Using Ambient Seismic Noise to Determine Short-Period Phase Velocities and Shallow Shear Velocities in Young Oceanic Lithosphere

2007 ◽  
Vol 97 (6) ◽  
pp. 2009-2023 ◽  
Author(s):  
N. Harmon ◽  
D. Forsyth ◽  
S. Webb
Keyword(s):  
Seismic Noise ◽  
Oceanic Lithosphere ◽  
Ambient Seismic Noise ◽  
Phase Velocities ◽  
Short Period

scholarly journals Structure of the Suasselkä postglacial fault in northern Finland obtained by analysis of local events and ambient seismic noise

Solid Earth ◽  
2017 ◽  
Vol 8 (2) ◽  
pp. 531-544 ◽  
Author(s):  
Nikita Afonin ◽  
Elena Kozlovskaya ◽  
Ilmo Kukkonen ◽  
Keyword(s):  
Seismic Noise ◽  
Ambient Seismic Noise ◽  
Seismic Events ◽  
S Wave ◽  
Noise Sources ◽  
Surface Wave Dispersion ◽  
Velocity Models ◽  
Wave Velocities ◽  
Short Period ◽  
Single Station

Abstract. Understanding the inner structure of seismogenic faults and their ability to reactivate is particularly important in investigating the continental intraplate seismicity regime. In our study we address this problem using analysis of local seismic events and ambient seismic noise recorded by the temporary DAFNE array in the northern Fennoscandian Shield. The main purpose of the DAFNE/FINLAND passive seismic array experiment was to characterize the present-day seismicity of the Suasselkä postglacial fault (SPGF), which was proposed as one potential target for the DAFNE (Drilling Active Faults in Northern Europe) project. The DAFNE/FINLAND array comprised an area of about 20 to 100 km and consisted of eight short-period and four broadband three-component autonomous seismic stations installed in the close vicinity of the fault area. The array recorded continuous seismic data during September 2011–May 2013. Recordings of the array have being analysed in order to identify and locate natural earthquakes from the fault area and to discriminate them from the blasts in the Kittilä gold mine. As a result, we found a number of natural seismic events originating from the fault area, which proves that the fault is still seismically active. In order to study the inner structure of the SPGF we use cross-correlation of ambient seismic noise recorded by the array. Analysis of azimuthal distribution of noise sources demonstrated that during the time interval under consideration the distribution of noise sources is close to the uniform one. The continuous data were processed in several steps including single-station data analysis, instrument response removal and time-domain stacking. The data were used to estimate empirical Green's functions between pairs of stations in the frequency band of 0.1–1 Hz and to calculate corresponding surface wave dispersion curves. The S-wave velocity models were obtained as a result of dispersion curve inversion. The results suggest that the area of the SPGF corresponds to a narrow region of low S-wave velocities surrounded by rocks with high S-wave velocities. We interpret this low-velocity region as a non-healed mechanically weak fault damage zone (FDZ) formed due to the last major earthquake that occurred after the last glaciation.

High-frequency seismic noise at Lajitas, Texas

1984 ◽  
Vol 74 (5) ◽  
pp. 2015-2033
Author(s):  
Todd M. C. Li ◽  
John F. Ferguson ◽  
Eugene Herrin ◽  
Howard B. Durham
Keyword(s):  
High Frequency ◽  
Seismic Noise ◽  
Preliminary Analysis ◽  
Unknown Origin ◽  
Substantial Improvement ◽  
Body Waves ◽  
Degree Of Polarization ◽  
Ambient Seismic Noise ◽  
Noise Power ◽  
Phase Velocities

Abstract A preliminary analysis of high-frequency (1 to 20 Hz) ambient seismic noise at a very quiet site in southwest Texas is presented. At frequencies greater than 1 Hz, the displacement noise power decreases at a rate between f−4 and f−5. The ambient seismic noise is also characterized by persistent narrow-band peaks (Δf < 0.2 Hz) of unknown origin. The noise appears to be propagating at phase velocities 2.5 to 4 km/sec or greater which suggests higher mode surface or body waves. Estimates of coherence and degree of polarization of three-component array data indicate that the high-frequency ambient noise is relatively well organized over distances of at least 600 to 700 m for a single component but is relatively unorganized in a three-component sense. A principal result of this preliminary analysis is that the use of three-component, high-frequency (1 to 20 Hz) arrays at very quiet sites, coupled with three-component processors, may result in substantial improvement of the thresholds for detection and discrimination of weak seismic events.

scholarly journals Structure of Suasselkä Postglacial Fault in northern Finland obtained by analysis of local events and ambient seismic noise

2016 ◽  
Author(s):  
Nikita Afonin ◽  
Elena Kozlovskaya ◽  
Ilmo Kukkonen ◽  
DAFNE/FINLAND Working Group
Keyword(s):  
Seismic Noise ◽  
Dispersion Curves ◽  
Ambient Seismic Noise ◽  
Seismic Events ◽  
S Wave ◽  
Noise Sources ◽  
Velocity Models ◽  
Wave Velocities ◽  
Short Period ◽  
Single Station

Abstract. Understanding inner structure of seismogenic faults and their ability to reactivate is particularly important in investigating continental intraplate seismicity regime. In our study we address this problem using analysis of local seismic events and ambient seismic noise recorded by the temporary DAFNE array in northern Fennoscandian Shield. The main purpose of the DAFNE/FINLAND passive seismic array experiment was to characterize the present-day seismicity of the Suasselkä post-glacial fault (SPGF) that was proposed as one potential target for the DAFNE (Drilling Active Faults in Northern Europe) project. The DAFNE/FINLAND array comprised the area of about 20 to 100 km and consisted of 8 short-period and 4 broad-band 3-component autonomous seismic stations installed in the close vicinity of the fault area. The array recorded continuous seismic data during September, 2011–May, 2013. Recordings of the array have being analyzed in order to identify and locate natural earthquakes from the fault area and to discriminate them from the blasts in the Kittilä Gold Mine. As a result, we found several dozens of natural seismic events originating from the fault area, which proves that the fault is still seismically active. In order to study the inner structure of the SPGF we use cross-correlation of ambient seismic noise recorded by the array. Analysis of azimuthal distribution of noise sources demonstrated that during the time interval under consideration the distribution of noise sources is close to the uniform one. The continuous data were processed in several steps including single station data analysis, instrument response removal and time-domain stacking. The data were used to estimate empirical Green’s functions between pairs of stations in the frequency band of 0.1–1 Hz and to calculate correspondent surface wave dispersion curves. The S-wave velocity models were obtained as a result of dispersion curves inversion. The results suggest that the area of the SPGF corresponds to a narrow region of low S-wave velocities surrounded by rocks with high S-wave velocities. We interpret this low velocity region as a non-healed mechanically weak fault damage zone (FDZ) that remained after the last major earthquake that occurred after the last glaciation.

The impact of the COVID-19 lockdown measures on the seismic monitoring in the Bucharest (Romania) metropolitan area

2021 ◽  
Author(s):  
Bogdan Grecu ◽  
Alexandru Tiganescu ◽  
Natalia Poiata ◽  
Felix Borleanu ◽  
Raluca Dinescu ◽  
...  
Keyword(s):  
Frequency Band ◽  
Urban Areas ◽  
Seismic Noise ◽  
Free Field ◽  
Substantial Reduction ◽  
Urban Traffic ◽  
Ambient Seismic Noise ◽  
Mobility Data ◽  
Short Period ◽  
The Impact

<p>The lockdown measures taken to control and stop the spread of the novel coronavirus (COVID-19) in cities around the globe caused an unprecedented reduction of anthropic activities. The signature of this reduction, different from one place to another, has been captured by the seismic stations installed in the urban areas where lockdown restrictions have been implemented. Bucharest, the capital of Romania, was no exception from this phenomenon.</p><p>In this paper, we investigate the effect of the COVID-19 lockdown measures imposed by the Romanian authorities on the high-frequency ambient seismic noise (ASN) data recorded by the Bucharest Metropolitan Seismic Network (BMSN). BMSN consists of 26 stations of which 19 are equipped with strong motion sensors and 7 have both short-period velocity and accelerometer sensors. All the stations are continuously recording the ground motion and the data is sent in real-time to the data center of the National Institute for Earth Physics.         </p><p>The reduction of ASN was first observed at stations installed in educational units (kindergartens, schools) starting with 11th of March 2020, when the Romanian government decided to close the schools in Romania. For these stations, the largest reduction of ASN, up to 82%, was noticed in the 25-40 Hz frequency band. On 16th of March the state of emergency was imposed in Romania and a few days later, on 25th of March, the stay-at-home order was issued. These new restrictions caused substantial reduction in urban traffic and people’s mobility and reflected in significant reduction of ASN at almost all the other BMSN stations, located either free-field or in buildings. For these stations, we observed a decrease of the noise levels by as much as 66% in the 15-25 Hz frequency band. We also correlated the ambient seismic noise with other types of data that might be affected by human activity, such as the mobility data from Google and Apple, and we found good correlation between ASN in different frequency bands and various mobility data categories. Finally, we showed that the noise reduction due to lockdown measures improved the signal-to-noise ratio of the stations in the Bucharest area, allowing us to record smaller earthquakes which otherwise would not have been recorded.</p>

Short-period seismic noise

1967 ◽  
Vol 57 (1) ◽  
pp. 55-81
Author(s):  
E. J. Douze
Keyword(s):  
Surface Waves ◽  
Rayleigh Waves ◽  
Seismic Noise ◽  
Body Waves ◽  
Deep Hole ◽  
Period Range ◽  
Short Period ◽  
The Subject ◽  
Hole Arrays

abstract This report consists of a summary of the studies conducted on the subject of short-period (6.0-0.3 sec period) noise over a period of approximately three years. Information from deep-hole and surface arrays was used in an attempt to determine the types of waves of which the noise is composed. The theoretical behavior of higher-mode Rayleigh waves and of body waves as measured by surface and deep-hole arrays is described. Both surface and body waves are shown to exist in the noise. Surface waves generally predominate at the longer periods (of the period range discussed) while body waves appear at the shorter periods at quiet sites. Not all the data could be interpreted to define the wave types present.

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