Seismic vibrator control and the downgoing P-wave

Geophysics ◽  
1984 ◽  
Vol 49 (6) ◽  
pp. 732-740 ◽  
Author(s):  
J. J. Sallas
Keyword(s):  
Phase Locking ◽  
Theoretical Work ◽  
Drive Level ◽  
Reaction Mass ◽  
P Wave ◽  
Far Field ◽  
Particle Displacement ◽  
Force Reaction ◽  
Coupling Medium ◽  
Seismic Vibrator

While the need for phase compensation is well established, the best method to measure the seismic vibrator output is not. Phase control of the force exerted by a seismic vibrator upon the earth’s surface (ground force) is shown to be useful in producing consistent downhole P-wave signatures. Experimental results are presented which compare the downhole correlation wavelets produced by phase‐locking to ground force; reaction mass acceleration and baseplate acceleration as changes in vibrator type, sweep bandwidth, drive level, and coupling medium are made. The empirical results support earlier theoretical work which predicts with suitable assumptions that ground force and far‐field particle displacement are in phase except for a time delay.

P Wave and Far-Field R Wave Detection in Pacemaker Patient Atrial Electrograms

2000 ◽  
Vol 23 (4) ◽  
pp. 434-440 ◽  
Author(s):  
HEINZ THERES ◽  
WEIMIN SUN ◽  
WILLIAM COMBS ◽  
ERIC PANKEN ◽  
HARDWIN MEAD ◽  
...  
Keyword(s):  
P Wave ◽  
Far Field ◽  
Wave Detection ◽  
Atrial Electrograms

scholarly journals Spectral boundary integral method for simulating static and dynamic fields from a fault rupture in a poroelastodynamic solid

2021 ◽  
Author(s):  
Elias Heimisson ◽  
Antonio Pio Rinaldi
Keyword(s):  
Pore Pressure ◽  
Integral Method ◽  
Near Field ◽  
Boundary Integral ◽  
Pressure Response ◽  
Boundary Integral Method ◽  
P Wave ◽  
Computational Time ◽  
Far Field ◽  
Pore Pressure Response

The spectral boundary integral method is popular for simulating fault, fracture, and frictional processes at a planar interface. However, the method is less commonly used to simulate off-fault dynamic fields. Here we develop a spectral boundary integral method for poroelastodynamic solid. The method has two steps: first, a numerical approximation of a convolution kernel and second, an efficient temporal convolution of slip speed and the appropriate kernel. The first step is computationally expensive but easily parallelizable and scalable such that the computational time is mostly restricted by computational resources. The kernel is independent of the slip history such that the same kernel can be used to explore a wide range of slip scenarios. We apply the method by exploring the short-time dynamic and static responses: first, with a simple source at intermediate and far-field distances and second, with a complex near-field source. We check if similar results can be attained with dynamic elasticity and undrained pore-pressure response and conclude that such an approach works well in the near-field but not necessarily at an intermediate and far-field distance. We analyze the dynamic pore-pressure response and find that the P-wave arrival carries a significant pore pressure peak that may be observed in high sampling rate pore-pressure measurements. We conclude that a spectral boundary integral method may offer a viable alternative to other approaches where the bulk is discretized, providing a better understanding of the near-field dynamics of the bulk in response to finite fault ruptures.

scholarly journals Disturbance study of seismic vibrator reaction mass and piston

PLoS ONE ◽  
2019 ◽  
Vol 14 (12) ◽  
pp. e0225259
Author(s):  
Zhen Chen ◽  
Zhiqiang Huang ◽  
Shuang Jing ◽  
Yang Zhou ◽  
Yan Chen ◽  
...  
Keyword(s):  
Reaction Mass ◽  
Seismic Vibrator

Far-field pulse shapes from circular sources with variable rupture velocities

1997 ◽  
Vol 87 (5) ◽  
pp. 1288-1296
Author(s):  
Nicholas Deichmann
Keyword(s):  
Stress Drop ◽  
Seismic Moment ◽  
Total Duration ◽  
Source Model ◽  
P Wave ◽  
Far Field ◽  
Rupture Velocity ◽  
P Waves ◽  
S Waves ◽  
Rate Functions

Abstract Recently, Sato (1994) developed a simple earthquake source model of a circular rupture expanding outward from the center of a fault with constant stress drop. In contrast to previous models, the rupture velocity is allowed to vary over the duration of faulting. This model is used to synthesize apparent moment-rate functions for a three-stage source process: first, the rupture starts out with a gradually increasing velocity, then, it continues to expand uniformly until, finally, it slows to a gradual stop. Synthetic velocity seismograms are obtained from a convolution of the apparent moment-rate functions with a causal Q-operator and an appropriate instrument response. Comparisons with an example of an earthquake signal show that, in the context of the proposed model, the observed emergent P-wave onset, which is not compatible with a constant rupture velocity, can be explained by a gradually accelerating rupture front. Systematic departures from the generally expected scaling relationship between seismic moment and rupture duration are often interpreted as evidence for a dependence of stress drop on seismic moment. However, the trade-off between stress drop and rupture velocity inherent in all kinematic source models implies that such deviations can just as well be attributed to systematic variations of rupture velocity. Whereas, in general, the total duration of the far-field displacement pulse is shorter for P waves than for S waves, the model predicts that the rise time, τ1/2, of the displacement pulse should be longer for P waves than for S waves. This feature could constitute a critical test of the model and also provide a constraint on the rupture velocity.

Empirical Green's functions: A comparison between pulse width measurements and deconvolution by spectral division

1999 ◽  
Vol 89 (1) ◽  
pp. 178-189
Author(s):  
Nicholas Deichmann
Keyword(s):  
Initial Phase ◽  
Pulse Width ◽  
Circular Crack ◽  
P Wave ◽  
Far Field ◽  
Velocity Pulse ◽  
Zero Crossing ◽  
Northern Switzerland ◽  
Field Displacement ◽  
Width Measurements

Abstract Data from a microearthquake cluster in northern Switzerland and synthetic seismograms simulating the observed signals are used to compare two different techniques of obtaining information about earthquake source-time functions. Comparisons between the observed P-wave velocity pulse widths and the rise times of far-field displacement pulses obtained from empirical Green's function (EGF) deconvolutions show significant discrepancies. Whereas the observed velocity pulse widths of the larger events scale with seismic moment over a broad range, this scaling is practically lost in the deconvolutions. The reason is that velocity pulse widths are usually measured at high trace magnifications from the first break to the first zero crossing. At lower magnifications, these pulse widths are seen to include an emergent onset, which can be attributed to an initial phase of gradual rupture acceleration and whose duration scales with moment. Synthetic simulations, based on a source model of a circular crack with constant stress drop and rupture propagating outward from the center with a gradually increasing velocity, correctly reproduce these emergent onsets. Deconvolutions using the synthetic signals show that the slow initial phase is masked by the noise amplification and stabilizing measures inherent in the deconvolution. Therefore, despite the uncertainties in the necessary corrections for attenuation and scattering along the path, relative pulse width measurements are more reliable and provide better resolution for small earthquakes than rise-time measurements on far-field displacement pulses obtained from EGF deconvolutions by spectral division.

Phase locking of a two-dimensional laser array by controlling the far-field pattern

2004 ◽  
Vol 84 (16) ◽  
pp. 3025-3027 ◽  
Author(s):  
Yi Zhou ◽  
Liping Liu ◽  
Candice Etson ◽  
Yonatan Abranyos ◽  
Angela Padilla ◽  
...  
Keyword(s):  
Phase Locking ◽  
Field Pattern ◽  
Far Field ◽  
Two Dimensional ◽  
Laser Array ◽  
Far Field Pattern

Stochastic optimization using MATLAB code for the determination of in situ horizontal stress magnitudes from wellbore logging data

2020 ◽  
Author(s):  
Insun Song ◽  
Chandong Chang
Keyword(s):  
Compressive Strength ◽  
Stochastic Optimization ◽  
Rock Strength ◽  
Horizontal Stress ◽  
P Wave ◽  
Far Field ◽  
Principal Stresses ◽  
Matlab Code ◽  
Sonic Logging

<p>We report a MATLAB code for the stochastic optimization of in situ horizontal stress magnitudes from wellbore wall image and sonic logging data in a vertical borehole. In undeformed sedimentary formations, one of the principal stresses is commonly assumed to be vertical, and its magnitude (σ<sub>v</sub>) is simply related to the gravitational overburden. The two horizontal far-field principal stresses (σ<sub>H</sub> and σ<sub>h</sub>) are then theoretically constrained by the relationship between the breakout width (or angular span) and rock compressive strength at a given depth. However, the deterministic relationship yields indeterminate solutions for the two unknown stresses. Instead of using the deterministic relationship between their average values in an interval of borehole, we introduce probabilistic distributions of rock strength and breakout width in the interval. This method optimizes the complete set of in situ principal stresses (σ<sub>H</sub>, σ<sub>h</sub>, and σ<sub>v</sub>) by minimizing the objective function. For the rock failure model, we use a true triaxial failure criterion referred to as the modified Wiebols and Cook criterion that incorporates all three principal stresses. This criterion is expressed in the form of an implicit function with two equation parameters; the uniaxial compressive strength UCS and the internal friction coefficient μ. The Weibull distribution model of UCS in a borehole section (~30 m interval) is obtained from the wellbore sonic logging data using the relation between UCS and P-wave velocity. The value of μ is assumed to be constant at 0.6 based on a previous experimental study. The breakout model is established based on the probabilistic distribution of rock strength at the margins of the breakout for a uniform set of far-field stresses. The inverse problem is solved with a MATLAB algorithm for the optimization by choosing the best-fit set of far-field stresses in a stress polygon. This process also enables one to evaluate the statistical reliability in terms of sensitivity and uncertainty. The stochastic optimization process is demonstrated using borehole images and sonic logging data obtained from the Integrated Ocean Drilling Program (IODP) Hole C0002A, a vertical hole near the seaward margin of the Kumano basin offshore from the Kii Peninsula, southwest Japan.</p>

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