bluuebunny/crossref_metadata_2025_split huggingface dataset:
Observed variations of earthquake motion across a sediment-filled valley
Authors: King J. L. , Tucker B. E. 
Published: July 2021

Abstract
The response to earthquake motion of a site in one sediment-filled valley was observed to depend strongly on frequency and the position of the site within the valley and weakly on the input signal's azimuth and incidence angles. The observed input motion was weak, varying between 10−5 and 10−3g. Measurements of ground velocity were made on profiles across and along the valley and simultaneously on two nearby rock sites. The valley was 400 m wide and 700 m long, with a maximum sediment thickness of 60 m. The average seismic impedance contrast between the sediments and underlying basement rock was about 6:1.
Ratios of Fourier spectra from soil sites to spectra from nearby rock sites showed apparent site amplifications of as much as a factor of ten, depending strongly on frequency and the distance of the site from the valley edge. The scatter in spectral ratios for earthquakes with different azimuths and angles of incidence was about a factor of two; thus local site effects that changed the amplitude of incident motion by a factor of two or more could be identified in the records of most earthquakes. Ground motion at valley-edge and mid-valley sites, separated by less than 100 m, differed by as much as a factor of five. This difference could cause large differential motion in structures spanning these sites.
A theoretical, flat layer model of sediment response predicts the average behavior of the middle of the valley but not that of the valley edge. The lowest frequency responance apparently involves the sediments across the width of the valley, not just the vertical column of soil beneath each site.
Study of the 6 June 1977 Lorca (Spain) earthquake and its aftershock sequence
Authors: Mezcua J. , Herraiz M. , Buforn E. 
Published: July 2021

AbstractOn 2 May 1977, a portable array of five stations was installed for the reconnaisance of the Alhama de Murcia fault in southern Spain. During this survey on 6 June 1977, a 4.2 mb (Lg) shock took place within the array and was followed by a long series of aftershocks. Due to the good quality of the records, a comprehensive study of location, magnitude, seismic moment, focal mechanism, and related parameters has been carried out. In the seismic moment calculation, we have used the coda wave analysis, which also gives information about Q values of approximately 320 and 617 for body and surface waves, respectively. In evaluating the focal mechanisms of the sequence, we have used a joint treatment which permits us to separate the two types of faulting involved in the rupture process. Finally, to interpret these results in terms of the tectonics of the region, the focal mechanism of the earthquake of 5 March 1981, which occurred in a neighboring area, has also been studied.
Earthquake frequency and prediction
Authors: Liu Zheng-rong 
Published: July 2021

AbstractThe coefficient p in n(t) = n1t−p, where n(t) is the daily count of earthquakes and n1 is the number of earthquakes on the first day following a larger earthquake, is ≦1 for foreshock sequences, ≳1 for double-main shock sequences, and »1 for aftershock sequences with a single largest earthquake. For p »1, the magnitude of the largest aftershock and the cutoff time of the aftershocks can be estimated. These observations are the basis for an earthquake prediction technique successfully used in the Peoples Republic of China (PRC).
An experiment in the retrieval of depth and source mechanism of large earthquakes using very long-period Rayleigh wave data
Authors: Romanowicz Barbara , Guillemant Philippe 
Published: July 2021

AbstractThe possibility of obtaining an estimate of depth for large earthquakes from low-frequency mantle wave data alone is investigated using moment tensor formalism.After illustrating the sensitivity to depth of the eigenfunctions in the period range of 160 to 350 sec, we give several examples of application of the two-step inversion procedure proposed earlier for shorter period Rayleigh wave data (Romanowicz, 1982). We find that for earthquakes below a depth of about 50 km, we are able to resolve depth even when a spherically symmetric average Earth model is used for propagation corrections. This is particularly interesting in the case of large subduction zone earthquakes for which an estimate of the vertical extent of faulting can thus be obtained, independently of aftershock studies, in a very fast and simple manner which does not involve any synthetic seismogram calculations or lateral heterogeneity modeling.For shallower earthquakes, especially those with one steeply dipping nodal plane, the resolution of depth is less precise. Taking lateral heterogeneity into account by using available regionalized phase velocities improves the results marginally. We anticipate that accounting more accurately for the low-order harmonics in the worldwide phase velocity distribution should prove most helpful, since these interfere the most with the theoretical radiation patterns of earthquakes. The determination of depth depends more critically on the source process time, which has to be accounted for especially for horizontally propagating faults.
Seismicity and waveforms of the microearthquakes before and after the Shizuoka-Seibu earthquake, central Japan
Authors: Ishida Mizuho , Ohtake Masakazu 
Published: July 2021

AbstractInvestigating the foreshock-main shock-aftershock sequence of the Shizuoka-Seibu earthquake (M = 2.8, 16 January 1981), central Japan, we found evidence that suggests high stress conditions for the foreshock period. The source dimension of the main shock was roughly estimated to be about 0.5 × 0.2 km2. The m value of the Ishimoto-lida's formula was 1.87 for foreshocks and 2.37 for aftershocks.Waveforms of the foreshocks, main shock, and aftershocks were similar to each other. However, the amplitude ratio of the low (0.9 to 0.8 Hz) to high (3.5 to 10 Hz) frequency band was different between the foreshocks and aftershocks. The ratio for the foreshocks was lower than that for the aftershocks, indicating that the foreshocks contain more high-frequency energy than the aftershocks. The Shizuoka-Seibu sequence included a larger number of foreshocks (70) compared to aftershocks (43). This characteristic, in contrast with large earthquakes, was found common to small-sized earthquakes occurring in the neighborhood areas. These observations can be interpreted based on the asperity model.
Stochastic slip-predictable model for earthquake occurrences
Authors: Kiremidjian Anne S. , Anagnos Thalia 
Published: July 2021

AbstractA slip-predictable stochastic model is presented based on Markov renewal theory. Times between successive events are assumed to be Weibull-distributed with an increasing hazard rate. The model forecasts probabilities of earthquake occurrences conditional on the time of occurrence of the last event. The hazard along the Middle America Trench, Mexico, where data has suggested slip-predictable behavior, is obtained for illustrative purposes. Comparisons of this model with the Poisson model show that probability forecasts are underestimated with the Poisson model when there has been a seismic gap. The slip-predictable stochastic model presented in this paper represents a considerable improvement over the existing seismic hazard analysis methods. However, further testing of the model is necessary prior to wider application.
The effects of tectonic release on short-periodPwaves from NTS explosions
Authors: Lay Thorne , Wallace Terry C. , Helmberger Don V. 
Published: July 2021

AbstractThe first cycle (ab amplitude) of teleseismic short-period P waves from underground nuclear explosions at Pahute Mesa (NTS) show a systematic azimuthal amplitude pattern that can possibly be explained by tectonic release. The amplitudes vary by a factor of three, with diminished amplitudes being recorded at azimuths around N25°E. This azimuthal pattern has a strong sin(2φ) component and is observed, to varying degrees, for 25 Pahute Mesa events, but not for events at other sites within the NTS. Events that are known to have large tectonic release have more pronounced sin(2φ) amplitude variations. A synthesis of long-period body and surface wave investigations of tectonic release for Pahute Mesa events shows that, in general, the nonisotropic radiation is equivalent to nearly vertical, right-lateral strike-slip faulting trending from N20°W to due north. Long-period P waves at upper mantle distances demonstrate that there is a significant high-frequency component to the tectonic release. Using the long-period constraints on orientation, moment, and frequency content of the tectonic release, the expected short-period P wave effects are predicted. For models in which the downgoing P wave from the explosion triggers tectonic release within a few kilometers below the shot point, a factor of 2.5 amplitude variation with azimuth is predicted for the short-period ab amplitudes, with the lowest amplitudes expected near N25°E. Rather subtle azimuthal variations in the waveforms are expected, particulary for downward propagating ruptures, which is consistent with the absence of strong variations in the data. The occurrence of the azimuthal pattern, albeit with varying strength, for all of the Pahute Mesa events suggests a tectonic release model in which the shatterzone surrounding the explosion cavity is extended preferentially downward by driving a distributed network of faults and joints underlying the Mesa several kilometers beneath the surface. In this model, all events could have a component of tectonic release which would reflect the regional stress regime, although there may be slight spatial and temporal variations in the tectonic release contribution. Some events may trigger slip on larger throughgoing faults as well. While it is shown that tectonic release can affect teleseismic short-period signals significantly, and may contribute to the Pahute Mesa amplitude pattern, other possible explanations are considered.
Seismicity changes prior to several great earthquakes in the circum-Pacific area
Authors: Acharya Hemendra 
Published: July 2021

Abstract
Spatio-temporal variation in earthquake activity, prior to several post-1950 earthquakes with magnitude ≧ 8.0 in the circum-Pacific area, has been examined in order to identify a common precursory pattern. Strain energy ΣE released in the rupture zone of these great earthquakes was computed for every year between 1910 and the time of the great earthquake. An examination of strain energy release as a function of time shows that maximum strain energy Σ(EB) is released in the rupture zone at a time which depends on the magnitude (M) of the subsequent great earthquake. The ratio of strain energy ΣEM released in the great earthquake to the strain energy ΣEB varies between 3 and 30, i.e., this burst of activity is equivalent to a single earthquake of magnitude between 12 to 2 units less than the magnitude of the great earthquake. The amount of maximum deformation and the time at which it occurs appears to depend on the magnitude of the great earthquake.
Estimates of magnitudes and short-period wave attenuation of Chinese earthquakes from Modified Mercalli intensity data
Authors: Chen Peishan , Nuttli Otto W. 
Published: July 2021

AbstractIntensity data for Chinese earthquakes are used to estimate the body-wave magnitude, mb, of selected historical earthquakes and to estimate Q0, the 1-sec period Q value of Lg waves for various geographical areas of China. In order to derive the necessary empirical relation between the intensity distribution and mb, data are used from recent earthquakes, for which instrumentally obtained mb values as well as isoseismal maps are available. Average Qo values are approximately 175 for the mountainous regions of southwest China, 550 for southeastern China, and 150 for Taiwan. These values agree qualitatively with those obtained by Evernden (1983) and Chen et al. (1983), who utilized a different method of analysis of the intensity data
A two-state Poisson model for seismic hazard estimation
Authors: Bender Bernice 
Published: July 2021

Abstract
Most seismic hazard analyses assume that earthquakes have a Poisson distribution and that data from recorded earthquakes can be used to predict future seismic activity in a region. Historic catalogs, however, may show different earthquake occurrence rates for regions that are geologically similar, suggesting, on a local scale at least, temporal variations in seismicity. The simple two-state model presented here allows a region to have both seismically “active” and “inactive” states; in this model, earthquakes have a Poisson distribution during both states, but occur at a higher rate when the region is “active.” The probability of changing from one state to the other at any time is constant. The two-state model reduces to the usual Poisson model if the region is always “active” or if the rate is the same for both states.
Analysis of upper mantle structure using wave field continuation ofPwaves
Authors: Walck Marianne C. , Clayton Robert W. 
Published: July 2021

AbstractWave field continuation transforms seismic record section data directly into velocity-depth space, simultaneously providing an estimate of model nonuniqueness. This inversion, previously used for reflection and refraction data, converts readily to spherical earth problems through simple adjustments in each of the two linear transformations: the slant stack and downward continuation. Because the time resolution inherent in the data transforms to depth resolution in the model space, this method is extremely useful for analysis of data compatibility with preexisting models and direct comparison between data sets, as well as the complete inversion of raw data for structure. Wave field inversion demands densely sampled, digital data, and assumes source coherency and lateral homogeneity along the profile.We test this technique for upper mantle analysis using a previously studied, large, array-recorded data set representative of structure beneath the Gulf of California. We compare slant stacks and downward continuations of both synthetic and data record sections to illustrate the method's resolution capability. Wave field continuation proves particularly useful in comparing entire data sets to various models; even subtle structural differences are resolvable given good data quality.
Historical seismicity and rates of crustal deformation along the margins of the Ordos block, north China
Authors: Wesnousky S. G. , Jones L. M. , Scholz C. H. , Deng Qidong 
Published: July 2021

AbstractEarthquakes in China show an empirical relation between seismic moment (M0) and the areal distribution of Modified Mercalli intensities VI and VIII (log M0 = 16.66 + 0.91 log AVIII and log M0 = 14.35 + 1.16 log AVI, where A and M0 are measured in squared kilometers and Newton-meter, respectively). The empirical relations may be used to estimate M0 for historical earthquakes in China to within a factor of three, on average, when sufficient isoseismal data exist. This observation and an extensive collection of isoseismal maps are used to estimate M0 for large earthquakes that occurred along the margins of the Ordos block during the last 700 yr. Focal parameters of the historical events are inferred from the orientation and displacements across Quaternary faults. Average rates of crustal deformation are then estimated from the 700-yr historical record with formulas that relate the occurrence rate of seismic moment in a region to rates of crustal strain. The Shanxi and northern Ningxia graben systems are situated along the eastern and northwestern edges of the Ordos block, respectively. Normal faults in the two systems trend northeasterly and are characterized by a component of right-lateral slip. The deformation resulting from slip during earthquakes in each of the respective fault systems is estimated at about 0.5 to 1.0 mm/yr of both right-lateral shear and north by northwest extension. The Weihe graben system bounds the southern edge of the Ordos block, strikes easterly and conjugate to the Shanxi and northern Ningxia fault systems, and exhibits left-lateral normal fault displacements. The average rate of deformation across Weihe is described by about 1.0 mm/yr of north by northwest extension and 1.5 mm/yr left-lateral east-west shear. The Hetao fault system delineates the northern edge of the Ordos block and displays Quaternary faults similar in orientation and mechanism to that observed in Weihe. Although mapped faults in Hetao exhibit evidence of Quaternary displacement, crustal deformation rates are not estimated because there exists no historical record of large earthquakes in the area. In southern Ningxia, at the southwest boundary of the Ordos block, deformation occurs by slip on left-lateral strike-slip faults oriented in an easterly azimuth and thrust faults with strikes ranging from southeast to south. The average deformation rate in southern Ningxia is found to be about 4.0 mm/yr of east by northeast contraction and 10.0 mm/yr of left-lateral shear. Deformation of each of the fault systems is consistent with a regional compressive stress that trends northeast and results in an average of about 3.0 mm/yr each of contraction at N70°E and extension of N160°E across the entire region. Inasmuch as uncertainties in estimates of M0 for historical earthquakes are about a factor of three, a similar uncertainty is attached to rates of crustal strain determined in this manner.
TheMLscale in central California
Authors: Bakun William H. , Joyner William B. 
Published: July 2021

AbstractNine hundred fifty-seven maximum zero-to-peak Wood-Anderson amplitudes A (synthesized or recorded) from 40 horizontal-component seismographs (20 sites) with 0 ≲ Δ ≲ 400 km for 106 earthquakes with 18 ≦ log M0 ≦ 22.3 in central California have been fit in a least-squares sense using the parametric form log A ij = − n log R ij − K R ij − ∑ l = 1 40 S l δ ij + ∑ k = 1 106 C k δ ik where Aij = A (mm) for earthquake i on seismograph component j, δik = Kronecker delta, R = hypocentral distance, and n, K, Sl, and Ck are variables determined by regression analysis. The Ck are a magnitude measure, and the Sl are station corrections constrained to have zero average. We find n = 1.018 ± 0.107 and K = 0.00291 ± 0.00070 km−1. Setting n = 1, appropriate for body-wave propagation in homogeneous media, yields K = 0.00301 ± 0.00036 km−1. Following Richter's definition of an ML = 3 earthquake as one for which A = 1 mm at Δ = 100 km and S1 = 0, we express the local magnitude ML as ML = log A − log A0, where -log A0 = n log (R/100) + K (R − 100) + 3. For 30 ≲ Δ ≲ 475 km, the -log A0 values using n = 1 and K = 0.00301 km−1 are within 0.15 of Richter's values for southern California. For Δ ≲ 30 km, Richter's values are significantly smaller than those obtained here, a result consistent with recent studies of −log A0 for southern California. Our results suggest that the ML scale as commonly used underestimates the sizes of small shocks that are predominantly recorded at Δ ≲ 30 km.
Array analysis of the ground velocities and accelerations from the 1971 San Fernando, California, earthquake
Authors: Liu Hsui-Lin , Heaton Thomas 
Published: July 2021

AbstractProfiles of ground velocity and acceleration, displayed as a function of epicentral distance, are analyzed for recordings of the 1971 San Fernando earthquake. Three long profiles (&gt;50 km) and three short profiles (&lt;2 km) are studied. Although there is considerable variation in waveforms and peak amplitudes observed along the long profiles, there are also many examples of coherent phases seen on adjacent stations. There are striking differences in the amplitudes and durations of ground velocity observed at stations located on hard rock sites as opposed to stations located within the large sedimentary basins of the Los Angeles area. Furthermore, the San Fernando Basin, which is adjacent to the source area, seems to respond quite differently from the Los Angeles Basin which is about 30 km from the earthquake source area. Ground acceleration profiles, however, show that there is no corresponding change in the duration or amplitude of high-frequency shaking with site characteristics. We infer that the excitation of surface waves within sedimentary basins is the reason that large peak velocities and displacements are observed for soft sites. The ground velocity waveforms are nearly identical along the three short profiles, which are all located within the Los Angeles Basin. Greater variation of waveforms and amplitudes are seen for ground acceleration along these short profiles, although strong phase coherence is still observed.
Pwaveform of large, shallow earthquakes along the Mexican subduction zone
Authors: Singh S. K. , Dominguez T. , Caştro R. , Rodriguez M. 
Published: July 2021

AbstractWe combine qualitative analysis of Wiechert seismograms with quantitative analysis of Galizin-Wilip and Press-Ewing seismograms from Europe to draw conclusions regarding simplicity/complexity of P waveforms of large, shallow earthquakes since 1907 which occurred along the Mexican subduction zone. These seismograms are compared with LP WWSSN seismograms of recent earthquakes. It is found that the earthquakes in Oaxaca are simple with two exceptions. The earthquake of 15 January 1931 (MS = 8.0) was a complex, intraplate event with normal or strike-slip faulting. Some earthquakes are simple, and others are complex in the subregions of Guerrero and Michoacan. All three earthquakes in Jalisco are complex. The depths of the events are shallow (10 ≲ H ≲ 20 km) with the majority being at 16 km. The simplicity of events, the evidence of a characteristic magnitude of MS ≃ 7.8, and the ratio of surface wave to P-wave seismic moment of about 1.5 in Oaxaca suggest rather homogeneous asperities of nearly equal dimension separated by barriers. Elsewhere, the interface of the plates is characterized by smaller asperities of differing sizes separated by areas where aseismic deformation may occur. The earthquakes of 22 February 1943 (MS = 7.7) and 14 March 1979 (MS = 7.6) which were supposed to have broken the same area show drastically different P waveforms. It appears that the location of the 22 February 1943 earthquake is in error. Alternatively, the same area may have been broken with entirely different rupture processes.