Global Volcanism Program | Image GVP-01942
The seismogram for 15 June 1991 shows the intense seismicity accompanying the catastrophic eruption of Mount Pinatubo in the Philippines. This seismic record shows earthquakes over a two-hour period beginning at 0508 hours. The arrow points to the earthquake accompanying a major explosion at 0555, which was preceded by long-period earthquakes. At about 0640 continuous overlapping long-period earthquakes or tremor began, and much of the following record was saturated so that individual earthquakes could not be distinguished.
Photo by Ed Wolfe, 1991 (U.S. Geological Survey).