Spatial Variations in the Frequency-Magnitude Distribution of Earthquakes at Mount Pinatubo Volcano
Digital Object Identifier (DOI)
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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Citation / Publisher Attribution
Bulletin of the Seismological Society of America, v. 94, no. 2, p. 430-438
Scholar Commons Citation
Sanchez, John J.; McNutt, Stephen R.; Power, J. A.; and Wyss, Max, "Spatial Variations in the Frequency-Magnitude Distribution of Earthquakes at Mount Pinatubo Volcano" (2004). School of Geosciences Faculty and Staff Publications. 302.