bluuebunny/crossref_metadata_2025_split huggingface dataset:
Peru earthquake of May 31, 1970; engineering geology observations
Authors: Cluff Lloyd S. 
Published: September 2021

abstract
At 3:23 p.m. local time, on May 31, 1970, an earthquake of magnitude 7 ¾; occurred approximately 15 miles off the coast of Peru, west of Chimbote. It is estimated that the earthquake took the lives of 70,000 people, caused 50,000 injuries, destroyed roughly 200,000 homes and buildings, and left approximately 800,000 people homeless.
Within the affected region, roughly 40,000 square miles, many villages were almost totally destroyed and several were swept away. The single, most devastating event was the large debris avalanche that originated from the north peak of Huascaran, falling 12,000 ft and traveling 7 miles at an average speed of roughly 200 miles per hour to destroy the villages of Yungay and Ranrahirca. Field evidence strongly suggests that the area near Yungay and Ranrahirca will continue to be overridden by future debris avalanches.
Damage resulting from vibrational effects was severe. The most intense vibrational damage occurred along the coast at Chimbote and Casma where most houses and buildings of adobe construction were destroyed or severely damage. Severe vibrational damage also occurred in cities and villages located in the Santa Valley at epicentral distances ranging from 60 to 100 miles inland.
The single, most important factor contributing to the massive damage from ground motion was the poor adobe construction. The influence of the underlying geological and soil conditions was an important secondary factor.
Unusual accelerograms recorded at Lima, Peru
Authors: Cloud William K. , Perez Virgilio 
Published: September 2021

abstract
Accelerograms recorded in downtown Lima, Peru, appear to have two unusual characteristics in comparison with accelerograms recorded outside of Peru. First, the predominant period is approximately 0.1 sec, regardless of epicentral distance of earthquakes. Second, maximum accelerations are high in relation to epicentral distance of major earthquakes. For example, 0.40 g at an epicentral distance of over 160 km during the magnitude 7.5, October 17, 1966, earthquake, and 0.13 g at an epicentral distance of over 320 km during the May 31, 1970, earthquake, whose magnitude was rated by various agencies from 7.6 to 7.8. If the source of energy at Lima were closer than the earthquake epicenters, the accelerograms would appear less unusual, but there is no proof that this is the case.
The effect of Yucca Fault on seismic wave propagation
Authors: Hays Walter W. , Murphy John R. 
Published: September 2021

abstractYucca Fault is a major structural feature of Yucca Flat, a well-known geological province of the Nevada Test Site (NTS). The trace of the Fault extends north-south over a distance of about 32 km. The fault plane is nearly vertical and offsets Quaternary alluvium, Tertiary volcanic tuffs and pre-Cenozoic basement rocks (quartzites, shales and dolomites) with relative down displacement of several hundred feet on the east side of the fault. Data recorded from the CUP underground nuclear detonation in Yucca Flat typify the effect of the fault on near-zone (i.e., inside 10 km) seismic wave propagation. The effect of the fault is frequency dependent. It affects the frequency components (3.0, 5.0, 10.0 Hz) of the seismic waves which have characteristic wavelengths in the order of the geological discontinuity. Little or no effect is observed for low-frequency components (0.5, 1.0 Hz) which have wave-lengths exceeding the dimensions of the geological discontinuity. The effect of the fault does not represent a safety problem.
A theory for pressure radiation from ocean-bottom earthquakes
Authors: Richards Paul G. 
Published: September 2021

abstract
An ocean-bottom earthquake is modelled as motion of a rigid boundary adjacent to a fluid half-space. The resulting water pressure, for a wide class of source motions, is obtained exactly as a convolution integral. The kernel has a physical interpretation as a fundamental solution, and may be obtained explicitly by a Cagniard method. A worked example is given, in which the convolution is carried out, and steps in pressure are found which are approximately equivalent to an extra 200 m in the water column.
Detection of interfering Rayleigh waves at LASA
Authors: Capon Jack , Evernden Jack F. 
Published: September 2021

abstract
The problem of detecting one Rayleigh wave in the presence of the coda of another larger Rayleigh wave is considered. A detection method is proposed in which a high-resolution, wave number analysis technique is applied to prefiltered data from the Large Aperture Seismic Array (LASA) to determine the direction of arrival of the 40-sec-period Rayleigh-wave group at the appropriate arrival time. The performance of this detection method is considered in great detail. A necessary concomitant of the study of the detection method is the determination of the phases which comprise the coda. It is shown that one component of the coda consists of fundamental-mode Rayleigh waves which propagate along multiple paths and may be caused by either reflections at continental margins or diffraction effects. As has been demonstrated many times, the coda is shown to consist also of fundamental-mode Rayleigh waves which have propagated around the Earth in the direction of the back azimuth. Multiply reflected P and S waves, which propagate primarily in the upper mantle, are detected easily.
Surface waves on multilayered anelastic media
Authors: Schwab Fred , Knopoff Leon 
Published: September 2021

abstract
Surface-wave dispersion computations for perfectly-elastic media are generalized to allow dispersion-attenuation computations for anelastic media. In each layer, frequency-dependent, body-wave phase velocity and attenuation are taken into account directly. For a 50-layer structure, a single Love-wave dispersion-attenuation point can be determined in 0.28 sec—the phase velocity containing about 16 significant figures and the phase attenuation about 14, where 16 decimal digits are used in computations on an IBM 360/91 computer. Accuracies of 7 significant figures can be obtained in 0.13 sec. To this latter accuracy, the determination of the Love-wave dispersion and attentuation for an anelastic structure takes about 6.8 times the amount of computation time required to compute the dispersion for the comparable perfectly-elastic structure.
The technique is applied to Love waves on an anelastic, radially heterogeneous sphere. A family of low-velocity zone channel waves is identified and investigated. A possible explanation for the disappearance of Lg across large oceanic paths is offered.
The destruction of Bahia Solano, Colombia, on September 26, 1970 and the rejuvenation of a fault
Authors: Ramírez J. E. 
Published: September 2021

abstract
On September 26, 1970, three main earthquakes, followed by over 300 aftershocks, caused havoc in Puerto Mutis and neighboring towns on the Pacific Coast of the Department of Chocó, Colombia. It was the first time in the seismic history of Colombia that an old fault showed clear signs of rejuvenation. The total earthquake damage is calculated as $200,000. Although no one was killed, and only two people injured, 39 per cent of a total of 287 houses collapsed completely, and one-third of the 2,400 frightened inhabitants of Puerto Mutis were evacuated through the good offices of the Navy and Air Force, by air and sea, these being the only means of transport between Puerto Mutis and the interior of Colombia.
Most of the hypocenters were normal. However, the three main shocks of September 26 had depths of about 10 km only. They took place at 12h02m29s and 14h57m02s on September 26 and at 03h38m36s on September 27 (G.M.T.). These earthquakes were felt in the central and northwestern part of the Republic and caused minor damage in the nearby towns of the sea coast.
Overestimation of epicentral distances for earthquakes in the middle-America region from Ann Arbor, Michigan, seismograms
Authors: Chander Ramesh , Fountain David M. 
Published: September 2021

abstract
A re-examination of Ann Arbor, Michigan (AAM), seismograms for 18 earthquakes occurring in the middle-America region (between latitudes 5° and 20°N and longitudes 80° and 105°W) during 1967 and 1968 reveals that, on the long-period seismograms, more than one distinct arrival is recorded within 30 sec of the Jeffreys-Bullen (J-B) S arrival time. The earliest of these arrivals, at the J-BS time, has the smallest amplitude. For earthquakes of magnitude (mb) smaller than about 5.5, the amplitude of the arrival at the J-BS time on the AAM long-period seismograms (magnification 1,500) is so small that it is frequently overlooked during routine interpretation of seismograms. In such cases, one of the subsequent arrivals is interpreted as the S phase, and the epicentral distances are overestimated by 3° to 5° using J-BP and S tables. Examination of seismograms published in the literature suggests that epicentral distances of small magnitude earthquakes occurring in the middle-America region may be overestimated at other North American stations during routine interpretation of seismograms using J-BP and S tables.
Seismicity of northern and central California, 1965-1969
Authors: Bolt Bruce A. , Miller Roy D. 
Published: September 2021

abstractDetailed seismicity (M ≧ 2.5) of northern and central California for 1965-1969 is analyzed. The largest earthquakes were nine with magnitudes 5.0 &lt; M &lt; 6.0. Since the interval, 1962-1965, seismic activity has increased north of Corralitos on the San Andreas fault. Seven shocks were located in the western reaches of Monterey Bay. The histogram of focal depths (d) for the coast ranges shows all d &lt; 16 km and 50 per cent with 0 &lt; d &lt; 5 km.North of Cape Mendocino, the new Fickle Hill telemetry station shows that within 30 &lt; Δ &lt; 85 km of FHC, (a) only 15 per cent of recorded earthquakes (M ≧ 2.5) has M &gt; 3.0 and (b) an average of 14 earthquakes (M ≧ 2.5) occurs each month. Some foci are as deep as 25 km in this region.For northern California, the linear recurrence law gives b = 0.78 ± 0.04, slightly less than southern California. For the coast ranges, b = 1.00 ± 0.04. The water loading of Oroville reservoir in 1967-1968 has not been associated with increased seismicity in the area. On the present homogeneous data, a statistical t-test shows that the short-term occurrence rate of northern California earthquakes was not altered by large underground nuclear tests in Nevada.
Structures in earth noise beyond twenty seconds—a window for earthquakes
Authors: Savino John , McCamy Keith , Hade George 
Published: September 2021

Abstract
The nature of earth noise in the period range 20 to 130 sec has been investigated at the deep (543 m) mine observatory and at a temporary surface installation at Ogdensburg, New Jersey, and its structure, in part, explained. The earth noise spectrum displays a pronounced and stable minimum between 30 and 40 sec, thought to be a transition between the swell-generated microseisms at periods less than 30 sec and nonpropagating ground motion of atmospheric origin at periods greater than 40 sec. We estimate the yearly mean amplitude at 35 sec to be 0.5 mμ/mHz, which is 100 times smaller than estimates of the mean amplitude of the 5- to 9-sec microseisms. At periods greater than 40 sec, the noise spectrum rises at 12 to 14 db/oct. Above 30 sec, the earth noise is quite stable, varying by no more than a factor of 3 over a year with higher levels in the winter and lower levels in the summer. By contrast, microseisms with periods less than 20 sec can change by a factor of 10 to 100 in a few days. The shape and amplitude of the earth noise spectrum beyond 20 sec, as well as its attenuation with depth, can be explained by a model of atmospheric pressure cells loading the Earth on equal-area sectors. There is a secondary source of background disturbance—the long-period coda of earthquakes. These higher-mode free oscillations are excited by relatively small events (mb = 5.8) and can dominate the background for as much as 10 per cent of the time during active periods.
The structure and stability of the earth noise spectrum at these longer periods allows an important improvement in seismometer design. By shaping the response of the three-component set of long-period high-gain seismographs to resemble the inverse of the mean noise spectrum, the instruments record approximately 10 times as many long-period body and surface waves as the standard long-period seismographs. The elevated signal-to-noise ratio in the 30- to 40-sec window decidedly improves the sensitivity of seismic source-type discriminants.
Some discriminatory characteristics of earthquakes near the Kariba, Kremasta, and Koyna artificial lakes
Authors: Gupta Harsh K. , Rastogi B. K. , Narain Hari 
Published: September 2021

abstractThe behavior of earthquakes near the artificial lakes at Kariba, Kremasta, and Koyna, where earthquakes of magnitude exceeding 6 have occurred, is examined. Foreshock-aftershock patterns of these earthquake sequences correspond with Mogi's type II model, whereas the normal earthquakes of these regions belong to type I. Three similar relations could be fitted in the time distribution of aftershocks of the main earthquakes. Quite contrary to normal earthquakes, foreshock b values are found to be comparable with the aftershock b values in the frequency-magnitude relations. Focal mechanisms of the largest earthquakes of these sequences have been determined and compared. Dip-slip components of the motion are such that the lakes are situated on the downthrown blocks. These regions are characterized by a volcanic past and the presence of rocks such as limestones and red boles which are easily affected by water. These findings are useful in distinguishing the reservoir-associated earthquakes from normal earthquakes and suggest that the artificial lakes are responsible for changing the mechanical properties of the strata and releasing the accumulated strains.
Stress estimates for the San Fernando, California, earthquake of February 9, 1971: Main event and thirteen aftershocks
Authors: Trifunac M. D. 
Published: September 2021

AbstractThe strong earthquake ground motion recorded in the center of and above the fault plane is combined with field evidence of faulting and instrumental studies of aftershocks to deduce stresses during and after the San Fernando earthquake of February 9, 1971. Stress computations based on Brune's near-field, shear-wave spectra, peak velocity of ground motion, energy calculated from the strong-motion record, and a model of circular dislocation give mutually consistent stress estimates, which suggest that the effective stress operating during the earthquake was approximately 100 bars, while during the earthquake it dropped several tens of bars. The energy of the main event is estimated to be 1022 dyne cm.Thirteen aftershocks, recorded during the first 6 min, were associated with stress drops ranging from 10 to 500 bars, these events clustering along the north-eastern end of the dislocation surface.The strong-motion accelerograms provide invaluable data for detailed investigations of the pattern of earthquake energy release during and immediately after an earthquake. Used for the first time in this study, strong-motion accelerograms gave an excellent picture of stress history and migration of seismic activity during the first 6 min.
Historical and recent seismic activity in South Carolina
Authors: Bollinger G. A. 
Published: September 2021

Abstract
The seismic history of South Carolina is dominated by the great Charleston earthquake of August 31, 1886. In addition to having several unusual aspects (region essentially free from shocks for preceding 200 years, large felt area, dual epicenter points, “low intensity zone” in West Virginia), that intensity X event seriously perturbed the seismic regime of the area for at least the following 30 years. Of 438 earthquakes reported to have occurred in the state between 1754 and 1971, 402 have been in the Charleston-Summerville area. The remaining 36 shocks form a southeasterly-trending zone of activity that is transverse to the structural grain of the Appalachians.
For the 60 shocks assigned an intensity value (1886-1971), a recurrence relationship between the number of earthquakes “N” of maximum intensity “I0” was found to be log N = 0.52-0.31 I0 for IV ≦ I0 ≦ VIII. This corresponds to a “b” value of 0.5 ± 0.1 in log N versus M relationship assuming M = 1 + (2/3)I0. These data suggest a frequency of seismic activity comparable to that reported for the New Madrid seismic zone.
Three months of microearthquake monitoring in the Charleston area during the summer of 1971 yielded 505 hr of low-noise data. Sixty-one earthquakes, primarily in swarm occurrence, were recorded. An h value of 1.8 ± 0.5 was determined for these microshock events. This value is similar to that previously observed for a swarm sequence in New Jersey.
Four shocks occurred in the state during 1971. Three of these events (May 19, July 31, August 11) were in the central part of the state near Orangeburg, while the third event (July 13) was near Seneca in northwestern South Carolina. All three events had 3.0 &lt; ML &lt; 4.0. Similar episodes of three or four shocks in 1 year happened in 1956 and again in 1965. The Orangeburg area had, according to historical data, been previously free of earthquake epicenters.
Statistical analysis of microearthquakes near Socorro New Mexico
Authors: Singh Surendra , Sanford Allan R. 
Published: September 2021

Abstract
Five year of data for microearthquakes originating in a small volume of crust near Socorro, New Mexico were analyzed to determine the temporal behavior of (1) the average number of shocks per unit time, (2) the slope of the earthquake-frequency graph, and (3) the energy release. Additional studies were made to establish the distribution function for the times observed between successive earthquakes and the hazard function.
The temporal behavior of the mean number of shocks per unit time and the slope of the earthquake-frequency law were found to be quite erratic until the observation period was increased to 2 or more years (more than 200 shocks detected). Large numbers of shocks generally produced large energy release but the converse was not always true. The distribution function for the observed interarrival times between events was found to differ significantly from exponential and normal distribution functions. This observation, along with the behavior of the hazard function, indicates that the microearthquake sequence studied did not follow a Poisson process.
Calculated compressional-wave arrivals from underground nuclear detonations
Authors: Murphy John R. 
Published: September 2021

Abstract
Analytical expressions have recently been derived by Červený (1965) for the principal waves generated at a plane interface between two elastic solids attributable to a spherical compressional wave arriving at an arbitrary angle of incidence. These results are generalized to incorporate a nuclear seismic source function acting in a multilayered, linearly inelastic half-space. Using a seismic source function appropriate for the nuclear event BOXCAR and an approximate crustal model, the particle velocity profiles corresponding to those compressional-wave types which are routinely identified on measured, near-field seismograms are calculated and compared with the observed data for this event. These comparisons indicate that the peak amplitudes of some important compressional-wave types can be predicted with reasonable accuracy using a relatively simple model of the seismic transmission path.
Influence of infill walls on building frames: An example from the May 12, 1971 earthquake in Turkey
Authors: Uzsoy Safak Z. , Citipitioglu E. 
Published: September 2021

Abstract
The Burdur earthquake of May 12, 1971, although only of moderate-sized magnitude, was responsible for much loss of life and property damage. The presence of full-height and/or partial-height infill walls in some reinforced concrete-framed structures completely altered the behavior of the frame elements. Damage to a four-story, reinforced concrete school building is described, as a typical example of this kind of failure.
Earthquakes caused by underground nuclear explosions on Pahute Mesa, Nevada Test Site
Authors: Hamilton R. M. , Smith B. E. , Fischer F. G. , Papanek P. J. 
Published: September 2021

Abstract
The underground nuclear explosions BENHAM, PURSE, JORUM, and HANDLEY, detonated on Pahute Mesa, initiated earthquake sequences lasting approximately 70, 10, 20, and 60 days, respectively. Earthquakes of magnitude 2.0 or larger in these sequences numbered 2012, 24, 159, and 231, respectively; earthquake magnitudes were all less than 5. The explosion PIPKIN, also detonated on Pahute Mesa, had no apparent effect on seismicity. Ninety-four per cent of the earthquakes with well-determined focal depths occurred at depths shallower than 5 km, and 95 per cent of the located earthquakes were within 14 km of ground zero of the preceding explosion. There is no evidence for explosion-stimulated earthquake activity extending outside the area of Pahute Mesa. The spatial distribution of earthquakes seems to be largely controlled by geological structure; however, the epicenter distribution can be correlated with observed fault movement only for aftershocks of HANDLEY. Fault-plane solutions indicate predominant dip-slip movement in the northern part of the Pahute Mesa area for aftershocks of BENHAM, JORUM, and HANDLEY. In the southern part, dextral strike-slip movement was found for aftershocks of BENHAM and HANDLEY. The frequency-magnitude relations are similar for earthquakes following BENHAM, PURSE, JORUM, and HANDLEY.
Rock dilatancy and strain accumulation near Parkfield, California
Authors: Cherry J. T. , Savage J. C. 
Published: September 2021

Abstract
The postearthquake deformation of a geodetic network which spans the zone of rupture of the 1966 Parkfield earthquake is not pure right-lateral shear as might be expected but rather is primarily an east-west extension. This deformation is consistent with that predicted by a dilatancy model.
Tectonic strain-release characteristics of CANNIKIN
Authors: Toksöz M. Nafi , Kehrer Harold H. 
Published: September 2021

abstractThe tectonic strain-release characteristics of the CANNIKIN nuclear explosion are determined from seismic surface waves and static strain changes associated with the event. The source is considered to be the superposition of an isotropic explosion component and a tectonic component consisting of a fault of arbitrary orientation. From Love-to-Rayleigh-wave amplitude ratios, the strength of the tectonic component (F) relative to the explosion is determined to be 0.6. The parameters of the fault are found to be consistent with nearby faults and displacements observed following the event. Reasonable agreement with observed static strains is also obtained with a fault 20 km long, but of different orientation. Discrepancies between observed and theoretical strains indicate the complexity of strain readjustment. The relatively small amount of tectonic strain release associated with CANNIKIN is probably due either to the low rigidity of the medium or to low ambient stresses near the surface.
Effect of earth layering on earthquake displacement fields
Authors: Chinnery Michael A. , Jovanovich Dushan B. 
Published: September 2021

abstract
The displacement fields due to a very long vertical strike-slip fault are calculated for earth models consisting of two layers over a half-space. It is shown that if zones of low rigidity are present beneath the Earth's surface, they will result in an amplification of the displacement field observed at the Earth's surface. The amount of amplification depends both on the structure and the distance from the fault. If thin soft layers exist in the upper mantle, it is shown that they will have a very strong effect on the observed displacements. It may eventually be possible to use static observations at the surface to detect such layers.