Spatial variations in the frequency-magnitude distribution of earthquakes at Mount Pinatubo volcano

Sanchez, J. J.; McNutt, S. R.; Power, J. A.; Wyss, M.

Abstract:

The frequency-magnitude distribution of earthquakes measured by the b-value is mapped in two and three dimensions at Mount Pinatubo, Philippines, to a depth of 14 km below the summit. We analyzed 1406 well-located earthquakes with magnitudes MD ???0.73, recorded from late June through August 1991, using the maximum likelihood method. We found that b-values are higher than normal (b = 1.0) and range between b = 1.0 and b = 1.8. The computed b-values are lower in the areas adjacent to and west-southwest of the vent, whereas two prominent regions of anomalously high b-values (b ??? 1.7) are resolved, one located 2 km northeast of the vent between 0 and 4 km depth and a second located 5 km southeast of the vent below 8 km depth. The statistical differences between selected regions of low and high b-values are established at the 99% confidence level. The high b-value anomalies are spatially well correlated with low-velocity anomalies derived from earlier P-wave travel-time tomography studies. Our dataset was not suitable for analyzing changes in b-values as a function of time. We infer that the high b-value anomalies around Mount Pinatubo are regions of increased crack density, and/or high pore pressure, related to the presence of nearby magma bodies.

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Article

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70026885

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Sanchez, J. J.; McNutt, S. R.; Power, J. A.; Wyss, M.

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438

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English

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Bulletin of the Seismological Society of America

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Spatial variations in the frequency-magnitude distribution of earthquakes at Mount Pinatubo volcano; 2004; Article; Journal; Bulletin of the Seismological Society of America; Sanchez, J. J.; McNutt, S. R.; Power, J. A.; Wyss, M.