Adaptive Waveform Correlation Detectors for Arrays: Algorithms for Autonomous Calibration
Abstract
Waveform correlation detectors compare a signal template with successive windows of a continuous data stream and report a detection when the correlation coefficient (CC), or some comparable detection statistic, exceeds a given threshold. Since these methods exploit characteristic details of the full waveform, they provide exquisitely sensitive detectors with far lower detection thresholds than typical STA/LTA algorithms. The drawback is that the form of the sought after signal needs to be known quite accurately a priori which limits such methods to instances of seismicity whereby a very similar signal has already been observed by every station used. Such instances include earthquake swarms, aftershock sequences, repeating industrial seismicity, and many other forms of controlled explosions. The reduction in the detection threshold is even greater when the techniques are applied to multiple channels since stacking can be performed on the correlation coefficient traces with a significant array-gain. A detected event that is co-located with the master event will record the same time-difference at every site in an arbitrarily spaced network which means that the correlation coefficient traces can be stacked coherently even when there is little or no similarity between the actual signals at the different sites. The focus in the first year of the contract was testing limits of detection capability for almost co-located seismic events. It was demonstrated that the signal from a magnitude 3.5 earthquake could be used as a template to detect nearby events 3 orders of magnitude smaller using multi-channel correlation detectors. This is an improvement better than one magnitude unit for an ARCES-style regional seismic array and better than 1.5 magnitude units for a larger network where coherent array processing was not possible.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 2008
- Accession Number
- ADA516232
Entities
People
- David B. Harris
- Frode Ringdal
- Steven J. Gibbons
Organizations
- Lawrence Livermore National Laboratory