Ambrym, Vanuatu: First results from a seismic campaign (July-August 2000)

Ambrym is a large basaltic volcano with a 12-km-wide, 1,900 years old caldera, sited in the Vanuatu archipelago, formerly known as New Hebrides. Two cones are currently active in the caldera, named Marum and Benbow, each with several active vents that hosted visible lava lakes until 26 November 1999, when an earthquake (Mw = 7.5) located few km S of the volcano caused important changes to the vents morphology. During July 2000, we installed a short period seismic station on the Eastern rim of Benbow crater in the Western side of the caldera. The station acquired continuous data for about one month. During this period volcanic tremor was recorded together with discrete events. In this talk first results from the analysis of these data will be discussed, focusing the attention in particular on the existence of transitions in the long term volcano dynamics. During the observation period, on 9 August 2000, another significant earthquake was recorded, (mb= 6.3, about 65 km N of the volcano). Possible influences of this event on the volcano dynamics are investigated.