scholarly journals Amplitude of PcP, PcS, ScS, and ScP in deep-focus earthquakes*

1953 ◽  
Vol 43 (1) ◽  
pp. 63-83
Author(s):  
Kazim Ergin
Keyword(s):  
Systematic Study ◽  
Transverse Wave ◽  
Vertical Component ◽  
Horizontal Component ◽  
P Waves ◽  
S Waves ◽  
Core Boundary ◽  
Deep Focus ◽  
The Waves ◽  
Good Agreement

abstract A systematic study has been made of the ratios of (displacementperiod) of PcP, PcS, ScS, and ScP to that of the corresponding incident wave {e.g.,(displacementperiod)PcP/(displacementperiod)P}, using intermediate and deep-focus earthquake seismograms. The results indicate that the observed ratios of the horizontal components of the waves that are reflected as P waves (i.e., PcP/P and ScP/S) and that of the vertical component of the waves that are reflected as S waves (i.e., ScS/S and PcS/P) at the mantle-core boundary are considerably larger than the theoretical ones, whereas the observed ratios of the vertical component of the first group and that of the horizontal component of the second group are in fairly good agreement with the theoretical values. Theoretical computations were based on the assumption that in the case of a longitudinal wave the vibration is in the direction of propagation and in the case of a transverse wave the vibration is perpendicular to the direction of propagation. It is further found that the behavior of the direct P and S waves is in accord with the theory, but the vibration of the ground is not in the direction of propagation for PcP and ScP and is not perpendicular to the direction of propagation for PcS and ScS.

Imaging beneath a high‐velocity layer using converted waves

Geophysics ◽  
1992 ◽  
Vol 57 (11) ◽  
pp. 1444-1452 ◽  
Author(s):  
Guy W. Purnell
Keyword(s):  
High Velocity ◽  
Energy Partitioning ◽  
P Wave ◽  
Converted Wave ◽  
P Waves ◽  
Lower Velocity ◽  
S Waves ◽  
High Velocity Layer ◽  
The Waves ◽  
Velocity Layer

High‐velocity layers (HVLs) often hinder seismic imaging of deeper reflectors using conventional techniques. A major factor is often the unusual energy partitioning of waves incident at an HVL boundary from lower‐velocity material. Using elastic physical modeling, I demonstrate that one effect of this factor is to limit the range of dips beneath an HVL that can be imaged using unconverted P‐wave arrivals. At the same time, however, partitioning may also result in P‐waves outside the HVL coupling efficiently with S‐waves inside. By exploiting some of the waves that convert upon transmission into and/or out of the physical‐model HVL, I am able to image a much broader range of underlying dips. This is accomplished by acoustic migration tailored (via the migration velocities used) for selected families of converted‐wave arrivals.

scholarly journals Observations on the recorded ground motion due to P, PcP, S, and ScS*

1952 ◽  
Vol 42 (3) ◽  
pp. 263-270
Author(s):  
Kazim Ergin
Keyword(s):  
Vertical Plane ◽  
Ground Vibration ◽  
S Phase ◽  
General Direction ◽  
S Waves ◽  
Long Period ◽  
The Earth ◽  
Core Boundary ◽  
A Minor ◽  
The Waves

Abstract The recorded motion of a point at the surface of the earth, in the vertical plane of propagation, upon the arrival of PcP and ScS, as well as of the direct P and S waves, is reproduced from the seismograms of the vertical, N-S and E-W component, long-period Benioff seismographs. It is found that P and PcP produce a back-and-forth vibration in the general direction of the incoming ray, and that S and ScS produce a motion the largest displacement of which is approximately perpendicular to the ray. PcP motion starts close to the vertical, but its horizontal component later increases. A minor S phase arriving close to and after PcP and a minor P phase arriving close to and before ScS are observed. The effect of these minor phases on the smaller component of the ground vibration caused by the waves reflected from the mantle-core boundary is discussed.

Calibrating the 2016 IRIS Wavefields Experiment Nodal Sensors for Amplitude Statics and Orientation Errors

2021 ◽  
Author(s):  
Oluwaseyi J. Bolarinwa ◽  
Charles A. Langston
Keyword(s):  
Signal To Noise Ratio ◽  
Vertical Component ◽  
Calibration Method ◽  
Horizontal Component ◽  
High Signal ◽  
Correction Factors ◽  
Small Aperture ◽  
S Waves ◽  
Amplitude Correction ◽  
Array Calibration

ABSTRACT We used teleseismic P and S waves recorded in the course of the 2016 Incorporated Research Institutions for Seismology (IRIS) community-planned experiment in northern Oklahoma, to estimate amplitude correction factors (ACFs) and orientation correction factors (OCFs) for the gradiometer’s three-component Fairfield nodal sensors and two other gradiometer-styled subarray nodal sensors. These subarrays were embedded in the 13 km aperture nodal array that was also fielded during the 2016 IRIS experiment. The array calibration method we used in this study is based on the premise that a common wavefield should be recorded over a small-aperture array using teleseismic observation. In situ estimates of ACF for the gradiometer vary by 2.3% (standard deviation) for the vertical components and, typically, variability is less than 4.3% for the horizontal components; associated OCFs generally dispersed by 3°. For the two subarrays, the vertical-component ACF usually vary up to 2.4%; their horizontal-component ACFs largely spread up to 3.6%. OCFs for the subarrays generally disperse by 6.5°. ACF and OCF estimates for the gradiometer are seen to be stable across frequency bands having high signal coherence and/or signal-to-noise ratio. Gradiometry analyses of calibrated and uncalibrated gradiometer records from a local event revealed notable improvements in accuracy of attributes obtained from analyzing the calibrated horizontal-component waveforms in the light of catalog epicenter-derived azimuth. The improved waveform relative amplitudes after calibration, coupled with the enhanced wave attribute accuracy, suggests that instrument calibration for amplitude statics and orientation errors should be encouraged prior to doing gradiometry analysis in future studies.

Detector coupling corrections for vector infidelity of multicomponent OBC data

Geophysics ◽  
2007 ◽  
Vol 72 (3) ◽  
pp. V67-V77 ◽  
Author(s):  
James E. Gaiser
Keyword(s):  
Vertical Component ◽  
Low Frequency ◽  
Radial Component ◽  
Horizontal Component ◽  
Ocean Bottom ◽  
S Wave ◽  
S Waves ◽  
Resonance Modes ◽  
The Time Domain ◽  
Phase Distortions

Differences in the frequency response of horizontal and vertical detectors (vector infidelity) in ocean bottom cable (OBC) surveys can cause problems for multicomponent processing, such as S-wave birefringence and amplitude variation with azimuth (AVA) analyses, and combining vertical and hydrophone data for water-born multiple suppression. One source of this problem is poor detector coupling with the seabed that produces resonances and phase distortions. Coupling and data quality are generally excellent for the inline component. However, the crossline component often exhibits low-frequency resonance compared to the inline. Also, OBCs are susceptible to rotational modes about the cable axis that produce spurious S-waves on the vertical component. I derive a method for correcting the crossline and vertical components based on a model of OBC detector coupling, and design vector operators in the frequency domain from shots over many offsets and azimuths. The crossline data are corrected,relative to the inline, assuming linear polarization of early, near-offset arrivals on the radial-horizontal component. Thus, the transverse-horizontal component provides a convenient error or objective function to be minimized for operator design. Using the corrected crossline, as a model of rotational modes, leads to an estimate of spurious S-waves on the vertical component, which are adaptively subtracted. Data examples from the Gulf of Mexico and offshore Nigeria are presented to illustrate improvements in crossline frequency content and match to inline data. Typically there is [Formula: see text] reduction in error using the rms ratio of transverse-to-radial component data computed in the time domain. Suppression of spurious S-waves from the vertical component without undesirable effects of low-cut or [Formula: see text] filters is shown for prestack and poststack data. Also, vector operators indicate they contain important information related to resonance modes of crossline coupling and rotational modes associated with seabed-deployed versus buried OBCs.

scholarly journals Parametric Instability in Mathieu Equation in Earthquake Dynamics

2017 ◽  
pp. 73-75
Author(s):  
H. Torres-Silva ◽  
J. López-Bonilla ◽  
A. Iturri-Hinojosa ◽  
D. Torres Cabezas
Keyword(s):  
Parametric Resonance ◽  
Parametric Instability ◽  
Mathieu Equation ◽  
Nonlinear Phenomena ◽  
Bifurcation Diagrams ◽  
Earthquake Dynamics ◽  
P Waves ◽  
S Waves ◽  
Theoretical Predictions ◽  
Good Agreement

We propose an study of parametric resonance between P-waves and S-waves, which can be used to describe various nonlinear phenomena qualitatively and to obtain bifurcation diagrams quantitatively. We have shown that it is a good simulation of parametric phenomena, and our results are in good agreement with theoretical predictions. In particular, it may be used to study the influence of pump P waves on the instability’s threshold and amplitude of S waves in earthquake phenomena that could be simulated with an electronic model.The Himalayan Physics Vol. 6 & 7, April 2017 (73-75)

Galilean Relativity

2018 ◽  
Author(s):  
David M. Wittman
Keyword(s):  
Inertial Frame ◽  
Vertical Component ◽  
Horizontal Component ◽  
The Other ◽  
One Dimension ◽  
Everyday Experience ◽  
Low Speed ◽  
Principle Of Relativity ◽  
Galilean Relativity ◽  
Laws Of Motion

Galilean relativity is a useful description of nature at low speed. Galileo found that the vertical component of a projectile’s velocity evolves independently of its horizontal component. In a frame that moves horizontally along with the projectile, for example, the projectile appears to go straight up and down exactly as if it had been launched vertically. The laws of motion in one dimension are independent of any motion in the other dimensions. This leads to the idea that the laws of motion (and all other laws of physics) are equally valid in any inertial frame: the principle of relativity. This principle implies that no inertial frame can be considered “really stationary” or “really moving.” There is no absolute standard of velocity (contrast this with acceleration where Newton’s first law provides an absolute standard). We discuss some apparent counterexamples in everyday experience, and show how everyday experience can be misleading.

Peripheral representation of antennal orientation by the scapal hair plate of the cockroach Periplaneta americana

2001 ◽  
Vol 204 (24) ◽  
pp. 4301-4309 ◽  
Author(s):  
J. Okada ◽  
Y. Toh
Keyword(s):  
Single Unit ◽  
Periplaneta Americana ◽  
Vertical Component ◽  
Horizontal Component ◽  
Vertical Position ◽  
Horizontal Position ◽  
Joint Movement ◽  
Basal Segment ◽  
Dynamic Phase ◽  
Hair Sensilla

SUMMARY Arthropods have hair plates that are clusters of mechanosensitive hairs, usually positioned close to joints, which function as proprioceptors for joint movement. We investigated how angular movements of the antenna of the cockroach (Periplaneta americana) are coded by antennal hair plates. A particular hair plate on the basal segment of the antenna, the scapal hair plate, can be divided into three subgroups: dorsal, lateral and medial. The dorsal group is adapted to encode the vertical component of antennal direction, while the lateral and medial groups are specialized for encoding the horizontal component. Of the three subgroups of hair sensilla, those of the lateral scapal hair plate may provide the most reliable information about the horizontal position of the antenna, irrespective of its vertical position. Extracellular recordings from representative sensilla of each scapal hair plate subgroup revealed the form of the single-unit impulses in response to hair deflection. The mechanoreceptors were characterized as typically phasic-tonic. The tonic discharge was sustained indefinitely (>20 min) as long as the hair was kept deflected. The spike frequency in the transient (dynamic) phase was both velocity- and displacement-dependent, while that in the sustained (steady) phase was displacement-dependent.

Near earthquakes in Central California*

1939 ◽  
Vol 29 (3) ◽  
pp. 427-462 ◽  
Author(s):  
Perry Byerly
Keyword(s):  
Least Squares ◽  
Travel Time ◽  
Sierra Nevada ◽  
Accurate Determination ◽  
Depth Of Focus ◽  
Surface Layers ◽  
P Waves ◽  
Central California ◽  
The Waves

Summary Least-squares adjustments of observations of waves of the P groups at central and southern California stations are used to obtain the speeds of various waves. Only observations made to tenths of a second are used. It is assumed that the waves have a common velocity for all earthquakes. But the time intercepts of the travel-time curves are allowed to be different for different shocks. The speed of P̄ is found to be 5.61 km/sec.±0.05. The speed for S̄ (founded on fewer data) is 3.26 km/sec. ± 0.09. There are slight differences in the epicenters located by the use of P̄ and S̄ which may or may not be significant. It is suggested that P̄ and S̄ may be released from different foci. The speed of Pn, the wave in the top of the mantle, is 8.02 km/sec. ± 0.05. Intermediate P waves of speeds 6.72 km/sec. ± 0.02 and 7.24 km/sec. ± 0.04 are observed. Only the former has a time intercept which allows a consistent computation of structure when considered a layer wave. For the Berkeley earthquake of March 8, 1937, the accurate determination of depth of focus was possible. This enabled a determination of layering of the earth's crust. The result was about 9 km. of granite over 23 km. of a medium of speed 6.72 km/sec. Underneath these two layers is the mantle of speed 8.02 km/sec. The data from other shocks centering south of Berkeley would not fit this structure, but an assumption of the thickening of the granite southerly brought all into agreement. The earthquakes discussed show a lag of Pn as it passes under the Sierra Nevada. This has been observed before. A reconsideration of the Pn data of the Nevada earthquake of December 20, 1932, together with the data mentioned above, leads to the conclusion that the root of the mountain mass projects into the mantle beneath the surface layers by an amount between 6 and 41 km.

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