scholarly journals Monochromatic Long-Period Seismicity Prior to the 2012 Earthquake Swarm at Little Sitkin Volcano, Alaska

2021 ◽  
Vol 9 ◽  
Author(s):  
Matthew M. Haney ◽  
Helena Buurman ◽  
Stephen Holtkamp ◽  
Stephen R. McNutt
Keyword(s):  
Resonant Frequency ◽  
Quality Factor ◽  
Earthquake Swarm ◽  
Aleutian Islands ◽  
S Wave ◽  
Magma Body ◽  
Long Period ◽  
Magmatic Intrusion ◽  
Lateral Extent ◽  
Western Side

Detection of the earliest stages of unrest is one of the most challenging and yet critically needed aspects of volcano monitoring. We investigate a sequence of five unusual long-period (LP) earthquakes that occurred in the days prior to the onset of a months-long volcano-tectonic (VT) earthquake swarm beneath Little Sitkin volcano in the Aleutian Islands during late 2012. The long-period earthquakes had two distinctive characteristics: their signals were dominated by a monochromatic spectral peak at approximately 0.57 Hz and they had impulsive P and S-wave arrivals on a seismometer located on Amchitka Island 80 km to the southeast of the volcano. In each case, the monochromatic earthquakes ended with a higher-frequency event after approximately 2 min of duration. We find evidence that the five monochromatic LP earthquakes resulted from the resonance of a tabular magma body at middle crustal depths (15 km) on the western side of Little Sitkin. Based on the resonant frequency and quality factor of the monochromatic LP earthquakes, we infer the magma body to have a lateral extent of 500 m and a thickness of 9 m. We interpret that a magmatic intrusion excited the monochromatic LP earthquakes and subsequently increased the stress beneath the volcano, leading to the onset of the shallow (<10 km depth) VT swarm five days later.

scholarly journals S wave attenuation structure on the western side of the Nankai subduction zone: Implications for fluid distribution and dynamics

2014 ◽  
Vol 119 (10) ◽  
pp. 7805-7822 ◽  
Author(s):  
Tsutomu Takahashi ◽  
Koichiro Obana ◽  
Yojiro Yamamoto ◽  
Ayako Nakanishi ◽  
Shuichi Kodaira ◽  
...  
Keyword(s):  
Subduction Zone ◽  
Wave Attenuation ◽  
Fluid Distribution ◽  
S Wave ◽  
Nankai Subduction Zone ◽  
Attenuation Structure ◽  
Western Side

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.

Medium damping influences on the resonant frequency and quality factor of piezoelectric circular microdiaphragm sensors

2011 ◽  
Vol 21 (4) ◽  
pp. 045002 ◽  
Author(s):  
M Olfatnia ◽  
Z Shen ◽  
J M Miao ◽  
L S Ong ◽  
T Xu ◽  
...  
Keyword(s):  
Resonant Frequency ◽  
Quality Factor

Observations of Loma Prieta aftershocks from a dense array in Sunnyvale, California

1991 ◽  
Vol 81 (5) ◽  
pp. 1900-1922
Author(s):  
Arthur Frankel ◽  
Susan Hough ◽  
Paul Friberg ◽  
Robert Busby
Keyword(s):  
Surface Waves ◽  
Body Waves ◽  
Love Waves ◽  
Apparent Velocity ◽  
Dense Array ◽  
S Wave ◽  
Small Aperture ◽  
Long Period ◽  
Santa Clara Valley ◽  
Loma Prieta

Abstract A small aperture (≈300 m), four-station array was deployed in Sunnyvale, California for 5 days to record aftershocks of the Loma Prieta earthquake of October 1989. The purpose of the array was to study the seismic response of the alluvium-filled Santa Clara Valley and the role of surface waves in the seismic shaking of sedimentary basins. Strong-motion records of the Loma Prieta mainshock indicate that surface waves produced the peak velocities and displacements at some sites in the Santa Clara Valley. We use the recordings from the dense array to determine the apparent velocity and azimuth of propagation for various arrivals in the seismograms of four aftershocks with magnitudes between 3.6 and 4.4. Apparent velocities are generally observed to decrease with increasing time after the S wave in the seismograms. Phases arriving less than about 8 sec after the S wave have apparent velocities comparable to the S wave and appear to be body waves multiply reflected under the receiver site or reflected by crustal interfaces. For times 10 to 30 sec after the direct S wave, we observe long-period (1 to 6 sec) arrivals with apparent velocities decreasing from 2.5 to 0.8 km / sec. We interpret these arrivals to be surface waves and conclude that these surface waves produce the long duration of shaking observed on the aftershock records. Much of the energy in the 40 sec after the S-wave is coming approximately from the direction of the source, although some arrivals have backazimuths as much as 60° different from the backazimuths to the epicenters. Two of the aftershocks show arrivals coming from 30 to 40° more easterly than the epicenters. This energy may have been scattered from outcrops along the southeastern edge of the basin. In contrast, the deepest aftershock studied (d = 17 km) displays later arrivals with backazimuths 30 to 40° more westerly than the epicenter. A distinct arrival for one of the aftershocks propagates from the southwest, possibly scattered from the western edge of the basin. Synthetic seismograms derived from a plane-layered crustal model do not produce the long-period Love waves observed in the waveforms of the ML 4.4 aftershock. These Love waves may be generated by the conversion of incident S waves or Rayleigh waves near the edge of the basin.

A Microcontroller Approach to Measuring Transmissibility of MEMS Devices

2015 ◽  
Vol 2015 (DPC) ◽  
pp. 001564-001593
Author(s):  
Chong Li ◽  
Yixuan Wu ◽  
Haoyue Yang ◽  
Luke L. Jenkins ◽  
Robert N. Dean ◽  
...  
Keyword(s):  
Resonant Frequency ◽  
Quality Factor ◽  
Real Time ◽  
High Speed ◽  
Mechanical Quality Factor ◽  
Quantization Noise ◽  
Mems Devices ◽  
Input And Output ◽  
Mechanical Quality ◽  
Mems Device

The transmissibility reveals two very useful characteristics of a micro-electro-mechanical systems (MEMS) device, the resonant frequency and the mechanical quality factor. Real time knowledge on these two important factors can enhance application performance or avoid potential problems from environmental disturbances due to fabrication tolerances and the resulting operational differences in otherwise identical devices. Expensive laboratory equipment is typically used to measure the transmissibility. However, these test systems are not readily adaptable to field use. Therefore, it is important to be able to measure the transmissibility using a real time technique with a simplified test setup. This study proposes a technique that can compute the transmissibility in real time using a low cost microcontroller. This technique utilizes two laser vibrometers to detect the input and output motions of the proof mass in a MEMS device, which are fed to high speed 500 KHz analog to digital converters (ADC) in the microcontroller. A filtering step is performed to decrease noise. After the sampling and pre-filtering, a Fast Fourier Transform (FFT) is performed to convert the time-domain signals to frequency domain signals. The amplitude of the output signal at each frequency is divided by the amplitude of the corresponding input signal at each frequency to obtain the transmissibility. To overcome the difficulties resulting from measurement and quantization noise, a recursive calculating algorithm and a de-quantization filter are introduced. The recursive calculating process guarantees that the system updates the results continually, which results in a transmissibility plot covering the entire bandwidth. The de-quantization filter considers the validity of the data and performs the transmissibility division step accordingly. A cantilevered structure was chosen as the device-under-test to verify and evaluate this technique. The cantilevered device was attached to an electromechanical shaker system for vibratory stimulation. Two laser vibrometers were used to detect the input and output motion and this data was fed into a microcontroller. The microcontroller was STM32F407, which is 32-bit and 168 MHz controller. The tests demonstrated that this technique can measure the transmissibility and therefore the resonant frequency and mechanical quality factor accurately compared to a professional signal analyzer.

A MEMS PPA Based Active Vibration Isolator - STUDENT AWARD 3RD PLACE $500

2016 ◽  
Vol 2016 (DPC) ◽  
pp. 000853-000880
Author(s):  
Chong Li ◽  
C. Lavinia Elana ◽  
Robert N. Dean ◽  
George T. Flowers
Keyword(s):  
Resonant Frequency ◽  
Quality Factor ◽  
Proof Mass ◽  
Control Voltage ◽  
Stable Range ◽  
Vibration Isolator ◽  
Operating Range ◽  
Stable Operating ◽  
Mass Damper ◽  
Active Vibration

Several types of micro-devices are adversely affected by high frequency mechanical vibrations present in the operating environment. Examples include MEMS vibratory gyroscopes and resonators, and micro-optics. Various types of MEMS vibration isolators have been developed for use in the packaging of these vibration sensitive devices. Passive isolators consist of a spring-mass-damper MEMS device and usually have a very high mechanical quality factor, which makes them susceptible to ringing at the isolator's resonant frequency. Active isolators have been realized by using state sensing of the proof mass motion and feeding one or more of these states back through an actuator to adjust the frequency response of the isolator. For example, the technique known as skyhook damping uses velocity feedback to adjust, and typically increase, the damping of the isolator. Although these technique are doable, they require state sensing or state estimation, with feedback electronics to drive the actuator. A simpler MEMS active vibration isolator architecture employs only a parallel plate actuator (PPA) with the MEMS spring-mass-damper structure. The PPA driven with a DC voltage, in its stable operating range, displaces the proof mass, which results in a change in the effective system spring constant due to the electrostatic spring softening effect. This results in a change in the resonant frequency and the quality factor of the isolator. However, due to the nonlinearities inherent in this type of device, the stable operating range is reduced as the PPA voltage is increased. Furthermore, even when the isolator is stable in steady-state, a sufficiently large transient response can also drive it into the unstable regime, resulting in the electrodes snapping into contact. In this study, the PPA based active vibrator isolator is developed and its performance is evaluated. The characteristics of the transient instability are investigated and its stable range of operation is specified, for booth external disturbances and rapid application of the control voltage. This MEMS PPA based active vibration isolator can improve performance compared to passive isolators, while being much simpler than state feedback active isolators.

scholarly journals A Geometrical Study on the Roof Tile-Shaped Modes in AlN-Based Piezoelectric Microcantilevers as Viscosity–Density Sensors

Sensors ◽  
2019 ◽  
Vol 19 (3) ◽  
pp. 658 ◽  
Author(s):  
Víctor Ruiz-Díez ◽  
Javier Toledo ◽  
Jorge Hernando-García ◽  
Abdallah Ababneh ◽  
Helmut Seidel ◽  
...  
Keyword(s):  
Resonant Frequency ◽  
Quality Factor ◽  
Q Factor ◽  
Liquid Media ◽  
Roof Tile ◽  
Aln Film ◽  
Monitoring Applications ◽  
Media Monitoring ◽  
Comprehensive Study

Cantilever resonators based on the roof tile-shaped modes have recently demonstrated their suitability for liquid media monitoring applications. The early studies have shown that certain combinations of dimensions and order of the mode can maximize the Q-factor, what might suggest a competition between two mechanisms of losses with different geometrical dependence. To provide more insight, a comprehensive study of the Q-factor and the resonant frequency of these modes in microcantilever resonators with lengths and widths between 250 and 3000 µm and thicknesses between 10 and 60 µm is presented. These modes can be efficiently excited by a thin piezoelectric AlN film and a properly designed top electrode layout. The electrical and optical characterization of the resonators are performed in liquid media and then their performance is evaluated in terms of quality factor and resonant frequency. A quality factor as high as 140 was measured in isopropanol for a 1000 × 900 × 10 µm3 cantilever oscillating in the 11th order roof tile-shaped mode at 4 MHz; density and viscosity resolutions of 10−6 g/mL and 10−4 mPa·s, respectively are estimated for a geometrically optimized cantilever resonating below 1 MHz.

Analysis of a circular microstrip antenna on isotropic or uniaxially anisotropic substrate using neurospectral approach

2013 ◽  
Vol 33 (1/2) ◽  
pp. 567-580 ◽  
Author(s):  
Sami Bedra ◽  
Siham Benkouda ◽  
Tarek Fortaki
Keyword(s):  
Resonant Frequency ◽  
Quality Factor ◽  
Microstrip Antenna ◽  
Numerical Results ◽  
Spectral Domain ◽  
Quality Factors ◽  
Resonant Frequencies ◽  
Content Type ◽  
Anisotropic Substrate ◽  
Circular Microstrip Antenna

Purpose – The paper aims to propose an artificial neural network (ANN) in conjunction with spectral domain formulation for fast and accurate determination of the resonant frequency and quality factor of circular microstrip antenna printed on isotropic or anisotropic substrate. This neurospectral approach reduces the problem complexity. Design/methodology/approach – The moment method implemented in the spectral domain provides good accuracy but its computational cost is high due to the evaluation of the slowly decaying integrals and the iterative nature of the solution process. The paper introduces the electromagnetic knowledge combined with ANN in the analysis of circular microstrip antenna on isotropic or uniaxially anisotropic substrate to reduce the complexity of the spectral approach and to minimize the CPU time necessary to obtain the numerical results. Findings – The resonant frequency results obtained from the neural model are in very good agreement with the experimental and theoretical results available in the literature. Finally, numerical results for the substrate anisotropy effect on the resonant frequency, quality factor and radiation pattern are also presented. Originality/value – The paper develops fast and accurate model based on ANN technique to calculate the resonant frequencies and quality factors of circular microstrip antennas. ANN is used to model the relationship between the parameters of the microstrip antenna and the resonant frequencies and quality factors obtained from the spectral domain approach. This relatively simple model allows designers to predict accurately the resonant frequencies and quality factors for a given design without having to develop or run the spectral method codes themselves. The main advantages of the method are: less computing time than the spectral model, results with accuracy equivalent to that of full-wave models and cost effectiveness, since the client can use a simple PC for implementation. Another advantage of the proposed ANN model is that it takes into account the uniaxial anisotropy in the substrate without increasing the network size. This is done by combining ANN with electromagnetic knowledge.

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