bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evidence of tectonic release in long-periodSwaves from underground nuclear explosions at the Novaya Zemlya test sites
Authors: Burger R. W. , Lay T. , Wallace Terry C. , Burdick L. J. 
Published: July 2021

AbstractEvidence of tectonic release produced by underground nuclear explosions at Novaya Zemlya is present in teleseismic, long-period S waves. SH waveforms from representative events at the Southern and Northern Novaya Zemlya test sites were modeled to determine the SH radiation patterns. Long-period P and SV waves were also investigated to further constrain the equivalent double-couple orientation of the tectonic release. Events within each test site have similar faulting mechanisms, but there are definite differences in the tectonic release orientation between the two sites. The southern test site double-couple orientation is either vertical strike slip or 45°-dipping thrust, while the northern test site has an oblique-normal dip slip orientation. The limited resolution of SH signals and complexity of the observed SV waveforms, along with uncertainties in the absolute explosion source strengths and t*, prevent unique solutions for both test sites. Assuming a strike slip orientation, the 27 October 1973 Southern Novaya Zemlya event has the largest tectonic release moment (1.6 × 1024 dyne-cm) and 14 October 1969 northern event has the smallest moment (0.9 × 1023 dyne-cm) of the 12 events studied. The ratio of tectonic release moment to explosion strength varies by as much as a factor of 3 at the northern test site and by a factor of 2 at the southern site. The variability of the tectonic release orientation and strength at the two test sites allows us to address the question of whether tectonic release affects yield estimation.
Prediction of strong ground motion in the Puget Sound region: The 1965 Seattle earthquake
Authors: Ihnen S. M. , Hadley D. M. 
Published: July 2021

AbstractSpatial variations in strong ground motion in the 1965 Seattle, Washington, earthquake (MS = 6.5) can be accurately reproduced using three-dimensional ray tracing techniques. Synthetic accelerograms calculated at nearly 1600 receivers spread over the Puget Sound region indicate that peak ground accelerations are significantly affected by subsurface structure as well as by near-receiver soil properties. The large synthetic accelerations computed for the Harbor Island/downtown Seattle area appear to be due to subsurface focusing of rays within a deep sedimentary basin and are consistent with the observed isoseismal distribution. In extreme circumstances, such as a bedrock site adjacent to a site situated upon a soft sedimentary lens, peak accelerations may vary by nearly an order of magnitude. Predicted values of peak ground acceleration as a function of distance reproduce both the trend and scatter in data from subduction zone earthquakes of comparable depth in Japan.
A seismic zone on the Oregon-Idaho border: The powder river earthquakes of 1984
Authors: Zollweg J. E. , Jacobson R. S. 
Published: July 2021

AbstractTwo magnitude 3.8 earthquakes occurred south of the Wallowa Mountains in northeastern Oregon in August and September 1984. Locations of 15 aftershocks recorded on portable seismographs cluster around the Oregon-Idaho border near the mouth of the Powder River. A composite fault-plane solution indicates normal faulting on planes striking north or north-northwest, consistent with stresses observed in the Basin and Range Province to the east. The record of historical earthquakes in the region suggests periodicity with intervals of 11 to 21 yr between cycles of events consisting of several main shocks within a 3-yr time span. A magnitude 3.6 earthquake on 29 September 1981 may have begun the present cycle.
Lgmagnitudes of selected East Kazakhstan underground explosions
Authors: Nuttli Otto W. 
Published: July 2021

AbstractThe amplitude of 1-sec period Lg waves, as recorded on seismograms of WWSSN stations in southern Asia and Scandinavia, are used to determine mb(Lg) values for 62 underground nuclear explosions in the eastern portion of the East Kazakhstan Test Site. The explosions were selected to be of mb(P) = 5.5 or greater in the period 1965 to 1985.The yields of the explosions are estimated, assuming that a Nevada Test Site-derived relation between mb(Lg) and yield for water-saturated rock is also applicable to the East Kazakhstan Test Site. Assuming that lateral variations in crustal structure and in depth of emplacement of the explosion do not affect mb(Lg) values, the Lg data indicate that the mb(P) bias between the Nevada Test Site and East Kazakhstan is 0.35 magnitude units.
Thermoelastic strain in a half-space covered by unconsolidated material
Authors: Ben-Zion Yehuda , Leary Peter 
Published: July 2021

AbstractAn algorithm to predict crustal thermoelastic strain from observed local atmospheric temperature is given and applied to a 24-month crustal strain record of one test strainmeter site located near Bouquet Reservoir in southern California. We use a crustal model that consists of an elastically decoupled layer overlying a uniform elastic half-space, and a thermal source that is given by a stationary temperature wave whose wavelength is related to local topography and/or lateral material heterogeneity. The decoupled layer delays, attenuates, and low-pass filters the source temperature field. The thermoelastic strain in the underlying half-space, resulting from the temperature variations at the base of the decoupled layer, is calculated using the Berger (1975) solution for thermoelastic strain in a uniform half-space. Applying our model to the test data, we obtain a good fit between predicted and observed strains if we filter the surface thermal signal through a 63-cm-thick decoupled layer. Much of the remaining strain variations clearly correspond to other environmental sources (reservoir loading and rainfall). Our analysis suggests that the horizontal thermoelastic strain is inversely proportional to the wavelength of local topography and/or lateral material heterogeneity. Thus, the horizontal thermoelastic strain will be greater in areas of local topography and/or lateral material heterogeneity and smaller in more homogeneous and flat areas. An upper layer of loose material, natural or artificial, acts as a thermoelastic strain insulator. Burial of strainmeters in places where such a layer exists can reduce the thermoelastic strain noise considerably even for shallow strainmeter emplacements.
The 1930 Santa Monica and the 1979 Malibu, California, earthquakes
Authors: Hauksson Egill , Saldivar Geoffrey V. 
Published: July 2021

AbstractThe Malibu earthquake (ML = 5.0) that occurred 1 January 1979 in Santa Monica Bay was located at 33°56.9′N and 118°41.3′W and at a depth of 10 km. The focal mechanism of the main shock as determined from first motions recorded by short-period, high-gain seismic stations in southern California shows reverse faulting with one plane dipping 55° to 60° to the north striking 275° to 290°, and the second plane dipping 30° to 38° to the south and striking 100° to 120°. More than 400 aftershocks were recorded during 1979. Focal mechanisms for 20 aftershocks of M ≧ 3.0 show similar reverse mechanisms as the main shock. The main shock and aftershocks (M ≧ 2.5) were relocated using a local velocity model and a set of corresponding station delays. The aftershocks define a volumetric hypocentral zone, 4 km × 6 km, west-trending with depths ranging from 6 to 11 km. This 1979 Malibu main shock-aftershock sequence probably occurred on the eastern end of the Anacapa-Dume fault. The Santa Monica earthquake (ML = 5.2) that occurred 31 August 1930 was relocated using station delays calculated from the 1979 date set. The relocated 1930 epicenter is located near the western end of the Santa Monica fault. The 1979 and 1930 main shocks can be interpreted to define a 8- to 10-km north-south sidestep between the Anacapa-Dume and Santa Monica faults. Possible segmentation of these two fault systems suggests that they are unlikely to rupture simultaneously in one large earthquake.
14 February 1983 earthquake sequence in the Shumagin Islands, Alaska
Authors: Taber J. John , Beavan John 
Published: July 2021

Abstract
Two moderate events (MS = 6.3 and 5.6) occurred just outside a local network in the Shumagin Islands, Alaska, on 14 February 1983. These were the first events of magnitude greater than 5.5 in the region since 1979. They occurred within the subduction zone at a depth of 26 km. Of the more than 50 aftershocks that were recorded at one or more stations, 12 events ranging from mb = 2.5 to 4.0 were recorded digitally and located. Focal mechanisms were calculated for the two main events from first-motion polarities and teleseismic body-wave modeling. The mechanisms for both events show similar nodal planes, with P axes in the approximate direction of plate convergence and nearly vertical T axes. The plane of motion is not constrained by the aftershocks but the shallowly dipping plane parallel to the subduction zone interface is the preferred solution. Dynamic stress drops of 80 and 70 bars are calculated from local strong-motion records. These events occurred in a mature seismic gap. They nucleated in a shallow portion of the main thrust zone that apparently has a relatively low state of stress and thus were not capable of rupturing into the higher strength region at the base of the main thrust zone.
Representation of an extended seismic source in a propagator-based formalism
Authors: Chouet Bernard 
Published: July 2021

AbstractA method is presented for the computation of synthetic seismograms for an arbitrary seismic source embedded in a stratified medium. The technique is applied to a source extending in three space dimensions for which the radiation has been decoupled into P, SV, and SH motions. A matrix formulation is given in which the displacements and stresses due to individual plane wave components of the P-SV and SH radiations from the source are separated into contributions at the upper and lower interfaces of the source layer where they are subtracted from the displacement-stress vector due to the total wave field. With this method, the propagator in the source layer connects only the reverberated components of the waves at the upper and lower layer interfaces, and there are no discontinuities in the displacements and stresses at the source depth. An application of Dunkin's formulation of the Thompson-Haskell algorithm is given for the solution of the P-SV problem, along with a brief summary of the well-known propagator matrix formulation for the associated SH problem. The formulation is extended to the case of a shallow source penetrating two layers, and examples are presented for both shear and tensile sources.
Picking noisy refraction data using semblance supplemented by a Monte Carlo procedure and spectral balancing
Authors: Zelt C. A. , Drew J. J. , Yedlin M. J. , Ellis R. M. 
Published: July 2021

Abstract
In crustal refraction experiments, the crucial deeply refracted and head wave arrivals often have a low signal-to-noise ratio. A method to aid in the picking of noisy refraction data is presented which is applicable to any branch of a seismic section whose waveform is approximately invariant throughout the branch. The technique exploits the spatial correlation of arrivals and is based on the lateral coherency which results if the refracted arrivals are aligned by applying appropriate time shifts to each trace of the branch. The alignment of arrivals occurs iteratively and is accomplished through a cross-correlation of each trace with the stack of the section of the previous iteration. The iteration yielding the section with the highest degree of lateral coherency (semblance) is used to extract the travel-time pick of each trace. The pick, plus a possible d.c. component, is the negative of the time shift required to achieve arrival alignment.
Two modifications can improve the performance of the picking routine. To prevent a cycle skipping problem, a Monte Carlo technique is implemented in which the cross-correlation function is transformed into a probability distribution so that the lag corresponding to the maximum cross-correlation is most probably selected. Second, to increase the coherency of the arrivals, a spectral balancing technique is applied in either the time or frequency domain.
The picking routine is applied to both a synthetic and real data example, and the results suggest that the routine can be applied successfully to data with a signal-to-noise ratio as low as one. Also, the Monte Carlo procedure together with spectral balancing increases the final semblance over that obtained with the unmodified method.
AverageQand yield estimates from the Pahute Mesa test site
Authors: Burger R. W. , Lay T. , Burdick L. J. 
Published: July 2021

AbstractAttenuation models, with and without frequency dependence, have been developed through analysis of time-domain amplitude measurements and teleseismic spectral shape data from Pahute Mesa nuclear explosions. The time-domain analysis is based on a near-field to far-field amplitude comparison. The near-field amplitude information is incorporated in two parameterized explosion source models (Mueller-Murphy and Helmberger-Hadley) based on analyses of near-field data. The teleseismic amplitude observations are from a large data set of WWSSN short-period analog recordings. For the narrow-band time-domain data, the various source and attenuation models are indistinguishable. We utilize the spectral shape data in the 0.5- to 4-Hz band as a constraint on the source-attenuation models at higher frequencies, concluding that either source model, when convolved with the appropriate frequency-dependent Q model, can be consistent with both the near-field and far-field time-domain amplitudes and the spectral shape data. Given the trade-off between source and attenuation models and the similarity of the different source models in the 0.5- to 4-Hz band, it is difficult to prefer clearly one source model over the other. The Mueller-Murphy model is more consistent with surface wave amplitude measurements because of larger predicted long-period energy levels. Whether or not frequency dependence is included in the attenuation model, the value of t* near 1 Hz is about 1.0 sec (assuming the Mueller-Murphy source model) or 0.8 sec (assuming the Helmberger-Hadley source model). This 0.2 sec difference results from greater 1-Hz energy levels for the Mueller-Murphy source model. Adopting an average attenuation model, predicted amplitudes and yields are shown to be within the uncertainty of the data for all the events analyzed.
Air blast recognition and location using regional seismographic networks
Authors: Johnston Arch C. 
Published: July 2021

Abstract
Regional seismic networks are occasionally useful for purposes other than earthquake studies. Three such applications which involve surface and atmospheric phenomena are described in this report: (1) the detection and location of a missile silo explosion in Arkansas; (2) analysis of an aircraft sonic boom; and (3) attempts to determine the time and location of ground impacts of aircraft and a meteorite. When the source of the disturbance is in the air, seismic instruments respond to the air-coupled surface waves generated in the wake of the atmospheric shock front advancing with the speed of sound in air. Thus, the disturbance's point and time of origin can be determined using a standard iterative hypocenter program with a “crustal” velocity model appropriate to the prevailing atmospheric temperature and pressure conditions. Simplified theory predicts that air-coupling is significant only when the speed of sound in air is close to the shear wave velocity of the surface crustal layer. This is normally the case only when unconsolidated material is present at the surface. The observations discussed here support this prediction: seismic network instruments sited on soft ground recorded signals from atmospheric disturbances much more clearly than did higher gain instruments on hard rock.
Observations of first-order mantle reverberations
Authors: Revenaugh Justin , Jordan Thomas H. 
Published: July 2021

AbstractWe have observed first-order mantle reverberations, specifically SH-polarized ScSn and sScSn phases reflected at near-normal incidence from upper mantle discontinuities, as discrete phases on long-period digital seismograms of the HGLP and SRO networks. Such arrivals correspond to an n or n + 1 member dynamic ray family denoted by {ScSn, Sd±S}, where n is the multiple number of the parent phase, “d+” signifies a reflection from the top of an internal discontinuity at depth d, and “d−” signifies a reflection from the bottom. The travel times and attenuation of these phases place important constraints on the nature of the transition zone. We have employed the phase equalization and stacking algorithm of Jordan and Sipkin (1977) to obtain the differential attenuation operators of {sScSn, S650+S} − sScSn and {ScSn, S650−S} − ScSn phase pairs from deep-focus Tonga events recorded by the HGLP station KIP on the island of Oahu. The apparent Q's of the zeroth-order and first-order reverberations over the frequency band of 10 to 30 mHz have been inverted for the average quality factors of the upper mantle (QUM) and lower mantle (QLM) and the reflection coefficient of the 650 km discontinuity (R650). At 20 mHz, the results are: QUM = 82 ± 18, QLM = 231 ± 60, and |R650| = 0.080 ± 0.004 (at normal incidence). The QLM estimate is significantly less than recent normal mode solutions, suggesting that lower mantle attenuation structure is frequency-dependent at very low frequencies. We have measured the differential travel times between the first-order reverberations {sScSn, S400+S} and {sScSn, S650+S}, which yields a direct estimate of the vertical shear-wave travel time between the discontinuities along the Tonga-to-KIP path. The observed two-way time, 92.2 ± 1.5 sec, is less than predicted by some recent oceanic upper mantle models, indicating either a smaller separation of the discontinuities and/or greater shear velocity in the transition zone. Measurements of differential travel times between first-order reverberations and multiple ScS phases suggest that the former is more likely and are consistent with depths of 400 and 650 km for the transition zone discontinuities. Observations of first-order mantle reverberations can potentially provide unique constraints on lateral heterogeneity of the earth's mantle, especially within the transition zone.
Yield estimation from spectral amplitudes of direct P and P coda recorded by the wake island deep ocean hydrophone array
Authors: McCreery Charles S. 
Published: July 2021

Abstract
Spectral amplitudes of direct P and P coda between 0.5 and 6 Hz have been measured for 14 Eastern Kazakh test explosions using 8 hydrophones of the Wake Island Array, and a new model for these data has been developed to estimate relative yields of those explosions. Each log spectral amplitude is considered to be the sum of four parameters and an error term. Three parameters are frequency-dependent and represent: (1) the average Eastern Kazakh spectrum at the Wake Island Array; (2) the spectral shape characteristics unique to each event; and (3) the station or hydrophone corrections. The fourth parameter represents relative yield. A total of 346 parameters, including the 14 relative yields, were needed to model all 901 spectral amplitudes that were measured, and first-order linear regression techniques were used to invert the data for these parameters. Standard deviations of the computed relative yields are very small, averaging only 0.015 mb units. Deviations between the relative yields and their corresponding relative NEIS body-wave magnitudes, however, are larger, averaging 0.14 mb units. This difference is interpreted to be an indicator of the level of inhomogeneity in the worldwide pattern of energy radiated from Eastern Kazakh tests. There is evidence that this pattern can be correlated with the precise epicentral location of each explosion within the test site and is due to focusing and defocusing near the source. It is proposed that the yield of a large explosion might be disguised by siting the explosion at a location that selectively defocuses energy towards continents where most seismic stations are located. The precision with which a relative yield is determined from the data of any single hydrophone averages 0.035 mb units. Thus, the model appears to provide a very stable measure of yield. Errors associated with frequencies greater than 2 Hz are only slightly greater than errors associated with frequencies less than 2 Hz, verifying the utility of using the higher frequencies observed in direct P and P coda to estimate yield.
Surface effects and tectonic setting of the 13 December 1982 North Yemen earthquake
Authors: Plafker George , Agar Robert , Asker A. H. , Hanif M. 
Published: July 2021

Abstract
The North Yemen earthquake (Mb = 6.0) of 13 December 1982 is the first earthquake in the southern Arabian Peninsula known to be accompanied by surface displacements. The extensive destruction and loss of lives resulted entirely from widespread collapse of unreinforced masonry and mud brick structures; maximum Modified Mercalli intensity was probably VII to VIII. The only surface manifestation of tectonic activity was the occurrence of earthquake-related extensional ground cracks in the epicentral region. The cracks occur mainly in four relatively continuous north- to northwest-trending linear zones that range from a few hundred meters to 15 km in length and in irregular areas of polygonal extension cracks. The area within which the cracks occur is 22.5 km long by about 10 km wide. Continued dilation across some cracks was measured almost 1 month after the main shock. Seismicity and active volcanism in this region are inferred to reflect slow extension of the southwestern margin of the Arabia plate perpendicular to the Red Sea spreading axis.
Wave conversions from earthquakes and a new velocity model for the South Carolina coastal plain
Authors: Rhea Susan 
Published: July 2021

Abstract
Phase conversions from P to SV and from SV to P occur at a high impedance boundary near the surface in Charleston, South Carolina. Four arrivals (P, converted P, converted S, and S) are observed on three-component records of earthquakes in this area. Using arrival-time differences between paired arrivals of direct and converted phases, a shallow surface layer Vp/Vs ratio of 2.9 was determined. Applying the Wadati method to travel times derived at the base of the surface layer yields a Vp/Vs ratio in deeper layers of 1.73. Relocating earthquakes using this more appropriate velocity structure for direct and converted shear waves alters hypocentral parameters such that epicenters diverge and depths converge. It is inferred that these relocated earthquakes are not exclusively associated with a single seismogenic fault.
Експериментальне дослідження стійкості підкріплених циліндричних оболонок при осьовому стисканні
Authors: Todchuk Volodymyr 
Published: July 2021

Мета: показати реальний вплив початкових недосконалостей на верхнює критичне навантаження циліндричних оболонок. Метод: Аналіз експериментальних даних. Результати: У статті представлені результати експериментальних досліджень стійкості циліндричних оболонок, підкріплених стрінгерами з початковими несовешенствамі форми, при осьовому стисненні. Проведено детальний аналіз експериментальних даних. Зроблено висновок про стійкість циліндричних оболонок. Дано рекомендації щодо напрямків подальших досліджень. Обговорення: велика різниця між експериментальними і теоретичними осьовими критичними навантаженнями циліндричних оболонок змусила дослідників шукати причини цієї відмінності. Вважалося, що однією з основних причин є наявність первинних дефектів в оболонках. Потім виникли сумніви в правдивості цього твердження. Були суперечливі думки. Виникла необхідність з'ясувати реальний вплив початкових дефектів на стійкість циліндричних оболонок.