TY - JOUR
T1 - Spatial Variations in the Frequency-Magnitude Distribution of Earthquakes at Mount Pinatubo Volcano
AU - Sanchez, John J.
AU - McNutt, Stephen R.
AU - Power, J. A.
AU - Wyss, Max
PY - 2004/4/1
Y1 - 2004/4/1
N2 - 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.
AB - 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.
UR - https://digitalcommons.usf.edu/geo_facpub/302
UR - https://doi.org/10.1785/0120020244
U2 - 10.1785/0120020244
DO - 10.1785/0120020244
M3 - Article
VL - 94
JO - Bulletin of the Seismological Society of America
JF - Bulletin of the Seismological Society of America
ER -