Hydroacoustic records and a numerical records of the source mechanism from the first historical eruption of Anatahan Volcano, Mariana Islands

Abstract

Anatahan Volcano in the Commonwealth of the Northern Mariana Islands (CNMI) erupted for the first time in recorded history on 10 May 2003. The underwater acoustic records (T-waves) of earthquakes, explosions, and tremor produced during the eruption were recorded on a sound-channel hydrophone deployed in February 2003. Acoustic propagation models show the seismic to acoustic conversion at Anatahan is particularly efficient, aided by the upward slope of the seamount toward the hydrophone. The hydrophone records confirm the onset of earthquake activity between 0100-0200Z on 10 May, with a substantial increase in seismicity beginning at ~0620Z. In addition, the onset of continuous, low-frequency (3-40 Hz) acoustic energy that is likely volcanic tremor related to magma intrusion was also observed at 0620Z. The hydrophone recorded 1401 earthquakes during the first 3 days of the eruption. A histogram of seismicity indicates two main periods of explosion/eruption activity, the first beginning at ~0620Z on 10 May and the second at ~0000Z on 11 May. Relative earthquake depth estimates indicate both eruption periods were accompanied by earthquake activity from deep within the Anatahan volcanic edifice. A numerical representation of the Anatahan volcano-seismic source was developed to examine the character of acoustic signals generated from the eruption governed by the geometry of the source and the physical properties of the magma. A magma pipe source mechanism within a partially submerged volcano was used to produce estimates of the seismo-acoustic wavefield within the Anatahan volcanic edifice.