|Title||A method for detecting and locating geophysical events using groups of arrays|
|Publication Type||Journal Article|
|Year of Publication||2015|
|Authors||de Groot-Hedlin C.D, Hedlin MAH|
|Journal||Geophysical Journal International|
|Type of Article||Article|
|Keywords||Acoustic properties; america; atmosphere; chelyabinsk; meteor; north; propagation; Time-series analysis; USArray; wave propagation|
We have developed a novel method to detect and locate geophysical events that makes use of any sufficiently dense sensor network. This method is demonstrated using acoustic sensor data collected in 2013 at the USArray Transportable Array (TA). The algorithm applies Delaunay triangulation to divide the sensor network into a mesh of three-element arrays, called triads. Because infrasound waveforms are incoherent between the sensors within each triad, the data are transformed into envelopes, which are cross-correlated to find signals that satisfy a consistency criterion. The propagation azimuth, phase velocity and signal arrival time are computed for each signal. Triads with signals that are consistent with a single source are bundled as an event group. The ensemble of arrival times and azimuths of detected signals within each group are used to locate a common source in space and time. A total of 513 infrasonic stations that were active for part or all of 2013 were divided into over 2000 triads. Low (0.5-2 Hz) and high (2-8 Hz) catalogues of infrasonic events were created for the eastern USA. The low-frequency catalogue includes over 900 events and reveals several highly active source areas on land that correspond with coal mining regions. The high-frequency catalogue includes over 2000 events, with most occurring offshore. Although their cause is not certain, most events are clearly anthropogenic as almost all occur during regular working hours each week. The regions to which the TA is most sensitive vary seasonally, with the direction of reception dependent on the direction of zonal winds. The catalogue has also revealed large acoustic events that may provide useful insight into the nature of long-range infrasound propagation in the atmosphere.
"As shown, the method uses incoherent processing of data from a network that is dense by most standards but not dense enough for signals to be coherent between adjacent stations. The fact that incoherent processing works indicates that, with appropriate modifications, the method can be applied to a wide variety of data sets such as seismic data recorded by the TA, or even to much sparser networks."