scholarly journals The Marsquake Catalogue from InSight, Sols 0-478

2020 ◽  
Author(s):  
John Clinton ◽  
Savas Ceylan ◽  
Martin van Driel ◽  
Domenico Giardini ◽  
Simon C. Stähler ◽  
...  
Keyword(s):  
Seismic Data ◽  
High Frequency ◽  
Thermal Stresses ◽  
Low Frequency ◽  
Local Source ◽  
First Year ◽  
Seismic Events ◽  
Long Period ◽  
Seismic Catalogue ◽  
Seismic Origin

The InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission began collecting high quality seismic data on Mars from February 2019. This manuscript documents the seismicity observed by SEIS, InSight’s seismometer, since this time until the end of March, 2020. Within the InSight project, the Marsquake Service (MQS) is responsible for prompt review of all seismic data collected by InSight, detection of events that are likely to be of seismic origin, and curation and release of seismic catalogues. In the first year of data collection, MQS have identified 465 seismic events that we interpret to be from regional and teleseismic marsquakes. Seismic events are grouped into 2 different event families: the low frequency family are dominated by energy at long period below 1 second, and the high frequency family primarily include energy at and above 2.4~Hz. Event magnitudes, from Mars-specific scales, range from 1.3 to 3.7. A third class of events with very short duration but high frequency bursts have been observed 712 times. These are likely associated with a local source driven by thermal stresses. This paper describes the data collected so far in the mission and the procedures under which MQS operates; summarises the content of the current MQS seismic catalogue; and presents the key features of the events we have observed so far, using the largest events as examples.

scholarly journals Observations of volcanic earthquakes and tremor at Deception Island - Antarctica

1999 ◽  
Vol 42 (3) ◽  
Author(s):  
G. Alguacil ◽  
J. C. Almendros ◽  
E. Del Pezzo ◽  
A. Garcia ◽  
J. M. Ibañez ◽  
...  
Keyword(s):  
Volcanic Activity ◽  
High Frequency ◽  
Low Frequency ◽  
Volcanic Tremor ◽  
Shallow Aquifer ◽  
Seismic Events ◽  
Deception Island ◽  
Rapid Phase ◽  
Long Period ◽  
Frequency Phase

Deception Island - South Shetlands, Antarctica is site of active volcanism. Since 1988 field surveys have been carried out with the aim of seismic monitoring, and in 1994 a seismic array was set up near the site of the Spanish summer base in order to better constrain the source location and spectral properties of the seismic events related to the volcanic activity. The array was maintained during the Antarctic summer of 1995 and the last field survey was carried out in 1996. Data show the existence of three different groups (or families) of seismic events: 1) long period events, with a quasi-monochromatic spectral content (1-3 Hz peak frequency) and a duration of more than 50 s, often occurring in small swarms lasting from several minutes to some day; 2) volcanic tremor, with a spectral shape similar to the long period events but with a duration of several minutes (2-10); 3) hybrid events, with a waveform characterised by the presence of a high frequency initial phase, followed by a low frequency phase with characteristics similar to those of the long period events. The high frequency phase of the hybrid events was analysed using polarisation techniques, showing the presence of P waves. This phase is presumably located at short epicentral distances and shallow source depth. All the analysed seismic events show back-azimuths between 120 and 330 degrees from north (corresponding to zones of volcanic activity) showing no seismic activity in the middle of the caldera. Particle motion, Fourier spectral and spectrogram analysis show that the low frequency part of the three groups of the seismic signals have similar patterns. Moreover careful observations show that the high frequency phase which characterises the hybrid events is present in the long period and in the tremor events, even with lower signal to noise ratios. This evidence suggests that long period events are events in which the high frequency part is simply difficult to observe, due to a very shallow source and/or hypocentral distance higher than that of hybrids, while the tremor is composed of rapidly occurring hybrid events. We propose a possible interpretation for the three groups of seismic events. These may be generated by multiple pressure-steps due to the rapid phase change from liquid to vapour in a shallow aquifer which comes in contact with hot materials. The pressure change can put a crack in resonance or excite the generation of multiple surface waves modes in the shallow layered structure.

Broadband seismic over/under sources and their designature-deghosting

Geophysics ◽  
2017 ◽  
Vol 82 (5) ◽  
pp. P61-P73 ◽  
Author(s):  
Lasse Amundsen ◽  
Ørjan Pedersen ◽  
Are Osen ◽  
Johan O. A. Robertsson ◽  
Martin Landrø
Keyword(s):  
Seismic Data ◽  
High Frequency ◽  
Low Frequency ◽  
Point Sources ◽  
High Frequency Side ◽  
Frequency Content ◽  
Source Depth ◽  
Deep Sources ◽  
The Cost ◽  
High Frequency Content

The source depth influences the frequency band of seismic data. Due to the source ghost effect, it is advantageous to deploy sources deep to enhance the low-frequency content of seismic data. But, for a given source volume, the bubble period decreases with the source depth, thereby degrading the low-frequency content. At the same time, deep sources reduce the seismic bandwidth. Deploying sources at shallower depths has the opposite effects. A shallow source provides improved high-frequency content at the cost of degraded low-frequency content due to the ghosting effect, whereas the bubble period increases with a lesser source depth, thereby slightly improving the low-frequency content. A solution to the challenge of extending the bandwidth on the low- and high-frequency side is to deploy over/under sources, in which sources are towed at two depths. We have developed a mathematical ghost model for over/under point sources fired in sequential and simultaneous modes, and we have found an inverse model, which on common receiver gathers can jointly perform designature and deghosting of the over/under source measurements. We relate the model for simultaneous mode shooting to recent work on general multidepth level array sources, with previous known solutions. Two numerical examples related to over/under sequential shooting develop the main principles and the viability of the method.

scholarly journals Analyzing Low Frequency Seismic Events at Cerberus Fossae as Long Period Volcanic Quakes

2021 ◽  
Author(s):  
Sharon Kedar ◽  
Mark P. Panning ◽  
Suzanne E. Smrekar ◽  
Simon C. Stähler ◽  
Scott D. King ◽  
...  
Keyword(s):  
Low Frequency ◽  
Seismic Events ◽  
Long Period ◽  
Cerberus Fossae

Seismic low-frequency shadows and their application to detect CO2 anomalies on time-lapse seismic data: a case study from Sleipner field, North sea

Geophysics ◽  
2021 ◽  
pp. 1-45
Author(s):  
Emmanuel Anthony ◽  
Nimisha Vedanti
Keyword(s):  
North Sea ◽  
Seismic Data ◽  
High Frequency ◽  
Seismic Waves ◽  
Decomposition Analysis ◽  
Low Frequency ◽  
Time Lapse ◽  
Underlying Mechanism ◽  
Real Field ◽  
Saturated Medium

The detection and underlying mechanism of prospect-scale seismic low-frequency shadows (LFS) has been an issue of debate. Even though the concept of LFS is widely accepted, the practical applicability of the method remains limited due to few real field case studies and little understanding of the underlying attenuation mechanism. To characterize the attenuation phenomenon responsible for the occurrence of LFS in CO2 saturated formations, we use the diffusivity and viscosity of the fluid saturated medium to derive a complex velocity function that characterizes a high-frequency attenuation phenomenon responsible for the occurrence of LFS in a CO2 saturated formation. Synthetic seismic data sets representing pre- and post- CO2 injection scenarios were generated using 2D diffusive viscous equations to model the LFS and understand its occurrence mechanism. Furthermore, to demonstrate the applicability of LFS in a real field, a spectral decomposition analysis of time-lapse 3D seismic data of the Sleipner field, North Sea, was carried out using the continuous wavelet transform. LFSs were clearly detected below the reservoir base at frequencies lower than 30 Hz in the post- CO2 injection surveys. It is shown that the seismic low-frequency shadows are not artefacts but occur due to attenuation of the high frequency components of the propagating seismic waves in the CO2 saturated Utsira Formation. The attenuation of these frequencies is a result of the diffusivity and viscosity of the fluid saturated medium. The low-frequency shadows are localized anomalies at the base of the formation; hence with the present approach, these anomalies cannot be related to the migration of the CO2 plume in the Utsira Formation.

The influence of the planted geophone on seismic land data

Geophysics ◽  
1980 ◽  
Vol 45 (8) ◽  
pp. 1239-1253 ◽  
Author(s):  
G. M. Hoover ◽  
J. T. O’Brien
Keyword(s):  
Seismic Data ◽  
High Frequency ◽  
Mineral Exploration ◽  
Low Frequency ◽  
Soil Consolidation ◽  
Pass Filter ◽  
Low Pass Filter ◽  
Strong Damping ◽  
Local Soil ◽  
Oscillatory Coupling

Characteristics of the seismic data acquisition system that previously have been ignored become important as more sophisticated interpretive methods based on broader frequency bandwidths are developed to extract stratigraphic information from land data in hydrocarbon and mineral exploration. Theoretical and experimental results indicate that the geophone plant can be approximated by a damped oscillatory coupling, properties dependent upon the geophone mass, dimension of earth contact, and local soil consolidation. A massive geophone with minimal earth contact exhibits a low‐frequency plant resonance with weak damping and acts as a low‐pass filter to eliminate the high‐frequency components of a recorded signal. A lightweight geophone with large earth contact exhibits a high‐frequency plant resonance with strong damping and, consequently, filtering effects are minimal if the plant resonance is well above the signal bandwidth. Although signal filtering influences are weak for strong damping, phase delays can introduce errors of several milliseconds which resemble static errors. Additional complications arise since these time shifts are frequency dependent and, consequently, not identical for all reflection events in a seismic trace. The resonant frequency of the geophone plant increases with increased soil consolidation; however, damping demonstrates only a weak dependence upon consolidation. All of these factors can limit the effectiveness of common‐depth‐point (CDP) stacking methods if the proper technique is not practiced in the acquisition of broad‐bandwidth seismic data.

scholarly journals Tutorial: Spectral bandwidth extension — Invention versus harmonic extrapolation

Geophysics ◽  
2017 ◽  
Vol 82 (4) ◽  
pp. W1-W16 ◽  
Author(s):  
Chen Liang ◽  
John Castagna ◽  
Ricardo Zavala Torres
Keyword(s):  
Seismic Data ◽  
High Frequency ◽  
Low Frequency ◽  
Original Data ◽  
Spectral Bandwidth ◽  
Bandwidth Extension ◽  
Seismic Resolution ◽  
Earth Structures ◽  
Seismic Sections ◽  
Phase Acceleration

Various postprocessing methods can be applied to seismic data to extend the spectral bandwidth and potentially increase the seismic resolution. Frequency invention techniques, including phase acceleration and loop reconvolution, produce spectrally broadened seismic sections but arbitrarily create high frequencies without a physical basis. Tests in extending the bandwidth of low-frequency synthetics using these methods indicate that the invented frequencies do not tie high-frequency synthetics generated from the same reflectivity series. Furthermore, synthetic wedge models indicate that the invented high-frequency seismic traces do not improve thin-layer resolution. Frequency invention outputs may serve as useful attributes, but they should not be used for quantitative work and do not improve actual resolution. On the other hand, under appropriate circumstances, layer frequency responses can be extrapolated to frequencies outside the band of the original data using spectral periodicities determined from within the original seismic bandwidth. This can be accomplished by harmonic extrapolation. For blocky earth structures, synthetic tests show that such spectral extrapolation can readily double the bandwidth, even in the presence of noise. Wedge models illustrate the resulting resolution improvement. Synthetic tests suggest that the more complicated the earth structure, the less valid the bandwidth extension that harmonic extrapolation can achieve. Tests of the frequency invention methods and harmonic extrapolation on field seismic data demonstrate that (1) the frequency invention methods modify the original seismic band such that the original data cannot be recovered by simple band-pass filtering, whereas harmonic extrapolation can be filtered back to the original band with good fidelity and (2) harmonic extrapolation exhibits acceptable ties between real and synthetic seismic data outside the original seismic band, whereas frequency invention methods have unfavorable well ties in the cases studied.

Integrating distributed acoustic sensing, borehole 3C geophone array, and surface seismic array data to identify long-period long-duration seismic events during stimulation of a Marcellus Shale gas reservoir

2019 ◽  
Vol 7 (1) ◽  
pp. SA1-SA10 ◽  
Author(s):  
Payam Kavousi Ghahfarokhi ◽  
Thomas H. Wilson ◽  
Timothy Robert Carr ◽  
Abhash Kumar ◽  
Richard Hammack ◽  
...  
Keyword(s):  
Hydraulic Fracture ◽  
Seismic Data ◽  
Fiber Optic ◽  
Marcellus Shale ◽  
Low Frequency ◽  
Seismic Array ◽  
Long Period ◽  
Long Duration ◽  
Distributed Acoustic Sensing ◽  
Stimulation Of

Microseismic monitoring by downhole geophones, surface seismic, fiber-optic distributed acoustic sensing (DAS), and distributed temperature sensing (DTS) observations were made during the hydraulic fracture stimulation of the MIP-3H well in the Marcellus Shale in northern West Virginia. DAS and DTS data measure the fiber strain and temperature, respectively, along a fiber-optic cable cemented behind the casing of the well. The presence of long-period long-duration (LPLD) events is evaluated in the borehole geophones, DAS data, and surface seismic data of one of the MIP-3H stimulated stages. LPLD events are generally overlooked during the conventional processing of microseismic data, but they represent significant nonbrittle deformation produced during hydraulic fracture stimulation. In a single stage that was examined, 160 preexisting fractures and two faults of suboptimal orientation are noted in the image logs. We identified two low-frequency ([Formula: see text]) events of large temporal duration (tens of seconds) by comparing the surface seismic data, borehole geophone data, and DAS amplitude spectra of one of the MIP-3H stages. Spectrograms of DAS traces in time and depth reveal that the first low-frequency event might be an injection noise that has footprints on all DAS channels above the stimulated stage. However, the surface seismic array indicates an LPLD event concurrent with the first low-frequency event on DAS. The second LPLD event on DAS data and surface seismic data is related to a local deformation and does not have footprints on all DAS channels. The interpreted events have duration less than 100 s with frequencies concentrated below 10 Hz, and are accompanied by microseismic events.

scholarly journals Study on mechanism and filter efficacy of AGO/IAGO in the frequency domain

2020 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Changhai Lin ◽  
Zhengyu Song ◽  
Sifeng Liu ◽  
Yingjie Yang ◽  
Jeffrey Forrest
Keyword(s):  
Frequency Domain ◽  
High Frequency ◽  
Statistical Data ◽  
Low Frequency ◽  
Digital Signal ◽  
Good Effect ◽  
Data Sequence ◽  
Content Type ◽  
Noise Interference ◽  
Long Period

PurposeThe purpose of this paper is to analyze the mechanism and filter efficacy of accumulation generation operator (AGO)/inverse accumulation generation operator (IAGO) in the frequency domain.Design/methodology/approachThe AGO/IAGO in time domain will be transferred to the frequency domain by the Fourier transform. Based on the consistency of the mathematical expressions of the AGO/IAGO in the gray system and the digital filter in digital signal processing, the equivalent filter model of the AGO/IAGO is established. The unique methods in digital signal processing systems “spectrum analysis” of AGO/IAGO are carried out in the frequency domain.FindingsThrough the theoretical study and practical example, benefit of spectrum analysis is explained, and the mechanism and filter efficacy of AGO/IAGO are quantitatively analyzed. The study indicated that the AGO is particularly suitable to act on the system's behavior time series in which the long period parts is the main factor. The acted sequence has good effect of noise immunity.Practical implicationsThe AGO/IAGO has a wonderful effect on the processing of some statistical data, e.g. most of the statistical data related to economic growth, crop production, climate and atmospheric changes are mainly affected by long period factors (i.e. low-frequency data), and most of the disturbances are short-period factors (high-frequency data). After processing by the 1-AGO, its high frequency content is suppressed, and its low frequency content is amplified. In terms of information theory, this two-way effect improves the signal-to-noise ratio greatly and reduces the proportion of noise/interference in the new sequence. Based on 1-AGO acting, the information mining and extrapolation prediction will have a good effect.Originality/valueThe authors find that 1-AGO has a wonderful effect on the processing of data sequence. When the 1-AGO acts on a data sequence X, its low-pass filtering effect will benefit the information fluctuations removing and high-frequency noise/interference reduction, so the data shows a clear exponential change trends. However, it is not suitable for excessive use because its equivalent filter has poles at the non-periodic content. But, because of pol effect at zero frequency, the 1-AGO will greatly amplify the low-frequency information parts and suppress the high-frequency parts in the information at the same time.

CROSSTALK BY NONLINEAR GRATING COMBINATIONS IN PHOTOREFRACTIVE HOLOGRAMS COMPUTED DIRECTLY FROM THE BAND-TRANSPORT MODEL

2001 ◽  
Vol 10 (01) ◽  
pp. 53-63
Author(s):  
PREBEN BUCHHAVE
Keyword(s):  
High Frequency ◽  
Transport Model ◽  
Low Frequency ◽  
Transport Equations ◽  
Reduction Factor ◽  
Free Carrier ◽  
Long Period Grating ◽  
Long Period ◽  
The Difference ◽  
Local Modulation

The crosstalk between two photorefractive holograms caused by nonlinear grating interactions is computed directly from the band-transport equations without using an empirical reduction factor to describe the difference between the modulation index of the impressed intensity grating and the resulting free carrier modulation. The long period grating modulation resulting from the interference between closely spaced object beams cannot write a holographic grating, but is treated as a local modulation of the high frequency part of the grating. The method can be applied as long as the low frequency envelope does not in itself write a photorefractive grating. With this limitation the method can be used for arbitrary values of modulation indices and beam ratios where the simple band-transport equations apply.

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