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|Authors: ||Wang, J.*|
White, R. S.*
|Title: ||Application of frequency-dependent multichannel Wiener ﬁlters to detect events in 2D three-component seismometer arrays|
|Title of journal: ||Geophysics|
|Series/Report no.: ||6/74 (2009)|
|Publisher: ||Society of Exploration Geophysicists|
|Issue Date: ||2009|
|Keywords: ||Weiner filters, noise suppression, cavola array|
|Abstract: ||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
|Appears in Collections:||01.01.08. Instruments and techniques|
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