A forward test for interaction between remote earthquakes and volcanic eruptions: the case of Sumatra (June 2000) and Denali (November 2002) earthquakes Jacopo Selva a, * , Warner Marzocchi a , Francesca Zencher b , Emanuele Casarotti c , Antonio Piersanti c , Enzo Boschi b,c a INGV-Bologna, Via Donato Creti, 12, 40128 Bologna, Italy b Alma Mater Studiorum, Universita ` di Bologna, Dipartimento di Fisica, Settore di Geofisica, viale Berti Pichat, 8, 40127 Bologna, Italy c INGV-Roma, via di Vigna Murata, 605, 00143 Rome, Italy Received 22 March 2004; received in revised form 28 July 2004; accepted 2 August 2004 Available online 15 September 2004 Editor: S. King Abstract We propose a formal procedure to validate the hypothesis of a causal relationship between great tectonic earthquakes and volcanic eruptions through a forward statistical test. This approach allows such a hypothesis to be evaluated in an objective way, ruling out any possible unconscious overfitting of the past data. The procedure consists of two steps: (a) the computation of the stress perturbation in a volcanic area due to some selected seismic event, by means of a spherical, layered, viscoelastic and self- gravitating earth model; and (b) the application of a statistical test to check the differences in the spatio-temporal distribution of eruptions before and after the earthquake, weighting each eruption with the stress perturbation induced at the volcano at the time of the eruption. Finally, for the sake of example, we apply the method to the case of the recent Engano earthquake in Sumatra (June 2000) and the Denali earthquake in Alaska (November 2002). D 2004 Elsevier B.V. All rights reserved. Keywords: earthquake–volcano interaction; post-seismic stress perturbation; forward test; Engano earthquake; Denali earthquake 1. Introduction It has been proposed that one of the most relevant parameters to promote volcanic unrest and/or erup- tions may be the interaction with great tectonic earthquakes [1–10]. In particular, the stress perturba- tion due to earthquakes seems to have triggered unrest in volcanic systems, at different spatio-temporal scales. The occurrence of any earthquake induces a perturbation in the stress field at any point on the Earth’s crust. Generally speaking, there are three 0012-821X/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.epsl.2004.08.006 * Corresponding author. Tel.: +39 051 4151 453; fax: +39 051 4151 498. E-mail address: selva@bo.ingv.it (J. Selva). Earth and Planetary Science Letters 226 (2004) 383 – 395 www.elsevier.com/locate/epsl