  The regional phase Lg is used to estimate location and magnitude for sources
closer than 1500 km. The complexity of Lg waveforms makes it difficult to
consistently determine Lg arrival time, thus affecting source location with a
single station or array. This study tests an automatic method for timing Lg
arrivals using wavelet transforms to decompose the Lg signal into its
components localized both in time and scale. A Continuous Wavelet Transform
(CWT) using a Daubechies order two (db2) wavelet is applied to 10 seconds of
raw data, containing the start of Lg. Initial positioning of the window is
obtained using the standard Lg travel time tables. The coefficients at scale 8
from the db2 decomposition are squared and the resulting time series is
represented by an approximation of the 4'th level Discrete Wavelet Transform
(DWT) using a Haar wavelet. A threshold detector is then applied to the
resulting time series to determine the Lg arrival time. The method was tested
using well located earthquakes (USGS) and explosions from known mines (mb less
than 4.0), recorded on the vertical components at TXAR (Lajitas, Texas) and
PDAR (Pinedale, Wyoming) arrays. The Lg arrival time was automatically picked
with a standard deviation of less than 1.5 seconds (less than 10 km location
error) for well known locations. Location errors are larger with the increase
in distance and smaller with the increase in signal to noise ratio of events.
