Utilization of seismically recorded infrasonic-acoustic signals to monitor volcanic explosions: The El Chichon Sequence 1982—A case study
Infrasonic-acoustic signals from five explosive eruptions of El Chichon volcano during March 29 through April 4, 1982, were recorded by a microbarograph array and Seismic Research Observatory (SRO) seismograph collocated near McKinney, Texas. Analyses of these signals for frequencies from 0.0033 to 0.025 H have demonstrated functional relationships of amplitude to frequency consistent with ω-1 for microbarometric data, ω-2 for vertical mode seismic data, and ω-3 for radial mode seismic data. These observed slopes are in agreement with those theoretically predicted by Sorrells (1971). Estimations of kinetic energy releases by the explosions of El Chichon are presented and range from 4.9×1022 ergs to 2.0×1023 for the largest eruption on April 4, 1982, to 4.2×1021 to 6.1×1021 ergs for the smallest eruption on April 3, 1982. The method of Posey and Pierce (1971) to estimate the explosivity from long-period infrasonic signals is not likely to be applicable, strictly speaking, to the shorter-period data. Thus it is believed that the energy release for the smallest eruption is overestimated by possibly an order of magnitude. Comparable estimations of volcanic explosivity from SRO radial seismic data and microbarometric array data strongly recommend using SRO and International Deployment Accelerometers network data for far-field analyses of volcanic explosions and construction of a rigorous volcanic explosivity scale.