"The use of seismic arrays for local, regional and teleseismic event analysis"
19 novembre 2008, ore 14.30 | Thomas Braun | Sala Conferenze Roma | Sede Centrale | Seminari Sezione Roma 1
The use of seismic arrays for local, regional and teleseismic event analysis
A seismic array differs from a local network of seismic stations mainly by the techniques used for data analysis. Thus, in principle, a network of seismic stations can be used as an array and data from an array can be analyzed as from a network. However, most array processing techniques require high signal coherency across the array, and this puts important constraints on the array geometry, spatial extent, and data quality. Furthermore, proper analysis of array data is dependent on a stable, high precision relative timing of all array elements. This is required because the measurement of (usually very small) time differences of the arrival of seismic signals between the different sensors plays an important role in all array-processing techniques.
The improved signal detection capability of arrays is obtained by applying “beamforming” techniques, which suppress the noise while preserving the signal, thus enhancing the Signal-to-Noise Ratio (SNR). Arrays can also provide estimates of the station-to-event azimuth (backazimuth), and of the apparent velocity of seismic signals. These estimates are important both for event location purposes and for classification of signals, e.g., P, S, local, regional, or teleseismic. The first seismic arrays have been installed at the beginning of the sixties with the purpose to monitor nuclear explosions.
Recently also in Italy array techniques are being applied for the seismic monitoring of the seismic activity in volcanic and non-volcanic areas. Since May 2002 a small aperture dense array of short period seismometers (UNDERSEIS) is operative in the Gran Sasso (central Italy) underground Physics Laboratories.
After introducing the principles of array seismology, the presentation reports the results from two recently installed temporary small aperture array installations in the Northern Apennines (Città di Castello (2000) and Casentino (2005)), which aimed to monitor the local seismicity and nonvolcanic tremor like signals.
A further “Italian” array application is the use of the , causing strong subterranean degassing.
Italian Seismic Broadband Network (ISBN) that together with MedNet consists of more than 100 seismic stations. According to the bandwidth of the recording seismometers (40s and 120s) different subnet-configurations of the ISBN can be designed to apply array methods to regional and teleseismic events.
In order to study the source process of the 2004 Sumatra Earthquake the entire ISBN was used as large aperture seismic array (extension > 1000 km). Assuming curved wavefronts, we applied a source scanning algorithm to directly image the spatio-temporal evolution of 450 s lasting rupture.
qui puoi trovare gli abstract in inglese ed in italiano.
A seismic array differs from a local network of seismic stations mainly by the techniques used for data analysis. Thus, in principle, a network of seismic stations can be used as an array and data from an array can be analyzed as from a network. However, most array processing techniques require high signal coherency across the array, and this puts important constraints on the array geometry, spatial extent, and data quality. Furthermore, proper analysis of array data is dependent on a stable, high precision relative timing of all array elements. This is required because the measurement of (usually very small) time differences of the arrival of seismic signals between the different sensors plays an important role in all array-processing techniques.
The improved signal detection capability of arrays is obtained by applying “beamforming” techniques, which suppress the noise while preserving the signal, thus enhancing the Signal-to-Noise Ratio (SNR). Arrays can also provide estimates of the station-to-event azimuth (backazimuth), and of the apparent velocity of seismic signals. These estimates are important both for event location purposes and for classification of signals, e.g., P, S, local, regional, or teleseismic. The first seismic arrays have been installed at the beginning of the sixties with the purpose to monitor nuclear explosions.
Recently also in Italy array techniques are being applied for the seismic monitoring of the seismic activity in volcanic and non-volcanic areas. Since May 2002 a small aperture dense array of short period seismometers (UNDERSEIS) is operative in the Gran Sasso (central Italy) underground Physics Laboratories.
After introducing the principles of array seismology, the presentation reports the results from two recently installed temporary small aperture array installations in the Northern Apennines (Città di Castello (2000) and Casentino (2005)), which aimed to monitor the local seismicity and nonvolcanic tremor like signals.
A further “Italian” array application is the use of the , causing strong subterranean degassing.
Italian Seismic Broadband Network (ISBN) that together with MedNet consists of more than 100 seismic stations. According to the bandwidth of the recording seismometers (40s and 120s) different subnet-configurations of the ISBN can be designed to apply array methods to regional and teleseismic events.
In order to study the source process of the 2004 Sumatra Earthquake the entire ISBN was used as large aperture seismic array (extension > 1000 km). Assuming curved wavefronts, we applied a source scanning algorithm to directly image the spatio-temporal evolution of 450 s lasting rupture.
qui puoi trovare gli abstract in inglese ed in italiano.