bluuebunny/crossref_metadata_2025_split huggingface dataset:
MLobservations in the Great Basin andM0 versusMLrelationships for the 1980 Mammoth Lakes, California, earthquake sequence
Authors: Chávez David E. , Priestley Keith F. 
Published: July 2021

AbstractThe local magnitude distance correction term, log A0(Δ), has been estimated for paths within the Great Basin by converting seismograms of earthquakes in the vicinity of Mammoth Lakes, California, into equivalent Wood-Anderson seismograms and measuring the decay of peak amplitude with distance. The shape of the log A0(Δ) curve which results suggests more attenuation of energy in the Wood-Anderson passband than in southern California. For Great Basin paths we find, for events with ML ≦ 5.5, thatlog A 0 ( Δ ) = { log 10 [ e − 0.016 R R ] − 0.31 0 ≦ Δ ≦ 9 0 km log 10 [ e − 0.006 R R 0.83 ] − 1.08 90 ≦ Δ ≦ 6 0 0 kmwhere Δ is epicentral distance, R=Δ2+h2 is hypocentral distance, and h is focal depth. Our data also suggest a magnitude bias in the correction term, in that for events above ML ≈ 5.5, peak amplitudes recorded at epicentral distances below 20 km decay less rapidly than those for smaller events recorded at the same sites. This observation is consistent with the hypothesis that there is a near-source saturation of ML due to the effects of a finite source size for large earthquakes. Using the revised magnitude scale and seismic moments, M0, estimated from spectral analysis, the data are well fit by the straight linelog ⁡ M 0 = ( 1.20 ± 0.05 ) M L + ( 17.49 ± 0.19 )for 1 ≦ ML ≦ 6. M0 versus ML values from model calculations which assume constant stress drop predict curved moment-magnitude plots over this magnitude range. The fact that we observe a linear relationship suggests that the stress drop of these events is not constant but rather increases with ML, in particular for events above ML ≈ 5.5.
An empirical estimate of near-source ground motion for a major,mb= 6.8, earthquake in the eastern United States
Authors: Campbell Kenneth W. 
Published: July 2021

AbstractThree empirical techniques are used to estimate ground-motion amplitudes in the near-source region of a major earthquake hypothesized to occur along the east coast of the United States. These techniques include the estimation of strong-motion parameters from the statistical analysis of selected strong-motion records, from empirical and theoretical attenuation relations, and from Modified Mercalli intensity. Source parameters for the hypothesized earthquake were selected to be similar to those inferred for the 1886 Charleston, South Carolina, earthquake. The epicentral region is characterized by a Modified Mercalli intensity of X, from which magnitudes of mb = 6.8, Ms = 7.2, and M = 7.2 were estimated. Inferred fault mechanisms for the hypothesized event vary from strike-slip on a vertical fault to reverse or reverse-oblique slip on a fault dipping as shallow as 45°.The median estimate of peak horizontal acceleration for a point located 15 km from the surface projection of fault rupture is 0.30 g, independent of site geology. Corresponding estimates of peak horizontal velocity are 35 cm/sec for soil and soft sedimentary rock sites and 18 cm/sec for crystalline basement rock sites. Strong-motion parameters for a point located 15 km from the epicenter, corresponding to a point located directly above the rupture zone of the hypothesized earthquake, are estimated to be approximately 80 per cent higher than these estimates, or about 0.55 g for peak acceleration and about 63 and 33 cm/sec for peak velocity on soil/soft rock and crystalline rock, respectively. Corresponding velocity-acceleration ratios are 115 cm/sec/g for soil/soft-rock sites and 60 cm/sec/g for crystalline rock sites. Standard deviations associated with the natural logarithm of peak horizontal acceleration and velocity are estimated to be 0.5 and 0.7, respectively, representing an 84th percentile estimate (or equivalently an upper 68 per cent confidence limit) that is approximately 65 per cent higher than the median for acceleration and 100 per cent higher than the median for velocity. While these strong-motion values are generally higher than those currently used in the seismic design of most structures in the Eastern United States, their impact on the seismic safety of specific sites in the region will depend on an assessment of the probability of occurrence of an earthquake of this size within the near-source region of these sites.
Spatial and temporal variations in seismicity in the Imperial Valley (1902-1984)
Authors: Doser Diane I. , Kanamori Hiroo 
Published: July 2021

abstractEarthquakes with ML ≧ 4.5 that occurred between 1932 and 1973 in the Imperial Valley region and their related foreshocks and aftershocks are relocated using station delays derived from calibration events that were well recorded at regional distances between 1979 and 1981. The relocated seismicity shows that there was an increase in seismicity in regions northeast of the Imperial fault 5 to 6 yr prior to the 1940 (Ms = 7.1) Imperial Valley earthquake. A study of intensity reports for felt earthquakes prior to 1932 also suggests an increase in seismicity in regions surrounding the Imperial fault as early as 1917. Isoseismal patterns, description of the mainshock sequence, and patterns of seismicity before and after the 1915 Imperial Valley earthquakes suggest that the earthquakes occurred off the Imperial fault. In this case, seismicity between 1906 and 1940 would nearly encircle the portion of the Imperial fault that ruptured during 1940. In both the 1940 and 1979 Imperial Valley earthquake sequences, aftershocks of ML ≧ 4.5 occurred only for 2 months following the mainshock. The aftershock sequences were followed by periods of quiescence lasting up to 10 yr in the region within 30 km of the mainshock. This is in contrast to ML &gt; 6.0 earthquakes occurring near the edges of the Imperial Valley that had aftershocks of ML ≧ 4.5 occurring for up to 4 yr after the mainshock. These differences may be related to the high heat flow within the Imperial Valley.
HYPOCENTER: An earthquake location method using centered, scaled, and adaptively damped least squares
Authors: Lienert Barry R. , Berg E. , Frazer L. Neil 
Published: July 2021

AbstractWe present an earthquake location method, HYPOCENTER, which combines features of the two well-known algorithms HYPO71 and HYPOINVERSE, with a new technique which we term adaptive damping. Each column of the linearized condition matrix T, which relates changes in arrival time to changes in hypocentral position, is centered and scaled to have zero mean and a norm of one. Origin time is defined as the mean arrival time minus the mean travel time. The three least-squares normal equations for hypocentral coordinates, with diagonal terms equal to one, are then solved iteratively by adding a variable damping factor, θ2, to their diagonal terms before inversion. If the residual sum of squares increases, we return to the previous iteration, increase θ2, then try again. This procedure, which we term adaptive damping, always results in residuals which are less than or equal to the HYPO71 or HYPOINVERSE residuals. We demonstrate HYPOCENTER by comparing it to HYPO71 and HYPOINVERSE using synthetic and real arrival time data for four- and eight-station seismic arrays.
A method for the inversion of refraction and reflection travel times for laterally varying velocity structures
Authors: Huang Huaiyong , Spencer Carl , Green Alan 
Published: July 2021

Abstract
In an attempt to speed up the lengthy process of modeling seismic refraction/wide-angle reflection data, a two-dimensional ray tracing routine is used as the basis for an automated travel-time inversion scheme. Laterally varying P-wave velocity structures are represented by arbitrary-shaped blocks of constant velocity gradient. Velocities, gradients, and boundary points of the blocks are parameters in the inversion scheme, and the input data are refraction and reflection travel-time arrivals from both directions of a reversed seismic line. Damped least-squares techniques are used to solve the equations of condition, and inversions are allowed to proceed automatically for several iterations. A synthetic example is presented, and the data from two reversed seismic refraction profiles recorded recently in eastern Canada are inverted to demonstrate the utility of the method under less than ideal conditions. The synthetic test demonstrates that several iterations of the procedure are necessary for accurate recovery of input models and provides a resolving power analysis of the problem, while the real data example produces models comparable to those obtained by experienced interpreters using trial and error methods.
The effect of strong-motion array configuration on source inversion
Authors: Miyatake Takashi , Iida Masahiro , Shimazaki Kunihiko 
Published: July 2021

AbstractBy using the method of prediction analysis, the accuracy of source inversion of strong-motion data is investigated for various arrays, and the effects of array configuration are evaluated. In the case of a circular array in which Ns array stations are uniformly distributed within radius R and when the strike-slip fault is located at the center of the array, an empirical relationship between the array parameters and the standard deviation of the seismic moment of each subfault, normalized by the seismic moment, is obtained asσ M 0 = c ⋅ N e 2 ⋅ 10 R / 5 / N swhere c is a constant, and Ne is the number of subfaults. The constant c depends upon the fault mechanism (dip slip or strike slip), aspect ratio of the fault, focal depth, the array configuration, rupture mode (unilateral or bilateral), crustal structure, etc. However, it would be useful for both the source inversion study and a future installation plan of strong-motion arrays.An application of the method to several specific cases leads us to conclude that highly dense local array is not advantagenous for source inversion, but an array covering the earthquake fault with equally spaced stations is of benefit to the source inversion.Two cases of array configuration examined are a straight-line array, which is perpendicular to the fault and another straight-line array, which is parallel to the fault. The perpendicular array is unsuitable for source inversion, but the parallel array is advantageous for source inversion. Furthermore, the inversion study for the 1979 Imperial Valley earthquake is simulated for three cases of strong-motion station distributions (case A: 20 United States stations; case B: El Centro strong-motion array; and case C: all 26 stations of the United States and Mexico). Our simulation shows that case B gives a very poor result, and that the best of three is case C.
Amplitudes at the antipode
Authors: Butler Rhett 
Published: July 2021

AbstractSeismic amplitudes of 1 Hz compressional waves at the antipode are estimated using the body-wave magnitude formula and corrections for focusing at the antipode. Compressional wave amplitudes are found to be larger at the antipode than at other distances outside of the source region itself. Ellipticity effects at the antipode are found to be significant only for PP away from the earth's poles and for PKP near the equator. The effects of lateral heterogeneity on antipode focusing are estimated. Implications for monitoring nuclear explosions are discussed. An antipode experiment using small (12 ton) chemical explosions opposite a seismic array is found to be viable.
A test of two techniques for recognizing systematic errors in magnitude estimates using data from parkfield, California
Authors: Habermann R. E. 
Published: July 2021

Abstract
Selections of events from seismicity catalogs on the basis of size are universally made on the basis of magnitude. Such a selection implicitly assumes that these magnitudes provide a temporally consistent measure of earthquake size or that systematic errors in magnitudes are constant. Several techniques can be used to test this assumption. Results of application of these techniques to local and teleseismic catalogs indicate that in many cases this assumption cannot be justified. Two different techniques for identifying changes in systematic errors in magnitude are described here and applied to recent seismicity data from Parkfield, California. One technique relies on comparisons of seismicity rates before and after a possible change in magnitudes. The other uses station magnitude corrections to redetermine magnitudes. Both of these techniques indicate that a systematic decrease in magnitudes by 0.18 to 0.19 units occurred at Parkfield during November 1984. This decrease was associated with the installation of six low-gain stations in the Parkfield region. It is clear that changes in stations distributions can have significant effects on magnitudes and that these changes must be accounted for in all seismicity studies which use magnitude as a selection criteria. The results of past studies which have not accounted for these changes must be reevaluated.
Exact evaluation of the response of a layered elastic medium to an explosive point source using leaking modes
Authors: Haddon R. A. W. 
Published: July 2021

AbstractA simple and rigorous theory of leaking modes for liquid layer or SH elastic wave propagation problems is presented. By taking the frequency ω and wave-number k simultaneously as complex variables and choosing appropriate paths of integration in the ω-plane, the integration with respect to k is performed exactly using Cauchy residue theory. The remaining integration with respect to ω is then carried out by use of the Fast Fourier transform. The method is simply to apply, accurate, and computationally efficient. There are no spurious arrivals, and provided the number of points in the Fast Fourier transform can be taken sufficiently large, there are no restrictions on distance.The theoretical results established in the paper show conclusively that complete seismograms, including all possible body waves, can be expressed simply as a superposition of modes. No branch line integrals are required, contrary to the widespread supposition in the literature.The application of the theory is illustrated by producing complete theoretical seismograms for a model consisting of six liquid layers.
Rupture complexity of a moderate-sized (mb6.0) earthquake: Broadband body-wave analysis of the North Yemen earthquake of 13 December 1982
Authors: Choy George L. , Kind Rainer 
Published: July 2021

AbstractThe occurrence of the North Yemen earthquake of 13 December 1982 provides an important opportunity to study source properties of earthquakes in the southern Arabian Peninsula. Although moderate in size (mb 6.0), this earthquake is the largest to have occurred in the region since the deployment of the Global Digital Seismograph Network. P waves recorded at teleseismic distances can be obtained from stations of this network and of the Graefenberg array that are flat to displacement and velocity in the frequency range from 0.01 to 5.0 Hz. The broad bandwidth of the data is necessary for deriving a dynamic description of the earthquake as well as the static properties of the source. In contrast, inversions using only long-period data provide much less insight into the complexity of rupture. By fitting the displacement pulse shapes with synthetics, we find that the Yemen earthquake was a complex rupture consisting of two events that occurred about 3.0 sec apart. The depth of both hypocenters is estimated to be 7 km. The focal mechanisms of the events each have a nodal plane that strikes 340° and dips 60° to the east. However, the slip directions of the focal mechanisms are in slightly different directions, 230° and 300°, respectively. The total moment of the earthquake is 3.0 ×1025 dyne-cm, with the second event having three times the moment of the initial event. By inverting P-wave arrival time differences at each station, we find the second hypocenter is located 7.5 km from the initial hypocenter in a direction that is nearly colinear with the NNW-striking nodal plane of the focal mechanisms of each event. The trend of extensional ground cracks in the epicentral region and the predominant strike of composite focal mechanisms of locally recorded aftershocks are also in a NNW direction. From the consistency of these observations, we infer that the east-dipping NNW-striking nodal planes are the fault planes. The static stress drop of the first and second events are 44 and 31 bars, respectively. Inverting the energy flux in the velocity waveforms, we find the energy radiated by the earthquake is 4.8 ×1020 dyne-cm. This implies an average apparent stress of 4 bars.At different times during the aftershock sequence, seismicity tended to cluster about one or another of two different planes which, although having roughly the same strike, had conjugate dips. One of these planes, delineated late in the aftershock sequence, coincides with the inferred fault plane for the main shock. The complexity of the main shock and of the aftershock sequence suggests that strain accumulated on a system of strongly interdependent faults. As the region became critically loaded, the effect of a major rupture was to critically stress faults adjacent to the initial nucleation. The second event of the main shock represents the rapid release of stress from the fault system, while the ensuing aftershock sequence represents the gradual release of stress.
Microseismicity and source mechanism study: Shillong Plateau, northeast India
Authors: Kayal J. R. 
Published: July 2021

AbstractMicroearthquakes recorded by two surveys in the Shillong Plateau during December 1982-July 1983 and January-February 1984, respectively, have been analyzed for seismicity and tectonic study in the region. Of 1,000 events recorded during the surveys, 180 events with reliable P and S readings (which are observed within 50 km radius of the network), are relocated by the homogeneous station method. It is found that the events are mostly confined within a depth range of 10 to 35 km. The seismicity, in general, may be correlated with the major geological structure/lineaments in the area. High rates of seismicity are observed in the Shillong and Tura areas. On the other hand, an aseismic zone is delineated to the east of Shillong.Composite source mechanisms of two groups of microearthquakes show thrust-fault mechanisms. One group of microearthquakes (1982 to 1983) in the Shillong area shows pure thrust faulting with a SE-NW compressive stress (P axis), whereas the other group of microearthquakes (1984) in the Tura area shows thrust faulting with a strike-slip component and a ENE-WSW compressive stress (P axis). The stress orientations are compatible with the known tectonics of the region: collision of the Indian plate with the Eurasian plate at the Himalaya and subduction of the Indian plate beneath the Burmese plate at the Arakan-Yoma range.
Spectral scaling of earthquakes in the Miramichi region of New Brunswick
Authors: Chael Eric P. 
Published: July 2021

AbstractSeismograms of 12 earthquakes in the Miramichi region of New Brunswick were analyzed to determine source scaling relations. The events ranged in magnitude from 3.3 to 5.8 (mbLg). P-wave spectra between 1 and 20 Hz were calculated using digital records from station RSNY (Δ = 6°). Spectral ratios were then formed using the main shock as a reference event. Because the travel paths were virtually identical for all of the signals, the spectral ratios yield the scaling of the sources as a function of frequency. The spectral ratio curves show a smooth progression with event size, with their separation decreasing toward higher frequencies. These data were compared with theoretical curves for source models whose displacement spectra roll off as ω−2 and ω−3 above the corner frequencies. The data strongly favor the ω−2 models; the ω−3 models predict greater variation across the 1- to 20-Hz band than is observed. Comparison of the P-wave scaling at 15 Hz with the Rayleigh wave scaling at a period of 8 sec indicates that stress drop may increase with moment for these events, although not as fast as Nuttli (1983) has suggested for intraplate earthquakes.
A novel technique for measuringLgattenuation—results from Eastern Canada between 1 to 10 hz
Authors: Chun Kin-Yip , West Gordon F. , Kokoski Richard J. , Samson Claire 
Published: July 2021

AbstractSpectral amplitudes of regionally recorded Lg waves are studied in detail between 0.6 and 10 Hz, using vertical-component, velocity seismograms of the Eastern Canada Telemetered Network stations and a supplementary Seismic Research Observatory-type station at Glen Almond (GAC), Québec. We find that the site responses vary among these stations by more than a factor of 3 within the frequency range of interest. Furthermore, they are found to be strongly frequency dependent. Consequently, it is essential that they be taken into consideration in studies of Lg wave attenuation and Lg source spectra of regionally recorded seismic events.We present a new method of measuring interstation surface wave attenuation, which is closely related to the conventional two-station method. While retaining all the desirable features of the conventional two-station method, the new technique, which we will call the “reversed two-station method,” allows simple, direct (one-parameter) determination of the Lg wave attenuation from sparse spectral data in a manner unaffected by station site effects and associated instrument error.The reversed two-station method is successfully tested over weakly attenuating, short (53 to 210 km) interstation paths in eastern Canada, a difficult experimental condition by normal standards. The Lg attenuation coefficient (0.6 to 10 Hz) in eastern Canada is found to be frequency dependent and of the form γ(f) = 0.0008 f0.81 km−1. At higher frequencies, the Lg attenuation appears to be essentially frequency independent. This latter finding is preliminarily interpreted as evidence that regionally recorded Lg waves in the Canadian Shield are, as in the case of Lg waves propagating through the structurally complex Appalachian Province, contaminated by the high-frequency coda of Sn waves. The Lg contamination over the shield paths becomes severe starting at 14 Hz, twice the frequency above which the Lg signal propagating over the Appalachian Province becomes completely dominated by non-Lg arrivals.
Topographical and geological amplifications determined from strong-motion and aftershock records of the 3 March 1985 Chile earthquake
Authors: Çelebi M. 
Published: July 2021

AbstractSite-response experiments were performed 5 months after the MS = 7.8 central Chile earthquake of 3 March 1985 to identify amplification due to topography and geology.Topographical amplification at Canal Beagle, a subdivision of Viña del Mar, was hypothesized immediately after the main event, when extensive damage was observed on the ridges of Canal Beagle. Using frequency-dependent spectral ratios of aftershock data obtained from a temporarily established dense array, it is shown that there is substantial amplification of motions at the ridges of Canal Beagle. The data set constitutes the first such set depicting topographical amplification at a heavily populated region and correlates well with the damage distribution observed during the main event.Dense arrays established in Viña del Mar also yielded extensive data which are quantified to show that, in the range of frequencies of engineering interest, there was substantial amplification at different sites of different geological formations. To substantiate this, spectral ratios developed from the strong-motion records of the main event are used to show the extensive degree of amplification at an alluvial site as compared to a rock site. Similarly, spectral ratios developed from aftershocks recorded at comparable stations qualitatively confirm that the frequency ranges for which the amplification of motions occur are quite similar to those from strong-motion records. In case of weak motions, the denser arrays established temporarily as described herein can be used to identify the frequency ranges for which amplification occurs, to quantify the degree of frequency-dependent amplification and used in microzonation of closely spaced localities.