bluuebunny/crossref_metadata_2025 huggingface dataset:
Automatic seismic event recognition and later phase identification for broadband seismograms
Authors: Tong Cheng , Kennett Brian L. N.
Published: September 2021

Knowledge of the patterns of frequently observed seismic phases associated with specific distances and depths have been well developed and applied by seismologists (see, e.g., Richter, 1958; Kulhánek, 1990). However, up till now, the expertise of recognizing seismic event patterns for teleseisms has not been translated into automatic processing procedure. A new approach is developed to automate this kind of heuristic human expertise in order to provide a means of improving preliminary event locations from a single site.

An automatic interpretation system exploiting three-component broadband seismograms is used to recognize the pattern of seismic arrivals associated with the presence of a seismic event in real time accompanied by an identification of the individual phases. For a single station, such a real-time analysis can be used to provide a preliminary estimation of the location of the event. The inputs to the interpretation process are a set of features for detected phases produced by another real-time phase analyzer. The combinations of these features are investigated using a novel approach to the construction of an expert system. The automatic system exploits expert information to test likely assumptions about phase character and hence epicentral distance and depth. Some hypotheses about the nature of the event will be rejected as implausible, and for the remainder, an assessment is given of the likelihood of the interpretation based on the fit to the character of all available information.

This event-recognition procedure provides an effective and feasible means of interprating events at all distances, and characterizing information between hundreds of different possible classes of patterns even when the observation is incomplete. The procedure is based on “assumption trees” and provides a useful tool for classification problems in which a number of factors have to be identified. The control set of expert knowledge used in testing hypotheses is maintained separately from the computational algorithm used in the assumption search; in consequence, the information base can be readily updated.
A composite source model of the 1994 Northridge earthquake using genetic algorithms
Authors: Zeng Yuehua , Anderson John G.
Published: September 2021

The 17 January 1994 Northridge earthquake (Mw 6.7) occurred on a buried thrust fault in the northwest Los Angeles metropolitan area. We investigate the source process of this earthquake using the CSMIP strong motion records and a composite source model developed by Zeng et al. (1994a) for realistic earthquake strong ground motion prediction. Our previous studies demonstrated the realism of the synthetic strong motions generated from the composite source model by comparing them with observed records from earthquakes in many areas of the world. This article addresses an inverse study of the problem to find a specific composite source model for the Northridge earthquake. This is done by adjusting the location of a suite of composite subevents, using genetic algorithms (Holland, 1975), to best match the observed waveforms. A test run of the genetic algorithm on synthetic data sets finds a very good convergence of the approach. We reduce largely the intensive computation time by identifying subevents with major contribution to the waveform fit. Our result for the 1994 Northridge earthquake indicates a complex earthquake rupture process with three large slip zones: one at the hypocenter and the other two to the west of the hypocenter. We then use this model to compute the high-frequency strong-motion velocity and acceleration. The results show that the composite source model provides a very realistic broadband source description for the Northridge earthquake.
On some microearthquakes near Tarbela reservoir during three low water stands
Authors: Kalpna  , Chander R.
Published: September 2021

Detailed 3D stress analyses with a simulated model of Tarbela reservoir indicate that most nearby seismogenic faults inferred from observations of preimpoundment seismicity in the region should be stabilized even when the reservoir has low water levels during dry seasons. We hypothesize that the hypocenters of some microearthquakes occurring close to the reservoir during dry seasons of 1977, 1980, and 1981 were located on those of the above faults that are destabilized by accumulation of broadly north-south horizontal compressive stresses of plate tectonic origin. An order of magnitude analysis shows that the rate of accumulation of these stresses may be sufficiently rapid to overcome the stability imparted to the seismogenic faults by the Tarbela reservoir.
Location and source parameters of the 19 June 1994 (MW = 5.0) offshore Petrolia, California, earthquake
Authors: Braunmiller Jochen , Leitner Beate , Nábělek John , Tréhu Anne M.
Published: September 2021

The MW = 5.0, 19 June 1994 offshore Petrolia, California, earthquake was well recorded by nine ocean-bottom hydrophones (OBH) and seismometers (OBS), providing an opportunity to precisely locate an earthquake in the tectonically active Mendocino triple junction region. Adding the offshore data improves the azimuthal station coverage and essentially removes the epicenter's sensitivity to the choice of inversion parameters and velocity models. The hypocentral parameters, assuming an oceanic upper-mantle velocity of 7.9 km/sec, are 10:39:33.2 UTC for origin time, 40.376° N latitude, 124.441° W longitude, and a depth of 18.8 km. The moment-tensor solution obtained by modeling of low-frequency regional waveforms indicates predominantly strike-slip faulting with a north-south-trending P axis, as is typical for Gorda plate earthquakes, and confirms the depth estimate from the P-wave travel-time data.
Characteristics of nonlinear response of deep saturated soil deposits
Authors: Ni Shean-Der , Siddharthan Raj V. , Anderson John G.
Published: September 2021

Recent EPRI seismic design guidelines call for dynamic soil properties (shear modulus ratio and damping) and liquefaction strength curves to be characterized as a function of the effective vertical stress (or depth). A modified version of the DESRA2 constitutive model for saturated soil has been applied to study the nonlinear seismic response including liquefaction of medium dense soil deposits of various thicknesses. The results of the stress-dependent soil properties model show lower deamplification and higher first-mode (resonant) frequency than that of the stress-independent soil properties model. By using the stress-dependent model with impulse base excitation, the nonlinear behavior of various soil deposits has been investigated under a variety of conditions. The results show that (1) the saturated soil deposit has a smaller surface amplitude and significantly lower resonant frequency than the unsaturated soil deposit of the same thickness; (2) for the saturated soil conditions, the larger the base excitation, the lower the surface amplification and the resonant frequency; (3) the deep soil deposits show lower surface amplification and resonant frequency compared to the response of shallow deposits; (4) when shallow and deep deposits are compared, the shallow deposits develop much higher residual pore-water pressure; and (5) the amplification and residual pore-water-pressure response of deposits deeper than 100 m or so are very similar. The application of the method has also been illustrated using a strong synthetic base excitation applied to the base at a site near Reno. The results in general are consistent with those computed using the impulse loading. The study reveals that the response predicted from the conventionally used stress-independent soil properties model is unconservative for deep deposit.
The effect of the crust on the estimation of mantleQfrom spectral ratios of multipleScSphases
Authors: Isse Takehi , Nakanishi Ichiro
Published: September 2021

To estimate Qscs, previous studies used the spectral ratios of multiple ScS phases calculated for specific time windows. They assumed that the spectral ratios had linear relation with frequency. However, the spectral ratios very often did not seem to be linear, and the error bars were very large for frequencies higher than about 0.05 Hz.

We have performed numerical experiments to search for the cause of these anomalies and found that they are caused by the multiple reflection in the crust under the surface bounce point of ScS2. A method of suppressing the anomalies is to start the time of the time window at 40 sec prior to the theoretical arrival times of the multiple ScS phases. In numerical tests, the difference between the correct and estimated values of Qscs is only 0 to 5% using this method, but it is 10 to 50% in the conventional method. We find that the crustal effect is more important in the estimation of Qscs than background noise, which has been readily handled in previous studies using standard stacking techniques.
The paradox of the expected time until the next earthquake
Authors: Sornette D. , Knopoff L.
Published: September 2021

We show analytically that the answer to the question, (can it be that) “The longer it has been since the last earthquake, the longer the expected time till the next?” depends crucially on the statistics of the fluctuations in the interval times between earthquakes. The periodic, uniform, semi-Gaussian, Rayleigh, and truncated statistical distributions of interval times, as well as the Weibull distributions with exponent greater than 1, all have decreasing expected time to the next earthquake with increasing time since the last one, for long times since the last earthquake; the lognormal and power-law distributions and the Weibull distributions with exponents smaller than 1 have increasing times to the next earthquake as the elapsed time since the last increases, for long elapsed times. There is an identifiable crossover between these models, which is gauged by the rate of fall-off of the long-term tail of the distribution in comparison with an exponential fall-off. The response to the question for short elapsed times is also evaluated. The lognormal and power-law distributions give one response for short elapsed times and the opposite for long elapsed times. Even the sampling of a finite number of intervals from a Poisson distribution will lead to an increasing estimate of time to the next earthquake for increasing elapsed time since the last one.
The 14 September 1995 (M= 7.3) Copala, Mexico, earthquake: A source study using teleseismic, regional, and local data
Authors: Courboulex F. , Santoyo M. A. , Pacheco J. F. , Singh S. K.
Published: September 2021

We analyze source characteristics of the 14 September 1995, Copala, Mexico, earthquake (M = 7.3) using teleseismic, regional, and local seismograms. In the analysis of the teleseismic and the regional seismic waves, we apply the empirical Green's function (EGF) technique. The recording of an appropriate aftershock is taken as the EGF and is used to deconvolve the mainshock seismogram, thus obtaining an apparent far-field source-time function at each station. The deconvolution has been done using surface waves. For teleseismic data, we apply a spectral deconvolution method that enables us to obtain 37 apparent source-time functions (ASTFs) at 29 stations. In the analysis of the regional broadband seismograms, we use two different aftershocks as EGF, and the deconvolution is performed in the time domain with a nonlinear method, imposing a positivity constraint, and the best azimuth for the directivity vector is obtained through a grid-search approach.

We also analyze two near-source accelerograms. The traces are inverted for the slip distribution over the fault plane by applying a linear inversion technique. With the aid of a time-window analysis, we obtain an independent estimation of the source-time function and a more detailed description of the source process.

The analysis of the three datasets permits us to deduce the main characteristics of the source process. The rupture initiated at a depth of 16 km and propagated in two directions: updip along the plate interface toward 165° N and toward 70° N. The source duration was between 12 and 14 sec, with the maximum of energy release occurring 8 sec after the initiation of the rupture. The estimated rupture dimension of 35 × 45 km is about one-fourth of the aftershock area. The average dislocation over the fault was 1.4 m (with a maximum dislocation of 4.1 m located 10 km south of the hypocenter), which gives roughly 1 MPa as the average static stress drop.
Northridge aftershocks, a source study withTERRAscope data
Authors: Song Xi J. , Helmberger Donald V.
Published: September 2021

Broadband and long-period displacement waveforms from a selection of Northridge aftershocks recorded by the TERRAscope array are modeled to study source characteristics. Source mechanisms and moments are determined with long-period data using an algorithm developed by Zhao and Helmberger (1994). These results are compared with those by Hauksson et al. (1995) and Thio and Kanamori (1996). The width of the direct pulses at the nearest stations PAS and CALB are measured as indications of the source duration. Another measurement of the source-time functions of these earthquakes is obtained by comparing the short-period to long-period energy ratio in the data to that in the synthetics. These measurements are used to estimate the relative stress drop using a formula given by Cohn et al. (1982). The depth distribution of the relative stress drops indicates that the largest stress drops are in the depth range of 5 to 15 km for an aftershock population of 24 events. A correlation of extended surface wave train with source depth is demonstrated for paths crossing the San Fernando basin.
Statistical significance of the seismic coupling coefficient
Authors: McCaffrey Robert
Published: September 2021

Variations in the seismic coupling coefficient (χ), the ratio of the observed to expected seismic moment release rates, at subduction zones are commonly used to make inferences about the physics of subduction. Taking into account the power-law form of the earthquake frequency-moment relation, it is shown that the observed distribution of χ at the world's subduction zones based on the twentieth century's earthquakes can be matched by a single value of χ ≈ 0.3 if, as is likely the case, the 90-yr observation time is less than or comparable to the repeat time of the largest possible earthquake. It is shown that because our reliable earthquake record is short, global variations in χ, based on seismicity alone, are poorly resolved and cannot be used to distinguish among subduction models.
One minute after: Strong-motion map, effective epicenter, and effective magnitude
Authors: Teng Ta-liang , Wu Ludan , Shin Tzay-Chyn , Tsai Yi-Ben , Lee William H. K.
Published: September 2021

This article reports the recent progress on real-time seismic monitoring in Taiwan, particularly the real-time strong-motion monitoring by the Taiwan Central Weather Bureau's telemetered seismic network (CWBSN), which is presently aiming at rapid reporting immediately after a large earthquake occurrence. If rapid reporting can be achieved before the arrival of the strong shaking, earthquake early warning will become possible. CWBSN has achieved the generation of the intensity map, epicenter, and magnitude within 1 min of the occurrence of a large earthquake. Both rapid reporting and early warning are principally applied to large (M ≫ 5) events; the requirement of on-scale waveform recording prompted CWBSN in 1995 to integrate strong-motion sensors (e.g., force-balance accelerometers) into its telemetered seismic monitoring system. Time-domain recursive processing is applied to the multi-channel incoming seismic signals by a group of networked personal computers to generate the intensity map. From the isoseismal contours, an effective epicenter is immediately identified that resides in the middle of the largest (usually the 100-gal) contour curve of the intensity map. An effective magnitude is also defined that can be derived immediately from the surface area covered by the largest (usually the 100-gal) contour curve. For a large event with a finite rupture surface, the epicenter and magnitude so derived are more adequate estimates of the source location and of the strength of destruction. The effective epicenter gives the center of the damage area; it stands in contrast with the conventional epicenter location, which only gives the initial point of rupture nucleation. The effective magnitude reflects more closely the earthquake damage potential, instead of the classical magnitude definition that emphasizes the total energy release. The CWBSN has achieved in obtaining the above crucial source information well within 1 min. This time can further be reduced to better than 30 sec, as illustrated by the example in this article, showing that earthquake early warning is indeed an achievable goal. The rapid reporting and early warning information is electronically transmitted to users to allow rapid response actions, with or without further human intervention.
Dogtails versus rainbows: Synthetic earthquake rupture models as an aid in interpreting geological data
Authors: Ward Steven N.
Published: September 2021

Geologists have been collecting, for decades, information from historical and paleoearthquakes that could contribute to the formulation of a “big picture” of the earthquake engine. Observations of large earthquake ruptures, unfortunately, are always going to be spotty in space and time, so the extent to which geological information succeeds in contributing to a grander view of earthquakes is going to be borne not only by the quantity and quality of data collected but also by the means by which it is interpreted. This article tries to understand geological data more fully through carefully tailored computer simulations of fault ruptures. Dogtails and rainbows are two types of fault rupture terminations that can be recognized in the field and can be interpreted through these models. Rainbows are concave down ruptures that indicate complete stress drop and characteristic slip. Rainbow terminations usually coincide with fault ends or strong segment boundaries. Dogtails are concave up ruptures that indicate incomplete stress drop and noncharacteristic slip. Dogtail terminations can happen anywhere along a fault or fault segment. The surface slip pattern of the magnitude 6.6, 1979 Imperial Valley, California, earthquake shows both dogtail and rainbow terminations. The rainbow confirms the presence of a strong fault segment boundary 6 km north of the international border that had been suggested by Sieh (1996). The dogtail implies that the displacement observed in 1979 is not characteristic. By combining paleoseismic information with the surface slip patterns from this event and the magnitude 7.1, 1940 Imperial Valley earthquake, I develop a quantitative Imperial fault model with northern, central, and southern segments possessing 50, 110, and 50 bar strength, respectively. Both the 1940 and 1979 events caused 1-m amplitude dogtailed ruptures of the northern segment; however, characteristic slip of the segment is more likely to be about 3 m. To illustrate the full spectrum of potential rupture modes, models were run forward in time to generate a 2000 year rupture “encyclopedia.” Even with well-constrained segmentation and strengths, modest changes in two friction law parameters produce several plausible histories. Further discrimination awaits analysis of the extensive paleoseismic record that geologists believe exists in the shore deposits of the intermittent lakes of the Salton Trough.
Static stress drop in the 1994 Northridge, California, aftershock sequence
Authors: Hardebeck Jeanne L. , Hauksson Egill
Published: September 2021

We use time-domain pulse widths to estimate static stress drops for 279 ML 2.5 to 4.0 aftershocks of the 17 January 1994, MW 6.7 Northridge, California, earthquake. The stress drops obtained range from 0.02 to 40 bars, with a log average of 0.75 bar. Error bars computed for our estimates are typically a factor of 5, indicating that the three order of magnitude scatter in stress drops is not solely a result of measurement errors and that there is a significant amount of heterogeneity in the static stress drops of the aftershocks. Stress drops might be expected to increase with depth, since a fault can maintain a higher shear load at higher confining pressures. We observe an increase in log average stress drop at about 15 km depth, which is statistically significant at the 80% confidence level. The increase is due primarily to a lack of lower stress-drop events below this depth and may be controlled by material properties since the Northridge aftershocks are observed to intersect an anomalously high-velocity body at around this depth (Hauksson and Haase, 1997). An apparent increase in stress drop with magnitude is also observed over the entire magnitude range of the study, although whether this trend is real or an artifact of attenuation of high frequencies in the upper crust is unresolved.
Study of low-magnitude seismic events near the Novaya Zemlya nuclear test site
Authors: Ringdal Frode
Published: September 2021

A study of available seismic data shows that all but one of the 42 known underground nuclear explosions at Novaya Zemlya have been detected and located by stations in the global seismic network. During the past 30 years, only one seismic event in this area has been unambiguously classified as an earthquake (1 August 1986, mb = 4.3). Several other small events, most of which are thought to be either chemical explosions or aftereffects of nuclear explosions, have also been detected. Since 1990, a network of sensitive regional arrays has been installed in northern Europe in preparation for the global seismic monitoring network under a comprehensive nuclear test ban treaty (CTBT). This regional network has provided a detection capability for Novaya Zemlya that is shown to be close to mb = 2.5. Three low-magnitude events have been detected and located during this period, as discussed in this article: 31 December 1992 (mb = 2.7), 13 June 1995 (mb = 3.5), and 13 January 1996 (mb = 2.4). To classify the source types of these events has proved very difficult. Thus, even for the mb = 3.5 event in 1995, we have been unable to provide a confident classification of the source as either an earthquake or explosion using the available discriminants. A study of mb magnitude in different frequency bands shows, as expected, that the calculation of mb at regional distances needs to take into account source-scaling effects at high frequencies. Thus, when comparing a 4 to 8 or 8 to 16 Hz filter band to a “teleseismic” 2 to 4 Hz band, the smaller events have, relatively speaking, significantly more high-frequency energy (up to 0.5 mb units) than the larger events. This suggests that a P-wave spectral magnitude scale might be appropriate. The problem of accurately locating small events using a sparse array network is addressed using the 13 January 1996 event, which was detected by only two arrays, as an illustrative example. Our analysis demonstrates the importance of using accurately calibrated regional travel-time curves and, at the same time, illustrates how array processing can be used to identify an interfering phase from a local disturbance, thereby avoiding location errors due to erroneous phase readings.
Investigation of azimuth residuals observed at stations of the GSETT-3 Alpha network
Authors: Koch Karl , Kradolfer Urs
Published: September 2021

The GSETT-3 experiment was conducted for more than two years and the International Data Center (IDC) reported more than 20,000 events for 1995 in the Reviewed Event Bulletins (REB). We have used this data base to investigate the location bias of arrays and selected three-component stations in the Alpha network, for which the recorded data is automatically processed to determine earthquake locations in near-real time. The Alpha network, which consists of 14 arrays, provides estimates of event azimuths determined by f-k processing. We selected 19 three-component stations that were operated all or most of 1995 and for which event azimuth was estimated by polarization analysis. Only events with epicentral distances of less than 100° were considered in order to exclude phases with steep incidence angles, associated with unreliable azimuth estimates. Teleseismic P phases and the major regional and local phases were examined. Only data for which a signal-to-noise ratio was given were included in this analysis. The signal-to-noise ratios were used as a weighting factor for the statistical parameters and the graphical representation of the azimuth residuals. The preliminary analysis of azimuth residuals identified some arrays that give significantly erroneous azimuths; in some cases, the error is systematic, in other cases, it is random. One array with systematic azimuthal bias is CMAR. This array shows positive residuals for event paths from the south, while phases for events with paths from the north show negative residuals. Similar patterns, which strongly suggest azimuthal bias, are observed for PDAR, TXAR, and SPITS. In the case of MJAR, the large azimuthal errors observed particularly for regional and local distances are not a function of direction. The scatter in the azimuth residuals is much larger for 3-C stations than for the arrays. Clear systematic errors were identified for SCHQ and CPUP, which show constant offsets, and at VNDA, which has negative residuals for events to the north and positive residuals for events from the south. The most significant azimuth bias was observed for PDY, where the azimuth residuals change from about −90° to more than +90° at backazimuths near 120°, meaning that all rays appear from the northwest.
Wavelet transform methods for phase identification in three-component seismograms
Authors: Anant Kanwaldip Singh , Dowla Farid U.
Published: September 2021

We apply the wavelet transform to seismic signals for the purpose of automatically identifying the P and S phase arrivals of seismic events. In this article, an algorithm is presented that locates these arrivals in single-station three-component short-period seismograms using polarization and amplitude information contained in the wavelet transform coefficients of the signals. The main idea is that strong features of the seismic signal appear in the wavelet coefficients across several scales. The first step in the algorithm is the wavelet decomposition of each component of a three-component short-period seismogram. The resulting multi-scalar representation is used to construct “locator” functions that identify the P and S arrivals. The P locator function is constructed by using polarization information across scales, and the S locator function is constructed using transverse over radial amplitude information across scales. These functions prove to be very effective at identifying the important P and S arrivals in the test data. The results are compared with arrival times picked by an analyst.
Observations of high-frequency scattered waves using dense arrays at Teide Volcano
Authors: Del Pezzo E. , La Rocca M. , Ibanez J.
Published: September 2021

A study of the seismic coda of seven small earthquakes recorded on the Teide Volcano-Canary Islands (Spain) was carried out using a temporary, small-aperture, 12-station, seismic array. The purpose was to measure backazimuth, apparent velocity and the type of waves that compose the coda in the frequency range 4 to 6 Hz. We used the zero-lag cross-correlation (ZLC) method to obtain the components of the wave vector and three-component analysis techniques based on the covariance matrix of the signal in the time domain to investigate the polarization properties of the signals. The results show that a great part of the coda signals in the analyzed frequency range are almost uncorrelated, while a low number of isolated correlated arrivals show an apparent slowness between 2 × 10−3 and 2.5 × 10−4 sec/m and an almost random distribution of backazimuths. The correlated arrivals have been interpreted as generated by strong scatterers, probably related to the presence, in the study area, of surface topography irregularities (the volcanic cone and the caldera rim). The wave type varies from pure S-type waves to mixed surface waves with some Rayleigh components.
Do historical rates of seismicity in southern California require the occurrence of earthquake magnitudes greater than would be predicted from fault length?
Authors: Stirling Mark W. , Wesnousky Steven G.
Published: September 2021

The Working Group on California Earthquake Probabilities reported a discrepancy between the historical rates of large earthquakes in southern California and rates predicted from interpretation of geological, geodetic, and historical seismicity data. It was suggested that the discrepancy may be due to the assumption within their analysis that the magnitude of the largest earthquake on a fault is limited by the mapped fault length. Our analysis of the available data does not support the presence of a historical deficit in the rate of seismicity, nor does it require that earthquakes that rupture beyond the lengths of mapped active faults in southern California, or that rupture numerous subparallel faults, are needed to explain the historical distribution of seismicity.
Estimation of attenuation relations for strong-motion data allowing for individual earthquake magnitude uncertainties
Authors: Rhoades David A.
Published: September 2021

Standard errors of earthquake magnitudes are routinely calculated and vary appreciably between earthquakes. However, the uncertainties of magnitude determination are usually ignored in regression models of strong ground motion as a function of magnitude and distance from the earthquake source. This practice has the potential to bias estimates of strong ground motion. A method is given for taking account of the uncertainty of each magnitude determination in fitting such models. It extends previous methods in which the error variance is partitioned into between-earthquake and within-earthquake components. It allows for further decomposition of the between-earthquake component into a part attributable to magnitude uncertainties and a part attributable to other causes.

The method has been applied to the well-known attenuation data of Joyner and Boore (1981). The Mw determinations in this dataset fall into two subsets with distinctly different levels of precision, namely, those determined directly and those inferred from values of ML. It is shown that most of the between-earthquake component of variance can be attributed to the relatively low precision of the magnitudes in the latter subset.
A simple strategy to examine the sources of errors in attenuation relations
Authors: Lee Yajie , Zeng Yuehua , Anderson John G.
Published: September 2021

A new method is presented in this article to visualize two different sources in the uncertainty of attenuation regression relations. The method utilizes the residuals from regression equations, defined as the log of the ratio of observed to predicted ground-motion parameters, from stations that have recorded more than one earthquake. The earthquake-to-earthquake variance is first calculated. Then the residuals are corrected with the mean residual of the corresponding earthquake. The corrected residual from one event is plotted versus the corrected residual from another event for every station that has more than one record. If site effects are perfectly represented in the regression, the resulting scatter plot will show statistically uncorrelated points, while extension along the diagonal and a positive correlation coefficient is the result of a contribution from site effects. This simple strategy allows us to visualize the uncertainty caused by the earthquake source and path in regression relations and indicates quantitatively how much we can improve the prediction by adding additional site information. The results obtained from this method are very similar to those that are calculated directly from the method proposed by Joyner (personal comm., 1997). In southern California, we find that source and path effects dominate the uncertainties at high frequency, while at low frequency, the regression can be still improved more significantly by correcting for the site effects.
A technique for simulating strong ground motion using hybrid Green's function
Authors: Kamae Katsuhiro , Irikura Kojiro , Pitarka Arben
Published: September 2021

A method for simulating strong ground motion for a large earthquake based on synthetic Green's function is presented. We use the synthetic motions of a small event as Green's functions instead of observed records of small events. Ground motions from small events are calculated using a hybrid scheme combining deterministic and stochastic approaches. The long-period motions from the small events are deterministically calculated using the 3D finite-difference method, whereas the high-frequency motions from them are stochastically simulated using Boore's method. The small-event motions are synthesized summing the long-period and short-period motions after passing them through a pair of matched filters to follow the omega-squared source model. We call the resultant time series “hybrid Green's functions” (HGF). Ground motions from a large earthquake are simulated by following the empirical Green's function (EGF) method. We demonstrate the effectiveness of the method at simulating ground motion from the 1995 Hyogo-ken Nanbu earthquake (Mw 6.9).
Spectral structure in the earth's microseismic background between 20 and 40 seconds
Authors: Holcomb L. Gary
Published: September 2021

The long-term behavior of a narrow band peak near 26 sec in the microseismic background of the Earth has been studied over many years at several sites. The amplitude of this peak has been determined to be a function of the Earth's weather seasons; it is larger during the southern hemisphere winter. In addition, the microseismic background between 20 and 40 sec has been scanned for peaks in the spectra; three more lower-level peaks have been identified with the possible presence of more.
EURO-SEISTEST strong-motion array near Thessaloniki, Northern Greece: A study of site effects
Authors: Dimitriu P. P. , Papaioannou Ch. A. , Theodulidis N. P.
Published: September 2021

The effects of local geology on the characteristics of strong ground motion have been, and continue to be, a field of active research. Despite the considerable efforts made so far, there are still several unresolved and controversial issues remaining. In particular, debates still continue over the limits of applicability of one-dimensional (1D) wave-propagation models. There are also unresolved questions related to the implementation and reliability of site-response estimation techniques such as the standard spectral ratio (SSR) and the horizontal-to-vertical spectral ratio (HVSR). This study addresses these issues on the basis of data from the EURO-SEISTEST strong-motion array at Volvi, near Thessaloniki, Greece. The data set used consists of accelerograms of 32 earthquakes, almost exclusively local, covering a magnitude range from ML 2.0 to 6.1. The range of recorded accelerations is 0.001 − 0.042 g.

We implement two 1D wave-propagation models (the Haskell-Thompson matrix method and Kennett's reflectivity-coefficient method) and the HVSR site-response assessment technique. We test the applicability of the 1D models in a basin environment. We use both Fourier-amplitude and response spectra to compute HVSR and investigate how HVSR is influenced by the choice of the time window and smoothing procedure.

We found the HVSR technique and 1D SH-wave modeling to perform reasonably well in a sediment-valley environment (the modeling was performed for a site in the center of the valley).
TheMLscale in eastern North America
Authors: Kim Won-Young
Published: September 2021

An attenuation curve for the local magnitude scale, ML, of eastern North American (ENA) earthquakes was empirically determined using synthetic Wood-Anderson seismograms derived from newly available broadband recordings from the U.S. National Seismographic Network (USNSN) and from additional stations of comparable quality. Wood-Anderson peak amplitudes measured on approximately 210 three-component, broadband digital records from 38 earthquakes in the distance range of 50 to 800 km were inverted for the attenuation curve and magnitude of each event. The earthquakes ranged from ML = 2.2 to 4.6 and were recorded at about 20 stations in the region. Separate attenuation curves were determined for the N-S, E-W, and vertical components, as well as for the mean of the two horizontal components. All curves had similar slopes indicating that ML can be determined from any one of the three components available. The Wood-Anderson peak amplitude phases were predominantly Lg waves arriving with a mean group velocity of 3.40 ± 0.23 km/sec and a mean period of 0.50 ± 0.26 sec. ML for earthquakes in ENA can be obtained from the horizontal-component Wood-Anderson peak amplitude in millimeters, A(Δ), using the formula ML = log10A(Δ) (in mm) + 1.55 log10 Δ (in km) − 0.22 + C, for distances 100 to 800 km and 2.2 ≦ ML ≦ 4.6 and where C = station magnitude correction. The ML is tied to Richter's (1935) ML scale for southern California. A similar formula is given to determine ML from the vertical-component synthetic Wood-Anderson seismograms. ML is related to Nuttli's mb(Lg) by ML = 0.976 mb(Lg) − 0.05 for earthquakes with 2.2 ≦ ML ≦ 4.6 in ENA. Analysis of six additional large earthquakes with ML ≧ 5 indicates that ML ≈ mb(Lg) − 0.15 in a wide magnitude range of 2 ≦ ML ≦ 6.5 in ENA.
Structure of the Lake County uplift: New Madrid seismic zone
Authors: Purser Jodi L. , Van Arsdale Roy B.
Published: September 2021

The central segment of the New Madrid seismic zone lies within a left step-over zone between two northeast-striking, right-lateral, strike-slip fault systems. Within this compressional step-over zone is the topographically and structurally high Lake County uplift, which includes the Tiptonville dome and Ridgely ridge. We believe these structures are a consequence of deformation in the hanging wall above the northwest-striking, southwest-dipping Reelfoot reverse fault. Reelfoot fault dips 73° from the surface to the top of the Precambrian at a depth of approximately 4 km. From 4 to 12 km depth, the fault dips 32° and is seismically active. Based on a fault-bend fold model, we believe that the Reelfoot fault becomes horizontal and aseismic at the top of the quartz brittle-ductile transition zone, at approximately 12 km depth. Our data indicate that the western margin of the Tiptonville dome-Ridgely ridge and the western margin of the Lake County uplift are bounded by east-dipping kink bands (backthrusts). Recent work suggests that the Reelfoot fault is responsible for the 7 February 1812, M 8 New Madrid earthquake. However, the Reelfoot fault has a surface area that is less than that necessary for an M 8 earthquake. A possible solution to this discrepancy between magnitude and fault plane area is that the associated backthrusts are seismogenic.
Influence of viscous coupling on seismic reflection and transmission in saturated porous media
Authors: Yang Jun , Sato Tadanobu
Published: September 2021

Wave propagation in saturated porous media involves complicated couplings between the solid skeleton and pore fluid. In particular, viscous coupling plays a key role because in general it makes wave propagation dispersive and dissipative. Although the importance of the viscous coupling in wave propagation in an unbounded saturated medium was recognized, the knowledge of its effect on the reflection and transmission from a saturated porous boundary is limited. A detailed investigation is therefore carried out in this article on the influence of viscous coupling in the reflection and transmission at an interface between saturated porous media and ordinary elastic media. The interface is considered to be either permeable or impermeable to include the effect of hydraulic boundary condition. In particular, the dependence of viscous coupling effect on the hydraulic condition at the interface is studied in this article. The variations of the reflection and transmission coefficients with the angle of incidence as well as the frequency for different values of viscous coupling are computed and compared for permeable interface and impermeable interface. In addition, the seismic reflection in two extreme cases of viscous coupling, that is, null viscous coupling and infinite viscous coupling, is discussed. The results indicate that the effect of viscous coupling is complicated; it depends strongly on the hydraulic condition at the interface as well as the frequency of the incident wave. Additionally, it depends upon the angle of incidence.
Near-surface scattering effects observed with a high-frequency phased array at Pinyon Flats, California
Authors: Vernon Frank L. , Pavlis Gary L. , Owens Tom J. , McNamara Dan E. , Anderson Paul N.
Published: September 2021

Analysis of data collected by a high-frequency array experiment conducted at Pinyon Flat in southern California provides strong evidence that the high-frequency wave field from local earthquakes at this hard-rock site are strongly distorted by near-surface scattering. The seismic array we deployed consisted of 60, 2-Hz natural frequency, three-component sensors deployed in a three-dimensional array. Two of the sensors were located in boreholes at 150 and 275 m depth. The other 58 sensors were deployed in an areal array above these boreholes. Thirty-six of these were deployed in a 6-by-6 element grid array with a nominal spacing of 7 m centered over the borehole sensors. The remaining 22 seismometers were laid out in two 11-element linear arrays radiating outward from the grid. Coherence calculations reveal a rapid loss of coherence at frequencies over 15 Hz at all but the shortest length scales of this array. Three-dimensional visualization techniques were used to closely examine the spatial stability of particle motions of P and S waves. This reveals systematic variations of particle motion across the array in which the particle motion tracks tilt drastically away from the backazimuth expected for an isotropic medium. These variations, however, are frequency dependent. Below around 8 Hz, the particle motions become virtually identical for all stations. At progressively higher frequencies, the wave-field particle motion becomes increasingly chaotic. Frequency-wave-number analysis of these data provide quantitative measures of the same phenomena. We find that direct wave f-k spectra are bathed in a background of signal-generated noise that varies from 10 to 30 dB down from the direct arrival signal. This signal-generated noise appears to be nearly white in wavenumber indicating the wavelength of this “noise” on the scale of tens of meters and less. Refraction measurements we made on two lines crisscrossing the array reveal that the weathered layer velocities are highly variable and define a very strong wave guide. Measured surface P-wave velocities varied from 400 to 1300 m/sec, and velocities at depth of approximately 15 m varied from 1600 to 2700 m/sec. Previous measurements in the boreholes showed that the intact granite below about 65 m depth has a velocity of approximately 5400 m/sec. These results demonstrate the extreme velocity contrast and degree of velocity heterogeneity of the near surface at this site. We conclude that all the observations we made can be explained by strong scattering of incident body-wave signals into a complex mishmash of body-wave and surface-wave modes in this heterogeneous near-surface wave guide.
NET HATA VE NOKSAN HESABI BELİRLEYİCİLERİNİN ANALİZİ: TÜRKİYE ÖRNEĞİ
Authors: KEŞAP Doğan , SANDALCILAR Ali Rıza
Published: September 2021

Ödemeler dengesi, bir ülkenin belirli bir dönem içerisinde diğer ülkelerle olan ekonomik ilişkilerinin, diğer bir ifadeyle, ülkenin döviz işlemlerinin kayda alındığı hesaptır. Ödemeler dengesi sayesinde, ülkenin küresel ekonomideki ağırlığı, uluslararası varlık ve yükümlülükleri, yapısal sorunları gibi birçok önemli unsur takip edilebilmektedir. Ancak, ödemeler dengesinin özellikle ölçüm yöntemlerinden kaynaklanan sorunlar sebebiyle, döviz giriş ve çıkışlarını tam olarak yansıtmadığı ifade edilmektedir. Bu sebeple, ödemeler dengesi içerisinde bu eksikliği yansıtmak ve gidermek adına Net Hata ve Noksan adıyla bir hesap daha bulunmaktadır. Net Hata ve Noksan Hesabı, ödemeler dengesi içerisinde yer alan cari işlemler ile sermaye ve finans hesaplarının resmi kayıtlarla açıklanamayan kısmını ifade etmektedir. Türkiye’nin ödemeler dengesi incelendiğinde, Net Hata ve Noksan Hesabının dalgalı bir seyir izlediği ve belirli dönemler itibarıyla yüksek değerler aldığı görülmektedir. Bu bağlamda, Net Hata ve Noksan Hesabı’nda ortaya çıkan dönemsel farklılıkların sebeplerinin araştırılmasının, ödemeler dengesinin daha açık bir şekilde anlaşılması açısından dikkate değer olduğu düşünülmektedir. Bu çalışmada, net hata ve noksan hesabının belirleyicileri, 2008:1-2020:3 dönemi için ARDL eşbütünleşme yöntemiyle analiz edilmektedir. Analize, açıklayıcı değişkenler olarak bavul ticareti, turizm gelirleri, ihracat rakamları ve yurt içi yerleşiklerin yurt dışında tuttukları mevduatları dâhil edilmiştir. Elde edilen bulgular, değişkenler arasında eşbütünleşme ilişkisinin olduğunu göstermiştir. Diğer taraftan, Net Hata ve Noksan hesabını açıklayan en önemli değişkenin, yurt içi yerleşiklerin yurt dışı mevdu-atları olduğu sonucuna varılmıştır.
Mesa Python platform for agent-based modelling
Authors: Pigorev Dmitry
Published: September 2021

Mesa is a licensed by Apache development environment for agent-based models (or ABM) in Python. It allows users to create agent-based models using built-in basic components (such as spatial and agent schedulers) or custom implementations; visualize them using the interface in a web browser; and analyze their results using Python data analysis tools. The purpose of the development of the environment was the desire of the authors to create an alternative for NetLogo, Repast or MASON based on the Python language.
National security of countries all over the world
Authors: Makarov Valery
Published: September 2021

The article continues the study “Modeling and Assessment of National Power of Different Countries all over the World” dedicated to the calculation of national power indicator. It is currently the most informative and popular indicator in the world that integrally characterizes the aggregate potential of a particular country and at the same time allows comparing the level of its power and socio-economic development with other countries. The research results were published in the article “Modeling and Assessment of National Power of Different Countries all over the World”.
If national power of the state, in fact, determines its potential capabilities and gross indicators are mainly used for the calculation, then national security indicators are calculated on the basis of normalized values (as a rule, per capita) and indicate the level of development of one or another component of the social-ecological-economic system of the country, as well as the efficiency of using the existing potential.
In this article we will calculate national security indicators of UN member states using the methods of multivariate statistical analysis. Moreover, we will estimate threshold values for all national security factors considered herein. The last part of the paper will contain a forecast of national security for the medium term.