A P- and S-Wave Picking Technique Based on the Probabilistic Density Function of Seismic-Waveform Amplitude

2020 ◽  
Vol 110 (2) ◽  
pp. 763-782 ◽  
Author(s):  
Mitsutaka Oshima ◽  
Hiroshi Takenaka
Keyword(s):  
Density Function ◽  
Seismic Station ◽  
Amplitude Distribution ◽  
Random Waves ◽  
S Wave ◽  
S Waves ◽  
Seismic Waveform ◽  
Seismic Records ◽  
Waveform Amplitude ◽  
Probabilistic Density Function

ABSTRACT Picking of P and S waves is a fundamental process in seismology, and various kinds of picking techniques have been developed. Seismic waveforms change dramatically depending on the magnitude, the mechanism of the earthquake, and the positional relationship between the hypocenter and the seismic station. The availability of various picking techniques is supposed to be helpful for appropriately dealing with a variety of seismic records. Hence, in addition to the revision of conventional techniques, the development of new picking techniques is worthwhile. In the present study, we developed a new stochastic technique to detect P and S waves based on the statistical amplitude distribution in the seismic record amplitude. In the proposed method, the probabilistic density function (PDF) of the amplitude is calculated for each segment of seismic records, and the similarity between the PDF of the amplitude and that of the Rayleigh or Gaussian distribution is evaluated by divergence. Because Rayleigh and Gaussian distributions are typically found in amplitude distributions of highly random waves, such as coda waves, the divergence indicates the randomness of the seismic records. P and S waves are found by tracing the temporal change of the divergence. We tested the proposed method using local seismic records for a series of seismic events that occurred before and after the 2016 Kumamoto earthquake. The mean absolute errors for picking P and S waves are 2.72×10−2 and 7.38×10−2  s, respectively. The proposed method is a simple and new statistical picking method that enables automatic detection of P- and S-wave arrivals.

scholarly journals Responses of dipole-source reflected shear waves in acoustically slow formations

2019 ◽  
Author(s):  
Hao Wang ◽  
Ning Li ◽  
Caizhi Wang ◽  
Hongliang Wu ◽  
Peng Liu ◽  
...  
Keyword(s):  
Finite Difference Time Domain ◽  
Dipole Source ◽  
Sh Wave ◽  
S Wave ◽  
High Fracture ◽  
S Waves ◽  
Angle Fracture ◽  
Dip Angle ◽  
Difference Time

Abstract In the process of dipole-source acoustic far-detection logging, the azimuth of the fracture outside the borehole can be determined with the assumption that the SH–SH wave is stronger than the SV–SV wave. However, in slow formations, the considerable borehole modulation highly complicates the dipole-source radiation of SH and SV waves. A 3D finite-difference time-domain method is used to investigate the responses of the dipole-source reflected shear wave (S–S) in slow formations and explain the relationships between the azimuth characteristics of the S–S wave and the source–receiver offset and the dip angle of the fracture outside the borehole. Results indicate that the SH–SH and SV–SV waves cannot be effectively distinguished by amplitude at some offset ranges under low- and high-fracture dip angle conditions, and the offset ranges are related to formation properties and fracture dip angle. In these cases, the fracture azimuth determined by the amplitude of the S–S wave not only has a $180^\circ $ uncertainty but may also have a $90^\circ $ difference from the actual value. Under these situations, the P–P, S–P and S–S waves can be combined to solve the problem of the $90^\circ $ difference in the azimuth determination of fractures outside the borehole, especially for a low-dip-angle fracture.

scholarly journals Indicators for site characterization at seismic station: recommendation from a dedicated survey

2021 ◽  
Author(s):  
Giovanna Cultrera ◽  
Cécile Cornou ◽  
Giuseppe Di Giulio ◽  
Pierre-Yves Bard
Keyword(s):  
Seismic Station ◽  
International Workshop ◽  
Site Characterization ◽  
Companion Paper ◽  
Background Information ◽  
Online Questionnaire ◽  
Seismic Records ◽  
Seismic Networks ◽  
High Level ◽  
Data Acquisition And Processing

AbstractIn recent years, the permanent seismic networks worldwide have largely increased, raising the amount of earthquake signals and the applications using seismic records. Although characterization of the soil properties at recording stations has a large impact on hazard estimates, it has not been implemented so far in a standardized way for reaching high-level metadata. To address this issue, we built an online questionnaire for the identification of the indicators useful for a reliable site characterization at a seismic station. We analysed the answers of a large number of experts in different fields, which allowed us to rank 24 different indicators and to identify the most relevant ones: fundamental frequency (f0), shear-wave velocity profile (VS), time-averaged Vs over 30 m (VS30), depth of seismological and engineering bedrock (Hseis_bed and Heng_bed), surface geology and soil class. Moreover, the questionnaire proposed two additional indices in terms of cost and difficulty to obtain a reliable value of each indicator, showing that the selection of the most relevant indicators results from a complex balance between physical relevancy, average cost and reliability. For each indicator we propose a summary report, provided as editable pdf, containing the background information of data acquisition and processing details, with the aim to homogenize site metadata information at European level and to define the quality of the site characterization (see companion paper Di Giulio et al. 2021). The selected indicators and the summary reports have been shared within European and worldwide scientific community and discussed in a dedicated international workshop. They represent a first attempt to reach a homogeneous set of high-level metadata for site characterization.

Estimates of Q in central Asia as a function of frequency and depth using the coda of locally recorded earthquakes

1982 ◽  
Vol 72 (1) ◽  
pp. 129-149
Author(s):  
S. W. Roecker ◽  
B. Tucker ◽  
J. King ◽  
D. Hatzfeld
Keyword(s):  
Frequency Dependence ◽  
Central Asia ◽  
Wide Frequency Range ◽  
S Wave ◽  
Uppermost Mantle ◽  
Regional Heterogeneity ◽  
S Waves ◽  
Tectonic Processes ◽  
Hindu Kush ◽  
Attenuation Mechanism

abstract Digital recordings of microearthquake codas from shallow and intermediate depth earthquakes in the Hindu Kush region of Afghanistan were used to determine the attenuation factors of the S-wave coda (Qc) and primary S waves (Qβ). An anomalously rapid decay of the coda shortly after the S-wave arrival, observed also in a study of coda in central Asia by Rautian and Khalturin (1978), seems to be due primarily to depth-dependent variations in Qc. In particular, we deduce the average Qc in the crust and uppermost mantle (<100-km depth) is approximately four times lower than the deeper mantle (<400-km depth) over a wide frequency range (0.4 to 24 Hz). Further, while Qc generally increases with frequency at any depth, the degree of frequency dependence of Qc depends on depth. Except at the highest frequency studied here (∼48 Hz), the magnitude of Qc at a particular frequency increases with depth while its frequency dependence decreases. For similar depths, determinations of Qβ and Qc agree, suggesting a common wave composition and attenuation mechanism for S waves and codas. Comparison of these determinations of Qc in Afghanistan with those in other parts of the world shows that the degree of frequency dependence of Qc correlates with the expected regional heterogeneity. Such a correlation supports the prejudice that Qc is primarily influenced by scattering and suggests that tectonic processes such as folding and faulting are instrumental in creating scattering environments.

scholarly journals Array data processing techniques applied to long-period shear waves at Fennoscandian seismograph stations

1969 ◽  
Vol 59 (5) ◽  
pp. 1863-1887
Author(s):  
James H. Whitcomb
Keyword(s):  
Data Processing ◽  
Velocity Ratio ◽  
Underground Explosion ◽  
High Signal ◽  
S Wave ◽  
Array Data ◽  
S Waves ◽  
Long Period ◽  
Normal Record ◽  
The Individual

abstract Array data processing is applied to long-period records of S waves at a network of five Fennoscandian seismograph stations (Uppsala, Umeå, Nurmijärvi, Kongsberg, Copenhagen) with a maximum separation of 1300 km. Records of five earthquakes and one underground explosion are included in the study. The S motion is resolved into SH and SV, and after appropriate time shifts the individual traces are summed, both directly and after weighting. In general, high signal correlation exists among the different stations involved resulting in more accurate time readings, especially for records which have amplitudes that are too small to be read normally. S-wave station residuals correlate with the general crustal type under each station. In addition, the Fennoscandian shield may have a higher SH/SV velocity ratio than the adjacent tectonic area to the northwest.SV-to-P conversion at the base of the crust can seriously interfere with picking the onset of Sin normal record reading. The study demonstrates that, for epicentral distances beyond about 30°, existing networks of seismograph stations can be successfully used for array processing of long-period arrivals, especially the S arrivals.

Numerical simulation of azimuthal acoustic logging in a borehole penetrating a rock formation boundary

Geophysics ◽  
2016 ◽  
Vol 81 (3) ◽  
pp. D283-D291 ◽  
Author(s):  
Peng Liu ◽  
Wenxiao Qiao ◽  
Xiaohua Che ◽  
Xiaodong Ju ◽  
Junqiang Lu ◽  
...  
Keyword(s):  
Domain Model ◽  
P Wave ◽  
S Wave ◽  
Angle Variation ◽  
P Waves ◽  
Acoustic Logging ◽  
S Waves ◽  
Rock Formation ◽  
Logging Tool ◽  
Difference Time

We have developed a new 3D acoustic logging tool (3DAC). To examine the azimuthal resolution of 3DAC, we have evaluated a 3D finite-difference time-domain model to simulate a case in which the borehole penetrated a rock formation boundary when the tool worked at the azimuthal-transmitting-azimuthal-receiving mode. The results indicated that there were two types of P-waves with different slowness in waveforms: the P-wave of the harder rock (P1) and the P-wave of the softer rock (P2). The P1-wave can be observed in each azimuthal receiver, but the P2-wave appears only in the azimuthal receivers toward the softer rock. When these two types of rock are both fast formations, two types of S-waves also exist, and they have better azimuthal sensitivity compared with P-waves. The S-wave of the harder rock (S1) appears only in receivers toward the harder rock, and the S-wave of the softer rock (S2) appears only in receivers toward the softer rock. A model was simulated in which the boundary between shale and sand penetrated the borehole but not the borehole axis. The P-wave of shale and the S-wave of sand are azimuthally sensitive to the azimuth angle variation of two formations. In addition, waveforms obtained from 3DAC working at the monopole-transmitting-azimuthal-receiving mode indicate that the corresponding P-waves and S-waves are azimuthally sensitive, too. Finally, we have developed a field example of 3DAC to support our simulation results: The azimuthal variation of the P-wave slowness was observed and can thus be used to reflect the azimuthal heterogeneity of formations.

A computer program for focal mechanism determination combining P and S wave data

1969 ◽  
Vol 59 (2) ◽  
pp. 503-519
Author(s):  
Agustin Udias ◽  
Dieter Baumann
Keyword(s):  
Computer Program ◽  
Focal Mechanism ◽  
Total Error ◽  
Source Model ◽  
Polarization Angle ◽  
S Wave ◽  
Period Range ◽  
S Waves ◽  
Double Couple ◽  
The Relationship

abstract A computer program has been developed to find the orientation of a double couple source model for the mechanism of an earthquake which best satisfies the data from P and S waves. The relationship between the two axes of the solution given by the equations for the polarization angle of S is used in order to rapidly find the orientation of the source model for which a total error value involving the error of S and P data is a minimum. The program gives best results for data from homogeneous instruments of similar period range. Solutions for three earthquakes, selected because of the orientation of the source, are presented and the reliability of their solutions under ideal conditions is discussed.

Abstract 4130: Applicability Of Left Ventricular Hypertrophy Electrocardiographic Criteria In Professional Athletes

Circulation ◽  
2008 ◽  
Vol 118 (suppl_18) ◽  
Author(s):  
Nelson Samesima ◽  
Carlos A Pastore ◽  
Luciana D de Matos ◽  
Fernanda F Fumagalli ◽  
Mariane V Ferreira ◽  
...  
Keyword(s):  
Left Ventricular Hypertrophy ◽  
Ventricular Hypertrophy ◽  
Statistical Significance ◽  
False Negative ◽  
Left Ventricular ◽  
False Positives ◽  
Professional Athletes ◽  
Categorical Variables ◽  
S Wave ◽  
S Waves

Introduction. The widely known electrocardiographic criteria for diagnosing left ventricular hypertrophy (LVH) use QRS complex voltages to define whether there is left ventricle enlargement or not. Mild myocardial hypertrophy is detected in many professional athletes and this is a consequence of their daily intensity of training. Thus it is not unusual that athlete’s ECGs show large QRS voltages with normal hearts. Objective. To evaluate the applicability of the usual electrocardiographic criteria for LVH - Sokolow-Lyon, Romhilt-Estes, Cornell and Gubner - in a population of professional athletes. Methods. The four LVH criteria for diagnosing LVH were applied to analyse ECGs of 107 professional athletes (71% soccer players, 29% marathonists, all male, age 25± 10 years, training for 9± 8 years) by the same observer unaware of echocardiographic results. ECG was considered to be indicative of LVH if: Sokolow-Lyon ≥35mm (V 1or 2 S wave+V 5or 6 R wave); Romhilt-Estes score ≥5 points (frontal plane: R or S waves ≥ 20mm, horizontal plane: R or S waves ≥ 30mm, Morris indices, V 5or 6 strain pattern, left axis deviation ≥ − 30°, intrinsecoid deflection ≥ 0.04s, QRS duration ≥ 0.10s) ; Cornell ≥ 28mm (aV L R wave + V 3 S wave); Gubner ≥ 22mm (D I R wave + D III S wave). Hypertrophy was considered whenever: LV diastolic diameter ≥ 60mm and/or septum ≥ 13mm and/or LV posterior wall ≥ 13mm. Kruskal-Wallis was used to statistically analyse quantitative variables, corrected chi-square test for categorical variables. Significance level: p ≤ 0.05. Results. Romhilt-Estes showed the best results (75% sensitivity, 84% specificity, 16 false-positives, 1 false-negative), and was the only criteria with statistical significance (p = 0.047). Sokolow-Lyon showed 100% sensitivity, 15% specificity, p = 0.545, 88% false-positives, 0% false-negative. Cornell and Gubner showed 25% and 0% sensitivity, 95% and 99% specificity, p=0.205 and p = 0.449, respectively. Conclusion. In this male population of professional athletes, Romhilt-Estes score proved to be the best criterion for identifying left ventricular hypertrophy, while Sokolow-Lyon criterion did not discriminate normal from abnormal hearts. Cornell and Gubner criteria should not be used in this population because of their low sensitivity.

Green's function of the Lord–Shulman thermo-poroelasticity theory

2020 ◽  
Vol 221 (3) ◽  
pp. 1765-1776 ◽  
Author(s):  
Jia Wei ◽  
Li-Yun Fu ◽  
Zhi-Wei Wang ◽  
Jing Ba ◽  
José M Carcione
Keyword(s):  
Plane Wave ◽  
Green’S Function ◽  
Green's Function ◽  
Heterogeneous Media ◽  
Numerical Algorithms ◽  
Heat Diffusion ◽  
P Wave ◽  
Wave Analysis ◽  
S Wave ◽  
S Waves

SUMMARY The Lord–Shulman thermoelasticity theory combined with Biot equations of poroelasticity, describes wave dissipation due to fluid and heat flow. This theory avoids an unphysical behaviour of the thermoelastic waves present in the classical theory based on a parabolic heat equation, that is infinite velocity. A plane-wave analysis predicts four propagation modes: the classical P and S waves and two slow waves, namely, the Biot and thermal modes. We obtain the frequency-domain Green's function in homogeneous media as the displacements-temperature solution of the thermo-poroelasticity equations. The numerical examples validate the presence of the wave modes predicted by the plane-wave analysis. The S wave is not affected by heat diffusion, whereas the P wave shows an anelastic behaviour, and the slow modes present a diffusive behaviour depending on the viscosity, frequency and thermoelasticity properties. In heterogeneous media, the P wave undergoes mesoscopic attenuation through energy conversion to the slow modes. The Green's function is useful to study the physics in thermoelastic media and test numerical algorithms.

scholarly journals Automated measurement of quasar redshift with a Gaussian process

2020 ◽  
Vol 498 (4) ◽  
pp. 5227-5239
Author(s):  
Leah Fauber ◽  
Ming-Feng Ho ◽  
Simeon Bird ◽  
Christian R Shelton ◽  
Roman Garnett ◽  
...  
Keyword(s):  
Gaussian Process ◽  
Density Function ◽  
Area Under Curve ◽  
Sloan Digital Sky Survey ◽  
Automated Measurement ◽  
Quasar Spectra ◽  
Sky Survey ◽  
Automated Technique ◽  
Probabilistic Density Function ◽  
Process Method

ABSTRACT We develop an automated technique to measure quasar redshifts in the Baryon Oscillation Spectroscopic Survey of the Sloan Digital Sky Survey (SDSS). Our technique is an extension of an earlier Gaussian process method for detecting damped Lyman α absorbers (DLAs) in quasar spectra with known redshifts. We apply this technique to a subsample of SDSS DR12 with BAL quasars removed and redshift larger than 2.15. We show that we are broadly competitive to existing quasar redshift estimators, disagreeing with the PCA redshift by more than 0.5 in only $0.38{{\ \rm per\ cent}}$ of spectra. Our method produces a probabilistic density function for the quasar redshift, allowing quasar redshift uncertainty to be propagated to downstream users. We apply this method to detecting DLAs, accounting in a Bayesian fashion for redshift uncertainty. Compared to our earlier method with a known quasar redshift, we have a moderate decrease in our ability to detect DLAs, predominantly in the noisiest spectra. The area under curve drops from 0.96 to 0.91. Our code is publicly available.

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