bluuebunny/crossref_metadata_2025_split huggingface dataset:
The two-dimensional resonance of sediment-filled valleys
Authors: Bard Pierre-Yves , Bouchon Michel 
Published: July 2021

AbstractThis paper presents a numerical study of the response of relatively embanked sediment-filled valleys to incident plane SH, SV, and P waves, in the two-dimensional case. The Aki-Larner technique used here is shown to be reliable even for steep interface slopes. Numerical results show the existence and the importance in such valleys of specific two-dimensional resonance patterns, which may be classified in three categories: the antiplane shear modes, corresponding to SH motion; the in-plane shear modes (SV); and the in-plane bulk modes (P). Each of them is characterized by the consistency of the peak frequencies, and the in-phase motion (modulo 180°) across the whole valley. They induce a very large amplification, even in the case of significant damping (up to 4 times the corresponding one-dimensional prediction), a very long duration of motion, and large differential motion. The characteristics of the fundamental modes are in good qualitative agreement with the relevant experimental observations. The existence of this two-dimensional resonance is controlled by the shape ratio (thickness to half-width ratio) and the velocity contrast: a quantitative relationship is proposed in the SH case. The frequency of these resonance modes, for each pattern, is shown to depend only on two parameters: the one-dimensional resonance frequency at the valley center and the shape ratio. A simple model of a soft rectangular inclusion is shown to provide satisfactory quantitative formulas to estimate the fundamental resonance frequencies of any valley. As to the amplitude of this two-dimensional resonance, the general trends of its dependence on the different valley parameters (shape ratio, velocity contrast, Poisson ratio, damping) and on the incident wave field characteristics (wave type, incidence angle) are indicated. An important result, however, for earthquake engineering purposes is that both the two-dimensional resonant frequencies and amplification values differ a lot from their “classical” one-dimensional estimates.
Attenuation of intensities and effect of local site conditions on observed intensities during the Corinth, Greece, earthquakes of 24 and 25 February and 4 March 1981
Authors: Tilford N. R. , Chandra Umesh , Amick D. C. , Moran R. , Snider F. 
Published: July 2021

AbstractField investigations conducted immediately after the Gulf of Corinth earthquake of 24 February 1981 provide an extensive set of data on intensity at different sites for the main shock and two of its principal aftershocks. Each site of intensity observation was characterized by the local site geologic condition. The hypocenters of the three shocks were relocated by using the joint epicenter location technique, with the aftershock of 12 March, 1981 (01:49 UTC), recorded by six portable stations as well as stations of the Greek National Seismographic Network, as the calibration event. Isoseismal maps prepared by using all intensity data for the three shocks were used to derive new attenuation relations. Analysis of the intensity residuals (observed-calculated intensity) shows that local site geologic condition has a significant effect on the intensity observed at a site. On an average, under similar circumstances, sites located on soil foundations experience about one intensity unit more shaking than sites located on rock foundations. Likewise, sites located on Neogene sediments (intermediate foundation condition) experience about 12 unit greater intensity effect than sites located on rock foundations. Attenuation relations derived by using intensity data for the three February-March 1981 earthquakes show lower attenuation than the relation derived by using published isoseismal maps for 19 earthquakes which occurred in the Corinth-Saronikos region during 1861 to 1975.
A strategy for deploying a seismological network for global studies of Earth structure
Authors: Souriau Annie , Woodhouse J. H. 
Published: July 2021

AbstractBecause of the nonuniform distribution of earthquake epicenters, a uniform distribution of seismological stations is not necessarily optimal for sampling the Earth in order to determine global Earth structure. Taking into account the already existing digital long-period seismological stations (GDSN, IDA, and GEOSCOPE), we propose a strategy for the siting of additional stations. Here, we shall develop a criterion designed to optimize global resolution of upper mantle structre using mantle wave observations; other kinds of seismological studies will lead to different criteria, which should, however, be amenable to a similar treatment.For an Earth model developed in spherical harmonics up to a high degree M, and for a given distribution of epicenters and stations, the variance of the solution expanded to some lower degree L ≦ M is obtained at each point of the earth surface by use of averaging kernels, the width of which depends on L. Two measures of the efficiency of an additional station are the reduction of the mean variance and the reduction of the variance oscillations over the Earth's surface; these measures of “new station efficiency” are mapped as a function of the location of the new station (Figures 8 and 9) for the averaging kernels corresponding to L = 8.Considering the reduction of variance oscillations as the main aim, we find that a new station added in south east Africa, in the eastern Pacific, or in Pakistan is up to 6 times more efficient than a station added randomly, and many times more effective than a station added in the Central United States, the Philippines, or Japan.
Deformation near the epicenter of the 1984 Round Valley, California, earthquake
Authors: Gross W. K. , Savage J. C. 
Published: July 2021

Abstract
A trilateration network extending from near Mammoth Lakes to Bishop, California, was resurveyed following the 23 November 1984, Round Valley earthquake (ML = 5.8). The network had previously been surveyed in 1982. Deformation apparently associated with the Round Valley earthquake was detected as well as deformation due to the expansion of a magma chamber 8 km beneath the resurgent dome in the Long Valley caldera and right-lateral slip on the uppermost 2 km of the 1983 rupture surface in the south moat of the caldera. The deformation associated with Round Valley earthquake suggests left-lateral slip on the north-northeasterly striking vertical plane defined by the aftershock hypocenters located by A. S. Ryall. The earthquake moment implied by the deformation is about 3.8·1017 N-m, a value equivalent to an earthquake magnitude ML = 5.7 in good agreement with the observed magnitude of 5.8. A 0.053 km3 expansion of the magma chamber and 0.32 m slip on the 1983 rupture surface in the 1982-1985 interval was also required to account for the observed deformation.
Estimates of seismic wave attenuation in northern Baja California
Authors: Rebollar Cecilio J. , Traslosheros Carlos , Alvarez Rosa 
Published: July 2021

AbstractBy applying the spectral ratio method and the coda wave theory of Aki and Chouet (1975) to digital records of microearthquakes in Baja California, we have determined the seismic quality factors Qα, Qβ independent of frequency, and Qc(f) and Qβ(f) as a function of frequency. We found that Qα and Qβ, independent of frequency and in the range from 3 to 25 Hz, increase with the difference in epicentral distance between two stations. At short distances (∼ 16 km), Qβ is approximately 65, and at longer distances (∼83 km), Qβ increases to 700. We obtained only three values of Qβ/Qα (1.11, 1.47, and 0.87).Qc(f) and Qβ(f) were calculated from events recorded around the San Miguel fault at distances not greater than 30 km and source depths between 5 and 15 km. Qc(f) = (37 ± 13)f0.87±0.04 was found in the range of frequencies from 3 to 24 Hz. We found that the minimum mean free path was almost constant (15 km) for the range of frequencies analyzed. Determinations of Qβ(f) were performed using two lapse times. At short lapse time (10 sec), Qβ(f) was almost linear with frequency, increasing from 43 at 3 Hz to 392 at 24 Hz [Qβ(f) = 13f1.03]. These values correspond to near-surface attenuation. On the other hand, at relative long lapse time (16 sec), Qβ(f) increases from 147 at 3 Hz to 625 at 24 Hz [Qβ(f) = 70f0.74]. These last values of Qβ(f) are within the range of variation of Qc(f).
Effects of station coverage on moment tensor inversion
Authors: Satake Kenji 
Published: July 2021

AbstractThe effects of station distribution and focal mechanism on moment tensor inversion are examined by means of numerical experiment. The far-field displacements of P and Rayleigh waves computed from fault models are inverted to the moment tensor after the error corresponding to the observation error is added to the displacement. The rms error is defined as rms of the differences between the given fault parameters and the parameters obtained from the inverted moment tensor. Experiments are made for both ideal and actual station coverages. The rms errors are found to be proportional to the random error added. For the ideal station coverages, the rms errors are smaller for strike-slip type events than for dip-slip types when only P waves are used. Both types give similar errors when only Rayleigh waves are used. For the actual station distribution of the SRO/ASRO network and earthquakes all over the world, the rms errors vary significantly with the location and mechanism of the events. The minor double couple, which must vanish if no errors are added, reaches 30 per cent of the major double couple for some events when the standard deviation of the random error is 10 per cent of the amplitude. These experiments indicate that the station coverage causes serious effects on moment tensor inversion, and we must be careful to interpret the routinely determined results. Furthermore, uniform station distribution of the global seismograph network is desirable.
GeneralP, type-IS, and type-IISwaves in anelastic solids; inhomogeneous wave fields in low-loss solids
Authors: Borcherdt Roger D. , Wennerberg Leif 
Published: July 2021

AbstractThe physical characteristics for general plane-wave radiation fields in an arbitrary linear viscoelastic solid are derived. Expressions for the characteristics of inhomogeneous wave fields, derived in terms of those for homogeneous fields, are utilized to specify the characteristics and a set of reference curves for general P and S wave fields in arbitrary viscoelastic solids as a function of wave inhomogeneity and intrinsic material absorption. The expressions show that an increase in inhomogeneity of the wave fields causes the velocity to decrease, the fractional-energy loss (Q−1) to increase, the deviation of maximum energy flow with respect to phase propagation to increase, and the elliptical particle motions for P and type-I S waves to approach circularity. Q−1 for inhomogeneous type-I S waves is shown to be greater than that for type-II S waves, with the deviation first increasing then decreasing with inhomogeneity. The mean energy densities (kinetic, potential, and total), the mean rate of energy dissipation, the mean energy flux, and Q−1 for inhomogeneous waves are shown to be greater than corresponding characteristics for homogeneous waves, with the deviations increasing as the inhomogeneity is increased for waves of fixed maximum displacement amplitude. For inhomogeneous wave fields in low-loss solids, only the tilt of the particle motion ellipse for P and type-I S waves is independent to first order of the degree of inhomogeneity. Quantitative estimates for the characteristics of inhomogeneous plane body waves in layered low-loss solids are derived and guidelines established for estimating the effect of inhomogeneity on seismic body waves and a Rayleigh-type surface wave in low-loss media.
Surface-wave studies of some South Carolina earthquakes
Authors: Herrmann Robert B. 
Published: July 2021

AbstractLong-period surface waves generated by three South Carolina earthquakes are used to infer focal mechanisms and seismic moments of the events. The 3 February 1972 Bowman, South Carolina, earthquake is found to be shallow and to require an almost strike-slip focal mechanism with pressure axes trending northeast-southwest. The 22 November 1974 Charleston, South Carolina, earthquake was smaller and was recorded by only three long-period WWSSN stations. For this earthquake, only an estimate of the seismic moment and focal depth were possible. The focal mechanism of the 2 August 1974 Clarkhill reservoir earthquake indicated motion on a northwest striking almost vertical dip-slip fault. In order to specify preferred motions on the nodal planes, full waveform modeling of the long-period traces at ATL was necessary. The results are not without ambiguity, but represent the best estimates of source parameters for these earthquakes.
Studies of crustal converted waves using short-period seismograms recorded in the Vanuatu Island arc
Authors: Chiu Jer-Ming , Isacks Bryan L. , Cardwell Richard K. 
Published: July 2021

AbstractOn three-component, short-period, digital array recordings, S to P converted phases from three major crustal discontinuities beneath Efate Island are identified between the primary P and S arrivals. The time differences between the main S arrival and these converted phases (Sp1, Sp2, and Sp3) provide constraints on the crustal structure beneath Efate Island. A crustal model with three layers over a half-space is determined, which is consistent with the results of a published refraction experiment in the southern Vanuatu (formerly New Hebrides) island arc.
Modeling source zone boundary uncertainty in seismic hazard analysis
Authors: Bender Bernice 
Published: July 2021

AbstractMost probabilistic seismic hazard studies assume that future earthquakes will occur in clearly defined, seismically homogeneous areal source zones. This assumption means that modeled seismic rates change abruptly at source zone boundaries, with the result that predicted acceleration levels may differ considerably at sites a few kilometers apart near a boundary (e.g., changes of 50 to 80 per cent or more at sites 20 km apart). However, homogeneous source zones are at best an approximation, and the areal extent of such zones is usually not well determined. I propose modifying the model so that the seismicity originally associated with each point in a source zone instead be regarded as normally distributed with standard deviation σ about that point; this permits seismicity to vary smoothly across source zone boundaries. When this variability is modeled, if σ is 25 per cent or less of the width of the source zone, acceleration levels calculated at sites at the center of the zone and at sites on the boundary are about the same as those calculated when no location variability (σ = 0) is assumed; however, calculated levels decrease at sites between the center and the boundary, and increase at sites outside the boundary. The changes tend to become larger at the higher accelerations corresponding to longer exposure times.When earthquakes are modeled as ruptures along well-defined linear faults, predicted accelerations also increase significantly as the site location approaches the fault. However, in many cases, neither the location of a fault nor the definitions of its end points can be precisely stated. Acceleration as a function of site location will vary more smoothly if possible fault locations are regarded as either normally or uniformly distributed.
Rupture patterns and preshocks of large earthquakes in the southern San Jacinto fault zone
Authors: Sanders Chris , Magistrale Harold , Kanamori Hiroo 
Published: July 2021

AbstractWe relocated the large 1937, 1942, and 1954 earthquakes in the San Jacinto fault zone. The epicenters of the main shocks, aftershocks, and some preshocks were determined using empirical station corrections from recent small events in the study areas. The 1937 (ML 5.9) earthquake has an epicenter between the surface traces of the San Jacinto and Buck Ridge faults, and aftershocks suggest about 7 km of rupture predominantly to the northwest. A significant increase in small earthquake activity occurred about 112 yr before this event. The 1954 (ML 6.2) earthquake is located at the southeast end of the mapped trace of the San Jacinto fault, and aftershocks suggest about 15 km of rupture further southeast into an area of folded young sediments with no surface fault trace. This event was preceded by a cluster of small earthquakes which occurred within an 8-hr period 10 weeks before the main event and in the eventual rupture zone. The 1942 (ML 6.3) earthquake is located southwest of the southeast end of the Coyote Creek fault. Large aftershocks of this event are spread over a 15 by 18 km area southwest of the Coyote Creek fault and are not associated with any one fault. The relation of the 1942 event to the San Jacinto fault zone is not simple.
Moment magnitude scale for local earthquakes in the Petatlan region, Mexico, based on recorded peak horizontal velocity
Authors: Mahdyiar M. , Singh S. K. , Meyer R. P. 
Published: July 2021

AbstractAssigning moment magnitude to local earthquakes based on peak recorded amplitude and hypocentral distance is the principal concern of this paper. For 38 aftershocks of the Petatlan earthquake (14 March 1979) with moments between 2.8 × 1018 and 1.4 × 1022 dyne-cm, we developed an empirical relationship for the estimation of moment based on peak horizontal velocity (V) and hypocentral distance (R). This empirical relationship in conjunction with the definition of moment magnitude (Hanks and Kanamori, 1979) allows direct estimation of moment magnitude, knowing peak horizontal velocity and hypocentral distance. We call this estimation of moment magnitude “Mw′” to distinguish it from its original definition. Equation for Mw′ for our data set isM w ' = 2 . 2 7 + 0 . 7 7 log ( V ⋅ R ) + 6 . 5 9 × 1 0 - 3 R ,where V is in millimeters/second, and R is in kilometers.In order to be able to estimate the moment magnitude from coda duration (Tc), we sought and found correlation between log(Tc) and log of moment (M0) as followslog M 0 = ( 2 . 2 5 ± 0 . 1 7 ) log ⁡ T c + ( 15.88 ± 0.29 ) ,where M0 is in dyne-cm, and Tc is in seconds.
Phase speed perturbations and three-dimensional scattering effects of surface waves due to topography
Authors: Snieder Roel 
Published: July 2021

AbstractLinearized scattering theory is used to describe three-dimensional surface wave scattering by topography on a layered medium. A short derivation for the scattered surface wave is presented. The implications and limitations of the scattering theory are discussed qualitatively. Furthermore, an expression is presented for the partial derivatives of the surface wave phase velocities with respect to topography. It is shown that for periods between 15 and 30 sec, the fundamental mode phase velocity perturbation due to topography is of the order of 1 per cent for a mountain of 1 km height. For the higher mode phase velocities, the effects of topography are negligible.
Estimation of earthquake source parameters by the inversion of waveform data: Global seismicity, 1981-1983
Authors: Spikin Stuart A. 
Published: July 2021

Abstract
A waveform inversion algorithm, based on optimal filter theory, has been applied to the P waves from 260 of the largest earthquakes occurring during the years 1981 through 1983. Estimates of average focal depth, scalar moment, and deviatoric source mechanism have been obtained. For all except the largest events (M0 &gt; 1027 dyne-cm), the scalar moments obtained in this study are close to, but somewhat larger than, the Harvard centroid-moment tensor (CMT) scalar moments. The CMT estimates of scalar moment are probably biased to low values due to the way unmodeled lateral heterogeneity affects the fitting procedure. For the largest events, however, source complexity can bias the scalar moments determined in this study to lower values, and the CMT scalar moments are probably more accurate. The moment tensor, CMT, and U.S. Geological Survey first-motion source mechanisms have been objectively compared by computing the locations of the vector representations of the mechanisms on the unit sphere. We find that the similarities and differences between these mechanisms can be related to the uncertainties inherent in each method for certain types of earthquakes: (1) lack of constraint on one of the nodal planes for dip-slip type mechanisms from first-motion analysis; (2) lack of resolution of the moment tensor elements defining the dip-slip component of faulting for shallow-focus earthquakes in the CMT method; and (3) lack of resolution of the moment tensor elements defining the strike-slip component of faulting in the P-wave inversion method used here. Thus, on the average, the first-motion and CMT methods yield the more reliable mechanisms for strike-slip-type earthquakes, and the method used in this study gives a more reliable result for shallow-focus earthquakes with dip-slip-type mechanisms. Finally, both of the moment tensor methods should yield reliable solutions for intermediate- and deep-focus earthquakes.
Interplate coupling and temporal variation of mechanisms of intermediate-depth earthquakes in Chile
Authors: Astiz Luciana , Kanamori Hiroo 
Published: July 2021

Abstract
We investigated the temporal variation of the mechanism of large intraplate earthquakes at intermediate depths in relation to the occurrence of large under-thrusting earthquakes in Chile. Focal mechanisms were determined for three large events (1 March 1934: M = 7.1, d = 120 km; 20 April 1949: M = 7.3, d = 70 km; and 8 May 1971: MW = 7.2, d = 150 km) which occurred down-dip of the great 1960 Chilean earthquake (MW = 9.5) rupture zone. The 1971 event is down-dip compressional: θ (strike) = 12°, δ (dip) = 80°, and λ (rake) = 100°. The 1949 earthquake focal mechanisms is θ = 350°, δ = 70°, and λ = −130°. The data available for the 1934 event are consistent with a down-dip tensional mechanism. Thus, the two events which occurred prior to the great 1960 Chilean earthquake are down-dip tensional. Published fault plane solutions of large intermediate-depth earthquakes (28 March 1965 and 7 November 1981) which occurred down-dip of the Valparaiso earthquakes of 1971 (MW = 7.8) and 1985 (MW = 8.0) are also down-dip tensional. These results suggest that before a major thrust earthquake, the interplate boundary is strongly coupled, and the subducted slab is under tension at intermediate depths; after the occurrence of an interplate thrust event, the displacement on the thrust boundary induces transient compressional stress at intermediate depth in the down-going slab. This interpretation is consistent with the hypothesis that temporal variations of focal mechanisms of outer-rise events are due to changes of interplate coupling.