Shallow seismicity, triggered seismicity, and ambient noise tomography at the long-dormant Uturuncu Volcano, Bolivia |
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Authors: | Jennifer A Jay Matthew E Pritchard Michael E West Douglas Christensen Matthew Haney Estela Minaya Mayel Sunagua Stephen R McNutt Mario Zabala |
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Institution: | (1) Department of Earth and Atmospheric Science, Cornell University, 3162 Snee Hall, Ithaca, 14853, NY, USA;(2) Geophysical Institute, University of Alaska Fairbanks, Fairbanks, AK, USA;(3) Alaska Volcano Observatory, U.S. Geological Survey, Anchorage, AK, USA;(4) Observatorio San Calixto, La Paz, Bolivia;(5) SERGEOTECMIN, La Paz, Bolivia |
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Abstract: | Using a network of 15 seismometers around the inflating Uturuncu Volcano from April 2009 to 2010, we find an average rate
of about three local volcano-tectonic earthquakes per day, and swarms of 5–60 events a few times per month with local magnitudes
ranging from −1.2 to 3.7. The earthquake depths are near sea level, more than 10 km above the geodetically inferred inflation
source and the Altiplano Puna Magma Body. The Mw 8.8 Maule earthquake on 27 February 2010 triggered hundreds of earthquakes
at Uturuncu with the onset of the Love and Rayleigh waves and again with the passage of the X2/X3 overtone phases of Rayleigh
waves. This is one of the first incidences in which triggering has been observed from multiple surface wave trains. The earthquakes
are oriented NW–SE similar to the regional faults and lineaments. The b value of the catalog is 0.49, consistent with a tectonic origin of the earthquakes. We perform ambient noise tomography using
Love wave cross-correlations to image a low-velocity zone at 1.9 to 3.9 km depth below the surface centered slightly north
of the summit. The low velocities are perhaps related to the hydrothermal system and the low-velocity zone is spatially correlated
with earthquake locations. The earthquake rate appears to vary with time—a seismic deployment from 1996 to 1997 reveals 1–5
earthquakes per day, whereas 60 events/day were seen during 5 days using one seismometer in 2003. However, differences in
analysis methods and magnitudes of completeness do not allow direct comparison of these seismicity rates. The rate of seismic
activity at Uturuncu is higher than at other well-monitored inflating volcanoes during periods of repose. The frequent swarms
and triggered earthquakes suggest the hydrothermal system is metastable. |
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