Mount St. Helens is twitching again. Earthquake activity below the mountain gradually has increased in recent months, with the pace accelerating in May. Seismic activity has increased from about 60 quakes a month last winter to 165 in May, scientists at the Cascades Volcano Observatory in Vancouver, WA report. The earthquakes are small and unfelt, with only three of them greater than magnitude 2, according to William E. Scott, acting scientist in charge of the observatory. He stressed that no evidence indicates the closely monitored volcano is heading fro a return to large explosive eruptions. None of the quakes is typical of the large number of shallow quakes that typically occur before an eruption