Temporal variations of Qc− 1 and b-values associated to the December 2000–January 2001 volcanic activity at the Popocatepetl volcano, Mexico

Abstract

We correlated temporal variations of coda attenuation Q c − 1 at 6 Hz and b-values with the 11 December 2000–23 January 2001, major eruptive activity at the Popocatepetl volcano, Mexico. We interpreted a total of 225 volcanic earthquakes with magnitudes between 1.9 and 3.3 located between 2 and 8 km from the summit of the volcano and registered from January 1999 to June 2001. Q c − 1 was estimated using a single-scattering model and values of b were obtained applying the method of maximum likelihood. Our results indicate that from January 1999 to March 2000 (Period 1), Q c − 1 varied within the same range without significant changes. Then, values of Q c − 1 steadily decreased during April–mid-December 2000 (Period 2). From about mid-December 2000 (onset of the major volcanic activity) up to February 2001 (Period 3), Q c − 1 sharply increased reaching its peak value. From March to June 2001 (Period 4), Q c − 1 decreased and increased in response to the post-eruptive phase of dome formation and destruction process that took place. During Periods 2 and 3, average b-values behaved opposite to the Q c − 1 trend. Within Period 2, when Q c − 1 decreased, b slowly increased. At the start of Period 3, b reached its peak value and returned to low values by the end of this time interval. We associate the temporal changes of the two analyzed parameters to variations of pressure and/or the variation in the degree of saturation of pore fluids that took place before, during and after the major eruption. During Periods 2 and 3, Q c − 1 correlated negatively with b with a correlation coefficient of − 0.61 and − 0.83, respectively. The significance of correlation cannot be rejected at the confidence level of 0.975. Our observations may have important implications for future prediction studies of large eruptions at the Popocatepetl volcano.