bluuebunny/crossref_metadata_2025 huggingface dataset:
Amplitudes of horizontally refracted Love waves
Authors: Gregersen S. , Alsop L. E.
Published: September 2021

abstract

Love-wave transmission and reflection are studied numerically for a vertical interface between two layered models. By a new method of approximation, the transmission and reflection coefficients can be computed for propagation directions differing from normal incidence. We consider the Love mode as a superposition of propagating plane SH waves in a surface layer and an inhomogeneous plane SH wave falling off with depth in the half-space below. The method is based on satisfying all boundary conditions on the vertical interface and computing the coupling between the interface stress displacement pattern and the transmitted/reflected Love modes. The computations are done rapidly on a small computer.

The transmission coefficients change rapidly with period. For propagation from ocean to continent, they increase with decreasing periods in the interval 60 to 20 sec. The opposite trend is found for propagation from continent to ocean. The amplitude transmission coefficient curves show almost no dependence on the angle of incidence except for large angles. The fine structure of the curves is similar to that for plane SV waves incident on an interface between two homogeneous elastic media. Love-wave amplitude observations at OBS on the ocean bottom northwest of San Francisco and at BKS in Berkeley also show these trends as a function of period and of angle of incidence.
A dislocation model for the Parkfield earthquake
Authors: Anderson John
Published: September 2021

abstract

Using the Haskell formulation relating the displacement time history on a fault surface to the displacement time history at a point in an infinite space, a propagating dislocation has been used to model the Parkfield, California, earthquake of June 27, 1966. Reasonable agreement is obtained with displacement from doubly integrated accelerograms using a model with a propagation velocity of 2.8 to 3.0 km/sec, displacement of 25 cm, and particle velocity at the fault of greater than 10 cm/sec. From the model, trigger times of the accelerometers can be estimated and are up to 4 sec after the first P arrivals. A high-frequency phase on the vertical accelerogram can be related to P waves originating from irregularities of the rupture process. Calculation of surface-wave arrival times shows that (1) surface waves may be important on the displacement records before body-wave arrivals ended and (2) when the observations diverge from the model, it could be due to surface waves.
Evidence for postearthquake slip in the Fairview Peak, Dixie Valley, and Rainbow Mountain fault areas of Nevada
Authors: Savage J. C. , Church J. P.
Published: September 2021

abstract

The U.S. Coast and Geodetic Survey ran first-order level surveys in 1934, 1955, and 1967 across the fault zone associated with the 1954 sequence of earthquakes at Rainbow Mountain (M = 6.6 and 6.8), Dixie Valley (M = 6.8), and Fairview Peak (M = 7.1) in Nevada. The difference between the 1955 and 1967 surveys clearly shows distinct anomalies over distances of several kilometers at all but one of the fault scarps mapped after the 1954 earthquakes. The anomalies resemble deformation produced by normal faulting extending to a depth of at least several kilometers and, consequently, are interpreted as implying continued slip on the earthquake faults in a period beginning at least 6 months after the earthquake. At the Fairview Peak Fault, the inferred postearthquake slip is about 5 per cent of the displacement observed at the time of the earthquake. The difference between the 1955 and 1967 surveys suggests an overall tilt of 2 mm/km down to the west extending over a 90-km distance crossing the fault zone. The difference between the 1934 and 1955 surveys suggests an overall tilt of 0.8 mm/km down to the east extending over a 200-km section. However, these regional tilts might be due to unusually large systematic errors in the level surveys. Gravity and seismic-refraction surveys indicate that the region as a whole is isostatically compensated, although the mountain ranges and intervening basins are not individually compensated. Thus, the regional elevation changes, if they exist, cannot be accounted for by isostasy.
A seismic refraction survey along the southern Rocky Mountain Trench, Canada
Authors: Bennett G. T. , Clowes R. M. , Ellis R. M.
Published: September 2021

abstract

An unreversed seismic refraction profile has been recorded in the southern Rocky Mountain Trench from 50°N to 53°N. Using blasts from two open-pit coal mines, 44 recordings were obtained over a distance of 540 km. These were combined into a record section in which instrument and shot variations were included to show amplitude variations along the profile. Interpretation involved Weichert-Herglotz integration of p-delta curves to obtain a velocity-depth structure and the calculation of synthetic seismograms for comparison with the record section.

Refractors with apparent P-wave velocities of 6.5 to 6.6 km/sec and 8.22±0.04 km/sec are interpreted as the surface of the Precambrian basement and the Mohorovičić discontinuity, respectively. A prominent travel-time delay associated with the 6.5 km/sec branch is interpreted in two possible ways. One explanation is the existence of a crustal low-velocity zone beginning 3 km beneath the basement, depth of 6.5 km, and having a depth extent of 9 to 15 km with associated velocities of 5.5 to 6.1 km/sec, respectively. The second interpretation proposes a high-angle crustal fault near Radium. The resultant model has an up-fault structure with depth to basement of 6.5 km and depth to the M-discontinuity of 51 km and a down-fault structure with corresponding values of 12.1 and 58 km. On the basis of gravity and magnetic trends, the fault strikes northeasterly. In either interpretation, a velocity gradient is present in the lower crustal section and the thickness of the crust is in excess of 50 km. Analysis of larger amplitude arrivals shortly after the Pn phase is consistent with the interpretation of a low-velocity zone, 8 km beneath the M-discontinuity and approximately 7 km thick.
Pulse distortion and Hilbert transformation in multiply reflected and refracted body waves
Authors: Choy George L. , Richards Paul G.
Published: September 2021

abstract

Many seismic body waves are associated with rays which are not minimum travel-time paths. Such arrivals contain pulse deformation due to a phase shift in each frequency component. For sufficiently high frequencies, the phase shift each time a ray touches an internal caustic is π/2 and frequency-independent. The distorting effect of a frequency-independent phase shift is successfully observed in seismograms from events in several regions. The data examined are long-period (T > 9 sec). They include deep earthquakes (depth > 500 km), in which a series of well-separated S phases (S, sS, SS and sSS) are available. These show that the wave form of SS, which has been distorted in propagation through the Earth, can be derived from the wave form of sS, which is not distorted. Shallow events, in which multiple S phases overlap, also exhibit behavior predicted by phase distortion. Rays supercritically reflected or refracted at a discontinuity in the Earth also suffer a constant phase shift, which in general can have any value. An important case is SKKS: its undistorted wave form resembles that of SKS, which has a minimum travel-time path.

Without exception, all the distorted wave forms bear little or no resemblance to the original wave form. That is, neither the first arrival of energy nor the subsequent relative position of peaks and troughs on a distorted wave form appear at the ray theoretical times. Thus, T-Δ curves constructed by choosing arrival times to correspond to the first arrival of energy may be biased. Similarly, doubt is cast on differential travel times chosen from first motions, or from averaging several points on what appear to be corresponding peaks and troughs of two wave forms. Some of the rays most important to seismology, in which the distortion phenomenon occurs, include P and S (where d2T/dΔ2 > 0), PKPAB, PP, SS, and SKKS. Removal of phase distortion in the data is computationally straightforward. By exploiting the resulting wave forms to full advantage in correctly picking arrival times, we may hope to improve velocity models of the Earth. It is shown that matched filtering to obtain differential travel times is appropriate for certain pairs of body waves if they are phase-corrected.
Crustal structure of the Baltic Shield beneath Umeå, Sweden, from the spectral behavior of long-period P waves
Authors: Leong Lap Sau
Published: September 2021

abstract

The method of spectral ratio response for crustal thickness determination beneath a receiving station, using long-period P waves of teleseismic events, has been applied. The purpose of this study is to investigate further the already well-depicted shield structure in Sweden beneath the WWSSN station at Umeå, the methodical procedure involved in this inversion problem, and possible sensitivity of the method to lateral variations of the shield area beneath the recording station. Teleseismic events from the Okhotsk Sea, Mongolia, and Hindu Kush regions are considered. Results suggest a value of 42 km for the two-layer crustal model beneath Umeå with possible lateral variations in velocity and/or dipping M-discontinuity surface to the east. It is proposed that a quantitative measure of the reliability of amplitudes and periodicity of peaks of the response ratios and indications of possible lateral anisotropy are obtained by treating the horizontal P-wave component both as a radial component of a three-component vector field and as being along the great circle through the epicenter and the receiving station.
From antimoment to moment: Plane-strain models of earthquakes that stop
Authors: Andrews D. J.
Published: September 2021

abstract

Some simple cases of the seismic gap model are examined in plane strain. Numerical solutions are found for near-field elastodynamic motion coupled to frictional sliding on a fault. Rupture velocity is specified, but the dynamic solution is otherwise dependent only on the initial state. The initial seismic gap is a non-uniformity of past slip on the fault plane. It is termed an antidislocation and is characterized by its antimoment and its energy. Sliding stops naturally in this model, even with uniform material properties. The moment of the calculated earthquake is dependent on the difference between the kinetic friction level and the background shear-stress level and is independent of rupture velocity. If initial states are scaled to have equal antimoments, and if the stress scale is normalized according to the initial energy, then the earthquake moment is nearly independent of the shape of the initial antidislocation. The ratio of radiation reaction stress (apparent stress) to weighted mean stress drop is 0.36±0.04 for all cases calculated. Non-dependence of earthquake moment on rupture velocity and the shape of the initial antidislocation is expected to carry over to three-dimensional cases. The final fault dislocation is smoother than the initial dislocation in every case calculated. Nonuniform friction or a nonplanar fault is required to get a dislocation rough enough to produce succeeding earthquakes.
Strong ground motion of the San Fernando, California, earthquake: Ground displacements
Authors: Hanks Thomas C.
Published: September 2021

abstract

Two hundred and thirty-four components of ground displacement are the basis of an investigation of long-period strong ground motion in southern California arising from the San Fernando, California, earthquake. The displacement data are obtained from the double integration of strong-motion accelerograms via the base-line adjustment and filtering operations routinely performed in the series “Strong Motion Earthquake Accelerograms”. These procedures can recover long-period data from strong-motion accelerograms with considerable accuracy. Many-station comparisons of displacement data for which the station spacing is small compared to the wavelengths of interest reveal that uncertainties in displacement are less than 1 cm in the period range 5 to 8 sec, 1 to 2 cm at periods near 10 sec, and 2 to 4 cm in the period range 10 to 15 sec, for a data sensitivity of approximately 7.6 cm/g. For limited variations in epicentral distance (R) and source-station azimuth (ϕ), ground displacements show a strong coherence; for wider variations in R and ϕ, many of the observed variations in the displacement wave forms are easily attributable to well-understood seismological phenomena. Seismic moment, source dimension, radiation pattern, rupture propagation, the development of surface waves and their subsequent dispersion, and azimuthal variations in the gross geological structure all appear to have first-order significance in fashioning the gross amplitude and frequency content of the displacement wave forms and in explaining observed variations with R and ϕ. The essential simplicity of these displacement wave forms offers considerable optimism that long-period strong ground motion can be realistically synthesized with advance knowledge of the earthquake source parameters and gross geological structure.
On correlation of seismoscope response with earthquake magnitude and Modified Mercalli Intensity
Authors: Trifunac M. D. , Brady A. G.
Published: September 2021

abstract

A quantitative measure of the Modified Mercalli Intensity Scale for earthquakes in the western United States has been developed by correlating the peak seismoscope relative displacement response, Sd, with the reported site intensity, IMM. This correlation can be approximated by

S ̄ d ( cm ) ≈ 1 49.2 10 0.288 I MM

for IMM ≦ VIII and is characterized by one standard deviation of about 0.7 S̄d. The data used in this study do not indicate an obvious type of dependence of Sd on local site conditions.

A method for computing the analog of the local earthquake magnitude, Mseismoscope, has been presented for possible use in strong-motion seismology and for scaling earthquakes by close-in measuremients, when other seismological instruments may go off scale.
Bear Valley, California, earthquake sequence of February-March 1972
Authors: Ellsworth William L.
Published: September 2021

abstract

The earthquake sequence of late February and March 1972 involved movement along the San Andreas fault and within the crustal wedge enclosed by the branching San Andreas and San Benito faults near Bear Valley, San Benito County, California. Activity was mainly confined to three distinct zones of strike-slip faulting: the short north-trending aftershock zone of the M 3.5 earthquake of February 22, 1972, the aftershock zone of the M 5.0 Bear Valley earthquake of February 24, 1972 located along the San Andreas fault, and the west-trending aftershock zone of the M 4.6 earthquake of February 27, 1972. The north-trending and west-trending zones lie between the two major splays of the branching fault system. Focal mechanism solutions from events in these zones are consistent with the transfer of horizontal, dextral displacement from the San Andreas fault to the San Benito, Paicines and Calaveras faults within the Bear Valley region. During the 18 months preceding the February 1972 sequence, the hypocentral regions of both the M 5.0 and M 4.6 shocks were characterized by concentrations of small earthquakes. Aftershock source areas of these two events progressively expanded during the course of the aftershock sequence. Estimates of the mainshock rupture surface for these events based on the distribution of aftershocks range over a factor of 4 owing to the irregular distribution of aftershocks and the rapid growth of the aftershock zone.
The origin of short-period precursors to PKP
Authors: Wright C.
Published: September 2021

abstract

An investigation of the origin of precursors to short-period PKP phases has been undertaken using 23 earthquakes recorded at the Yellowknife Array at distances between 123° and 143°. In particular, the pattern of slowness and azimuth changes with time has been examined for coherent bursts of energy occurring throughout the precursor wave train. These temporal changes demonstrate that the precursor energy is most satisfactorily explained by scattering from small inhomogeneities at the core-mantle boundary or in the lowermost mantle, both before P-wave energy enters the core and when it re-emerges into the mantle. Moreover, scattering before entry into the core seems to generate the larger amplitudes. The bulk of the data cannot be attributed to reflection or sharp upward refraction from velocity discontinuities within the lower part of the outer core, although there is some ambiguous evidence for a reflecting interface at a depth of about 4850 km.
Epicentral deformation based on the dilatancy-fluid diffusion model
Authors: Singh Shri Krishna , Sabina Federico J.
Published: September 2021

The dilatancy-fluid diffusion model of the earthquake mechanism implies deformation of the epicentral area. Based on a result in the theory of thermoelasticity, we present a method for computing such deformation. Details are given for a dilating sphere and a dilating infinite cylinder buried in an elastic half-space. Given the volumetric strain of the dilatant region, the deformation measurements could be used to estimate the magnitude of the impending earthquake. Alternatively, a constraint on the volumetric strain can be obtained from deformation measurements before earthquakes that are preceded by dilatancy.
Relationship of mine tremors to induced stresses and to rock properties in the focal region
Authors: McGarr A. , Spottiswoode S. M. , Gay N. C.
Published: September 2021

Focal coordinates for a suite of tremors associated with deep-level tabular mining were determined with uncertainties of about 35 m and the tremor positions were analyzed in terms of the stress field induced by mining in the immediate vicinity. All tremors occurred in a region of 300 m in extent and at depths near 3.1 km; their magnitudes ranged from −1.5 to 2.5. The source rock in this region has no groundwater, whatsoever. The two major factors governing the occurrence of tremors appear to be the change in the stress field from its virgin state and the strength of the rock. The positions of tremor foci coincide closely with the region where changes in the stress field due to mining are maximal. Most of the tremors were located in regions where the maximum principal stress induced by mining exceeded 1 kb or where the minimum principal induced stress was less than −160 bars, compressive stresses taken as positive. Nearly all of the tremors were located above the gold-bearing reef. Strength tests in uniaxial compression indicated that the rock above the reef is about 1.4 kb stronger than that below; Young's modulus is also higher for rock above the reef. These results suggest that tremors tend to occur in regions where the rock is capable of storing the most elastic strain energy before failure. Underground observations of shear failure indicate that tremors are the result of the rupture of previously intact rock. The fact that the majority of seismic foci occurred in regions where the stress field is calculated to be well below that required for rock fracture argues for the existence of localized residual stresses of large magnitude.
Surface strong motion associated with a stick-slip event in a foam rubber model of earthquakes
Authors: Archuleta Ralph J. , Brune James N.
Published: September 2021

In this paper, we present and interpret dynamic displacement data for a stick-slip event in a foam rubber model of earthquake faulting. Static displacement data are used to infer the stress drop of about 0.016 μ, where μ is the shear modulus. The rupture velocity 0.7 β, where β is the shear-wave speed, is also inferred from the data. The observed particle displacement and particle velocity data are compared with analytical and numerical predictions. Doppler focusing of energy by rupture propagation is clearly observed. No large transverse displacement pulse such as that observed at Station 2 of the Parkfield earthquake is observed. In addition to its value for testing analytical and numerical predictions, the laboratory model provides much needed information on the distribution of strong ground motion in the neighborhood of a fault and thus helps in the problem of microzonation for earthquakes.
A magnitude scale for local earthquakes in South Australia
Authors: Stewart Ian C. F.
Published: September 2021

To minimize dispersion in local magnitude estimates due to different instrumental bandwidths, a scale has been established to allow for the average source spectrum, geometrical attenuation, and frequency-dependent absorption. The data used to derive the scale parameters were from S waves recorded in South Australia from 1967 through 1970, in the frequency range 1 to 10 Hz, and for epicentral distances up to 5°. The magnitudes were mainly in the range 1.5 to 3.5. The local scale MN is given by

M N = 4.85 + log A g + 0.84 log Δ + 0.0003 f Δ / 2.3 − 2.89 log f + 2.45 ( log f ) 2 + c

where Ag mm is the ground amplitude at f Hz at Δ km epicentral distance, and c is a station correction.

The dispersion in observations of magnitude has probably been reduced by use of the scale to near the theoretical limits, allowing for possible source radiation patterns. The relationship of the scale to other measures of magnitude is uncertain, but MN may be approximately equivalent to the local Richter magnitude ML for the magnitude range (1.5 < ML < 3.5) commonly observed in South Australia.

The scle is limited in use to data in the ranges given above, for local earthquakes in South Australia. Modification is necessary before such a magnitude scale can be applied elsewhere or to different data ranges.
A source theory for complex earthquakes
Authors: Blandford R. R.
Published: September 2021

Earthquake source theories of Haskell, Brune, and Savage have been drawn upon to develop a description of an earthquake as a major slip accompanied by many smaller tensional and slip events. We find natural explanations of several previously unexplained observations, such as:

Robustness of the MS: mb discriminant,

P corner frequency higher than S corner frequency for shallow earthquakes,

High-frequency P/S amplitude ratio higher for shallow earthquakes than previous theories predict,

Increase of complexity as a function of third moment,

Small mb relative to MS for transform faults.

(This can also be explained by emergent short-period P wave forms or by a low-Q region underlying the source).

The theory predicts that MS:mb populations of earthquakes and explosions will not converge at small magnitudes. The theory also suggests that the standard interpretations of corner-frequency measurements can provide only a lower limit to fault-plane dimensions and, in combination with the moment, only an upper limit on stress drop.
The effect of oceanic sediments on surface-wave propagation
Authors: Weidner Donald J.
Published: September 2021

abstract

Several characteristics of oceanic surface waves can be altered by the presence of low rigidity sediments along the propagation path. Love and Rayleigh waves from mid-Atlantic ridge earthquakes bear many effects of oceanic sediments. The general absence of these surface waves for periods shorter than about 15 sec can be attributed to either attenuation or scattering in thin sediments. Thin sediments also disperse short-period Love waves. Sediments whose thickness exceeds about 2 km are responsible for removing surface-wave energy with periods up to 40 sec. These sediments also alter the particle motion of Rayleigh waves and are responsible for a complicated dispersion relation. These thick sediments substantially reduce the surface-wave phase velocity at periods in excess of 100 sec.
A technique for computing surface-wave properties
Authors: Massé Robert P.
Published: September 2021

abstract

A technique is presented which makes possible the calculation of total-path properties of surface waves which traverse any number of geological regions. Rayleigh- and Love-wave parameters which may be computed with the technique include phase- and group-velocity dispersion, travel time, matched filters, attenuation, quality factors, lateral refraction, and multipathing. The technique has applications both in research of Earth structure and in automatic signal processing.
Microearthquakes at Flathead Lake, Montana: A study using automatic earthquake processing
Authors: Stevenson Peter R.
Published: September 2021

abstract

A nine-station portable seismic net, 50 km in diameter, was operated for 50 days in late 1971 near Flathead Lake, Montana at the juncture of the southern extension of the Rocky Mountain trench and the northern section of the Intermountain Seismic Belt. During the time the net was in operation, 259 locatable earthquakes ranging in coda magnitude from 0.1 to 3.3 were recorded. The earthquakes fall in two source regions approximately 15 km apart. In the northern region, the focal depths average 5 km, while those in the southern region range from 5 to 12 km. During part of the recording period, the activity in the southern region defined a planar zone striking north-northwest with a dip of 70° to the east-northeast. The better-defined fault-plane solutions in the region suggest northsouth compression. A procedure for automatically picking the first arrivals with a computer was used in analyzing the data.
Spatial attenuation of intensities for central U.S. earthquakes
Authors: Gupta Indra N. , Nuttli Otto W.
Published: September 2021

abstract

Attenuation of ground motion in the central United States has to be determined principally using the Modified Mercalli (MM) intensity observations because of the absence of instrumental strong ground-motion data. Nuttli's previous studies of Mississippi Valley earthquakes indicate that higher-mode surface waves produce the largest ground motion except possibly in the near-field region. Particle velocity rather than acceleration correlates directly with intensity and the coefficient of anelastic attenuation has an average value of 0.10 per degree. Using data from isoseismals of the November 9, 1968, southern Illinois and the December 16, 1811, New Madrid, Missouri earthquakes and assuming a linear relationship between log(A/T) and MM intensity, attenuation is expressed by the equation, valid for I(R) ≧IV (MM), I ( R ) = I 0 + 3.7 − 0.0011 R − 2.7 log ⁡ R ; for R ≧ 20 k m where R is the epicentral distance in kilometers.

This relationship shows fairly good agreement with isoseismals of many large earthquakes in the central United States and may therefore be useful in providing realistic estimates of spatial attenuation and hence of design earthquakes for a given site. It can also be sometimes useful in estimating the epicentral intensity of an earthquake whose maximum intensity is not reliably known.
Seismicity of Northern Anatolia
Authors: Dewey James W.
Published: September 2021

abstract

Earthquakes of magnitude 5.0 and greater that occurred in 1930-1972 in northern Anatolia have been relocated in order to define more accurately the characteristics of recent seismicity. The revised epicenters were determined either by joint epicenter determination (JED) or singly, with travel-times modified by JED-calculated source-station adjustments. Calibration epicenters were assigned on the basis of published field studies of the earthquakes.

Many characteristics of the occurrence of magnitude 5.0 and greater earthquakes on the North Anatolian fault are similar to characteristics of small-earthquake seismicity on California's San Andreas fault. Earthquakes tend to be concentrated on or near particular sections of the North Anatolian fault, suggesting intrinsic differences in mechanical properties along the fault. The relocated epicenters support the hypothesis that fault rupture in large and great earthquakes will begin in regions of small and moderate earthquakes; the rupture of the large earthquake then propagates into sections of the fault that normally have a low level of activity.

From 1939 through 1967, seven earthquakes of magnitude 6.8 or greater ruptured the North Anatolian fault from east to west for a distance of 800 km. Several sections of the fault zone were active before the occurrence of the large earthquakes of 1939-1967. Foreshock activity also extended tens of kilometers away from the fault zone. The time intervals between successive magnitude 6.0 or greater earthquakes on the fault are not consistent with a constant velocity of source migration; a model is proposed here in which these time intervals are equal to the duration of nonelastic effects precursory to the earthquakes.

In western Turkey, the burst of normal-fault earthquakes in 1969-1970 was concentrated in distinctly separated source areas. The distribution of aftershocks to the earthquake of March 28, 1970 suggests that the surface fault scarps accompanying this earthquake are a distorted representation of the normal fault plane at depth.
The Kinnaur earthquake of January 19, 1975: A field report
Authors: Singh S. , Jain A. K. , Sinha P. , Singh V. N. , Srivastava L. S.
Published: September 2021

abstract

On January 19, 1975 an earthquake of magnitude 6.8 occurred in the border districts of Himachal Pradesh, India. The earthquake caused considerable loss of life and varying degrees of damage to construction in the area. Traditional and recent buildings suffered extensive damage. Landslides, rock falls and avalanches caused considerable damage to the Hindustan-Tibet road. Extensive fissures in the ground developed at the epicenter. Greatest damage was noted along the N-S trending Kaurik-Chango fault following the Parachu and Spiti river valleys, suggesting its genetic interrelationship with the earthquake.
Local changes of sea level before large earthquakes in South America
Authors: Wyss M.
Published: September 2021

abstract

Vertical movements of the crust along the South American west coast are estimated from mean annual sea level (MASL). At an average distance of 400 km, 13 stations recorded sea level more or less continuously since 1941. The standard deviation of MASL from 20-year means is typically about 3 cm. Using reference stations reduces the standard deviation to 0.5 to 1.5 cm and therefore elevation changes of 3 cm can be resolved with 99 per cent confidence, if they last for more than 5 years. At Chimbote (Peru) uplift of about 5 cm was recorded in 1961. Six and nine years later the 1966 and 1970 Peru earthquakes (M = 7.6 and 7.8) occurred at distances of 130 and 23 km, respectively. An uplift of about 3 cm appears to have preceded the Antofagasta earthquake (M = 6.8) by 6 years. At 100 km north of the 1960 Chile rupture (M = 8.6) sea level remained unchanged between 1955 and 1970. Because all tide gauge stations in South America are located in active tectonic areas it is difficult to identify small land elevation changes by comparison with reference stations.
Preliminary empirical model for scaling Fourier Amplitude Spectra of strong ground acceleration in terms of earthquake magnitude, source-to-station distance, and recording site conditions
Authors: Trifunac M. D.
Published: September 2021

abstract

An empirical model for scaling Fourier Amplitude Spectra of strong earthquake ground acceleration in terms of magnitude, M, epicentral distance, R, and recording site conditions has been presented. The analysis based on this model implies that:

It has been shown that the uncertainties which are associated with the forecasting of Fourier amplitude spectra in terms of magnitude, epicentral distance, site conditions, and component direction are considerable and lead to the range of spectral amplitudes which for an 80 per cent confidence interval exceed one order of magnitude. A model has been presented which empirically approximates the distribution of Fourier spectrum amplitudes and enables one to estimate the spectral shapes which are not exceeded by the presently available data more than 100 (1 - p) per cent of time where p represents the desired confidence level (0 < p <1).
Seismic study of earthquakes in the Lake Mead, Nevada-Arizona region
Authors: Rogers A. M. , Lee W. H. K.
Published: September 2021

abstract

A nine-station telemetered array was installed around the Boulder Basin portion of Lake Mead, Nevada-Arizona. During 112 years of monitoring, approximately 1,360 events were detected in the magnitude range −1.0 ≦ ML ≦ 2.9, and half this number were locatable. Many of the events, which ranged in depth from 0 to 13 km, can be associated with mapped faults. In particular, epicenter lineations clearly indicate activity on portions of steeply dipping faults on the east side of Boulder Basin, which generally confirms Carder's earlier work (Carder, 1945, 1948, 1970). The strike of these faults is approximately north. Focal mechanisms are in agreement with this strike and show right-lateral motion on near-vertical faults. The tension axis for this solution is oriented northwest-southeast in agreement with the stress pattern for other parts of the Basin and Range Province.

Although lake load increased 20 per cent during the monitoring period, neither number of events nor energy release shows a correlation with this change. Carder (1970) found similar results for periods after 1949. A higher b value (1.45) was obtained than in the past, and lower monthly energy release was observed than in the late 1930's and 1940's when seismic activity at Lake Mead was first recorded. A 2-yr seismicity map of southern Nevada, including the monitoring period, shows that Lake Mead activity is now no greater than that of the surrounding area.

The pre-Lake Mead seismic history is not well known because the founding of Boulder City occurred just a few years before Lake Mead was impounded. The existence of earthquakes in the region before the reservoir was filled has been questioned in the liteature. However, a search of the Las Vegas Review Journal for felt reports pre- and postimpoundment and compilation of a catalog of the largest events from the literature confirm that there was a significant increase in the number of felt events at Las Vegas after the reservoir was filled.

The results indicate that the filling of Lake Mead has triggered release of tectonic stresses having the same orientation as the regional stress field. These stresses are probably being released in a way that is more dependent on tectonic stress buildup than on small changes in pore pressure (∼ 1 bar) due to fluctuating lake level. Given that the shear strength of rock decreases with increasing pore pressure, one might explain the decreasing energy release since the 1940's and the high b value as due to a decrease in elastic-energy density of the rock. A test of this hypothesis based on the order of magnitude of energy released seems to support it.
Filling of Ramganga reservoir, Kalagarh, U.P., India and its possible influence on seismic activity
Authors: Singh S. , Agrawal P. N. , Arya A. S.
Published: September 2021

abstract

The construction of a 125-m-high earth-and-rock-fill dam across the river Ramganga near Kalagarh was completed in early 1974. Its reservoir with a capacity of 2.49 ×109 m3 was partially filled during the 1974 summer monsoon. A detailed seismicity study has been made using the data from 2 month's microearthquake recording to determine the possible effect of reservoir filling. No interrelationship of seismic activity and reservoir filling has been found.
Seismic source functions and magnitude determinations for underground nuclear detonations
Authors: Murphy John R.
Published: September 2021

abstract

A variety of near-regional, regional, and teleseismic ground-motion data have been used to evaluate proposed models of the nuclear seismic source function for underground detonations in tuff/rhyolite emplacement media. It has been found that both the near-regional broad-band seismic data and the teleseismic body-wave magnitude data are consistent with the modified source model proposed by Mueller and Murphy (1971) but not with the simple cube-root of the yield-scaling source model. In particular, the observed linearity and slopes of the body-wave magnitude-yield curves as well as the observed variation of P-wave period with yield have been found to be fully compatible with the modified source model. On the other hand, it has been concluded that the observed long-period surface-wave data are inconsistent with a simple, spherically symmetric source model. The results of a preliminary analysis have suggested that this discrepancy may be related to the spall closure phenomenon.
Acoustic emission and creep in rock at high confining pressure and differential stress
Authors: Lockner D. , Byerlee J.
Published: September 2021

Two samples each of Weber Sandstone and Westerly Granite were tested under triaxial compression at 1 kb confining pressure. Axial load was increased in steps, and the acoustic emission generated in the samples during primary creep was monitored. The rate v of acoustic emission events was found to decrease exponentially at each stress level, obeying the law log v = β − αN, where N is the total number of microseismic events that have occurred and α and β are constants. By assuming that acoustic emission is proportional to inelastic deformation, this relation can be compared to empirical creep laws. It is similar to the relation given by Lomnitz and fits the data more closely than other creep laws that were functions of time rather than number of acoustic emission events. The value of α was found to decrease systematically with increasing differential stress, and in one experiment became negative before sample failure.
Source parameters of moderate size earthquakes and the importance of receiver crustal structure in interpreting observations of local earthquakes
Authors: Helmberger Donald V. , Johnson Lane R.
Published: September 2021

Broadband observations of three central California earthquakes as recorded on opposite sides of the San Andreas fault zone are studied. The earthquake mechanisms are of the strike-slip type occurring along the fault at epicentral distances between 15 and 30 km. The seismograms obtained at the two sites are distinctly dissimilar in both amplitude and wave shape even though they are at roughly the same azimuth. We suppose that the earthquake excitation is identical for the two sites and that the differences in seismograms are caused by the receiver structure. The problem is idealized by assuming that the first 10 sec of each record can be modeled synthetically with a point shear dislocation embedded in a half-space with a two-layer upper-crustal model appropriate for each site. The results determined by matching the observations indicate that the durations for these events with ML = 4 to 5 are about 0.3 to 0.6 sec. Furthermore, the results demonstrate that accurate estimate of source parameters can only be accomplished after a detailed appreciation of crustal structure.
A method for the separation of interfering surface waves and the computation of their dispersion
Authors: Michaels Paul
Published: September 2021

A practical technique for separating two surface waves that interfere, producing beats, is accomplished by a generalized least-squares inversion. A sinusoid consisting of a polynomial phase function is fit via least squares to both the envelope and the carrier wave forms of a digitized signal. The phase functions of the two interfering waves are then determined via a modulation equation. The derivative with respect to time of each phase function yields the frequency dispersion curves. Determinations of both group- and phase-velocity dispersion curves are discussed and a numerical example of the technique is given.
Seismic velocity determinations in the New Madrid seismic zone: A new method using local earthquakes
Authors: Mitchell Brian J. , Hashim Braik M.
Published: September 2021

A new method is developed and used to determine compressional- and shear-wave models for the crust in the northernmost portion of the Mississippi embayment. A nonlinear least-squares process fits contiguous straight lines to data obtained using a seismic network, and yields apparent velocities and points of intersection of the lines.

The compressional-wave model consists of a 5.6-km-thick layer with a velocity of 6.19 km/sec overlying an 18.1 -km-thick layer with a velocity of 6.38 km/sec. These are underlain by material having a velocity of 7.17 km/sec. Since the shear-wave data are characterized by a large amount of scatter, only a two-layer model was obtained. It consists of a 21.5-km-thick layer having a velocity of 3.62 km/sec above material with a velocity of 4.10 km/sec. These models are overlain by variable thicknesses of sediments of the Mississippi embayment.

The travel times of compressional waves at short distances indicate that the great preponderance of earthquake foci lie at shallow depths. Although the travel times are relatively insensitive to small changes in depth for these shallow earthquakes, few data points imply depths greater than about 10 km, and most are compatible with shallower depths.
The island of Hawaii earthquakes of November 29, 1975: Strong-motion data and damage reconnaissance report
Authors: Rojahn Christopher , Morrill B. J.
Published: September 2021

Two earthquakes occurred on the island of Hawaii on November 29, 1975, a magnitude (Ms) 5.7 event at 0335 (local time) and a magnitude (Ms) 7.2 event at 0447. During the larger event, a maximum acceleration of 0.22 g was recorded in the southern part of Hilo, 43 km north of the epicenter. A 0.05 g threshold duration of 13.7 sec was measured for the same component. Smaller amplitude accelerograph records were obtained at two other locations on the island along with four seismoscope records.

During or subsequent to the larger event, a large sector of the southeastern coastline subsided by as much as 3.5 meters. A tsunami generated by the larger event caused at least one death (one person also missing), injury to 28 persons, and significant structural and nonstructural damage.

Only scattered evidence of strong ground shaking was observed in the epicentral area, and most of the several dozen nearby structures sustained little or no structural damage from ground shaking. In Hilo, 45 km north of the Ms = 7.2 epicenter, structural and nonstructural damage was slight to moderate but more extensive than elsewhere on the island.
Earthquake hazard in the Nevada region
Authors: Ryall Alan
Published: September 2021

The seismic cycle in Nevada, corresponding to the re-rupture time for major faults, is of the order of thousands of years long. Following the occurrence of a large (M > 7) earthquake, aftershock activity in the rupture zone continues for about a century. From earthquakes reported in the meizoseismal zones of the 1915 Pleasant Valley and 1954 Dixie Valley earthquakes, it appears that great Nevada earthquakes are also preceded by a moderate increase in seismicity, lasting several decades. Faults considered to be “active” on geologic grounds are distributed fairly evenly over most of the Nevada region, so that fault mapping alone is not enough for determination of seismic potential. In addition, because of the length of the seismic cycle, the distribution of large historic earthquakes is by itself inadequate for seismic regionalization. A better method for this region may be to spatially correlate epicenter lineups for microearthquakes and small earthquakes with mapped geologic faults or lineaments. A correlation of this type based on earthquakes recorded for the period 1970-1974 suggests that a number of northwest-trending zones in an area of west-central Nevada may have high potential for large earthquakes in the future. On the other hand, high seismicity, complex faulting and scattered epicenter distribution in the seismic “gap” between the 1932 Cedar Mountains and 1872 Owens Valley earthquakes suggests that tectonic stress in this zone may be relieved by a continuous series of small-to-moderate earthquakes.
THE SURABAYA CITY GOVERNMENT’S CRISIS COMMUNICATION STRATEGY THROUGH “BANGGA SURABAYA” MEDIA
Authors: Amalia Adhi Murti Citra , Putri Gabriella Sagita
Published: September 2021

Kemajuan teknologi digital memaksa institusi pemerintah membenahi cara berkomunikasinya dengan masyarakat, termasuk dalam hal mengkomunikasikan krisis. Komunikasi krisis sebelumnya banyak menggunakan bantuan media massa, namun kemudian semakin bergeser ke media digital, seperti yang dilakukan oleh Pemerintah Kota-Pemkot Surabaya yang menciptakan medianya sendiri yaitu “Bangga Surabaya”. Tujuan dari penelitian ini untuk mendeskripsikan strategi komunikasi krisis Pemkot Surabaya melalui media “Bangga Surabaya”, yang diterapkan mulai dari pre-crisis, crisis events, hingga post-crisis. Metode yang digunakan dalam penelitian ini kualitatif dengan teknik pengumpulan data observasi dan wawancara. Berdasarkan hasil penelitian menunjukkan bahwa strategi komunikasi Pemkot Surabaya terdiri dari penentuan khalayak, pesan, saluran media, hingga komunikator. Pemkot Surabaya lebih mengedepankan pesan yang bersifat edukatif, informatif, dan membangun optimisme positif, untuk menjaga masyarakat tetap tenang dan kondusif selama penanggulangan krisis berlangsung. Pada tahapan pre-crisis, Pemkot Surabaya melakukan monitoring media untuk isu-isu yang berpotensi menjadi krisis, edukasi pencegahan krisis, dan penyampaian informasi tentang persiapan krisis. Di tahap crisis events, Pemkot Surabaya mengkolaborasikan media “Bangga Surabaya” dengan media massa lainnya untuk mengkomunikasikan perkembangan krisis. Terakhir, di tahap post-crisis Pemkot Surabaya melakukan evaluasi atas penanganan krisis dan memonitor kembali tentang potensi krisis.
Análisis de la cobertura vegetal en incendios forestales mediante índices espectrales: caso de estudio Cerros Orientales (Bogotá, Colombia)
Authors: Capador Aguilar Yezid Esteban , González Angarita Gina Paola , Suarez Daza Paula Andrea
Published: September 2021

Forest fires are a problem that arises in different places of the world, either for anthropogenic or natural causes bringing adverse effects on the environment like changes in the land cover. The aim of this research was to analyse land cover change through Normalized Difference Vegetation Index and Land Surface Temperature during forest fires. Using and processing satellite images Landsat 5,7, 8 the NDVI and LST at the Cerros Orientales of Bogotá city were established. The results showed that land quality cover changes in Cerros Orientales, due to the wildfires, changing the NDVI and LST at a study area; also there is evidence that the most susceptible areas are Usaquén, Chapinero and Santa Fe, because the land cover quality is moderate and scarce. The NDVI and LST are useful indicators that show the impact of photosynthetic activity of vegetation, after forest fires.
Cultivating Innovation Capacity of Undergraduates in a Technology Commercialization Academy in Midwest America
Authors: Chlebowski Arthur , Hawkins William , McWilliams Joshua , El Tawil Stephanie
Published: September 2021

The Technology Commercialization Academy (TCA) was launched to promote the identification, assessment, and exploitation of economically viable innovations by undergraduates and retain those graduates in the southwest Indiana region. Further, as part of the I-69 Innovation Corridor initiative, the TCA was part of increasing the regional Innovation Index score 20% by 2025. Through the seven years of implementation, the program has determined that there is a crucial tool set that is necessary for new graduates entering industry, including instilling that innovation is a balance; innovation is agile; innovation must fail, pivot, and focus quickly; and lastly the program must realize its capabilities, be diverse in thought, and recognize that the personnel are key. By instilling these practices in the participants, using available programmatic information and surveys, 100% of job seekers post-graduation were employed within six months, 9% began their own startup from the program, and 64% of these high impact graduates stayed in southwest Indiana. Overall, the TCA program structure has shifted to demand side iterative processes that create long-tail value for the region and made the participants attractive hires who are keenly aware of practices to move from opportunity to execution.