Time trend analysis of basaltic volcanism for the Yucca Mountain site

Abstract

Abstract The possible recurrence of volcanic activity near the proposed nuclear waste repository at Yucca Mountain, Nevada, U.S.A. is evaluated by estimating the instantaneous recurrence rate using a nonhomogeneous Poisson process with Weibull intensity and by using a homogeneous Poisson process to predict future eruptions. Analysis on the post-6-Ma volcanism near the Yucca Mountain region indicates a moderate developing time trend ( p -value = 0.01) of volcanic activity. A similar time trend is obtained by trimming the observation period to 3.7 Ma and younger (period of the youngest episode). Data from the Quaternary basaltic volcanism also show a slight developing time trend, although the developing volcanic activity is not significant at the 0.05 level. Thus, it would oversimplify the assessment of the volcanic risk to the proposed Yucca Mountain repository site if a simple Poisson model were used to model the volcanism. Based on the Quaternary data, the estimated instantaneous recurrence rate is about 5.5 × 10 −6 /yr. An estimate of the mean time to the next eruption is about 1.8 × 10 5 years from now, if it is assumed that the intensity remains constant thereafter. Also, the risk (probability of at least one major eruption during the projected time frame) increases approximately linearly with the time frame chosen as the required interval for radioactive waste to decay to an acceptable level. Our study concludes that the estimated risk for an isolation time of 10 4 years is about 5%, which increases to 42% if 10 5 years is used as the required isolation time.