Recording the Aurora at Seismometers across Alaska

2020 ◽  
Vol 91 (6) ◽  
pp. 3039-3053 ◽  
Author(s):  
Carl Tape ◽  
Adam T. Ringler ◽  
Don L. Hampton
Keyword(s):  
Magnetic Field ◽  
Seismic Data ◽  
Vertical Component ◽  
Seismic Array ◽  
Magnetic Shielding ◽  
Data Sets ◽  
S Waves ◽  
Auroral Activity ◽  
Seismic Sensors ◽  
Magnetometer Data

Abstract We examine three continuously recording data sets related to the aurora: all-sky camera images, three-component magnetometer data, and vertical-component, broadband seismic data as part of the EarthScope project (2014 to present). Across Alaska there are six all-sky cameras, 13 magnetometers, and >200 seismometers. The all-sky images and magnetometers have the same objective, which is to monitor space weather and improve our understanding of auroral activity, including the influence on magnetic fields in the ground. These variations in the magnetic field are also visible on seismometers, to the extent that during an auroral event, the long-period (40–800 s) waves recorded by a seismometer are magnetic field variations, not true ground motion. Although this is a problem—one that can be rectified with magnetic shielding at each seismometer site—it is also an opportunity because the present seismic array in Alaska is much broader than the coverage by magnetometers and all-sky cameras. Here we focus on three aurora events and document a direct link between aurora images in the night sky and seismometer recordings on ground. Simultaneous recordings by magnetometers provide a critical link between the sky images and the seismometer recordings. We document qualitative correlations among sky, magnetic, and seismic data. The findings suggest that the signature of auroral activity is widespread across seismometers in Alaska, implying that the seismic array could be used to enhance the spatial resolution of the existing network of all-sky cameras and magnetometers. Future efforts to improve the multisensor seismic stations in Alaska, for the purpose of monitoring seismic and auroral activity, should consider installation of all-sky cameras, installation of magnetometers, and magnetic shielding of seismic sensors.

A robust workflow for performing joint impedance inversion and its applications

2020 ◽  
Vol 8 (1) ◽  
pp. T141-T149
Author(s):  
Ritesh Kumar Sharma ◽  
Satinder Chopra ◽  
Larry R. Lines
Keyword(s):  
Time Domain ◽  
Seismic Data ◽  
Sedimentary Basin ◽  
Vertical Component ◽  
Data Sets ◽  
Data Set ◽  
Matching Process ◽  
Multicomponent Seismic ◽  
Impedance Inversion ◽  
Straightforward Approach

Multicomponent seismic data offer several advantages for characterizing reservoirs with the use of the vertical component (PP) and mode-converted (PS) data. Joint impedance inversion inverts both of these data sets simultaneously; hence, it is considered superior to simultaneous impedance inversion. However, the success of joint impedance inversion depends on how accurately the PS data are mapped on the PP time domain. Normally, this is attempted by performing well-to-seismic ties for PP and PS data sets and matching different horizons picked on PP and PS data. Although it seems to be a straightforward approach, there are a few issues associated with it. One of them is the lower resolution of the PS data compared with the PP data that presents difficulties in the correlation of the equivalent reflection events on both the data sets. Even after a few consistent horizons get tracked, the horizon matching process introduces some artifacts on the PS data when mapped into PP time. We have evaluated such challenges using a data set from the Western Canadian Sedimentary Basin and then develop a novel workflow for addressing them. The importance of our workflow was determined by comparing data examples generated with and without its adoption.

scholarly journals Characterization of the umbra–penumbra boundary by the vertical component of the magnetic field

2020 ◽  
Vol 638 ◽  
pp. A25
Author(s):  
P. Lindner ◽  
R. Schlichenmaier ◽  
N. Bello González
Keyword(s):  
Magnetic Field ◽  
Near Infrared ◽  
Statistical Study ◽  
Vertical Component ◽  
Fundamental Property ◽  
Field Vector ◽  
Data Sets ◽  
Data Set ◽  
Geometric Difference ◽  
The Magnetic Field

Context. The vertical component of the magnetic field was found to reach a constant value at the boundary between penumbra and umbra of stable sunspots in a recent statistical study of Hinode/SP data. This finding has profound implications as it can serve as a criterion to distinguish between fundamentally different magneto-convective modes operating in the sun. Aims. The objective of this work is to verify the existence of a constant value for the vertical component of the magnetic field (B⊥) at the boundary between umbra and penumbra from ground-based data in the near-infrared wavelengths and to determine its value for the GREGOR Infrared Spectrograph (GRIS@GREGOR) data. This is the first statistical study on the Jurčák criterion with ground-based data, and we compare it with the results from space-based data (Hinode/SP and SDO/HMI). Methods. Eleven spectropolarimetric data sets from the GRIS@GREGOR slit-spectograph containing fully-fledged stable sunspots were selected from the GRIS archive. SIR inversions including a polarimetric straylight correction are used to produce maps of the magnetic field vector using the Fe I 15648 Å and 15662 Å lines. Averages of B⊥ along the contours between penumbra and umbra are analyzed for the 11 data sets. In addition, contours at the resulting B⊥const are drawn onto maps and compared to intensity contours. The geometric difference between these contours, ΔP, is calculated for each data set. Results. Averaged over the 11 sunspots, we find a value of B⊥const = (1787 ± 100) gauss. The difference from the values previously derived from Hinode/SP and SDO/HMI data is explained by instrumental differences and by the formation characteristics of the respective lines that were used. Contours at B⊥ = B⊥const and contours calculated in intensity maps match from a visual inspection and the geometric distance ΔP was found to be on the order of 2 pixels. Furthermore, the standard deviation between different data sets of averages along umbra–penumbra contours is smaller for B⊥ than for B∥ by a factor of 2.4. Conclusions. Our results provide further support to the Jurčák criterion with the existence of an invariable value B⊥const at the umbra–penumbra boundary. This fundamental property of sunspots can act as a constraining parameter in the calibration of analysis techniques that calculate magnetic fields. It also serves as a requirement for numerical simulations to be realistic. Furthermore, it is found that the geometric difference, ΔP, between intensity contours and contours at B⊥ = B⊥const acts as an index of stability for sunspots.

A comparison of streamer and OBC seismic data at Beryl Alpha field, U. K. North Sea

Geophysics ◽  
2007 ◽  
Vol 72 (3) ◽  
pp. B69-B80 ◽  
Author(s):  
Jonathan Stewart ◽  
Andrew Shatilo ◽  
Charlie Jing ◽  
Tommie Rape ◽  
Richard Duren ◽  
...  
Keyword(s):  
North Sea ◽  
Seismic Data ◽  
Signal To Noise Ratio ◽  
Vertical Component ◽  
Hard Water ◽  
Detailed Comparison ◽  
P Wave ◽  
Data Sets ◽  
Ocean Bottom ◽  
Streamer Data

Compressional P-wave ocean-bottom-cable (OBC) seismic data from the Beryl Alpha field in the U. K. North Sea provide a superior image of the subsurface compared to heritage streamer seismic data. To determine the reason for the superiority of OBC data, the results of a detailed comparison of these OBC and streamer data sets are compared. The streamer and OBC data sets are reprocessed using a strategy that attempts to isolate the roles of processing, fold, azimuth, PZ combination, and hydrophone and geophone data have on the improved OBC image. The vertical component of the geophone (OBC Z) provides the major contribution to the improved OBC image. The imaged OBC Z datacontain fewer multiples and have a higher signal-to-noise ratio than the streamer. The OBC data have a lower level of multiple contamination because of the contribution from the OBC Z component, together with an effective suppression of receiver-side water-column reverberations as a result of the combination of the OBC hydrophone and geophone traces (PZ combination). The increased fold and wider azimuths of OBC data improve the OBC image slightly. Wider azimuths improve fault imaging, especially for faults oriented obliquely to the inline and crossline directions. The particular conditions at Beryl Alpha field that make the OBC survey successful are the relatively hard water bottom and the presence of multiples that are difficult to remove from streamer data using standard demultiple techniques.

scholarly journals Integrated magnetotelluric and seismic investigation of Cenozoic graben structure near Obrzycko, Poland

2021 ◽  
Author(s):  
Adam Cygal ◽  
Michał Stefaniuk ◽  
Anna Kret
Keyword(s):  
Seismic Data ◽  
Geophysical Methods ◽  
Geological Structure ◽  
Data Sets ◽  
Low Velocity ◽  
Shallow Subsurface ◽  
Geophysical Model ◽  
Novel Approach ◽  
Loose Deposits ◽  
Static Corrections

AbstractThis article presents the results of an integrated interpretation of measurements made using Audio-Magnetotellurics and Seismic Reflection geophysical methods. The obtained results were used to build an integrated geophysical model of shallow subsurface cover consisting of Cenozoic deposits, which then formed the basis for a detailed lithological and tectonic interpretation of deeper Mesozoic sediments. Such shallow covers, consisting mainly of glacial Pleistocene deposits, are typical for central and northern Poland. This investigation concentrated on delineating the accurate geometry of Obrzycko Cenozoic graben structure filled with loose deposits, as it was of great importance to the acquisition, processing and interpretation of seismic data that was to reveal the tectonic structure of the Cretaceous and Jurassic sediments which underly the study area. Previously, some problems with estimation of seismic static corrections over similar grabens filled with more recent, low-velocity deposits were encountered. Therefore, a novel approach to estimating the exact thickness of such shallow cover consisting of low-velocity deposits was applied in the presented investigation. The study shows that some alternative geophysical data sets (such as magnetotellurics) can be used to significantly improve the imaging of geological structure in areas where seismic data are very distorted or too noisy to be used alone

scholarly journals Comparing global tomography-derived and gravity-based upper mantle density models

2020 ◽  
Vol 221 (3) ◽  
pp. 1542-1554 ◽  
Author(s):  
B C Root
Keyword(s):  
Seismic Tomography ◽  
Upper Mantle ◽  
Seismic Data ◽  
Gravity Data ◽  
Heterogeneous Data ◽  
Clear Correlation ◽  
Data Sets ◽  
Satellite Gravity ◽  
Similar Density ◽  
Similar Peak

SUMMARY Current seismic tomography models show a complex environment underneath the crust, corroborated by high-precision satellite gravity observations. Both data sets are used to independently explore the density structure of the upper mantle. However, combining these two data sets proves to be challenging. The gravity-data has an inherent insensitivity in the radial direction and seismic tomography has a heterogeneous data acquisition, resulting in smoothed tomography models with de-correlation between different models for the mid-to-small wavelength features. Therefore, this study aims to assess and quantify the effect of regularization on a seismic tomography model by exploiting the high lateral sensitivity of gravity data. Seismic tomography models, SL2013sv, SAVANI, SMEAN2 and S40RTS are compared to a gravity-based density model of the upper mantle. In order to obtain similar density solutions compared to the seismic-derived models, the gravity-based model needs to be smoothed with a Gaussian filter. Different smoothening characteristics are observed for the variety of seismic tomography models, relating to the regularization approach in the inversions. Various S40RTS models with similar seismic data but different regularization settings show that the smoothening effect is stronger with increasing regularization. The type of regularization has a dominant effect on the final tomography solution. To reduce the effect of regularization on the tomography models, an enhancement procedure is proposed. This enhancement should be performed within the spectral domain of the actual resolution of the seismic tomography model. The enhanced seismic tomography models show improved spatial correlation with each other and with the gravity-based model. The variation of the density anomalies have similar peak-to-peak magnitudes and clear correlation to geological structures. The resolvement of the spectral misalignment between tomographic models and gravity-based solutions is the first step in the improvement of multidata inversion studies of the upper mantle and benefit from the advantages in both data sets.

Signal detection using multi-channel seismic data

1996 ◽  
Vol 86 (1A) ◽  
pp. 221-231 ◽  
Author(s):  
Gregory S. Wagner ◽  
Thomas J. Owens
Keyword(s):  
Signal Detection ◽  
Seismic Data ◽  
Spatial Coherence ◽  
Vertical Component ◽  
Principal Component ◽  
Minimum Variance ◽  
Data Detection ◽  
Array Data ◽  
Detection Approach ◽  
Sample Covariance

Abstract We outline a simple signal detection approach for multi-channel seismic data. Our approach is based on the premise that the wave-field spatial coherence increases when a signal is present. A measure of spatial coherence is provided by the largest eigenvalue of the multi-channel data's sample covariance matrix. The primary advantages of this approach are its speed and simplicity. For three-component data, this approach provides a more robust statistic than particle motion polarization. For array data, this approach provides beamforming-like signal detection results without the need to form beams. This approach allows several options for the use of three-component array data. Detection statistics for three-component, vertical-component array, and three different three-component array approaches are compared to conventional and minimum-variance vertical-component beamforming. Problems inherent in principal-component analysis (PCA) in general and PCA of high-frequency seismic data in particular are also discussed. Multi-channel beamforming and the differences between principal component and factor analysis are discussed in the appendix.

scholarly journals Improved Interpretation of Deep Seismic Reflection Data in Areas of Complex Geology Through Integration With Passive Seismic Data Sets

2018 ◽  
Vol 123 (12) ◽  
pp. 10,810-10,830
Author(s):  
Michael Dentith ◽  
Huaiyu Yuan ◽  
Ruth Elaine Murdie ◽  
Perla Pina-Varas ◽  
Simon P. Johnson ◽  
...  
Keyword(s):  
Seismic Data ◽  
Seismic Reflection ◽  
Data Sets ◽  
Seismic Reflection Data ◽  
Deep Seismic Reflection ◽  
Reflection Data ◽  
Passive Seismic ◽  
Complex Geology

scholarly journals Influence of high-latitude geomagnetic pulsations on recordings of broadband force-balanced seismic sensors

2012 ◽  
Vol 1 (2) ◽  
pp. 85-101 ◽  
Author(s):  
E. Kozlovskaya ◽  
A. Kozlovsky
Keyword(s):  
Magnetic Field ◽  
Geomagnetic Field ◽  
Geomagnetic Latitude ◽  
Low Frequency ◽  
Auroral Oval ◽  
Polar Regions ◽  
Geomagnetic Pulsations ◽  
Seismic Sensors ◽  
Magnetic Poles ◽  
Magnetic Disturbances

Abstract. Seismic broadband sensors with electromagnetic feedback are sensitive to variations of surrounding magnetic field, including variations of geomagnetic field. Usually, the influence of the geomagnetic field on recordings of such seismometers is ignored. It might be justified for seismic observations at middle and low latitudes. The problem is of high importance, however, for observations in Polar Regions (above 60° geomagnetic latitude), where magnitudes of natural magnetic disturbances may be two or even three orders larger. In our study we investigate the effect of ultra-low frequency (ULF) magnetic disturbances, known as geomagnetic pulsations, on the STS-2 seismic broadband sensors. The pulsations have their sources and, respectively, maximal amplitudes in the region of the auroral ovals, which surround the magnetic poles in both hemispheres at geomagnetic latitude (GMLAT) between 60° and 80°. To investigate sensitivity of the STS-2 seismometer to geomagnetic pulsations, we compared the recordings of permanent seismic stations in northern Finland to the data of the magnetometers of the IMAGE network located in the same area. Our results show that temporary variations of magnetic field with periods of 40–150 s corresponding to regular Pc4 and irregular Pi2 pulsations are seen very well in recordings of the STS-2 seismometers. Therefore, these pulsations may create a serious problem for interpretation of seismic observations in the vicinity of the auroral oval. Moreover, the shape of Pi2 magnetic disturbances and their periods resemble the waveforms of glacial seismic events reported originally by Ekström (2003). The problem may be treated, however, if combined analysis of recordings of co-located seismic and magnetic instruments is used.

Kirchhoff elastic wave migration for the case of noncoincident source and receiver

Geophysics ◽  
1984 ◽  
Vol 49 (8) ◽  
pp. 1223-1238 ◽  
Author(s):  
John T. Kuo ◽  
Ting‐fan Dai
Keyword(s):  
Elastic Wave ◽  
Seismic Data ◽  
Signal To Noise Ratio ◽  
Horizontal Layer ◽  
P Wave ◽  
Seismic Section ◽  
S Waves ◽  
Surface Data ◽  
Marine Seismic ◽  
Wave Migration

In taking into account both compressional (P) and shear (S) waves, more geologic information can likely be extracted from the seismic data. The presence of shear and converted shear waves in both land and marine seismic data recordings calls for the development of elastic wave‐migration methods. The migration method presently developed consists of simultaneous migration of P- and S-waves for offset seismic data based on the Kirchhoff‐Helmholtz type integrals for elastic waves. A new principle of simultaneously migrating both P- and S-waves is introduced. The present method, named the Kirchhoff elastic wave migration, has been tested using the 2-D synthetic surface data calculated from several elastic models of a dipping layer (including a horizontal layer), a composite dipping and horizontal layer, and two layers over a half‐space. The results of these tests not only assure the feasibility of this migration scheme, but also demonstrate that enhanced images in the migrated sections are well formed. Moreover, the signal‐to‐noise ratio increases in the migrated seismic section by this elastic wave migration, as compared with that using the Kirchhoff acoustic (P-) wave migration alone. This migration scheme has about the same order of sensitivity of migration velocity variations, if [Formula: see text] and [Formula: see text] vary concordantly, to the recovery of the reflector as that of the Kirchhoff acoustic (P-) wave migration. In addition, the sensitivity of image quality to the perturbation of [Formula: see text] has also been tested by varying either [Formula: see text] or [Formula: see text]. For varying [Formula: see text] (with [Formula: see text] fixed), the migrated images are virtually unaffected on the [Formula: see text] depth section while they are affected on the [Formula: see text] depth section. For varying [Formula: see text] (with [Formula: see text] fixed), the migrated images are affected on both the [Formula: see text] and [Formula: see text] depth sections.

DIPOLE-FIELD TYPE MAGNETIC DISTURBANCES AND AURORAL ACTIVITIES

1961 ◽  
Vol 39 (2) ◽  
pp. 350-366 ◽  
Author(s):  
B. K. Bhattacharyya
Keyword(s):  
Magnetic Field ◽  
Current System ◽  
Field Vector ◽  
Maximum Magnitude ◽  
Horizontal Magnetic Field ◽  
Auroral Activity ◽  
The North ◽  
Initial Location ◽  
Sequence Relationship ◽  
Direction Of Movement

The characteristics of the magnetic field components at Agincourt have been calculated for a current system produced by an electric dipole located in the region of auroral activity near Ottawa. It is noted that, irrespective of the orientation of the dipole, the horizontal magnetic field component rotates in the clockwise and anticlockwise senses for motion of the dipole towards the east and the west respectively, when the dipole is situated in the north half of the sky as seen from the observing station.Next, the magnetograms obtained at Agincourt have been studied at those times of the night when auroral activity was recorded in the all-sky camera photographs at Springhill near Ottawa. It is noted that the horizontal magnetic field describes a loop during a particular phase of auroral activity because of its gradual growth and decay. The distributions of clockwise and anticlockwise rotations with respect to local time are found to be very similar in many respects to those of auroral motions to the east and west respectively. The sense of rotation of the loop is predominantly anticlockwise in the early part of the night and clockwise in the late hours of the night.It is found that eastward and westward orientations of the dipole are the most probable ones. The direction of movement and the initial location of the predominant auroral form in the sky are found to tally well with those of the dipole deduced from a study of the magnetograms.It seems that there is a time sequence relationship between successive phases of auroral activity and changes of characteristics of the loops described by the horizontal magnetic field vector. The area of a loop and the maximum magnitude of the field vector in the loop appear to be related to the brightness and horizontal extent of the auroral forms.

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