scholarly journals Processing of noisy magnetotelluric time series from Koyna-Warna seismic region, India: a systematic approach

2015 ◽  
Vol 58 (2) ◽  
Author(s):  
Ujjal K. Borah ◽  
Prasanta K. Patro ◽  
Vaddeboina Suresh
Keyword(s):  
Transfer Functions ◽  
Broad Band ◽  
Noisy Data ◽  
Processing Parameters ◽  
Seismic Zone ◽  
Hydroelectric Power ◽  
Seismic Region ◽  
High Tension ◽  
Power Line Noise ◽  
Cultural Noise

<p>Rolling array pattern broad band magnetotelluric (MT) data was acquired in the Koyna-Warna (Maharashtra, India) seismic zone during 2012-14 field campaigns. The main objective of this study is to identify the thickness of the Deccan trap in and around the Koyna-Warna seismic zone and to delineate the electrical nature of the sub-basalt. The MT data at many places got contaminated with high tension power line noise due to Koyna hydroelectric power project. So, in the present study an attempt has been made to tackle this problem due to 50 Hz noise and their harmonics and other cultural noise using commercially available processing software MAPROS. Remote site was running during the entire field period to stand against the cultural noise problem. This study is based on Fast Fourier Transform (FFT) and mainly focuses on the behaviour of different processing parameters, their interrelations and the influences of different processing methods concerning improvement of the S/N ratio of noisy data. Our study suggests that no single processing approach can give desirable transfer functions, however combination of different processing approaches may be adopted while processing culturally affected noisy data.</p>

A Comparison of Matched-Field and Pseudo-Inverse Methods for Source Identification on a Frame Structure

1999 ◽  
Author(s):  
Matthew A. Craun ◽  
David Feit
Keyword(s):  
Transfer Functions ◽  
Broad Band ◽  
Complete Characterization ◽  
Inverse Methods ◽  
Frame Structure ◽  
Vibration Source ◽  
Processing Methods ◽  
Finite Frame ◽  
Combined Use ◽  
Pseudo Inverse

Abstract The combined use of pseudo-inverse and matched-field processing methods is investigated for localizing and characterizing a broad-band random vibration source on a lightly-damped finite frame structure. The low-frequency range where global modes of the frame are dominant in the response is considered. Experimental results for two different sensor array geometries are compared. Also, the use of numerically-derived transfer functions is demonstrated for each of the processing methods. The results indicate that a combined use of matched-field and pseudo-inverse methods allows for a more complete characterization of the frame excitation than either method used exclusively.

Shaking in the Southeastern United States: Examining Earthquakes and Blasts in the Central Georgia–South Carolina Seismic Region

2021 ◽  
Author(s):  
Rachel E. Marzen ◽  
James B. Gaherty ◽  
Donna J. Shillington ◽  
Won-Young Kim
Keyword(s):  
United States ◽  
South Carolina ◽  
Southeastern United States ◽  
Horizontal Stress ◽  
Water Levels ◽  
Spectral Amplitude ◽  
Seismic Zone ◽  
Seismic Region ◽  
Temporal Cluster ◽  
Maximum Horizontal Stress

Abstract Seismicity in the southeastern United States is relatively poorly characterized and thus not well understood. Structures and heterogeneities from multiple stages of Appalachian orogenesis, continental rifting, and magmatism as well as rivers and reservoirs may be influencing seismic activity in the region, but previous constraints are limited. The addition of seismic stations from the U.S. Transportable Array and the Southeastern Suture of the Appalachian Margin Experiment Array in 2012–2014 provide an opportunity to characterize seismicity in the central Georgia–South Carolina region. We develop a seismic catalog of &gt;1000 events from March 2012 to May 2014 within or near the instrument array boundaries 30.1°–35.2°N, 80.9°– 85.7°W. Many of the events detected were industrial blasts, so multiple strategies were tested to discriminate between earthquakes and blasts based on event locations, timing, and spectral amplitude of the P and S arrivals. Based on this analysis, ∼10% of the events in the catalog were classified as earthquakes. Most earthquakes southeast of the eastern Tennessee seismic zone are located in the Carolina terrane, particularly where the Carolina terrane intersects major rivers or reservoirs. One prominent region of seismicity along the Savannah River near Thurmond Lake corresponds with an ∼4.5  m rise in water levels in 2013. A temporal cluster of earthquakes in April 2013 was followed by increased levels of ambient seismicity preceding the nearby Mw 4.1 earthquake in 2014. Focal mechanisms based on first-motion polarities indicate strike-slip to oblique-thrust motion on structures trending approximately north–south or east–west, and a maximum horizontal stress orientation consistent with the regional trend of ∼N60°E, implying that seismicity may reactivate more optimally oriented structures in the Carolina terrane that are oblique to the trend of the Appalachians. Seismicity in central Georgia appears to be controlled by a complex interaction between preexisting crustal structure and hydrologic variability.

scholarly journals Intelligent post processing of seismic events

1994 ◽  
Vol 37 (3) ◽  
Author(s):  
T. Kvaerna ◽  
F. Ringdal
Keyword(s):  
Standard Deviation ◽  
Kola Peninsula ◽  
Broad Band ◽  
Region Of Interest ◽  
Mining Area ◽  
Processing Parameters ◽  
Post Processing ◽  
Mining Sites ◽  
Initial Event ◽  
Median Error

The Intelligent Monitoring Systern (IMS) currently provides for joint processing of data from six arrays located in Northern and Central Europe. From experience with analyst review of events automatically defined by the IMS, we bave realized that the quality of the automatic event locations can be significantly improved if the event intervals are reprocessed with signal processing pararneters tuned to phases from events in the given region. The tuned processing parameters are obtained from off line analysis of events located in the region of interest. The primary goal of such intelligent post processing is to provide event definitions of a quality that minimizes the need for subsequent manual analysis. The first step in this post processing is to subdivide the arca to be monitored in order to identify sites of interest. Clearly, calibration will be the easiest and potential savings in manpower are the largest for areas of high, recurring seismicity. We bave identified 8 mining sites in Fennoscandia/NW Russia and noted that 65.6% of the events of ML > 2.0 in this region can be associated with one of these sites. This result is based on 1 year and a half of data. The second step is to refine the phase arrival and azimuth estimates using frequency filters and processing parameters that are tuned to the initial event location provided by the IMS. In this study, we have analyzed a set of 52 mining explosions from the Khibiny Massif mining area in the Kola peninsula of Russia. Very accurate locations of these events bave been provided by the seismologists from the Kola Regional Seismology Centre. Using an autoregressive likelihood technique we have been able to estimate onset times to an accuracy (standard deviation) of about 0.05 s for P phases and 0.15 0.20 s for S phases. Using fixed frequency bands, azimuth can be estimated to an accuracy (one standard deviation) of 0.9 degrees for the ARCESS array and 3 4 degrees for the small array recently established near Apatity on the Kola peninsula. The third step in the post processing is a relocation of the event, using refined arrivai times and recomputed azimuths from broad band flk analysis. By introducing region specific travel time corrections, a median error of 1.4 km from the reported location has been obtained. This should be compared to the median error of 10.8 km for the automatie IMS processing for these events. This improvement in location accuracy clearly demonstrates the usefulness of the intelligent post processing approach.

scholarly journals The Envoy® Totally Implantable Hearing System, St. Croix Medical

2002 ◽  
Vol 6 (2) ◽  
pp. 73-80 ◽  
Author(s):  
Kai Kroll ◽  
Iain L. Grant ◽  
Eric Javel
Keyword(s):  
Transfer Functions ◽  
High Sensitivity ◽  
Processing Parameters ◽  
The United States ◽  
Piezoelectric Transducers ◽  
Battery Life ◽  
High Fidelity ◽  
Acoustic Feedback ◽  
Hearing Device ◽  
Hearing System

The Totally Implantable Envoy® System is currently undergoing clinical trials in both the United States and Europe. The fully implantable hearing device is intended for use in patients with sensorineural hearing loss. The device employs piezoelectric transducers to sense ossicle motion and drive the stapes. Programmable signal processing parameters include amplification, compression, and variable frequency response. The fully implantable attribute allows users to take advantage of normal external ear resonances and head-related transfer functions, while avoiding undesirable earmold effects. The high sensitivity, low power consumption, and high fidelity attributes of piezoelectric transducers minimize acoustic feedback and maximize battery life ( Gyo, 1996 ; Yanagihara, (1987) and 2001 ). The surgical procedure to install the device has been accurately defined and implantation is reversible.

Chronic Laser Exposure Effects on Rabbit Retina

1972 ◽  
Vol 30 ◽  
pp. 54-55
Author(s):  
Burton B. Silver ◽  
Theodore Lawwill
Keyword(s):  
Laser Irradiation ◽  
Laser Light ◽  
Broad Band ◽  
Argon Laser ◽  
Atropine Sulfate ◽  
Ultrastructural Changes ◽  
Laser Exposure ◽  
Rabbit Retina ◽  
Histological Changes ◽  
Threshold Doses

Dutch-belted 1 to 2.5 kg anesthetized rabbits were exposed to either xenon or argon laser light administered in a broad band, designed to cover large areas of the retina. For laser exposure, the pupil was dilated with atropine sulfate 1% and pheny lephrine 10%. All of the laser generated power was within a band centered at 5145.0 Anstroms. Established threshold for 4 hour exposures to laser irradiation are in the order of 25-35 microwatts/cm2. Animals examined for ultrastructural changes received 4 hour threshold doses. These animals exhibited ERG, opthalmascopic, and histological changes consistent with threshold damage.One month following exposure the rabbits were killed with pentobarbitol. The eyes were immediately enucleated and dissected while bathed in 3% phosphate buffered gluteraldehyde.

A simple way for producing holographic filters suitable for image improvement

1978 ◽  
Vol 36 (1) ◽  
pp. 226-227
Author(s):  
K.-H. Herrmann ◽  
E. Reuber ◽  
P. Schiske
Keyword(s):  
Transfer Functions ◽  
Diffraction Order ◽  
Lateral Position ◽  
Simple Method ◽  
Spatial Frequencies ◽  
Resolution Electron ◽  
Wiener Filters ◽  
Image Improvement ◽  
Optical Reconstruction ◽  
Set Up

Aposteriori deblurring of high resolution electron micrographs of weak phase objects can be performed by holographic filters [1,2] which are arranged in the Fourier domain of a light-optical reconstruction set-up. According to the diffraction efficiency and the lateral position of the grating structure, the filters permit adjustment of the amplitudes and phases of the spatial frequencies in the image which is obtained in the first diffraction order.In the case of bright field imaging with axial illumination, the Contrast Transfer Functions (CTF) are oscillating, but real. For different imageforming conditions and several signal-to-noise ratios an extensive set of Wiener-filters should be available. A simple method of producing such filters by only photographic and mechanical means will be described here.A transparent master grating with 6.25 lines/mm and 160 mm diameter was produced by a high precision computer plotter. It is photographed through a rotating mask, plotted by a standard plotter.

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