A regional magnitude scale for Brazil

1983 ◽  
Vol 73 (1) ◽  
pp. 237-246
Author(s):  
Marcelo Assumpção
Keyword(s):  
Wave Train ◽  
Maximum Amplitude ◽  
P Wave ◽  
Magnitude Scale ◽  
Distance Curve ◽  
Distance Range ◽  
Wide Range ◽  
Q Factors

abstract An empirical amplitude-distance curve is determined for earthquakes registered at regional distances in conterminous Brazil. This curve is the basis of a regional magnitude scale, mR, using the maximum amplitude in the whole P-wave train with periods in the range 0.1 to 1.0 sec. In the distance range 200 ≦ R ≦ 1500 km, we find m R = log ⁡ ( A / T ) + 2.3 log ⁡ R − 1.48. This scale gives much better agreement with the teleseismic mb magnitudes than the values calculated using the regional Q factors of Gutenberg and Richter (1956). It is shown that, despite using a wide range of periods, mR should be a good estimate of the 1-sec teleseismic mb in the range 2 ≦ mb < 5.

Seismic phases and scaling associated with small high-explosive surface shots

1981 ◽  
Vol 71 (6) ◽  
pp. 1731-1741
Author(s):  
I. N. Gupta ◽  
R. A. Hartenberger
Keyword(s):  
Blast Wave ◽  
Rayleigh Waves ◽  
Wave Train ◽  
Simple Wave ◽  
P Wave ◽  
Peak Ground Velocity ◽  
Air Blast ◽  
Geological Conditions ◽  
Wide Range ◽  
First Arrival

Abstract An analysis of seismic field data from surface shots in two radically different geologic environments shows significantly different seismic phases at the two sites. At the first site, which has a layered sedimentary section, five distinct phases are observed: the P-wave first arrival; a complex wave train consisting of higher mode Rayleigh waves; a precursor to air-blast wave; the air blast wave; and the air-coupled Rayleigh waves. Records from the second site, overlying an unlayered mass of igneous rocks, show only three distinct seismic phases: the P-wave first arrival; a simple wave train of fundamental-mode Rayleigh and Love waves; and an air blast wave. Peak ground velocity, based on the average of the three largest amplitudes in the surface waves preceding the air blast wave, scales well with yield for both sites. Measurements of peak ground velocity may be used to estimate yields of explosive charges at either site within a factor of about 2 if the source distance is known. The scaling relationship appears to be valid over a wide range of yields and site geological conditions.

Magnitude from short-period P-wave data

1972 ◽  
Vol 62 (2) ◽  
pp. 435-452
Author(s):  
K. F. Veith ◽  
G. E. Clawson
Keyword(s):  
P Wave ◽  
Earth Model ◽  
Correction Factors ◽  
Surface Source ◽  
Distance Curve ◽  
Amplitude Correction ◽  
Short Period ◽  
Geometric Spreading ◽  
Deep Focus ◽  
Q Factors

abstract An empirical surface-focus amplitude-distance curve, based on approximately 2400 short-period P-wave amplitudes from 43 large explosions at 19 different sites, and a corresponding curve based on geometrical spreading in the Herrin earth model are developed. The relative amplitude differences are inverted to obtain the Q structure of the mantle. Theoretical, deep-focus, amplitude-distance curves incorporating geometric spreading and attenuation are developed. Corresponding distance and depth amplitude-correction P factors are given for computing magnitude (mp). The correction factors are evaluated and are shown to provide a significantly improved basis for computing magnitude relative to the presently used Q factors which yield mb. Values of mp were normalized to be equal on the average to values of mb for a surface source; differences in attenuation factors generally make mb larger than mp for deep earthquakes.

scholarly journals Reliable workflow for inversion of seismic receiver function and surface wave dispersion data: a “13 BB Star” case study

2019 ◽  
Vol 24 (1) ◽  
pp. 101-120
Author(s):  
Kajetan Chrapkiewicz ◽  
Monika Wilde-Piórko ◽  
Marcin Polkowski ◽  
Marek Grad
Keyword(s):  
Surface Wave ◽  
Inverse Problems ◽  
Receiver Function ◽  
Joint Inversion ◽  
Wave Dispersion ◽  
Receiver Functions ◽  
P Wave ◽  
Surface Wave Dispersion ◽  
Phase Velocity Dispersion ◽  
Wide Range

AbstractNon-linear inverse problems arising in seismology are usually addressed either by linearization or by Monte Carlo methods. Neither approach is flawless. The former needs an accurate starting model; the latter is computationally intensive. Both require careful tuning of inversion parameters. An additional challenge is posed by joint inversion of data of different sensitivities and noise levels such as receiver functions and surface wave dispersion curves. We propose a generic workflow that combines advantages of both methods by endowing the linearized approach with an ensemble of homogeneous starting models. It successfully addresses several fundamental issues inherent in a wide range of inverse problems, such as trapping by local minima, exploitation of a priori knowledge, choice of a model depth, proper weighting of data sets characterized by different uncertainties, and credibility of final models. Some of them are tackled with the aid of novel 1D checkerboard tests—an intuitive and feasible addition to the resolution matrix. We applied our workflow to study the south-western margin of the East European Craton. Rayleigh wave phase velocity dispersion and P-wave receiver function data were gathered in the passive seismic experiment “13 BB Star” (2013–2016) in the area of the crust recognized by previous borehole and refraction surveys. Final models of S-wave velocity down to 300 km depth beneath the array are characterized by proximity in the parameter space and very good data fit. The maximum value in the mantle is higher by 0.1–0.2 km/s than reported for other cratons.

A method for correcting acoustic finite-difference amplitudes for elastic effects

Geophysics ◽  
2014 ◽  
Vol 79 (4) ◽  
pp. T243-T255 ◽  
Author(s):  
James W. D. Hobro ◽  
Chris H. Chapman ◽  
Johan O. A. Robertsson
Keyword(s):  
Wave Equation ◽  
Finite Difference ◽  
Effective Means ◽  
Cost Effective ◽  
P Wave ◽  
S Waves ◽  
Velocity Models ◽  
Acoustic Simulation ◽  
Wide Range ◽  
Elastic Simulation

We present a new method for correcting the amplitudes of arrivals in an acoustic finite-difference simulation for elastic effects. In this method, we selectively compute an estimate of the error incurred when the acoustic wave equation is used to approximate the behavior of the elastic wave equation. This error estimate is used to generate an effective source field in a second acoustic simulation. The result of this second simulation is then applied as a correction to the original acoustic simulation. The overall cost is approximately twice that of an acoustic simulation but substantially less than the cost of an elastic simulation. Because both simulations are acoustic, no S-waves are generated, so dispersed converted waves are avoided. We tested the characteristics of the method on a simple synthetic model designed to simulate propagation through a strong acoustic impedance contrast representative of sedimentary geology. It corrected amplitudes to high accuracy for reflected arrivals over a wide range of incidence angles. We also evaluated results from simulations on more complex models that demonstrated that the method was applicable in realistic sedimentary models containing a wide range of seismic contrasts. However, its accuracy was reduced for wide-angle reflections from very high impedance contrasts such as a shallow top-salt interface. We examined the influence of modeling at coarse grid resolutions, in which converted S-waves in the equivalent elastic simulation are dispersed. These results provide some validation for the accuracy of the method when applied using finite-difference grids designed for acoustic modeling. The method appears to offer a cost-effective means of modeling elastic amplitudes for P-wave arrivals in a useful range of velocity models. It has several potential applications in imaging and inversion.

Short-period Lg magnitudes: Instrument, attenuation, and source effects

1983 ◽  
Vol 73 (6A) ◽  
pp. 1835-1850
Author(s):  
Robert B. Herrmann ◽  
Andrzej Kijko
Keyword(s):  
United States ◽  
Epicentral Distance ◽  
P Wave ◽  
Magnitude Scale ◽  
Source Effects ◽  
Anelastic Attenuation ◽  
Basic Conclusion ◽  
Short Period ◽  
Central United States ◽  
Definition Of

Abstract The applicaton of the Nutli (1973) definition of the mbLg magnitude to instruments and wave periods other than the short-period WWSSN seismograph is examined. The basic conclusion is that the Nuttli (1973) definition is applicable to a wider range of seismic instruments if the log10(A/T) term is replaced by log10A. For consistency and precision, the notation mbLg should be applied only to magnitudes based upon 1.0 Hz observations. The mbLg magnitude definition was constrained to be consistent with teleseismic P-wave mb estimates from four Central United States earthquakes. In general, for measurements made at a frequency f, the notation mLg(f) should be used, where m L g ( f ) = 2.94 + 0.833 log ⁡ 10 ( r / 10 ) + 0.4342 γ r + log ⁡ 10 A , and r is the epicentral distance in kilometers, γ is the coefficient of anelastic attenuation, and A is the reduced ground amplitude in microns. Given its stability when estimated from different instruments, the mLg(f) magnitude is an optimum choice for an easily applied, standard magnitude scale for use in regional seismic studies.

scholarly journals Research on prediction method of S-wave velocity based on deep learning

2021 ◽  
Vol 2083 (4) ◽  
pp. 042065
Author(s):  
Guojie Yang ◽  
Shuhua Wang
Keyword(s):  
Deep Learning ◽  
Wave Velocity ◽  
Prediction Method ◽  
P Wave ◽  
Learning Technology ◽  
S Wave ◽  
Advantages And Disadvantages ◽  
Wave Prediction ◽  
Wide Range ◽  
Velocity Prediction

Abstract Aiming at the s-wave velocity prediction problem, based on the analysis of the advantages and disadvantages of the empirical formula method and the rock physics modeling method, combined with the s-wave velocity prediction principle, the deep learning method is introduced, and a deep learning-based logging s-wave velocity prediction method is proposed. This method uses a deep neural network algorithm to establish a nonlinear mapping relationship between reservoir parameters (acoustic time difference, density, neutron porosity, shale content, porosity) and s-wave velocity, and then applies it to the s-wave velocity prediction at the well point. Starting from the relationship between p-wave and s-wave velocity, the study explained the feasibility of applying deep learning technology to s-wave prediction and the principle of sample selection, and finally established a reliable s-wave prediction model. The model was applied to s-wave velocity prediction in different research areas, and the results show that the s-wave velocity prediction technology based on deep learning can effectively improve the accuracy and efficiency of s-wave velocity prediction, and has the characteristics of a wide range of applications. It can provide reliable s-wave data for pre-stack AVO analysis and pre-stack inversion, so it has high practical application value and certain promotion significance.

Reflection seismic imaging of buried shallow salt structures – examples from ongoing case studies in Northern Germany

2021 ◽  
Author(s):  
Ulrich Polom ◽  
Rebekka Mecking ◽  
Phillip Leineweber ◽  
Andreas Omlin
Keyword(s):  
High Resolution ◽  
Water Resources ◽  
Industrial Development ◽  
Geophysical Methods ◽  
Hydrocarbon Exploration ◽  
P Wave ◽  
Depth Range ◽  
Reflection Seismic ◽  
Wide Range ◽  
Cap Rock

<p>In the North German Basin salt tectonics generated a wide range of evaporite structures since the Upper Triassic, resulting in e.g. extended salt walls, salt diapirs, and salt pillows in the depth range up to 8 km. Due to their trap and seal properties these structures were in the focus of hydrocarbon exploration over many decades, leading to an excellent mapping of their geometries below 300 m in depth. During salt rise Rotliegend formations were partly involved as a constituent. Some structures penetrated the salt table, some also the former surface. Dissolution (subrosion) and erosion of the salt cap rock by meteoric water took place, combined with several glacial and intraglacial overprints. Finally the salt structures were covered by pleistocene and holocene sediments. This situation partly resulted in proneness for ongoing karstification of the salt cap rock, leading to e.g. local subsidence and sinkhole occurrence at the surface. The geometry, structure and internal lithology of these shallow salt cap rocks are widely unknown. Expanding urban and industrial development, water resources management and increasing climate change effects enhance the demands for shallow mapping and characterization of these structures regarding save building grounds and sustainable water resources.</p><p>Results of shallow drilling investigations of the salt cap rock and the overburden show unexpectedly heterogenous subsurface conditions, yielding to limited success towards mapping and characterization. Thus, shallow high-resolution geophysical methods are in demand to close the gaps with preferred focus of applicability in urban and industrial environments. Method evaluations starting in 2010 geared towards shallow high-resolution reflection seismic to meet the requirements of both depth penetration and structure resolution. Since 2017 a combination of S-wave and P-wave seismic methods including depth calibrations by Vertical Seismic Profiling (VSP) enabled 2.5D subsurface imaging starting few meters below the surface up to several hundred meters depth in 0.5-5 m resolution range, respectively. The resulting profiles image strong variations along the boundaries and on top of the salt cap rock. Beside improved mapping capabilities, aim of research is the development of characteristic data features to differentiate save and non-save areas.</p>

P-wave amplitudes and magnitudes between 10° and 35°

1974 ◽  
Vol 64 (6) ◽  
pp. 1887-1899
Author(s):  
George A. McMechan ◽  
Warren G. Workman
Keyword(s):  
Upper Mantle ◽  
Epicentral Distance ◽  
Maximum Amplitude ◽  
Body Waves ◽  
P Wave ◽  
Ray Theory ◽  
Mantle Structure ◽  
Upper Mantle Structure ◽  
Wave Trains ◽  
Theory Technique

abstract The observed behavior of P-wave relative amplitudes, as a function of epicentral distance, between 10° and 35°, is controlled primarily by the velocity-depth structure of the upper mantle. P-wave synthetic seismograms calculated by the new quantized ray theory technique are used to determine theoretical log (A/T) versus log Δ curves from a number of upper mantle models. Maximum amplitude arrivals show less model dependence than the first arrivals in the same wave trains, and hence are more consistent magnitude indicators for regions where the upper mantle structure is poorly known. Log (A/T) versus log Δ curves vary considerably, but predictably, from model to model. This model-dependent variation can account for a major part of the large standard deviations usually associated with the calculation of magnitudes from body waves.

On the reductions of aerofoil-turbulence interaction noise through multi-wavelength leading edge serrations

2020 ◽  
pp. 095441002096574
Author(s):  
S Narayanan ◽  
Sushil Kumar Singh
Keyword(s):  
Noise Reduction ◽  
Maximum Amplitude ◽  
Leading Edge ◽  
Emission Angle ◽  
Broadband Noise ◽  
Dual Wavelength ◽  
Flat Plates ◽  
Wide Range ◽  
Multi Wavelength ◽  
Reduction Characteristics

This paper provides an experimental study into the use of multi-wavelength sinusoidal leading edge ( LE) serrations for enhancing the aerofoil-broadband noise reductions. The noise reduction performances of multi-wavelength serration profiles introduced on a flat plate are compared against those generated by single-wavelength profiles when applied separately. The multi-wavelength leading edge serration is made in such a way that its maximum amplitude is kept same as that of each single-wavelength ones to be compared. The present study reveals that the dual-wavelength serrations provide higher noise reductions over a narrow band of frequencies as compared to single and triple wavelength ones. Further, it reveals that the noise reduction characteristics of dual-wavelength serrated airfoils are similar to the flat plates. It shows that the baseline plate generate higher noise radiations for all emission angles as compared to leading edge serrated plates, but the common feature among them is the downstream directivity. For the range of frequencies 0.9 to 5 kHz, the highest directivity is seen at an emission angle of 55° for the baseline, while it occurs at 75° for the serrated plates. The dual wavelength serrations generate lowest acoustic radiations as compared to single and triple ones for all the emission angles. Also, it is noticed that the radiation levels of the dual serrations decrease with increase in amplitude of the serration, which shows that the longer dual serrations generate lowest acoustic radiations. Thus, the present study illustrates that the dual wavelength leading edge serrations act as the best passively modified serration profiles for achieving the highest noise reductions over a wide range of frequencies as compared to single and triple wavelength ones.

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