Hydroacoustic Records and Numerical Models of the Source Mechanisms from the First Historical Eruption of Anatahan Volcano, Mariana Islands

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 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 slope of the seamount toward the hydrophone. The hydrophone records confirm the onset of earthquake activity at 01:53Z on 10 May, as well as the onset (at ${\~}$06:20Z) of continuous, low-frequency (5-40 Hz) acoustic energy that is likely volcanic tremor related to magma intrusion. The hydrophone recorded a total of 458 earthquakes associated with the eruption. To predict the character of acoustic signals generated from Anatahan, we developed a moment-tensor representation of a volcano-seismic source that is governed by the geometry of the source and the physical properties of the magma. A buried magmatic pipe model was adopted, and numerically modeling source parameters such as the pipe radius and magma viscosity enable us to grasp the inward nature of Anatahan Volcano.