Publication Date:
2019-11-04
Description:
In order to evaluate the detection and localisation improvement of a small aperture array in the Northern Apennines, we installed an irregularly spaced test configuration in the vicinity of Città di Castello (CDC) for a period of two weeks. The experimental array consisted of nine 3-component stations with inter-station distances between 150 m and 2200 m. Seismic data were digitised at 125 Hz and telemetered to a mobile acquisition, processing and storage centre. The data could only be recorded in trigger mode. The peculiarity of the test array installation was the exclusive use of 3-component sensors at all array sites, which also allowed beamforming for S-phases on the horizontal components. Since the altitudes of the single array sites differed considerably among each other, for f-k analysis and beamforming an elevation correction was included. During the two weeks of operation about 20 local
earthquakes with magnitudes ML〈2.6, 1 regional, and several teleseismic events were recorded. In addition to these
events, the array occasionally triggered on coherent noise-signals generated by local industrial activity. The data analysis was performed by means of f-k analysis and beamforming, providing wavenumber characteristics of the incident plane wave. Typical apparent velocities were determined to be 4.8 km/s and 6 km/s for Pg-phases and ~10 km/s for Pn-phases. We observed local seismic events, which occurred just beneath the array. In these cases wavefronts
with unusual high apparent velocities, similar to those found for the Pn-phase, were observed. Since no continuously
recorded array data were available, we extrapolated the lower detection magnitude threshold as a result of the SNR improvement due to array beamforming. Compared to the actual detection threshold of MT ~1.6 reached by the national seismic network in this area, a nine element array would improve this value up to MT ~ 0.8.
Description:
Published
Description:
JCR Journal
Description:
open
Keywords:
seismic array
;
beamforming
;
f-kanalysis
;
Central Apennines
;
04. Solid Earth::04.06. Seismology::04.06.06. Surveys, measurements, and monitoring
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
Format:
2861057 bytes
Format:
application/pdf
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