Detection and source parameterization of small-energy fireball events in Western Alps with ground-based infrasonic arrays

2021 ◽  
Author(s):  
Giacomo Belli ◽  
Emanuele Pace ◽  
Emanuele Marchetti
Keyword(s):  
Western Alps ◽  
Apparent Velocity ◽  
Array Analysis ◽  
Small Energy ◽  
Small Aperture ◽  
Energy Estimation ◽  
Trajectory Reconstruction ◽  
Tnt Equivalent ◽  
Back Azimuth ◽  
Aperture Arrays

Summary We present infrasound signals generated by four fireball events occurred in Western Alps between 2016 and 2019 and that were recorded by small aperture arrays at source-to receiver distances < 300 km. Signals consist in a series of short-lived infrasonic arrivals that are closely spaced in time. Each arrival is identified as a cluster of detections with constant wave parameters (back-azimuth and apparent velocity), that change however from cluster to cluster. These arrivals are likely generated by multiple infrasonic sources (fragmentations or hypersonic flow) along the entry trajectory. We developed a method, based on 2D ray-tracing and on the independent optically determined time of the event, to locate the source position of the multiple arrivals from a single infrasonic array data and to reconstruct the 3D trajectory of a meteoroid in the Earth's atmosphere. The trajectories derived from infrasound array analysis are in excellent agreement with trajectories reconstructed from eyewitnesses reports for the four fireballs. Results suggest that the trajectory reconstruction is possible for meteoroid entries located up to ∼300 km from the array, with an accuracy that depends on the source-to-receiver distance and on the signal-to-noise level. We also estimate the energy of the four fireballs using three different empirical laws, based both on period and amplitude of recorded infrasonic signals, and discuss their applicability for the energy estimation of small energy fireball events ($\le 1{\rm{kt\,\,TNT\,\,equivalent}}$).

scholarly journals Infrasound array criteria for automatic detection and front velocity estimation of snow avalanches: towards a real-time early-warning system

2015 ◽  
Vol 3 (4) ◽  
pp. 2709-2737 ◽  
Author(s):  
E. Marchetti ◽  
M. Ripepe ◽  
G. Ulivieri ◽  
A. Kogelnig
Keyword(s):  
Risk Management ◽  
Real Time ◽  
Doppler Radar ◽  
Warning System ◽  
Velocity Estimation ◽  
Apparent Velocity ◽  
Snow Avalanches ◽  
Small Aperture ◽  
Back Azimuth ◽  
Threshold Criteria

Abstract. Avalanche risk management is strongly related to the ability to identify and timely report the occurrence of snow avalanches. Infrasound has been applied to avalanche research and monitoring for the last 20 years but it never turned into an operational tool for the ambiguity to identify clear signals related to avalanches. We present here a new method based on the analysis of infrasound signals recorded by a small aperture array in Ischgl (Austria), which overcome now this limit. The method is based on array derived wave parameters, such as back-azimuth and apparent velocity. The method defines threshold criteria for automatic avalanche identification considering avalanches as a moving source of infrasound. We validate efficiency of the automatic infrasound detection with continuous observations with Doppler Radar and we show how dynamics parameters such as the velocity of a snow avalanche in any given path around the array can be efficiently derived. Our results indicate that a proper infrasound array analysis allows a robust, real-time, remote detection of snow avalanches that could thus contribute significantly to avalanche forecast and risk management.

scholarly journals Infrasound array criteria for automatic detection and front velocity estimation of snow avalanches: towards a real-time early-warning system

2015 ◽  
Vol 15 (11) ◽  
pp. 2545-2555 ◽  
Author(s):  
E. Marchetti ◽  
M. Ripepe ◽  
G. Ulivieri ◽  
A. Kogelnig
Keyword(s):  
Risk Management ◽  
Real Time ◽  
Doppler Radar ◽  
Warning System ◽  
Velocity Estimation ◽  
Apparent Velocity ◽  
Snow Avalanches ◽  
Small Aperture ◽  
Forecast Models ◽  
Back Azimuth

Abstract. Avalanche risk management is strongly related to the ability to identify and timely report the occurrence of snow avalanches. Infrasound has been applied to avalanche research and monitoring for the last 20 years but it never turned into an operational tool to identify clear signals related to avalanches. We present here a method based on the analysis of infrasound signals recorded by a small aperture array in Ischgl (Austria), which provides a significant improvement to overcome this limit. The method is based on array-derived wave parameters, such as back azimuth and apparent velocity. The method defines threshold criteria for automatic avalanche identification by considering avalanches as a moving source of infrasound. We validate the efficiency of the automatic infrasound detection with continuous observations with Doppler radar and we show how the velocity of a snow avalanche in any given path around the array can be efficiently derived. Our results indicate that a proper infrasound array analysis allows a robust, real-time, remote detection of snow avalanches that is able to provide the number and the time of occurrence of snow avalanches occurring all around the array, which represent key information for a proper validation of avalanche forecast models and risk management in a given area.

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.

Matched-field source localization with multiple small-aperture arrays

2015 ◽  
Vol 138 (3) ◽  
pp. 1754-1754 ◽  
Author(s):  
Dag Tollefsen ◽  
Stan E. Dosso
Keyword(s):  
Source Localization ◽  
Small Aperture ◽  
Field Source ◽  
Aperture Arrays

A seismic passive imaging step beyond SPAC and ReMi

Geophysics ◽  
2013 ◽  
Vol 78 (5) ◽  
pp. KS63-KS72 ◽  
Author(s):  
Francesco Mulargia ◽  
Silvia Castellaro
Keyword(s):  
Passive Imaging ◽  
Small Aperture ◽  
Simple Geometry ◽  
Recording Station ◽  
Refraction Microtremor ◽  
A New Technique ◽  
Statistical Mode ◽  
The One ◽  
Aperture Arrays ◽  
The Waves

The basic property of passive imaging is that, given any two points, one of them can be taken as the source of the waves and the other as the recording station. This property can be derived from the statistical self-alignment of the rays along the vector joining the two points, and applies also to nondiffuse wavefields like seismic tremor. It provides a statistical basis for the use of the stationary phase integral, allowing passive interferometry under the mild constraint of mechanical homogeneity at a local scale. Combined with the tremor’s large spectral bandwidth, it allows one to recover the local Green’s function from spatial correlation. Furthermore, combining this property also with the azimuthal isotropy of either the wavefield or the array, and using the statistical mode as the estimator, provides a new technique to measure the local velocity dispersion in the subsoil. This technique exploits the potential of spatial autocorrelation (SPAC) and refraction microtremor (ReMi), allowing one (1) to use sparse small-aperture arrays with simple geometry, (2) to dispense with the fitting of Bessel functions, and (3) to measure, in a few minutes, the local (phase and group) wave velocity as a function of frequency of potentially all the wave-propagation modes — body and surface — and not just of the one prevailing at each frequency.

Observations of high-frequency scattered waves using dense arrays at Teide Volcano

1997 ◽  
Vol 87 (6) ◽  
pp. 1637-1647
Author(s):  
E. Del Pezzo ◽  
M. La Rocca ◽  
J. Ibanez
Keyword(s):  
Random Distribution ◽  
Great Part ◽  
Apparent Velocity ◽  
Frequency Range ◽  
Small Aperture ◽  
Analysis Techniques ◽  
Correlated Arrivals ◽  
Seismic Coda ◽  
The Time Domain ◽  
Teide Volcano

Abstract A study of the seismic coda of seven small earthquakes recorded on the Teide Volcano-Canary Islands (Spain) was carried out using a temporary, small-aperture, 12-station, seismic array. The purpose was to measure backazimuth, apparent velocity and the type of waves that compose the coda in the frequency range 4 to 6 Hz. We used the zero-lag cross-correlation (ZLC) method to obtain the components of the wave vector and three-component analysis techniques based on the covariance matrix of the signal in the time domain to investigate the polarization properties of the signals. The results show that a great part of the coda signals in the analyzed frequency range are almost uncorrelated, while a low number of isolated correlated arrivals show an apparent slowness between 2 × 10−3 and 2.5 × 10−4 sec/m and an almost random distribution of backazimuths. The correlated arrivals have been interpreted as generated by strong scatterers, probably related to the presence, in the study area, of surface topography irregularities (the volcanic cone and the caldera rim). The wave type varies from pure S-type waves to mixed surface waves with some Rayleigh components.

Bayesian hierarchical model for variations in earthquake peak ground acceleration within small-aperture arrays

2018 ◽  
Vol 29 (3) ◽  
pp. e2497 ◽  
Author(s):  
Sahar Rahpeyma ◽  
Benedikt Halldorsson ◽  
Birgir Hrafnkelsson ◽  
Sigurjón Jónsson
Keyword(s):  
Hierarchical Model ◽  
Peak Ground Acceleration ◽  
Bayesian Hierarchical Model ◽  
Ground Acceleration ◽  
Small Aperture ◽  
Bayesian Hierarchical ◽  
Aperture Arrays
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