lt; τ1), or to τ1 and τ2 (τ2 &lt; τ1), then the two remaining parameters, Qm and MR, or Qm and MR, can be obtained from Q(ω0). However, for highly attenuative media, e.g., Q(ω0) ≦ 5, Q(ω) can become highly skewed and negative at low frequencies (for the relaxation-function approach) or at high frequencies (for the creep-function approach) if this procedure is followed. A negative Q(ω) is unacceptable because it implies an increase in energy for waves propagating in a homogeneous and attenuative medium. This article shows that given (τ1, τ2, ω0) or (τ1, τ2, ω0), a lower limit of Q(ω0) exists for a bandlimited, four-parameter anelastic model. In the relaxation-function approach, the minimum permissible Q(ω0) is given by ln [(1 + ω20τ21)/(1 + ω20τ22)]/{2 arctan [ω0(τ1 − τ2)/(1 + ω20τ1τ2)]}. In the creep-function approach, the minimum permissible Q(ω0) is given by {2 ln (τ1/τ2) − ln [(1 + ω20τ21)/(1 + ω20τ22)]}/{2 arctan [ω0(τ1 − τ2)/(1 + ω20τ1τ2)]}. The more general statement that, for a given set of relaxation mechanisms, a lower limit exists for Q(ω0) is also shown to hold. Because a nearly constant midband Q cannot be achieved for highly attenuative media using a four-parameter anelastic model, a bandlimited, six-parameter anelastic model that yields a nearly constant midband Q for such media is devised; an expression for the minimum permissible Q(ω0) is given. Six-parameter anelastic models with quality factors Q ∼ 5 and Q ∼ 16, constant to 6% over the frequency range 0.5 to 200 Hz, illustrate this result. In conformity with field observations that Q(ω) for near-surface earth materials is approximately constant over a wide frequency range, the bandlimited, six-parameter anelastic models are suitable for modeling wave propagation in highly attenuative media for bandlimited time functions in engineering and exploration seismology.
Rotation of the principal stress directions due to earthquake faulting and its seismological implications
Authors: Yin Z.-M. , Rogers G. C. 
Published: September 2021

Abstract
Earthquake faulting results in stress drop over the rupture area. Because the stress drop is only in the shear stress and there is no or little stress drop in the normal stress on the fault, the principal stress directions must rotate to adapt such a change of the state of stress. Using two constraints, i.e., the normal stress on the fault and the vertical stress (the overburden pressure), which do not change before and after the earthquake, we derive simple expressions for the rotation angle in the σ1 axis. For a dip-slip earthquake, the rotation angle is only a function of the stress-drop ratio (defined as the ratio of the stress drop to the initial shear stress) and the angle between the σ1 axis and the fault plane, but for a strike-slip earthquake the rotation angle is also a function of the stress ratio. Depending on the faulting regimes, the σ1 axis can either rotate toward the direction of fault normal or rotate away from the direction of fault normal. The rotation of the stress field has several important seismological implications. It may play a significant role in the generation of heterogeneous stresses and in the occurrence and distribution of aftershocks. The rotation angle can be used to estimate the stress-drop ratio, which has been a long-lasting topic of debate in seismology.
Reliable automatic detection of long-period volcanic earthquakes at Long Valley caldera, California
Authors: Evans John R. , Pitt Andrew M. 
Published: September 2021

Abstract
Capturing the rare long-period (LP) volcanic earthquakes occurring in and near Long Valley caldera, California, is important to ongoing volcanic-hazards monitoring. It is difficult, however, because LP events are weak, emergent, and almost devoid of energy above a few hertz. Automatic systems designed for tectonic earthquakes routinely fail to capture LP events.
We applied a PC-based teleseism-specific event-detection computer program to capturing these events. Retuning the software for LP events involved only changing parameters originally designed for change in this algorithm. Our retuned algorithm has captured every known LP event at Long Valley from October 1992 through the end of 1994.
We monitored up to 16 stations known to produce good records of LP events, saving those events that triggered enough of these stations (typically 10 of 16) within a specified time window. The principal difficulty has been the algorithm's sensitivity to regional earthquakes, which have waveforms similar to LP events. During our test, the 1992 Landers, 1994 Northridge, and 1994 Double Springs Flat (Nevada) earthquakes each have swamped the detector, requiring careful, active management of PC disk resources.
The efficacy of this retuned algorithm and the poor performance of tectonic-earthquake detectors during some volcanic emergencies make this algorithm an attractive candidate for volcano monitoring.
SHwave propagation by discrete wavenumber boundary integral modeling in transversely isotropic medium
Authors: Karabulut Hayrullah , Ferguson John F. 
Published: September 2021

AbstractAn extension of the boundary integral method for SH waves is given for transversely isotropic media. The accuracy of the method is demonstrated for a simple flat interface problem by comparison to the Cagniard-de Hoop solution. The method is further demonstrated for a case with interface topography for both surface and vertical seismic profiles. The new method is found to be both accurate and effective.