GPS monitoring of crustal deformation at Taal Volcano, Philippines

Data from a dual-frequency GPS network operated continuously from May 1998- October 1999 on Taal volcano, Philippines, were processed on a daily basis to monitor processes of crust;ll deformation associated with volcanic activ ity. During the 16-month period of observations, displacements totaled near ly 30 mm in the horizontal and 50 mm in the vertical over 2.7 and 5.8 km ba selines. Relative site velocities, estimated from daily site coordinates us ing 60-day tapered windows, vary significantly and can exceed 150 mm yr(-1) in the horizontal. Velocity estimates were used to invert for parameters o f a point-source model of elastic strain. During periods in which velocitie s are significant, the motions have a localized source at very high confide nce, and the source magnitude term fluctuates between inflationary and defl ationary behavior on time scales of weeks to months. The largest site veloc ities land corresponding deformation model parameters) are time-correlative with anomalous bursts of hydrothermal activity and high-frequency local se ismicity. In each instance the onset of deformation precedes both seismicit y and hydrothermal activity, and the hydrothermal event coincides with a ra pid shift in the velocity behavior. The relative timing of these phenomena suggests that deformation and seismicity both are responding to punctuated migration of hydrothermal fluids. (C) 2001 Published by Elsevier Science B. V.