scholarly journals Unified explanation of envelope broadening and maximum-amplitude decay of high-frequency seismograms based on the envelope simulation using the Markov approximation: Forearc side of the volcanic front in northeastern Honshu, Japan

2005 ◽  
Vol 110 (B1) ◽  
Author(s):  
Tatsuhiko Saito
Keyword(s):  
High Frequency ◽  
Maximum Amplitude ◽  
Markov Approximation ◽  
Volcanic Front

2.5-D wave equations and high‐frequency asymptotics

Geophysics ◽  
1995 ◽  
Vol 60 (2) ◽  
pp. 556-562 ◽  
Author(s):  
John W. Stockwell
Keyword(s):  
Seismic Data ◽  
High Frequency ◽  
Wave Equations ◽  
Maximum Amplitude ◽  
Variable Density ◽  
Constant Density ◽  
Correction Factors ◽  
Wave Operators ◽  
Ray Series ◽  
D Wave

The need for modeling 3-D seismic data in a 2-D setting has motivated investigators to create so‐called 2.5-D modeling methods. One such method proposed by Liner involves the use of an approximate 2.5-D wave operator for constant‐density media. The traveltimes and amplitudes predicted by high‐frequency asymptotic ray series (WKBJ) analysis of the Liner 2.5-D wave equation match those predicted by Bleistein’s 2.5-D ray‐theoretic development in constant wavespeed media. However, high‐frequency analysis indicates that the Liner 2.5-D variable wavespeed equation will have a maximum amplitude error of ±35% in a linear c(z) model where the wavespeed doubles or halves from the beginning to the end of a raypath. These amplitudes are comparable to those produced by converting 2-D data to 2.5-D using correction factors of the type proposed by Emersoy and Oristaglio and Deregowski and Brown, with the exception being that the Liner equation lacks the half derivative waveform correction present in these operators. An alternate method of constructing 2.5-D wave operators based on the WKBJ analysis is proposed. This method permits variable density (acoustic) 2.5-D wave operators to be derived.

scholarly journals Attenuation contrast in mantle wedge across the volcanic front of northeastern Japan that controls propagations of high-frequency S-wave later phases

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Takahiro Shiina ◽  
Kei Katsumata ◽  
Kiyoshi Yomogida ◽  
Aitaro Kato
Keyword(s):  
High Frequency ◽  
Mantle Wedge ◽  
Volcanic Front ◽  
S Wave ◽  
High Attenuation ◽  
Northeastern Japan ◽  
Pass Through ◽  
High Frequency Waves ◽  
Forearc Region ◽  
Ne Japan

AbstractDistinct later phases of waves with rich high-frequency (> 8 Hz) components were observed for intraslab earthquakes that occurred at intermediate depths, particularly at depths exceeding 100 km, in the northeastern (NE) Japan subduction zone. These high-frequency later phases (HFLPs) showed anomalously large peak-amplitude delays, up to ~ 50 s after direct S-wave arrivals at stations in the backarc region. Using a source-scanning algorithm, we investigated the locations of passing points affecting the propagation of HFLPs. The passing points were estimated to be in the forearc region in the entire NE Japan, indicating that HFLPs are scattered waves that pass through the forearc region. The propagating HFLPs seem to bypass the backarc mantle wedge, as a consequence of the distinct attenuation contrast in the mantle wedge across the volcanic front in NE Japan. These HFLP observations suggest that the high-attenuation zone in the backarc mantle wedge controls propagations of the high-frequency waves of intraslab earthquakes, in addition to the scatterers possibly locate in the forearc region.

Utilizing Downhole Sampled High-Frequency Torsional Oscillation Measurements for Identifying Stringers and Minimizing Operational Invisible Lost Time ILT

2021 ◽  
Author(s):  
Andreas Hohl ◽  
Danial MacFarlane ◽  
David Selvaag Larsen ◽  
Kjetil Olsnes ◽  
Sergiy Grymalyuk ◽  
...  
Keyword(s):  
High Frequency ◽  
Systems Approach ◽  
Torsional Oscillation ◽  
Maximum Amplitude ◽  
Detection Algorithm ◽  
Directional Drilling ◽  
Operational Parameters ◽  
Rock Interaction ◽  
Horizontal Drilling ◽  
Lost Time

Abstract Horizontal drilling has been the industry standard for oil production wells in the North Sea for decades. Significant improvements have been made in the precision of directional drilling by rotary steerable systems (RSS), nevertheless there remain opportunities to mitigate operational challenges in complex drilling environments. One such challenge is the occurrence of hard stringers interbedded between soft sandstone and limestone formations within the reservoirs. The interaction between the bit and hard stringers at the interfaces can lead to a deflection of the bit, resulting in high local doglegs (HLDs), and excessive static loads unless mitigation actions are triggered in a timely fashion. Operational parameters have to be adjusted during hard-stringer drilling, but are also constrained in the underlying formation to avoid HLDs and guarantee bit and BHA integrity. The key to efficient stringer drilling presented here is a consistent, timely and reliable method of detecting stringers. This is enabled by a fit for purpose stringer detection algorithm embedded in a measurement-while-drilling (MWD) tool for vibration and load measurements, combined in a systems approach with an automated surface system. Different indicators such as vibrations, loads and ROP that are traditionally used for stringer detection have been analyzed in the development phase of the algorithm. High-frequency torsional oscillations (HFTO) have been found to be a leading indicator for stringer drilling: HFTO is a torsional vibration phenomenon with high frequencies (50Hz-450Hz) and is only excited by the bit-rock interaction in hard formations. The HFTO amplitudes in sand/lime stones and calcite stringers show well separated distributions. Finally, HFTO is unique in that it is not directly affected by the driller, or due to other downhole dysfunctions, e.g. compared to a change in weight on bit (WOB) which may be caused by a surface parameter change or a stabilizer. The physics-based algorithm embedded in the MWD tool combines tangential acceleration and dynamic torque measurements to calculate the maximum HFTO load in the BHA. A stringer is identified if an HFTO maximum amplitude threshold is exceeded and the energy is localized in one frequency. The downhole indicator is aggregated to a 1-bit value (stringer/no stringer) that enables a high telemetry update rate and thereby a timely reaction at surface. The stringer indicator and advice are displayed to the driller and are actively used for stringer drilling. The paper describes the technology as well as the operational setup, and experience from the first field deployments. By using the new technology, the driller can react faster to any stringer and use appropriate parameters to avoid costly HLDs. First field deployments demonstrate a significant improvement in invisible lost time (ILT) caused by deflections of the bit, resulting in a considerable reduction in well delivery costs.

scholarly journals Review of unprecedented ULF electromagnetic anomalous emissions possibly related to the Wenchuan <i>M</i><sub>S</sub> = 8.0 earthquake, on 12 May 2008

2013 ◽  
Vol 13 (2) ◽  
pp. 279-286 ◽  
Author(s):  
M. Li ◽  
J. Lu ◽  
M. Parrot ◽  
H. Tan ◽  
Y. Chang ◽  
...  
Keyword(s):  
High Frequency ◽  
Main Shock ◽  
Low Frequency ◽  
Maximum Amplitude ◽  
Field Measurements ◽  
Abnormal Behavior ◽  
Observation System ◽  
Observation Network ◽  
History Of ◽  
Electric Signals

Abstract. This work presents ground based ultra low frequency (ULF) electromagnetic field measurements in the frequency range 0.1–10 Hz from January 2007 to December 2008. In this time period a strong earthquake series hits the Wenchuan region with a main shock of magnitude MS = 8.0 on 12 May 2008. The Hebei ULF electromagnetic observation network includes eight observation stations in north China and the observation system named E-EM is employed to record the electric potential difference between two electrodes with an analog automatic real-time continuous pen recorder. First, weak electric signals appeared on 11 October 2007 at Ningjin station, most of which are with relative long periods ~0.4–3 s and unequal amplitudes ~0.5–20 mm. Then, similar signals appeared at Gaobeidian station at the end of October. Abnormal behavior with various time intervals appeared randomly and not every day. At the beginning of April 2008, one and a half months before the Wenchuan MS = 8.0 earthquake, the anomalies were gradually subject to an intensive increase mainly in Gaobeidian SN direction and Ningjin EW direction. The abnormal behavior appeared almost every day and the amplitudes of electric signals, with short periods of ~0.1–0.3 s, enhanced to ~3–30 mm. Qingxian station started to record marginally high frequency signals in SN and EW components in the middle of April. On 9 May, 3 days before the main shock, the amplitude of high frequency information increased sharply at the same time in two components at Gaobeidian station and the maximum amplitude was up to 70 mm, i.e. 1.3 mV m−1 for the electric field. This situation did not stop until 17 May, 5 days after the main event. However, this kind of climax phenomena did not happen at Ningjin station and Qingxian station. Then weak anomalous information lasted about four months again, and strong signals appeared again for a short time before several powerful aftershocks. It is the first time that an abnormity with so large an amplitude and so long a duration time in the observation history of this network though several strong earthquakes were recorded. Furthermore, no obvious interferences have been found during this period. So this event is possibly related to this shock although all these three stations are more than 1300 km away from the Wenchuan earthquake epicenter.

Zonal Asymmetries, Teleconnections, and Annular Patterns in a GCM

2005 ◽  
Vol 62 (1) ◽  
pp. 207-219 ◽  
Author(s):  
Benjamin A. Cash ◽  
Paul J. Kushner ◽  
Geoffrey K. Vallis
Keyword(s):  
Boundary Conditions ◽  
Linear Relationship ◽  
High Frequency ◽  
General Circulation ◽  
Maximum Amplitude ◽  
General Circulation Models ◽  
Storm Tracks ◽  
Longitudinal Distribution ◽  
Point Correlation ◽  
Zonal Asymmetry

Abstract The influence of zonally asymmetric boundary conditions on the leading modes of variability in a suite of atmospheric general circulation models is investigated. The set of experiments consists of nine model configurations, with varying degrees and types of zonal asymmetry in their boundary conditions. The structure of the leading EOF varies with the zonal asymmetry of the base state for each model configuration. In particular, a close relationship is found between the structure of the EOF and the model storm tracks. An approximately linear relationship is found to hold between the magnitude of the zonal asymmetry of the leading EOF and of the storm tracks in the models. It is shown that this linear relationship extends to the observations. One-point correlation maps centered on the regions where the EOFs reach their maximum amplitude show similar structures for all configurations. These structures consist of a north–south dipole, resembling the observed structure of the North Atlantic Oscillation (NAO). They are significantly more zonally localized than the leading EOF, but do resemble one-point correlation maps and sector EOFs calculated for a simulation with zonally symmetric boundary conditions. Thus, the leading EOF for each simulation appears to represent the longitudinal distribution of zonally localized NAO-like patterns. This longitudinal distribution appears to be tied to the distribution of high-frequency eddies, as represented by the storm tracks. A detailed momentum budget for each case confirms that high-frequency eddies play a crucial role in producing the NAO-like patterns. Other dynamical processes also play an important role, but vary with the details of the simulation.

scholarly journals Piezomagnetic effects induced by artificial sources at Mt. Vesuvius (Italy): preliminary results of an experimental survey

1998 ◽  
Vol 41 (3) ◽  
Author(s):  
C. Del Negro ◽  
E. Armadillo ◽  
E. Bozzo ◽  
L. Cafarella ◽  
A. Meloni ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Seismic Tomography ◽  
High Frequency ◽  
Geomagnetic Field ◽  
Maximum Amplitude ◽  
Remarkable Change ◽  
Frequency Monitoring ◽  
Piezomagnetic Effects ◽  
The Magnetic Field ◽  
Experimental Survey

In order to put new constrains on magnetic effects associated with mechanical stresses, high frequency monitoring of the geomagnetic field was carried out during a seismic tomography experiment (TOMOVES'96 project) at Mt. Vesuvius. Eight proton precession and one Cesium magnetometers were installed along a profile on the SW flank of the volcano to observe possible magnetic changes induced by explosions. Measurements were performed at different sampling frequencies (10 Hz, 0.5 Hz and 0.1 Hz). A remarkable change in the intensity of the magnetic field was observed in only one case. The magnetic transient lasted 12-13 min, reaching the maximum amplitude of slightly less than 15 nT.

scholarly journals The Mechanics of Temporal Interference Stimulation

2020 ◽  
Author(s):  
Jiaming Cao ◽  
Brent Doiron ◽  
Chaitanya Goswami ◽  
Pulkit Grover
Keyword(s):  
Membrane Potential ◽  
High Frequency ◽  
Single Neuron ◽  
Small Difference ◽  
Low Frequency ◽  
Maximum Amplitude ◽  
Neuron Models ◽  
Outward Currents ◽  
Sinusoidal Input ◽  
A Current

AbstractWe utilize single neuron models to understand mechanisms behind Temporal Interference (TI) stimulation (also called “Interferential Stimulation”). We say that a neuron exhibits TI stimulation if it does not fire for a high-frequency sinusoidal input, but fires when the input is a low-frequency modulation of the high-frequency sinusoid (specifically that generated by addition of two high frequency sinusoids with a small difference in their frequencies), while the maximum amplitude is kept the same in both cases. Our key observation – that holds for both FitzHugh-Nagumo and Hodgkin-Huxley neuron models – is that for neuron models that do exhibit TI stimulation, a high frequency pure sinusoidal input results in a current balance between inward and outward currents. This current balance leads to a subthreshold periodic orbit that keeps the membrane potential from spiking for sinusoidal inputs. However, the balance is disturbed when the envelope of the sinusoids is modulated with a high slope: the fast-changing envelope activates fast depolarizing currents without giving slow outward currents time to respond. This imbalance causes the membrane potential to build up, causing the neuron to fire. This mechanistic understanding can help design current waveforms for neurons that exhibit TI stimulation, and also help classify which neuron-types may or may not exhibit TI stimulation.

Holographic investigation of the impact response of human heads

1984 ◽  
Vol 60 (4) ◽  
pp. 718-723 ◽  
Author(s):  
Jürgen Dörheide ◽  
Heinz-E. Hoyer
Keyword(s):  
Shock Wave ◽  
High Frequency ◽  
Maximum Amplitude ◽  
Impact Response ◽  
Fracture Mechanisms ◽  
Deformation Wave ◽  
Content Type ◽  
Opposite Pole ◽  
Frequency Components ◽  
The Impact

✓ The impact response of intact human cadaver heads was studied by means of double-pulsed holography using a ruby laser, and the transient deformation process at the surface of the skull was recorded. Frequency and acceleration measurements following impact were obtained. On frontal impact, the shock wave reached the opposite pole after 0.2 to 0.3 msec, and maximum amplitudes were found in the temporal regions. On impact to the vault, the deformation wave reached the skull base after 0.15 to 0.175 msec. Centers of maximum amplitude were recorded in the parietal and temporal regions. Deviations in the interference lines occurred at some sutures, revealing discontinuities. High-frequency components of the shock wave were demonstrated. The authors believe that fracture mechanisms may be elucidated by further studies of impact responses.

scholarly journals Damping of layered porous composites and an application in machinery

2021 ◽  
Vol 1199 (1) ◽  
pp. 012068
Author(s):  
Z Murčinková ◽  
S Radchenko ◽  
G Kuchtová
Keyword(s):  
Mechanical Properties ◽  
Porous Material ◽  
Layered Structure ◽  
High Frequency ◽  
Base Material ◽  
Maximum Amplitude ◽  
Internal Damping ◽  
Vibration Process ◽  
High Frequency Vibrations ◽  
Porous Composites

Abstract The structured composite can involve the porous materials providing the important internal damping that is usable in mechanical engineering applications. The stiff base material is equipped by layer/s of softer porous material/s covered by constrained layer. Such layered structure is characterized by increased internal damping in vibration process. Paper analyses some either measured or simulated mechanical properties of designed layered porous composites. Novelty provided in paper is a specific application of structured composite for damping the high frequency vibrations in resonance frequency obtaining the beneficial results, e.g. 40-48% of maximum amplitude reduction.

The Microstructure of Steatite (Protoenstatite)

1985 ◽  
Vol 43 ◽  
pp. 236-237
Author(s):  
W. E. Lee ◽  
A. H. Heuer
Keyword(s):  
High Frequency ◽  
Glass Ceramics ◽  
Magnesium Silicate ◽  
Beam Current ◽  
Glassy Matrix ◽  
Angle Of Incidence ◽  
X Ray ◽  
Mechanical And Electrical Properties ◽  
Argon Ions ◽  
High Temperature Polymorph

IntroductionTraditional steatite ceramics, made by firing (vitrifying) hydrous magnesium silicate, have long been used as insulators for high frequency applications due to their excellent mechanical and electrical properties. Early x-ray and optical analysis of steatites showed that they were composed largely of protoenstatite (MgSiO3) in a glassy matrix. Recent studies of enstatite-containing glass ceramics have revived interest in the polymorphism of enstatite. Three polymorphs exist, two with orthorhombic and one with monoclinic symmetry (ortho, proto and clino enstatite, respectively). Steatite ceramics are of particular interest a they contain the normally unstable high-temperature polymorph, protoenstatite.Experimental3mm diameter discs cut from steatite rods (∼10” long and 0.5” dia.) were ground, polished, dimpled, and ion-thinned to electron transparency using 6KV Argon ions at a beam current of 1 x 10-3 A and a 12° angle of incidence. The discs were coated with carbon prior to TEM examination to minimize charging effects.

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