Spatial Variations in the Frequency-Magnitude Distribution of Earthquakes at Mount Pinatubo Volcano

John J. Sanchez, Stephen R. McNutt, J. A. Power, Max Wyss

Research output: Contribution to journalArticlepeer-review

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 M D ≥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.

Original languageAmerican English
JournalBulletin of the Seismological Society of America
Volume94
DOIs
StatePublished - Apr 1 2004
Externally publishedYes

Disciplines

  • Earth Sciences

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