Publication Date:
2017-04-04
Description:
Hydraulic-fracture induced microseismic events are usually small, and noise levels are high
at the surface due to the activities associated with a producing oil field. Similarly, local
arrays for the detection of local earthquakes will also benefit from reduced noise levels and
detect smaller events. We present a frequency-dependent multi-channel Wiener filtering
technique with linear constraints, which employs an adaptive least-squares technique to
remove coherent noise in seismic array data. The noise records on a number of reference
channels is used to predict the noise on a primary channel, which can then be subtracted.
We implement and test first an unconstrained version of this filter, where maximal noise
suppression can lead to signal distortion. Two methods of imposing constraints are then
introduced to achieve signal preservation. We test this technique with two case studies.
First, synthetic signals are added to actual noise from a pilot deployment of a hexagonal
array (9 three-component seismometers, approximate size 150 m × 150 m) in an oil field;
noise levels are suppressed by up to 11 dB (at 1 - 6 Hz). Secondly we use natural seismicity recorded at a dense array (∼10 m spacing) in Italy where the application of the filter
reduces the signal-to-noise ratio by more than 20 dB (at 8 - 15 Hz), using 35 stations.
In both cases, the performance of the multi-channel Wiener filters is significantly better
than stacking, especially at lower frequency where stacking does not help to suppress the
coherent noise. The unconstrained version of the filter yielded the best improvement in the
signal-to-noise ratio, but the constrained filter is useful when waveform distortion is not
acceptable.
Description:
Published
Description:
v133-v141
Description:
1.11. TTC - Osservazioni e monitoraggio macrosismico del territorio nazionale
Description:
JCR Journal
Description:
open
Keywords:
Weiner filters, noise suppression, cavola array
;
01. Atmosphere::01.01. Atmosphere::01.01.08. Instruments and techniques
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
