bluuebunny/crossref_metadata_2025_split huggingface dataset:
Methods for regression analysis of strong-motion data
Authors: Joyner William B. , Boore David M. 
Published: September 2021

Abstract
We introduce a new computational method for implementing Brillinger and Preisler's (1984, 1985) one-stage maximum-likelihood analysis of strong-motion data. We also reexamine two-stage methods and agree with Masuda and Ohtake (1992) that rigorous analysis requires off-diagonal terms in the weighting matrix for the second-stage regression but note that Masuda and Ohtake failed to account for the earthquake-to-earthquake component of variance. Analysis by Monte Carlo methods shows that both one-stage and two-stage methods, properly applied, are unbiased and that they have comparable uncertainties. Both give the same correct results when applied to the data that Fukushima and Tanaka (1990) have shown cannot be satisfactorily analyzed by ordinary least squares. The two-stage method is more efficient computationally, but for typical problems neither method requires enough time to make efficiency important. Of the two methods, only the two-stage method can readily be used with the techniques described by Toro (1981) and McLaughlin (1991) for overcoming the bias due to instruments that do not trigger.
On Cagniard's problem for a qSH line source in transversely isotropic media
Authors: H. T. Le Lawrence 
Published: September 2021

Abstract
This paper studies the response to a qSH pulse generated by a line source, of two homogeneous half-spaces (transversely isotropic elastic or viscoelastic) separated by a plane boundary.
For a simple model of two transversely isotropic half-spaces in welded contact, all the arrivals, including the incident, reflected, head, transmitted, and evanescent waves, that are predicted by the isotropic theory are present. For the 15% change in wave speeds considered here, anisotropy changes the dynamic and kinematic characteristics of the pulses. Depending on the anisotropy factor, the change can be pronounced. Because of the significant time shift and amplitude variation of the first arrivals due to anisotropy, proper consideration of the anisotropy of the medium is necessary in interpreting vertical seismic profiles or crosshole seismic data by means of any travel time or amplitude tomographic scheme.
Maximizing the signal-to-noise ratio of the electromagnetic seismometer: The optimum coil resistance, amplifier characteristics, and circuit
Authors: Rodgers Peter W. 
Published: September 2021

AbstractThis study finds the optimum coil resistance, rc.opt, which maximizes the signal-to-noise ratio (SNR) of an electromagnetic (EM) seismometer and amplifier combination. The optimum coil resistance is shown to be the product of a seismometer factor (SF) times the noise resistance, Rn, of the amplifier. The seismometer factors range from 1.13 to 3.66 for the nine EM seismometers considered. The minimum noise figure solution, in which the amplifier noise resistance is set equal to the coil resistance, is shown to correspond to the special case in which there is no damping resistor present. It is also shown that the optimum form for the noise resistance is a constant independent of frequency and that this feature can be approximated with FET-like components such as the MAT-02. Examples of using rc.opt are given using both the 5500-ohm and the 500-ohm 1-Hz L4-C seismometers paired with the OP-27 and LT1028 operational amplifiers, respectively. It is pointed out that, although the resulting amplitude signal-to-noise ratios (ASNRs) are approximately equal, it is best to choose the seismometer-amplifier pair having the larger generator constant because it results in a larger signal. Furthermore, if the coil resistance is not the optimum value, the resulting decrease in the ASNR is less if the coil resistance is chosen greater than the optimum rather than less.The deleterious effects of mismatching seismometer and amplifier are shown by comparing ASNRs for the GS-13 seismometer paired with three different amplifiers. The degradation in ASNR is found to be as large as a factor of 3. It is pointed out that mismatching would not be done purposely but can inadvertently occur when connecting an EM seismometer to a seismic recorder whose input noise resistance properties are unknown, as in generally the case. It is recommended that manufacturers of seismic recorders obtain the necessary input noise data from the component manufacturers and supply the input noise resistance to users.Finally, the three commonly used single-ended preamplifier circuits used for EM seismometers are compared in terms of their resulting ASNRs. The same seismometer and amplifier are used in all three circuits. For the GS-13/MAT-02 pair, the noninverting, parallel damping resistor circuit resulted in an ASNR that was 3.8 times larger than that for the inverting, parallel damping resistor circuit, and 3 times larger than that for the inverting, series damping resistor circuit.
Estimation of strong ground motions in Mexico City expected for large earthquakes in the Guerrero seismic gap
Authors: Kanamori Hiroo , Jennings Paul C. , Singh Shri Krishna , Astiz Luciana 
Published: September 2021

AbstractWe performed simulations of ground motions in Mexico City expected for large earthquakes in the Guerrero seismic gap in Mexico. The simulation method uses as empirical Green's functions the accelerograms recorded in Mexico City during four small to moderate earthquakes (8 Feb. 1988, Ms = 5.8; 25 April 1989, Mw = 6.9; 11 May 1990, Mw = 5.5; and 31 May 1990, Mw = 6.0) in the Guerrero gap. Because these events occurred in the Guerrero gap, and have typical thrust mechanisms, the propagation path and site effects can be accurately included in our simulation. Fault rupture patterns derived from the 1985 Michoacan earthquake and source scaling relations appropriate for Mexican subduction zone earthquakes are used. If the Guerrero event is similar to the 1985 Michoacan event, the resulting response spectrum in Mexico City will be approximately twice as large as that of the 1985 Michoacan earthquake at periods longer than 2 sec. At periods shorter than 2 sec, the amplitude will be 2 to 3 times larger than that for the Michoacan earthquake. If the events in the Guerrero seismic gap occur as a sequence of magnitude 7.5 to 7.8 events, as they did in the previous sequence around the turn of the century, the strong motion in Mexico City is estimated to be about half that experienced during the 1985 Michoacan earthquake at periods longer than 2 sec. However, several factors affect this estimate. The magnitude of the possible events has a significant range and, if a rupture sequence is such that it enhances ground-motion amplitude with constructive interference, as occurred during the second half of the Michoacan sequence, some components of the ground motion could be amplified by a factor of 2 to 3. To aid in the interpretation of the simulated motion for purposes of design or hazard assessment, design spectra for the CDAO site in Mexico City are derived from the response spectra of the simulated ground motions.
Source study of the 1906 San Francisco earthquake
Authors: Wald David J. , Kanamori Hiroo , Helmberger Donald V. , Heaton Thomas H. 
Published: September 2021

Abstract
All quality teleseismic recordings of the great 1906 San Francisco earthquake archived in the 1908 Carnegie Report by the State Earthquake Investigation Commission were scanned and digitized. First order results were obtained by comparing complexity and amplitudes of teleseismic waveforms from the 1906 earthquake with well calibrated, similarly located, more recent earthquakes (1979 Coyote Lake, 1984 Morgan Hill, and 1989 Loma Prieta earthquakes) at nearly co-located modern stations. Peak amplitude ratios for calibration events indicated that a localized moment release of about 1 to 1.5 × 1027 dyne-cm was responsible for producing the peak the teleseismic body wave arrivals. At longer periods (50 to 80 sec), we found spectral amplitude ratios of the surface waves require a total moment release between 4 and 6 × 1027 dyne-cm for the 1906 earthquake, comparable to previous geodetic and surface wave estimates (Thatcher, 1975). We then made a more detailed source analysis using Morgan Hill S body waves as empirical Green's Functions in a finite fault subevent summation. The Morgan Hill earthquake was deemed most appropriate for this purpose as its mechanism is that of the 1906 earthquake in the central portion of the rupture. From forward and inverse empirical summations of Morgan Hill Green's functions, we obtained a good fit to the best quality teleseismic waveforms with a relatively simple source model having two regions of localized strong radiation separated spatially by about 110 km. Assuming the 1906 epicenter determined by Bolt (1968), this corresponds with a large asperity (on the order of the Loma Prieta earthquake) in the Golden Gate/San Francisco region and one about three times larger located northwest along strike between Point Reyes and Fort Ross. This model implies that much of the 1906 rupture zone may have occurred with relatively little 10 to 20 sec radiation. Consideration of the amplitude and frequency content of the 1906 teleseismic data allowed us to estimate the scale length of the largest asperity to be less than about 40 km. With rough constraints on the largest asperity (size and magnitude) we produced a suite of estimated synthetic ground velocities assuming a slip distribution similar to that of the Loma Prieta earthquake but with three times as much slip. For purposes of comparison with the recent, abundant Loma Prieta strong motion data set, we “moved” the largest 1906 asperity into Loma Prieta region. Peak ground velocity amplitudes are substantially greater than those recorded during the Loma Prieta earthquake, and are comparable to those predicted by the attenuation relationship of Joyner and Boore (1988) for a magnitude MW = 7.7 earthquake.
Three-dimensional simulations of ground motions in the San Bernardino Valley, California, for hypothetical earthquakes on the San Andreas fault
Authors: Frankel Arthur 
Published: September 2021

AbstractThree-dimensional finite difference simulations of elastic waves in the San Bernardino Valley were performed for two hypothetical earthquakes on the San Andreas fault: a point source with moment magnitude M5 and an extended rupture with M6.5. A method is presented for incorporating a source with arbitrary focal mechanism in the grid. Synthetics from the 3-D simulations are compared with those derived from 2-D (vertical cross section) and 1-D (flat-layered) models. The synthetic seismograms from the 3-D and 2-D simulations exhibit large surface waves produced by conversion of incident S waves at the edge of the basin. Seismograms from the flat-layered model do not contain these converted surface waves and underestimate the duration of shaking. The seismograms from the 3-D simulations have larger amplitude coda than do the seismograms from the 2-D case because of the presence of off-azimuth surface wave arrivals in the 3-D simulations that are not included in the 2-D simulations. Snapshots of the wavefield of the 3-D simulation show that these off-azimuth arrivals represent surface waves reflected from the edges of the basin. The anelastic attenuation of the sediments is a key parameter controlling the overall duration of motion. Some of the coda energy at rock sites near the basin edges represents leakage of surface wave energy out of the basin. For the M6.5 earthquake simulation, the largest ground velocities occur where surface waves reflected from the edge of the basin interfere constructively with the trapped waves that follow the direct S-wave. Maps of maximum ground velocity are produced for two directions of rupture propagation. The largest velocities occur in localized portions of the basin. The location of the largest velocities changes with the rupture propagation direction. Contours of maximum shaking are also dependent on asperity positions and radiation pattern.
Modeling three-dimensional site response effects in the Marina District Basin, San Francisco, California
Authors: Graves Robert W. 
Published: September 2021

AbstractLoma Prieta aftershock data recorded in the Marina District of San Francisco clearly show a large amplification in ground motion and a much longer duration of shaking relative to the response recorded at nearby rock sites for frequencies between 1 and 10 Hz. Some of the amplification can be explained by the difference in impedance between the Marina sites and the rock sites; however, 1D models underpredict the amplification in the range 1 to 3 Hz and cannot account for the increased durations. The available geologic information within the Marina District indicates lateral variations in sediment thickness and composition. Our previous experience with modeling wave propagation in these types of basin environments has shown that these structures can greatly amplify and prolong the duration of the signals observed at sites within the basin. In this study, the seismic response of the Marina basin is modeled with a 3D finite-difference wave field simulation technique. Results from the numerical simulations at the basin sites indicate that the large amplitude arrivals following the direct S wave are surface waves traveling at relatively slow apparent velocities. In general, the surface waves contain the strongest recorded motions and produce the long duration of shaking observed at these sites. In addition, spectral ground motions from the 3D basin models do fairly well in reproducing the observed spectral amplification near 1 Hz that is characteristic of the basin sites. The simulation results suggest that focusing effects due to the geometry of the basin structure itself have a significant impact in determining the resonant periods at these basin sites.
Reflection and transmission of surface waves at a vertical interface in anisotropic elastic media
Authors: Its E. N. , Lee J. S. 
Published: September 2021

Abstract
Propagation of surface waves across a vertical interface between anisotropic blocks is considered in this paper. Dyadic representation of a far field Green's function for an anisotropic half-space is constructed first. An analytical procedure is then developed to determine the reflection and transmission coefficients of surface waves at the vertical interface between two laterally homogeneous anisotropic quarter-spaces. Numerical results of Rayleigh wave reflection at vertical interfaces between dissimilar blocks are presented and the trade-off between anisotropy and inhomogeneity is discussed.
Continuous measurements of microtremors on sediments and basement in Los Angeles, California
Authors: Yamanaka Hiroaki , Dravinski Marijan , Kagami Hiroshi 
Published: September 2021

Abstract
Continuous measurement of microtremors at two sites on basement rock and sediments was carried out in Los Angeles, California, in order to understand the fundamental characteristics of microtremors. A predominant peak with a period of about 6.5 sec was found in the microtremor spectra in both media. The spectral amplitude of the peaks varied gradually with time in a similar manner at the two sites. Their time-variant characteristics are in agreement with change in oceanic swell height observed at an oceanic buoy in the southwest of Los Angeles. This suggests that they originate from an oceanic disturbance. On the other hand, a clear daily variation of spectral amplitudes at a period of 0.3 sec indicates that short-period microtremors are caused by cultural noises. It was found that the spectral ratio of long-period microtremors between the basement and the sediments was repeatable, although the spectral amplitudes at the two sites were time-variant. The spectral ratio of the long-period microtremors was similar to that derived from strong motion records. This suggests the applicability of spectral ratios of microtremors to assess the effects of deep sediments on long-period earthquake ground motion.
Display and assessment of earthquake focal mechanisms by vector representation
Authors: Sipkin Stuart A. 
Published: September 2021

Abstract
The isomorphism between symmetric, three-dimensional, second-order tensors and six-dimensional vectors is exploited to display suites of seismic moment tensors and to asses their similarities and differences, both graphically and quantitatively. Using the southern Mid-Atlantic Ridge as an example, I show that this method successfully differentiates between different mechanism types and orientations. In addition, the dispersion within a group of mechanisms is successfully quantified.
Passcal instrument performance during the Tibetan Plateau Passive Seismic Experiment
Authors: Owens Thomas J. , Randall George E. , Wu Francis T. , Zeng Rongsheng 
Published: September 2021

Summary
The PASSCAL instrumentation performed very well in the Tibetan Plateau Seismic Experiment. This experiment has demonstrated the viability of recording high-quality broadband data at temporary sites in extreme environments. It also highlights some areas where further development is needed. Primarily, more effort is needed to develop more versatile triggering options for the PASSCAL instruments. Such developments could both increase the instrument's success at recording low magnitude teleseismic events for travel-time studies and save disk space when recording local events, thus further increasing the feasibility of long deployments in remote regions. Although the use of the PASSCAL instrument's calibration circuitry for sensor recentering is a valuable technique, more experience is needed in the construction of sensor pads to minimize tilt problems that require site visits to relevel the seismometer such as we experienced at a few sites in the winter. This may also lead to improved low-frequency noise levels, although signals with periods greater than 200 sec can be recovered from these sites.
The most exciting aspect of the data we have collected is its broad frequency content and spatial density. We anticipate that this type of experiment will be increasingly useful in the study of lithospheric interactions as well as deep Earth structure. This data was delivered to the IRIS Data Management Center in early September 1993 and is available to the community. Two other broadband passive-seismic experiments, the Baikal Rift experiment (Gao et al. 1992) and the Rocky Mountain Front experiment (Sheehan et al. 1992) should be delivered to the IRIS DMC in the Fall of 1993 as well. Temporary broadband seismic experiments represent an extension of the permanent Global Seismic Network (GSN). We encourage the seismological community to incorporate these data into any research using GSN data in order to maximize the potential utility of this new mode of seismic recording.
Changing indications of prenatal diagnosis in molecular era: experience of single centre in North India
Authors: Dwivedi Aradhana , Bhatt Reema Kumar , Kishore Kamal 
Published: September 2021

Background: About 3-5% of pregnancies are complicated by chromosomal aberrations and birth defects. In the past prenatal genetic testing is identified to be largely restricted to the detection of chromosomal abnormalities like aneuploidy. With advances in the field of medical genetics, there has been substantial rise in use of prenatal genetic testing and we wanted to find out the same in our cohort of patients.Methods: Study design was retrospective, single-center observational study. Pregnant patients who underwent invasive testing for prenatal genetic disorder at fetal medicine specialty were considered for inclusion in the study. The invasive procedures that were performed in our study were amniocentesis, chorionic villous sampling (CVS) and cordocentesis.Results: Total 515 pregnant women underwent prenatal testing. Amniocentesis was the most common procedure to be performed accounting for about 74% of total cases. In our cohort, abnormal aneuploidy screening was the most common indication for performing prenatal diagnosis (64% of cases), while 12.8 % underwent prenatal diagnosis due to abnormalities/genetic disorder in previous child. Abnormalities in antenatal ultrasonography accounted for 16% of cases. Quantitative fluorescene polymerase chain reaction, rapid aneuploidy testing (QFPCR) was performed in all the cases. Karyotype was performed in 273 cases while chromosomal microarray was performed on 92 samples. Multiplex ligation dependent probe amplification (MLPA) was done for 15 patients. Targeted mutation testing (Sanger sequencing) was done on 121 prenatal samples. Exome sequencing was performed on 14 fetuses. Out of 515 a total of 79 fetuses (15.3%) were found to have genetic disorder. Aneuploidies were identified in 11 fetuses (2.1%), 12 fetuses (2.3%) were found to have pathogenic CNVs (Copy number variants). Single gene disorders were found in 56 fetuses (10.8%). Conclusions: We have moved very rapidly from Karyotyping to chromosomal microarray to exome sequencing. There has been rapid change in the indications for prenatal Diagnosis from yesteryears with coming of new era of genetics.
Evaluation of hysterectomy in a tertiary care hospital of central India: a retroprospective study
Authors: Mahilange Anchala 
Published: September 2021

Background: Hysterectomy is the most common gynaecological surgical procedure after caesarean section. In India there is lower rate (4-6%) of hysterectomy has been reported, while there is higher frequency of hysterectomy (10-20%) in developed countries. Currently there are three main types of hysterectomy operations in practice for benign diseases abdominal hysterectomy, vaginal hysterectomy and laparoscopic hysterectomy. Abdominal hysterectomy remains the predominant method of uterus removal. The present study was planned t to analyse changes in the trends of hysterectomy from past 3 year in the study area.Methods: The present observational study was conducted in department of obstetrics and gynaecology and associated Dr. B.R.A.M. hospital Raipur (CG), India. Data was collected retrospectively from January 2009 to May 2012 from hospital medical records. Prospectively data was obtained from patient and his file from June 2013 to September 2014. Data was compiled in MS-excel and checked for its completeness and correctness, and then it was analyzed by using suitable software.Results: Total no of hysterectomy conducted in study duration was 1000. Study showed declining trend of hysterectomy in our institute. Most common age group of hysterectomy was 41-50 year. which 45.8% followed by age group 31-40 that is 32.5%. Most common indication of hysterectomy was fibroid uterus 33.6% followed by prolapse uterus 29.5%. 29% cases were operated via vaginal route for descent of uterus and 21% cases operated by vaginal route for non-descent uterus.50% cases were operated via abdominal route. Average operating time for TAH was 1.43±0.50, for VH was 1.08±0.03. Average hospital stay for TAH was 8.87±3.31 and VH was 5.27±1.07. Conclusions: In our study it had been seen that rate of hysterectomy is in decreasing trend as more conservative approach is now preferred. To minimize most of complications of hysterectomy second opinion fresh eyes and multi-disciplinary approach is recommend in all patients undergoing this procedure.