LASA anomalies and their relations to crust and upper-mantle structure

Body-wave data from nine teleseisms recorded at the Large Aperture Seismic Array (LASA), Montana, have been analyzed. The events were at different azimuths and distances from LASA. Apparent-velocity measurements using arrival-time data at the subarrays differed by about 30 percent for events in the northwest and southeast directions.Apparent velocities were high near the center of the array for events in the northwest and low for events in the southeast. For events in the other azimuths, the patterns were more complex, but anomalous values were found near the center. Apparent-velocity measurements at subarrays were made using a cross-spectral technique. The resulting values showed patterns similar to those obtained using arrival-time data near the center. Anomalous high and low values were found near the center and also at the E and F subarrays.