HR: 0830h
AN: V51J-0405    [PDF]
TI: Seismic and Geodetic Unrest at Uturuncu Volcano, Bolivia
AU: * McNutt, S R
EM: steve@giseis.alaska.edu
AF: Alaska Volcano Observatory, UAF Geophysical Institute, 903 Koyukuk Drive, P.O. Box 757320, Fairbanks, AK 99775 United States
AU: Pritchard, M E
EM: matt@gps.caltech.edu
AF: Seismological Laboratory, Caltech, 1200 E. California Blvd., 252-21, Pasadena, CA 91125 United States
AB: A large-scale concentric pattern of deformation has been observed between 1992 and 2000 centered on Uturuncu Volcano, Bolivia from satellite geodetic surveys (Pritchard and Simons, 2002). A reconnaissance investigation by a team composed of scientists from Bolivia (M. Sunagua and R. Muranca), Chile (J. Clavero), the USA (S. McNutt and M. Pritchard) and the UK (C Annen, M Humphreys, A le Friant, and R.S.J. Sparks) took place from 1-6 April 2003 to see if there were any other signs of volcanic unrest at Uturuncu. A single component vertical, one-second seismometer, was placed at five locations for periods up to 14 hours. Data were recorded at 100 samples per second on a laptop PC. Persistent low level seismicity was observed at all locations. The events were very similar to each other and most had a distinct P wave with a period of 0.1 sec and a clear S wave with longer period and higher amplitude. Nearly all the events at each station had similar S-P times, suggesting that the events came from mainly one source. Using bootstrapping methods we determine this to be from a source location on the north-west flank close to the center of deformation observed by satellite surveys. Several events with different S-P times and different waveforms suggest that two other sources exist within the volcanic edifice, but these cannot be located with the available data. The rate of volcanic earthquakes was up to 15 per hour; this is a surprisingly high rate for a dormant stratovolcano. The magnitudes were in the range 0.5 to 1.5 based on coda length. The sources were considered to be shallow within 3 - 4 km of the surface, although information on the velocity structure is not known. The summit region of Uturuncu (6,008 m) has an active fumarole field with substantial sulphur production and areas of silification. Temperatures in four fumaroles were measured at 79 - 80$\deg$C. A hot water spring on the NW flanks had a temperature of 20$\deg$C. The recent unrest manifested by substantial ground deformation, thermal activity and seismicity indicate that a magmatic system may still be present, and therefore further monitoring of this dormant volcano is warranted. Reference: M Pritchard and M Simons, "A satellite geodetic survey of large-scale deformation of volcanic centres in the Central Andes" Nature, 418, p167-170, 2002.
DE: 7205 Continental crust (1242)
DE: 7280 Volcano seismology (8419)
DE: 8414 Eruption mechanisms
DE: 8419 Eruption monitoring (7280)
DE: 8494 Instruments and techniques
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting